Boat Design Geekery (specialized)

[catsittingstill]

Boywizard and I are going to talk to each other about boat design here.  To spare the rest of my f-list I'm going to cut-tag it all.  If you're interested in the ongoing discussion (and want to take part, even?--cool!) you might consider bookmarking this post so you can come back to it, as it will probably continue to develop over time.  If boat design leaves you cold, by all means skip over it--I won't be the slightest bit offended.



Okay, two resources I've been thinking about are BearBoat,  which is a program specialized for designing boats (kayaks specifically but it should be useable for other kinds of boats.

And Rhino, recommended by Randwolf

Update: I have applied to evaluate the WIP (work in progress) Mac version of Rhino and received a download link.  I have spent a few minutes learning things like how to rotate the view and stuff.  This is complicated by the fact that the tutorial is written for people using the Windows version.  I'm told Rhino will do what I need in terms of translating the Bearboat output to something usable by humans but this may take me a while.

Both programs appear to be in beta of various sorts, so I'm not sure about this.  But at the moment I'm not really happy with either the Vayu or the Bear Mountain Rob Roy, and I'm running out of ideas.  There are various rule-of-thumb methods I could use to alter either design, but several months to a year of effort is a lot to spend on something that turns out to paddle like a dog, so I sure wouldn't mind having some way to check what I come up with.

And boywizard has promised to talk to me about boat design starting with 1/4 scale models.  Which sounds very cool--though it does occur to me that a model of a 13 foot canoe will be  3' 3' long.  But hey--you have to make it big enough to see what you're doing.  And that's still small enough to fit in the bathtub, provided I stay out of it.  So do you use 1/16' inch planks?  Do you check the load carrying capacity with 1/64th the amount of weight? Stay tuned--this could be cool!

Begin Boywizard's comment stream------------------
The Cheapskate's Approach to Canoe Plans, or, How to Save a Few Bucks and Have Some Fun

We will assume that you have decided what characteristics your boat will have: length, beam, depth, sheer, rocker, tumblehome, and anything else you deem important. Using this information, you will need to create some scale drawings from which you will make a model. The point of having a model is so that you can determine hull station shapes for making your construction form. The model will also reveal bad ideas that you may have had (who, me? what bad ideas?) because it just won't look right in three dimensions.

What scale should you use? The bigger the better, since any errors in your model will be exaggerated by the scale multiplier when you go to the full size. For example, suppose you have a one-eighth scale model of a sixteen-foot boat; the model will be two feet long, which is a nice easy size to handle, and would take relatively little effort to make. Now suppose you make an error of a sixteenth of an inch in the model (true to a sixteenth, it's true, you know). Now scale it up by a factor of eight when you draw a hull station cross section. Your minor error is now half an inch, which, I assure you, is going to be very noticeable. So, I like a quarter-scale model, which I think is a good compromise between ease of working and ultimate accuracy. One-third scale isn't out of the question, but any larger than that and you may as well go ahead and build the boat.

You will need three (or maybe four) scale drawings – a profile, which shows length, depth, rocker, and sheer – a cross section at the point of maximum beam – a plan view looking down on the boat from above, which shows the shape at the height of maximum beam – possibly a second plan view showing the shape at the gunwale, which may be useful if there is tumblehome. I usually make drawings on graph paper, which provides handy horizontal and vertical reference lines, but any paper will do if you draw your own reference lines. You'll want a fore-and-aft centerline with parallel maximum beam lines for the plan view. Imagine a rectangle as long as the boat, as wide as the max beam, and divided down the middle the long way. For the cross section, a rectangle as wide as the max beam, as tall as the max depth, and divided vertically at the centerline. Finally, for the profile, a rectangle as long as the boat, as high as the max depth, and divided vertically at the centerline. Do not forget to make copies of your drawings. I like to have three sets, since a lot of work has gone into creating them, and you will need a second set later.

Although ultimately you will only need half-drawings because you will be making a half model (assuming your design is symmetrical left-to-right (and it probably better be!)), I draw both sides to get a better picture of what the boat may actually look like. And, if your hull will be symmetric fore-and-aft, you really only need to draw a quarter of the boat (and make a quarter- rather than half- model), but.....

So, go ahead and draw! I will leave the techniques to you. I use French curves and an adjustable curve (a bunch of little plastic strips that slide against each other) to get the sharp and gentle curves I need. All this can undoubtedly be done efficiently with CAD software if you have it and the proficiency to use it, and access to a printer that can handle the sizes you need. I don't, so I do it the old-fashioned way.

OK, you have your drawings. Now it's time to convert them into a three-dimensional model. I use wood for my models, because it is cheap, easy to work, and holds detail well. Any material that is accessible, reasonably easy to carve, and durable would probably be OK though. Anyway, let's assume wood. Hardwoods can make really pretty models, but are tough to work with, so I like basswood, white pine, or cedar. Basswood is excellent, but a tad pricey. I've used Western red cedar because I had some left over from a project, but it is a bit soft, and prone to splinter. Clear white pine would be my wood of choice. You will need a block slightly larger than the length, width, and height of your (half) drawings. Let's say our boat will be sixteen feet long, thirty-two inches wide, and fifteen inches deep (top of bow/stern to bottom). This would be a boat without much sheer. Let us also assume that the hull is asymmetric, with maximum beam twelve inches aft of the centerline. Because of this asymmetry, we have to make a full-length (four foot) model. If the boat were symmetric, we could get by with a half-length model, since all the forward stations would be the same as the aft ones. We will need a wood block measuring four feet by four inches wide by three and three-quarters deep. I would add a half to an inch to these measurements. Since it is hard to come by pine of these dimensions, I would laminate the block using six pieces of three-quarter stock. Very small knots should not be a problem, but it's not hard to build up a block from small pieces that are knot-free. I use Titebond wood glue, and clamp things up pretty tight to get a thin glue line. It would be OK to make the laminations either vertical or horizontal, whichever suits the wood you have.

