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Question on Glued Lapstreake Boats Frame vs No Frames


MickG

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Hi: I started to find the article concerning the building of Blue Peter, a Lapwing. The internet says they can't find the piece. Anyway, what I am really looking for is an answer tot he question of frames vs no frames for a glued (epoxy) lapstrake boat. It would seem to me that they would be overkill and not needed. If any one will clarify this, I would be most appreciative.  

Thank you and Happy New Year

 

Mick

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Frames just are not needed in this type of construction. For one thing a boat built with 1/4 inch ply you actually have a 1/2 inch thick X overlap horizontal frame where the planks overlap. I built a Penobscot 14 and it had stringers running horizontally but they were in reality just to keep the boat and planks fair thru the building process with minimum bulkheads and temporary frames.

Scott

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With the individual planks glued along the lines of stress concentration (the plank edges), the hull no longer is an assembly of bits, but a homogenous hunk of wood. Adding to this as Scott mentions is the fact that, the overlapping portion of the planking (laps) form continuous longitudinal stringers. So you have a monocoque structure with built in stringers, before anything else is installed in the hull shell, which happens to be inherently strong and stiff. With most glued lapstrakes, you toss in a few well placed bulkheads and/or ring frames (a bulkhead with a big hole in it) and this is usually all you need, especially if cockpit seating, side decks and cabin furniture are also incorporated into the structure (tabbed to the hull shell).

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All true for the general case of glued plywood lapstrake boats but in a Lapwing there is another feature that is even more important in establishing the structural integrity of the boat.  For proof, look at the design source of Lapwing which is the CS15 and most of the smaller B&B sailboats.  These non-lapstrake boats have plywood panels of relatively large area but do not have and therefore cannot benefit from glued laps as they have none, but are still a strong and rigid structure.  The main reason for their structural integrity is the interior seat and air tank design which was arrived at over several years development.  The seats and air tanks with internal transverse bulkheads form rigid box structures that resist torsional forces.   The monocoque principle is the same as that used in aircraft and modern automobiles which eliminates any need for frames.  Sometimes a stringer may be useful for large open spans but even these are not usual in the smaller boats.

 

The result is that the CS boats are plenty strong and the round hulled glued lapstrake Lapwing is even stronger.  That these boats are lighter weight than more traditional plank-on-frame or ply-on-frame boats of equivalent strength is a major bonus and often the main reason for using this kind of structure. 

 

Edited:  Just reread PAR's post and see that he also wrote about the same feaures. 

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