Forums: Whisstock Designs: Design 55 - frames New Topic Post Reply
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Posted: Nov 21st, 2013 at 14:29   |   Subject: Design 55 - frames
Hi George
I am building 55 and want to include watertight compartments. A couple of questions;-
1. Can frame 1280 be solid (2 ply laminations)with access hatches?
2. Could frame 3840 also be solid or would this make the rear deck too deep? Obviously the cockpit would be smaller. I don't intend including an outboard well so this wouldn't be a problem.
3. What is your view on filling the compartments with high density foam insulation?

I intend laminating the visible intermediate frames but would probably make 640 from ply.

Thanks for your help.

Posted: Nov 22nd, 2013 at 02:33   |   Subject: Design 55 - frames
Hi David

I will email you PDF scale copies of the DXF files for ply frames. These are not dimensioned but they give you an idea of how the frames are made using ply.

I will be including a dimensioned set of plans for ply frames etc. in the standard plan package, but I simply haven't found time to do that yet!

Basically ply frames are three layers of 6mm ply or two layers of 9mm ply. The basic siding and depth is 30 x 18 (versus laminated frames 27 x 20). So for any frame you can substitute 2 off 9mm or 3 off 6mm ply layers for the laminated frame, just increasing the depth to 30mm.

With Frame -1280, this is a watertight bulkhead with the ply frames. As you can see from the PDF files I will be sending you, with three layers of 6mm, two layers are full bulkheads and the third layer is not. If you used two layers of 9mm, then one would be full (with the hatch apertures) and the other would be basically 30mm moulded depth, with extra in way of the floor section and so on.

The hatch apertures are shown for a simple ply hatch. If you are using proprietary hatches, then the apertures need to be changed to suit.

With regard to making Frame -3840 into a watertight bulkhead, you can do this structurally. I think it might make the cockpit rather too small for convenience and perhaps make the basic steering position a bit uncomfortable. But, with a slightly longer tiller that can be overcome. Other than that there really is no problem, though with more than two-up it may become a bit crowded.

When I was considering watertight compartments, I eventually opted to make forward of -1280 watertight and the whole length under the side decks watertight. Hence the uprights on all the frames in the files I am sending you. This was basically because the outboard well complicated a watertight compartment under the "standard" aft deck and provided little extra buoyancy for the complications involved.

As you are not having an outboard well, this doesn't apply of course. And in this case you might consider the under-sidedeck compartments plus a compartment aft of -4350 (the "standard" aft deck forward end).

If you make the larger watertight compartment aft of -3840, you won't need the under-sidedeck watertight compartments.

I can dimension up a set of frame drawings plus the under-sidedeck partition, if the would be useful to you. And I can give you a dimensioned drawing for a watertight partition at -4350.

I'm in two minds about foam filling watertight compartments:

- You solve the problem of water laying in the compartment.
- You don't need access hatches.
- You don't have to worry about drainage or ventilation.

- You lose an awful lot of valuable storage space, which is really necessary if you are going to do anything more than short day sails.
- You need to be very sure the foam quantities are perfect; sufficient so that the whole space is filled; and not too much so that the foam expands properly to a true uni-cellular structure and doesn't go all squishy with semi-liquid areas.

I think in the end, for me at least, I would not foam fill the compartments. But, provided it is done carefully and properly, there is no structural/maintenance/longevity reason not to do it.

I will email the PDF's in a few moments.

Best regards