The completed block should be jointed on two sides at a perfect right angle. These sides will be the fore-aft centerline plane, and the top or bottom. If the block's top and bottom are significantly un-parallel, it would be useful to run it through a thickness planer to get them parallel, but variations of an eighth or so shouldn't cause trouble. If you laminated the block from wood that is already surfaced on two sides, you should be close enough to parallel without planing. Now mark the position of the centerline on the block's center plane. A drafting triangle (or better yet, an engineer's square) works well for this. I generally use a .5 millimeter mechanical pencil. Continue the line across the top and bottom of the block. Now glue your profile drawing to the block center plane, aligning the drawing and block centerlines. Rubber cement is fine, or any other glue that won't cause your paper to wrinkle. Do the same on the top of the block, using half of the max beam plan view drawing.

What about the max beam cross section? Remember, since our hull is asymmetric, this does not fall at the fore/aft centerline, but behind it. Here's my approach. Using a piece of contrasting wood (walnut, cherry, mahogany, etc.) an eighth of an inch thick, glue onto it half the max beam cross section drawing. Cut the wood to the exact shape of the drawing. If you don't have any contrasting wood, it doesn't really matter; you can color the edge of whatever you use with a Sharpie marker. You just need a good color contrast with the block. Now, using a table saw with a .125 kerf blade, cut your block into two pieces, exactly on the max beam line. Glue your max beam shape between the two halves of the block, restoring it to its original length, but with a dark line at the max beam station position.

Switch to the band saw. Cut away the waste along the keel line, following the rocker, if any. Stay close to your line, but don't cut into it. You want to be able to sand to the line later. Cut away the waste along the gunwale line. Now temporarily glue the waste (THAT YOU DIDN'T LOSE) back into position on the top and bottom of the block. A dab of hot glue or double stick tape works well. Now you have restored a flat bottom to the block that can ride on the bandsaw table without rocking, and the flat top with the max beam gunwale drawing.

Cut away the lateral waste following the gunwale line, again leaving the line to sand to. If the max beam is at the gunwale, you may be able to tilt the bandsaw table a bit when you make this cut to reduce the amount of wood to be removed later, but it is certainly not necessary to do so. Temporarily glue the waste back onto the block so as to recover the profile drawing.

At this point, pop off the bottom waste piece, and sand the bottom exactly to the line on the drawing. I use a stationary belt sander, portable belt sander, palm sander, and sanding blocks. Use whatever works for you, but keep in mind that accuracy at this point is vital, since errors made here will be transmitted at four times the size to the actual building form. Do the same with the top, but after sanding the top to the profile line, restore the top waste with it's max beam drawing. Now remove the side waste and sand to the gunwale line (or max beam line, if there is tumblehome). Remove the top waste AGAIN. (I know, you overdid it with the glue, and it's hard to get those pieces off – sorry!). If your design has tumblehome, glue the gunwale half drawing to the top surface so you will know where the gunwale is.

Now you have a block of wood that looks a bit like half a canoe. Proceed to make it look exactly like half a canoe by cutting away anything that doesn't look canoe-like. I accomplish this by planing, sanding, gouging, whittling, Dremeling, rasping, and using anything that will cut away wood. Your block has three references that must not be removed without changing the design that you drew: the max beam cross section in contrasting color, the keel line, and the fore/aft max beam line if your design has no tumblehome. If there is tumblehome, the top drawing edge marks the gunwale line. To remind you that these lines can't be touched, color them with a Sharpie.

At this point you are working by eye, by feel, and by your designer's intuition. My attitude is that if it looks good, it will be good. If this boat is going to be an Olympic racing boat, that approach may not work, but I'm betting that aesthetics are just as important as performance for the kind of boats that we make, so don't worry overly about it. Other than appearance, I am only concerned with whether the boat is as stable as I want it to be, will it track as well as I need, can it carry me and whatever gear I generally have with adequate freeboard, and does it paddle easily. If I have done my homework on the original design, all these qualities should be within my desired parameters.

Darn it!! I just slipped with the power rasp, and now there is a huge gouge just where I don't want it. What to do? Bondo comes to the rescue. It's cheap, easy to mix and apply, sticks fine to wood, and sets to a workable state quickly. The only downside is that it smells bad. By the time I finished the model of my boat 2, it was almost all Bondo. You can also use various epoxy mixes at greater expense and less convenience. Mistakes are not the end of the world; they can always be repaired. We are not constructing Chippendale furniture here, and you will not be graded on appearance.

