Wharram Builders and Friends

A Photo & Discussion Forum for Wharram Design Enthusiasts

     Any boat will hobbyhorse in some conditions, and you can't always change course to get out of it.  Factors such as length compared to wave period, rocker, weight distribution, and longitudinal distribution of  displacement with greater displacement aft than forward, and of course size matters.   The modern catamaran hulls have benefited from many years of experience, and trial and error.  The transom stern with the bottom of the transom right at or slightly above the waterline is said to offer significant benefit in pitch dampening due to the rapid increase in displacement as it is pushed down.... Or that's how I read it.  

      Wharrams have always been double enders.... supposedly for ease of build, though that is hardly significant compared to what is lost.   You only build the boat once, and hull construction is the easy part of boat building....  It looks dramatic, and feels like a huge accomplishment, but like building a house, when the walls are up and the roof on, it looks "almost done", but in reality is only around 10% done.

     I've included a drawing showing the bulkheads on a 28' flat bottom plywood catamaran to show that the difference is one panel, not significantly more complex, no compound curves or anything tricky....an easy build.   You can see how much faster the displacement just above WL increases at the stern than the bow when the boat pitches.  When the bow pitches up, the stern cannot pitch down very much, and of course the sharp bow will slice more than pitch

       With this in mind, I wonder about the addition of stern sponsons just above WL on the inboard sides of the hulls designed just for pitch dampening..... a foam and glass "afterthought".............

                                                        DW

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And it could possibly be used as a step for swimmers. Win win win.

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