Date: 2010-12-20 11:07 am (UTC)
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.
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