Finally, after (mumblemumble) hours of work, you have half a quarter-scale model of a canoe. It's beautiful (Bondo not withstanding). Now you must proceed to destroy it. Well, you could opt to use some other approach to getting your stations, but this one seems easiest to me. Ah, wait! Before you ruin your beautiful model, you may want to get load waterline information. Since this is going to require immersing your model in water, I would recommend spraying the model with a couple of coats of polyurethane varnish, just to protect it from water absorption, which could cause the wood to swell, distorting your hard-earned lines. It won't be in the water for long, so a thick coat of varnish (which could alter your shape) isn't necessary.

I have never actually done this, but here is my guess as to how to go about it. As Cat has pointed out, the volume of a quarter-scale model is one sixty-fourth of the full-size version, so the test weight should be one sixty-fourth of the design weight as well. Suppose my target load is 260 pounds for boat, paddler, and gear. My model should weigh one sixty-fourth of that, or four pounds, one ounce. If we weigh the model and are lucky, it will be lighter that four pounds, so by adding a bit of weight we can bring it to the correct amount easily. Suppose that our model weighs six pounds. Maybe we should have made it from cedar instead of that old slab of oak we had lying around. Oh well, too late now. We are going to have to reduce the weight by about two pounds. We can do this by partially hollowing out the model, but we want to avoid removing wood where the stations will be, for reasons that will become apparent later. I would do this with a drill press and a Forstner bit, which is guided by its rim, enabling it to cut partial holes without wandering around. I would want to stay at least half an inch away from the locations of the stations (in other words, each station location should have an inch of wood), and half an inch from the centerline plane. One would have to be very careful not to drill through the hull, although an error or two could be corrected with Bondo. On second thought, in view of the difficulty of holding the model firmly while all this drilling is going on, perhaps a die grinder would be better. I leave this procedure as an exercise for the student.

Having gotten the model's weight to exactly four pounds, one ounce, we must now devise a scheme for holding it upright in the water. Being just half a canoe, it will tip over on its side if we don't. I would acquire a plastic soda straw, cut it in half, and glue the two pieces vertically and in parallel to the centerline plane. Then find two metal rods or dowel rods of appropriate size to slide into the straws (metal is slipperier, though), drill two socket holes into a board at the proper spacing to accept the rods, and insert them into the holes. We now have a fixture that will allow the model to slide up and down without tipping over. Fill a bathtub or other long container with a foot or so of water, drop the fixture into the water and weight it down with a brick or something to keep it firmly on the bottom. Now slide the straws over the rods and gently lower the model into the water until it is floating. She should be floating at the waterline we can expect of the actual boat.

We are now ready to take the dimensions and shapes of our building forms from the model. See part two, to follow soon.

(Current) End Boywizard's comment stream--------

And I for one am eagerly waiting :-)
 
Also--if you're reading in dreamwidth, and you're interested in following the discussion, it will probably be mostly at LiveJournal.  

Comments

[mdlbear]

Whee! Sounds like fun. I used to dream of building my own small sailboat, but never found the time/motivation. Maybe someday -- your boatbuilding posts are a real inspiration.

[boywizard.livejournal.com]

The Cheapskate's Approach to Canoe Plans, or, How to Save a Few Bucks and Have Some Fun

We will assume that you have decided what characteristics your boat will have: length, beam, depth, sheer, rocker, tumblehome, and anything else you deem important. Using this information, you will need to create some scale drawings from which you will make a model. The point of having a model is so that you can determine hull station shapes for making your construction form. The model will also reveal bad ideas that you may have had (who, me? what bad ideas?) because it just won't look right in three dimensions.

What scale should you use? The bigger the better, since any errors in your model will be exaggerated by the scale multiplier when you go to the full size. For example, suppose you have a one-eighth scale model of a sixteen-foot boat; the model will be two feet long, which is a nice easy size to handle, and would take relatively little effort to make. Now suppose you make an error of a sixteenth of an inch in the model (true to a sixteenth, it's true, you know). Now scale it up by a factor of eight when you draw a hull station cross section. Your minor error is now half an inch, which, I assure you, is going to be very noticeable. So, I like a quarter-scale model, which I think is a good compromise between ease of working and ultimate accuracy. One-third scale isn't out of the question, but any larger than that and you may as well go ahead and build the boat.

You will need three (or maybe four) scale drawings – a profile, which shows length, depth, rocker, and sheer – a cross section at the point of maximum beam – a plan view looking down on the boat from above, which shows the shape at the height of maximum beam – possibly a second plan view showing the shape at the gunwale, which may be useful if there is tumblehome. I usually make drawings on graph paper, which provides handy horizontal and vertical reference lines, but any paper will do if you draw your own reference lines. You'll want a fore-and-aft centerline with parallel maximum beam lines for the plan view. Imagine a rectangle as long as the boat, as wide as the max beam, and divided down the middle the long way. For the cross section, a rectangle as wide as the max beam, as tall as the max depth, and divided vertically at the centerline. Finally, for the profile, a rectangle as long as the boat, as high as the max depth, and divided vertically at the centerline. Do not forget to make copies of your drawings. I like to have three sets, since a lot of work has gone into creating them, and you will need a second set later.

Although ultimately you will only need half-drawings because you will be making a half model (assuming your design is symmetrical left-to-right (and it probably better be!)), I draw both sides to get a better picture of what the boat may actually look like. And, if your hull will be symmetric fore-and-aft, you really only need to draw a quarter of the boat (and make a quarter- rather than half- model), but.....

