JEM Watercraft

Maybe a good idea, maybe not.
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Author:  Derek Bowen [ Thu Jan 01, 2009 4:56 pm ]
Post subject:  Re: Maybe a good idea, maybe not.

İve had a look at my design mods sketch and fiddled about with the measurments and discussed it with "she who must be obeyed". The nesting idea, while being very neat wont work for our plan. İll try and explain. From the bow to first bulkhead İ want to fill as a boyancy chamber. Then reposition the main frame to lay over the butt block of the mid panel splices. The butt blocks will be increased in thickness to 12mm and doubled in length to take care of the unpleasant stress concentration. The space between the fwd bulkhead and the repositioned mainframe will be closed storage with hatches. All that applies to both ends since she,s a double ender and İ do love symmetry. That leaves 2m 58cm open cockpit for us crew.(if İ got my maths right). That leaves only the new connecting frames on the center line that need to be strong enough to bring back the lost strength caused by moving the main frames fwd & aft. 15mm by 60mm plywood and a few stratigically placed hardwood braces/knee,s should do it. Perforated inwhales and solid outwhales and bob,s yer uncle.
İ may fiddle with the idea of a sail later but İ think that will be a retrofit.
Any and all comments welcome chaps.
Jack, İ checked out the CL44. The D4 variant was a swing tail for fast cargo loading. They are all gone mate, scrapped or sitting around dodgy airfields sagging on the main gear.

Author:  Kayak Jack [ Thu Jan 01, 2009 7:09 pm ]
Post subject:  Re: Maybe a good idea, maybe not.

Two people in a 7' cockpit are OK if they are horizontal. Sitting one in front of the other is probably inadequate room, unless you're training as an integrated team for a marathon.

I would strongly advise a much longer cockpit. Much of hte utility and joy of a canoe comes form being open for general access, ingress, and egress. You seem to be locking up a lot of the hull in closed in compartments. You said there is no white water there, and you paddle in only easy conditions. Wooden boats float kind of naturally, and people in PFD's do too.

If you are wedded to the flotation idea, consider a large block of Styrofoam cut to fit, and simply lashed into place. It could be modified or removed easily. Just a thought.

Author:  Derek Bowen [ Fri Jan 02, 2009 1:28 pm ]
Post subject:  Re: Maybe a good idea, maybe not.

Hello Jack, İve been thinking about the boyancy chambers, the builders foam and various other bits and pieces İve picked up on this forum. İf the chamber in bow n stern was left open at the top and the inside lined with cling film (stretch film - sani wrap) and the foam injected into the space. İn effect you have made the bow / stern sections into molds and the cling film would be your release agent. Covering the open upper side (where the deck will go) with cling film to prevent things getting too messy. Let the stuff expand til its finished and trim up the excess after curing. There is no chance for the foam to bulge the hull as there is a large pressure release opening. You then have a very accurate, form fitting foam block that is removable. The deck panel then also needs to be removable which is fairly easy to do. Sealant and a dozen SS wood screws.
To seperate two well sealed surfaces ( deck from gunnel - Breaking joint frames midships) İ would use a stainless steel wire with two wooden handels. A kind of cheese cutter. The back n forth sawing motion will cut any kind of sealant. İve used that trick to release windscreens that are sealed in place with first class aviation sealant and aluminium fuselage skins too, so no problem with silicon sealant.
Obviously there must be no inwhales inside the boyancy chamber, smooth sides so you can remove the blocks for storage and drying.
Cockpit size is something İ will have to look at again. What you say about the ease of use is true and important. İ,ll have another look and get back to you.
Thanks mate. Derek.

Author:  Kayak Jack [ Fri Jan 02, 2009 2:49 pm ]
Post subject:  Re: Maybe a good idea, maybe not.

Sounds like you're refining your thinking, and getting the design down to the nitty gritty. As you say, the chamber must be larger at the top than at the bottom, and all sides must slope outwards with no impediments along the way.

You could cover that with simple lashing to hold in the block. Could consider cutting the block into two sections, upper and lower, for easier insertion and removal?

Sounds like you're on your way. Best of luck to you.

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