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Construction Questions

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Q Can I use local timbers in place of the timbers specified in the design?
Q Can I use 3mm plywood in place of laminate veneers?
Q Is it possible to substitute ply "sandwich" frames (like Design 152) for conventional laminated frames?
A Yes.

With some of the larger boats (say 7.5m – 25' and up) we may want to increase the frame depth a little.

Otherwise you can usually substitute three layers of ply for a standard frame and four layers of ply for a "strong" frame – usually the frame in way of the mast.

So a frame that is usually 25mm sided could be made of three layers of 9mm ply (ending up at 27mm sided). A 30 sided frame could be made from two 9mm outer layers and a 12mm core layer. A 35mm sided frame could be three 12mm layers. And so on.

The outside edge data from the ply layers can be taken from the Table of Offsets for the laminated frame. Make the fwd layer to the fwd face data and the aft layer to the aft face data. The centre layer can be made to data interpolated between the fwd and aft face data. This will give you an approximation of the edge bevel in three steps. Generally, the thickened epoxy used to bond on the hull skin, will fill the small voids in the stepped edge. Right forward, where the bevels are changing quite a lot from the aft face to the fwd face, you may need to clean off the sandwich ply frame edge to give a more consistent bevel.

You will need small location holes in the ply components to ensure that they are sandwiched together accurately. 8mm holes to take a short length of 8mm dowel are usually about right. You need to plan these out carefully.

You will also need to plan out the ply sections in each layer so that butt joins in one layer are covered by the other two. The face veneer on the ply does not need to run in any particular direction.

As we make DXF files for our designs, so that all the ply components can be CNC cut, we will be adding this type of ply frame in as an alternative,

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Q I've noticed that ply lapstrake is often thinner than a cold-moulded hull skin. Why is that?