So, go ahead and draw! I will leave the techniques to you. I use French curves and an adjustable curve (a bunch of little plastic strips that slide against each other) to get the sharp and gentle curves I need. All this can undoubtedly be done efficiently with CAD software if you have it and the proficiency to use it, and access to a printer that can handle the sizes you need. I don't, so I do it the old-fashioned way.

[boywizard.livejournal.com]

OK, you have your drawings. Now it's time to convert them into a three-dimensional model. I use wood for my models, because it is cheap, easy to work, and holds detail well. Any material that is accessible, reasonably easy to carve, and durable would probably be OK though. Anyway, let's assume wood. Hardwoods can make really pretty models, but are tough to work with, so I like basswood, white pine, or cedar. Basswood is excellent, but a tad pricey. I've used Western red cedar because I had some left over from a project, but it is a bit soft, and prone to splinter. Clear white pine would be my wood of choice. You will need a block slightly larger than the length, width, and height of your (half) drawings. Let's say our boat will be sixteen feet long, thirty-two inches wide, and fifteen inches deep (top of bow/stern to bottom). This would be a boat without much sheer. Let us also assume that the hull is asymmetric, with maximum beam twelve inches aft of the centerline. Because of this asymmetry, we have to make a full-length (four foot) model. If the boat were symmetric, we could get by with a half-length model, since all the forward stations would be the same as the aft ones. We will need a wood block measuring four feet by four inches wide by three and three-quarters deep. I would add a half to an inch to these measurements. Since it is hard to come by pine of these dimensions, I would laminate the block using six pieces of three-quarter stock. Very small knots should not be a problem, but it's not hard to build up a block from small pieces that are knot-free. I use Titebond wood glue, and clamp things up pretty tight to get a thin glue line. It would be OK to make the laminations either vertical or horizontal, whichever suits the wood you have.

The completed block should be jointed on two sides at a perfect right angle. These sides will be the fore-aft centerline plane, and the top or bottom. If the block's top and bottom are significantly un-parallel, it would be useful to run it through a thickness planer to get them parallel, but variations of an eighth or so shouldn't cause trouble. If you laminated the block from wood that is already surfaced on two sides, you should be close enough to parallel without planing. Now mark the position of the centerline on the block's center plane. A drafting triangle (or better yet, an engineer's square) works well for this. I generally use a .5 millimeter mechanical pencil. Continue the line across the top and bottom of the block. Now glue your profile drawing to the block center plane, aligning the drawing and block centerlines. Rubber cement is fine, or any other glue that won't cause your paper to wrinkle. Do the same on the top of the block, using half of the max beam plan view drawing.

What about the max beam cross section? Remember, since our hull is asymmetric, this does not fall at the fore/aft centerline, but behind it. Here's my approach. Using a piece of contrasting wood (walnut, cherry, mahogany, etc.) an eighth of an inch thick, glue onto it half the max beam cross section drawing. Cut the wood to the exact shape of the drawing. If you don't have any contrasting wood, it doesn't really matter; you can color the edge of whatever you use with a Sharpie marker. You just need a good color contrast with the block. Now, using a table saw with a .125 kerf blade, cut your block into two pieces, exactly on the max beam line. Glue your max beam shape between the two halves of the block, restoring it to its original length, but with a dark line at the max beam station position.

[boywizard.livejournal.com]

Switch to the band saw. Cut away the waste along the keel line, following the rocker, if any. Stay close to your line, but don't cut into it. You want to be able to sand to the line later. Cut away the waste along the gunwale line. Now temporarily glue the waste (THAT YOU DIDN'T LOSE) back into position on the top and bottom of the block. A dab of hot glue or double stick tape works well. Now you have restored a flat bottom to the block that can ride on the bandsaw table without rocking, and the flat top with the max beam gunwale drawing.

Cut away the lateral waste following the gunwale line, again leaving the line to sand to. If the max beam is at the gunwale, you may be able to tilt the bandsaw table a bit when you make this cut to reduce the amount of wood to be removed later, but it is certainly not necessary to do so. Temporarily glue the waste back onto the block so as to recover the profile drawing.

At this point, pop off the bottom waste piece, and sand the bottom exactly to the line on the drawing. I use a stationary belt sander, portable belt sander, palm sander, and sanding blocks. Use whatever works for you, but keep in mind that accuracy at this point is vital, since errors made here will be transmitted at four times the size to the actual building form. Do the same with the top, but after sanding the top to the profile line, restore the top waste with it's max beam drawing. Now remove the side waste and sand to the gunwale line (or max beam line, if there is tumblehome). Remove the top waste AGAIN. (I know, you overdid it with the glue, and it's hard to get those pieces off – sorry!). If your design has tumblehome, glue the gunwale half drawing to the top surface so you will know where the gunwale is.

Now you have a block of wood that looks a bit like half a canoe. Proceed to make it look exactly like half a canoe by cutting away anything that doesn't look canoe-like. I accomplish this by planing, sanding, gouging, whittling, Dremeling, rasping, and using anything that will cut away wood. Your block has three references that must not be removed without changing the design that you drew: the max beam cross section in contrasting color, the keel line, and the fore/aft max beam line if your design has no tumblehome. If there is tumblehome, the top drawing edge marks the gunwale line. To remind you that these lines can't be touched, color them with a Sharpie.

At this point you are working by eye, by feel, and by your designer's intuition. My attitude is that if it looks good, it will be good. If this boat is going to be an Olympic racing boat, that approach may not work, but I'm betting that aesthetics are just as important as performance for the kind of boats that we make, so don't worry overly about it. Other than appearance, I am only concerned with whether the boat is as stable as I want it to be, will it track as well as I need, can it carry me and whatever gear I generally have with adequate freeboard, and does it paddle easily. If I have done my homework on the original design, all these qualities should be within my desired parameters.

[boywizard.livejournal.com]

Darn it!! I just slipped with the power rasp, and now there is a huge gouge just where I don't want it. What to do? Bondo comes to the rescue. It's cheap, easy to mix and apply, sticks fine to wood, and sets to a workable state quickly. The only downside is that it smells bad. By the time I finished the model of my boat 2, it was almost all Bondo. You can also use various epoxy mixes at greater expense and less convenience. Mistakes are not the end of the world; they can always be repaired. We are not constructing Chippendale furniture here, and you will not be graded on appearance.

Finally, after (mumblemumble) hours of work, you have half a quarter-scale model of a canoe. It's beautiful (Bondo not withstanding). Now you must proceed to destroy it. Well, you could opt to use some other approach to getting your stations, but this one seems easiest to me. Ah, wait! Before you ruin your beautiful model, you may want to get load waterline information. Since this is going to require immersing your model in water, I would recommend spraying the model with a couple of coats of polyurethane varnish, just to protect it from water absorption, which could cause the wood to swell, distorting your hard-earned lines. It won't be in the water for long, so a thick coat of varnish (which could alter your shape) isn't necessary.

I have never actually done this, but here is my guess as to how to go about it. As Cat has pointed out, the volume of a quarter-scale model is one sixty-fourth of the full-size version, so the test weight should be one sixty-fourth of the design weight as well. Suppose my target load is 260 pounds for boat, paddler, and gear. My model should weigh one sixty-fourth of that, or four pounds, one ounce. If we weigh the model and are lucky, it will be lighter that four pounds, so by adding a bit of weight we can bring it to the correct amount easily. Suppose that our model weighs six pounds. Maybe we should have made it from cedar instead of that old slab of oak we had lying around. Oh well, too late now. We are going to have to reduce the weight by about two pounds. We can do this by partially hollowing out the model, but we want to avoid removing wood where the stations will be, for reasons that will become apparent later. I would do this with a drill press and a Forstner bit, which is guided by its rim, enabling it to cut partial holes without wandering around. I would want to stay at least half an inch away from the locations of the stations (in other words, each station location should have an inch of wood), and half an inch from the centerline plane. One would have to be very careful not to drill through the hull, although an error or two could be corrected with Bondo. On second thought, in view of the difficulty of holding the model firmly while all this drilling is going on, perhaps a die grinder would be better. I leave this procedure as an exercise for the student.

[boywizard.livejournal.com]

Having gotten the model's weight to exactly four pounds, one ounce, we must now devise a scheme for holding it upright in the water. Being just half a canoe, it will tip over on its side if we don't. I would acquire a plastic soda straw, cut it in half, and glue the two pieces vertically and in parallel to the centerline plane. Then find two metal rods or dowel rods of appropriate size to slide into the straws (metal is slipperier, though), drill two socket holes into a board at the proper spacing to accept the rods, and insert them into the holes. We now have a fixture that will allow the model to slide up and down without tipping over. Fill a bathtub or other long container with a foot or so of water, drop the fixture into the water and weight it down with a brick or something to keep it firmly on the bottom. Now slide the straws over the rods and gently lower the model into the water until it is floating. She should be floating at the waterline we can expect of the actual boat.

We are now ready to take the dimensions and shapes of our building forms from the model. See part two, to follow soon.

[catsittingstill.livejournal.com]

Oh, WOW! Excellent--and thank you for being so patient with the length restrictions on the comments. This is great stuff.

Tomorrow I will see if I can lift your explanations out of the comments and insert them in an edited LJ post. (I am messing with BearBoat tonight, and will probably be fooling around seeing if I can take screenshots and stuff.)

[msminlr.livejournal.com]

What does one DO with the completed model after the real boat is built?

[Since this is going to be a CatSittingStill original, I can easily visualize it in an Interfilk auction]

[boywizard.livejournal.com]

I'm afraid that if we use what I think is the easiest approach to taking form shapes from the model, there isn't going to be much of it left. A different approach would leave the model reasonably intact. I will describe both methods in the near future.

[catsittingstill.livejournal.com]

:-) I can picture what you have in mind.

This physical modelling approach seems similar to what is in "Canoe and Boat Building: A Manual For Amateurs" which was written in 1889, and which I got off the web in e-book form. One refinement is that they make their original block of wood of several layers of woods of contrasting colors, held together by screws so they can be taken apart and traced. If I understand the illustration correctly, their layers are horizontal (correspond to sections parallel to the water) They also go from plans to a physical model by building the model of layers of cross sections and then fairing.

I only just started reading this book and it's riddled with typos, which are amusing in the text but infuriating in the numbers. How deep is J inches of draft? 7, maybe? S inches is probably five, but what's x? The original scans are available online so maybe I'll be able to puzzle it out. I will probably post more on it when I'm done.

[randwolf.livejournal.com]

My sense is that you would get to an initial three-dimensional model from drawings much more quickly with Rhino than with any physical modeling process. But to a finished design? That, I don't know. It would depend on the process by which you finish the design. If you need something you can touch and shape, well, hmmm, I suppose a CNC mill could produce a wooden quarter-scale model from a Rhino model, and they are probably available in town, but I don't know what the process would cost and you would still have to take station points off the final model. Personally, I'd probably try shaping the model digitally, having one or more CNC-milled or 3D-printed physical models (1/8 scale?) along the way as checks, and then go straight to the final form, but that would be an experiment. I think it's got a good chance of working, but I don't know that it would.

I'll be interested to see how this works out, whatever you decide to do!

[catsittingstill.livejournal.com]

My plan was to do the modelling pretty much solely on the computer, using Bearboat (which is very hard to get a non-boat shape out of to begin with) and judging the design's suitablity by examining the sheer plan (for rocker and sheer) and body plan (for rocker and flare) onscreen, and using Bearboat's stability calculations to make sure it's not too tippy and its KAPER calculations to examine the design's calculated drag in the water compared to that of commercial boats of about the same size.

When I get a design I like, I intend to transfer it into Rhino simply to produce a table of offsets I could take to Carson Newman and use to draw plans for stations by hand. I'm willing to consider some kind of plotter, but it would have to be something I could use free or very cheap, and with no more setup and fuss than a couple of afternoons of peacefully drafting.

I guess the drafting part may not seem very efficient, but it's something I know how to do, and it worked fine for Constance.

[catsittingstill.livejournal.com]

I don't feel a need for something I can touch and shape per se, though I guess it would be nice.

I could use the method talked about above, that they laid out in the boatbuilding book from 1889, where you make slabs for each section (I guess I would use endgrain white pine) fasten them together, and fair with a scraper or a chisel or sandpaper. Actually, a spokeshave might work for a lot of it and I have one on my wish list.

Since the model would be small, I might be able to just take a screenshot of the body plan from Bearboat and use that to trace out my layers.

[boywizard.livejournal.com]

Some thoughts on boat design --- I have designed only one canoe, so I do not present myself as a pro, or even a skilled amateur, but since the boat I built from my design met my needs and I believe that it was a success, I will explain what I considered when executing my design. There are several factors involved when creating a canoe design, some of which are more important than others, but none can be completely ignored, or one risks ending up with a boat that has a serious deficiency. They are: 1. Ease of paddling; will the boat move quickly with minimal effort? 2. Stability; how tippy does the boat feel, and how much does it ultimately resist tipping over? 3. Maneuverability: can the boat be turned readily when necessary? 4. Load carrying: can the boat handle the anticipated weight that will be on board without any untoward behaviors? 5. Seakindliness; will the boat handle waves and winds that may be encountered? Ease of paddling is a measure of the effort we have to expend to get the boat to move forward at a particular speed, and can actually better be referred to as drag. Drag has two primary components: hydrodynamic drag, and aerodynamic drag. Hydrodynamic drag can be further divided into four components: form drag, parasite drag, wave drag, and steering drag. Form drag is a function of the physical shape that is moving through the water. Imagine holding your hand out the window of a car at speed. If your palm is facing forward, you feel a certain amount of force against your hand. Then change the shape that you present to the slipstream by turning your hand palm down. You will feel less force because the shape (form) now resists the air flow less. Boat hulls behave the same way. Think of a boat hull shaped like a shoebox, and imagine how much force will be needed to move it through the water. Change the shape from shoebox to cylinder, and the drag decreases; change from cylinder to barracuda, and we see an even larger drag decrease. We see from this that form drag is influenced both by the cross section of the hull shape (rectangle, semicircle, rectangle with the corners rounded, etc.) and by how we move the water as it approaches the maximum cross section. Imagine that we have half a canoe, with the open end sealed with a bulkhead. If we paddle the canoe with the bulkhead forward, we are going to see a very large amount of drag. If we then reverse and paddle with the pointy end forward, drag is much reduced, even though the maximum cross section is exactly the same in both cases. The drag is affected by how fast the water has to change its direction to get around the beamiest part of our boat. Therefore, boats that are intended to move rapidly with as little energy expended as possible are always streamlined. Think garbage scow versus attack submarine.

[boywizard.livejournal.com]

Parasite drag is due to skin friction with the water. Water is viscous (sticky), and when we move a hull through it, we drag some water along with us. The more hull touching the water, the more water we have to carry along. Consequently, the less the hull surface area for a given displacement, the easier the boat will be to paddle. Suppose we decide that to get the displacement we want, our hull cross section at the max beam point needs to be 192 square inches. Our hull shape below the waterline could therefore be a rectangle measuring 6 by 32 inches, and having a perimeter of 44 inches. We can reduce the perimeter length contacting the water by changing the hull shape to a semicircle; we would need a radius of 11 inches, and the perimeter would be only about 35 inches, giving a reduction of 20 percent. Sounds great, right? Unfortunately, a semicircular hull has no stability whatsoever; it might be great for a torpedo, but if used in a canoe, the paddler will be spending a lot of time upside down. So, the hull shape is going to have to be a compromise between paddling ease and stability. (We will be seeing a number of compromises as we work on our design.) Wave drag occurs because the hull displaces water; as we move forward, the energy we put into the water by moving it creates a wave which originates at the bow of the boat. The faster we try to go, the bigger the wave gets. There is a simple formula for calculating the theoretical maximum speed of a displacement hull: 1.34 times the square root of the waterline length. If our boat will have a 16 foot waterline (could be typical for a seventeen-foot canoe), our max speed will be 1.34 * 16 ** ½, or 1.34 *4, or 5.36 miles per hour. It is actually possible to exceed this speed, but probably not in a human-powered vessel, because it takes increasingly large amounts of power to accomplish it. So, what can we do if we want to go faster? Why, we build a longer boat! A 20 foot waterline gives us six mph; 24 feet gives us 6.6 mph, and so on. What, you say? You can't fit a 25 foot boat in your garage? Neither can I, so I guess I will have to make absolute speed less important in my design than other considerations. Perhaps I should mention hull asymmetry at this point. It is supposed that an asymmetric hull tracks better that a symmetric hull, and asymmetry tends to counteract the inclination of the boat to 'squat' when moving close to its hull speed. I can not honestly say whether either of these are true, but I designed some asymmetry into my boat, and it tracked well, and was fast for its length. YMMV Finally, we have the problem of steering drag. This isn't really drag, but it is a source of increased energy usage that we must address. When a single paddle is used to propel a boat, the force we exert to move the boat forward, because it is applied off the boat's center line, also tends to turn the boat. Assuming we want to go straight, we have to counteract this turning force by using a J-stroke, which essentially pushes the boat back to where we started before we paddled forward. This lateral stroking can use a lot of energy. The effect is most pronounced for a solo paddler, but is also present with two paddlers, even if they are paddling on opposite sides (as they should). (Aside: I prefer, when paddling solo, to use a double-bladed (kayak-style) paddle. This substantially reduces the effort wasted in steering, since strokes are balanced side-to-side.) We can reduce the effect of the off-center power stroke by making our boat longer, and by reducing the amount of rocker (the amount the keel line rises at the bow and stern). Most commercially produced aluminum boats also have a drop keel that extends an inch or so down, creating even more resistance to turning, but a strip-built boat will not have this. If we build a long boat with no rocker, it will be easy to keep in a straight line. We may find that ease of going straight is the same as difficulty in turning. Sad to say, sometimes we actually want the boat to turn.

[boywizard.livejournal.com]

Again, we will have to compromise by having at least some rocker in the keel, the appropriate amount being decided by whether the canoe will see river use, where some maneuverability is essential, and by our experience with paddling a variety of boats, and noting what varying rocker does, and by my personal favorite – stealing numbers from existing boats that are known to perform well. We mustn't forget that a canoe operates at the interface of two fluids. We have discussed hydrodynamic drag, the resistance we experience from the interaction of hull and paddle with water. We also have to cope with aerodynamic drag, which we get whenever there is a wind. If you have paddled into a strong headwind, you quickly realize that the air can be a much more difficult obstacle to overcome than the water. I recall a trip I made on the Ausable River in Michigan, which ends with a paddle across Mio Pond, an impoundment of about two miles length. My companion and I were fighting a fifteen mph wind straight in our faces; it took us three hours to make the two-mile distance. On a calm day it would have taken less than an hour. There is little that can be done to compensate for a direct headwind. It is when the wind is quartering or abeam that the shape of the boat above the waterline can have a major effect. A boat with a high bow and stern (think Indian birch-bark canoe) is very easily blown off-course by winds from the side. Obviously, making your bow/stern as low as possible reduces this problem. Likewise, a boat that is out of trim (riding bow high is the usual problem) will be influenced more by wind. Sea kayaks have bows and sterns which are much lower than the cockpit, which makes them relatively insensitive to crosswinds. In my design, the bow and stern were only about two inches higher than the center; in other words, the line of the gunwale seen from the side was nearly flat. So much for ease of paddling. Let's take a look at stability, which has three aspects – initial stability, terminal stability, and dynamic stability. Imagine you are sitting in your boat on a calm lake. Lean a couple of inches to the left. Does the boat feel like it wants to keep right on leaning, until it dumps you into the water? If so, it has low initial stability. If it hardly reacts at all to your lean, it has high initial stability. Lean a bit more. Are you still dry? See if you can get a little water to come over the gunwale. If you can, and the boat hasn't dumped you, it has high terminal stability. If you are swimming at this point, the terminal stability is low. A hull with very high initial stability feels safe to beginning paddlers; it doesn't seem tippy. Very often though, a stable-seeming boat will quickly shift into low-or- no terminal stability when leaned to its critical point, which may not be all that many degrees away from vertical. A hull that seems quite tippy and unstable when vertical can quickly firm up when leaned fifteen or twenty degrees, and be very resistant to actually going over. The rounder the underwater hull shape, the less stability of any kind (remember the semicircle?), and the boxier (more rectangular) the higher the initial stability (although the shoebox will dump you pretty fast when it hits its critical angle). Another problem with high initial stability occurs when the wind starts kicking up waves, or a powerboat passes nearby. A wave on the beam will cause a strong lean as it passes under the boat, whereas a boat that is initially unstable will hardly react to the wave at all. Now we are moving into the realm of dynamic stability – how does the boat react when it (or the surface it is on) is in motion?

[boywizard.livejournal.com]

Here's the reason I want to be able to lean the boat easily at first, but want it to stiffen up as the lean angle increases. Remember the long boat with very little rocker? Can't turn it. What if I lean it, though? The more lean, the more rocker I effectively have, as the curvature of the side of the hull is immersed more. If I could lean all the way to ninety degrees, I would have fifteen or sixteen inches of rocker, and could turn on a dime (just before I went swimming). My design, when leaned twenty degrees, had about four inches of rocker, quite enough to make turning simple. I would like the boat to become increasingly stable as the lean angle increases, because I am a poor swimmer, and want the boat to keep me out of trouble if I misjudge the lean. If you are designing for use in rivers, high initial stability is even less desirable – you HAVE to be able to lean the boat; otherwise entering and leaving eddies is going to become much too exciting. Whitewater boats are really another thing altogether, though, and I won't address them here. How do we get high terminal stability? One way is to flare the hull, so it has more beam at the gunwale. This means no tumblehome, or inward curvature at the gunwale, so it makes paddling more difficult. The paddler has to reach out farther, and the turning drag is higher, particularly when paddling solo. The double-bladed paddle goes a long way to addressing this difficulty. Another approach is to change the hull shape above the waterline so it bulges outward; rounded below the waterline, more rectangular above it. I have seen commercial designs that use this shape. Getting a smooth transition from one shape to the other is problematic though. Rather than trying to make the boat do all the work of staying upright, I find the best technique is to make the paddler responsible for staying dry. The boat can help, but we can achieve excellent dynamic stability through paddling skills. Good low and high paddle braces, upper body flexibility, and a low seating position all contribute greatly to keeping the open side up. I seem to have already incorporated maneuverability into the discussion, so I won't say much more about it, other than to mention that the uses to which you will put the boat have a considerable influence over how maneuverable it needs to be. As in everything, you may have to compromise to get the best mix of characteristics for your purposes, and only you can decide what those compromises must be.

[boywizard.livejournal.com]

It is pretty important to decide what kind of load your boat will be carrying. If you intend to make solo day trips, your body and your day bag are the only weights to worry about. If you will be doing wilderness camping with two paddlers and two weeks worth of gear in the boat, the weight will be substantially different. A short, beamy boat and a long, slender boat may have the same load capacity, but they will handle very differently. I had to design my boat for two paddlers, even though I knew that most of its uses would be solo, so it was larger than I would have preferred, but no larger than it absolutely had to be to carry two lightly equipped people on day trips. I ended up at sixteen feet, with a thirty-four inch maximum beam at the gunwale, which was flared, no tumblehome. I would have liked to build a solo boat at about fourteen and a half feet, but I couldn't afford two boats, and wanted the wife to be able to accompany me from time to time. Figuring out the displacement of your design without using the model technique described elsewhere is tricky. Boat design software can do it, if you are fortunate enough to have some. If you have a reasonable number of frame stations, you can do a kind of pseudo-integration and come up with something that way. If you have a hull shape that you like, but the displacement is off your desired number, rather than change the beam, change the length. Adding or subtracting a foot or two in the center won't cause much of a change in the overall shape of the hull. Going longer is better than shorter, in my opinion, so be conservative in your original dimensions, and add displacement if you need to. You want your trip to be enjoyable, and you want your boat to bring you home safely at day's end. Seakindliness will contribute to those goals. We have already considered stability, which in the case of a narrow boat like a canoe is an aspect of seakindliness, since the proper kind of stability can keep you out of the water when you don't want to be in it. Lower initial stability keeps the paddler from having to fight all the time when waves are on the beam. Another aspect of seakindliness is the ability of the boat to cope with bad weather, which in the case of canoes usually means wind and waves. We have already considered the effect of wind on the boat, and determined that low bows/sterns are better able to deal with wind. Unfortunately, they also allow waves to enter the boat more easily. I got around this problem by decking the first three feet of the bow, and by flaring the bow very substantially, which made it resistant to digging in to oncoming waves. It was a nontraditional approach, but my experience in whitewater kayaks led me to it, and I don't think it harmed the look of the boat, just the contrary in fact. Flared sides keep waves out better that sides with tumblehome. Make sure your design has adequate freeboard for the load that you anticipate. Nothing will put you in the water quicker in bad weather than waves coming in over the side because you only have four inches of freeboard.

[boywizard.livejournal.com]

Not an element of seakindliness, but important to the degree of pleasure one gets from using a boat, is its weight. Heavy boats are not much fun. My first strip-built boat weighed nearly as much as an aluminum boat of the same length; I wasn't all that skilled a craftsman, and I didn't have access to ideal materials, so she came in at seventy-two pounds, disappointingly heavy. Strippers are inherently light if built carefully from optimal materials. My motto is 'when in doubt, leave it out'. Those ash gunwales may be tough, and the walnut seats are pretty, but when you are halfway through that three-mile portage, you may have second thoughts. At my age, even carrying from the car to the dock (about fifty feet) can be a hassle when the boat is heavier than it needs to be. On compromise: a canoe is a system, each part of which affects all the other parts. Making it fast can cost maneuverability; making it maneuverable can make it tippy; making it stable can slow it down. Make it too light, it becomes fragile; make it too heavy, it's tricky in a seaway. My current boat is a Grumman Eagle 17 foot aluminum boat, about twenty-five years old. You can see all the compromises the designers incorporated, but overall, it's a pretty good general purpose boat. It's a little too stable initially, it's a bit harder to turn than I would prefer, and it is slow, but it could certainly be much worse in any of these ways. I am sure that with some thought and a bit of work, anyone can design a boat that is superior in every way. I am looking forward to doing just that, someday.