[Public-list] Cockpit coamings.

Jonathan Whittingham whittle at shaw.ca
Thu Dec 22 09:17:17 PST 2005 

Don Campbell wrote:

>>From your description, you are wanting to make a box that I presume fits over the deck so that it supports  the winches and offers a place for more storage with the inside face  where the coaming now is. This sounds to be something that would really impede the flow of water when (not if ) the rail is in the water. I would not attempt to join anything aft of the cockpit from side to side that would deflect the flow of water  into the cockpit. In fact, the early decks are much better at clearing water than the more recent ones and having a solid taffrail is not the greatest when well heeled.
>    As it is now , the winch pocket deflects enough water into the cockpit if we are well over and that is not my favorite way to get wet. If there were a wider stop more forward, I would be leery of added spray or input into the cockpit. Take your boat out and heel it over so that you can really look at the flow of water with the rail in the water before you begin this project and see how your proposed design might make your boat  unsafe.
>    To see how good epoxy on wood construction is,  go to Gougeon's technical sites  and Epoxyworks on the web. They still claim that an epoxy covered wooden core is the best possible solution for boat building and they proove it by the race results of epoxy coated wooden core  dinghies. Older well built epoxy/wood hulls are still more competative with age  than newer composite ones because of the resiliance of wood. Once the composite fatigues and oilcans with every wave, it is finished. But to use epoxy effectively, all 6 sides of every piece need to be sealed with epoxy. Then there is the UV factor, which epoxies do not cope with very well, so figure on covering it with a uv stable coating, pigmented is probably better.
>Don # 528
>
>Jonathan Whittingham wrote: Dear John,
>  
>
I think I have not been clear about the rear structure proposed. What I 
intend to do is bolt a timber directly under the traveller thereby 
uniting the two extreme ends of the raised cockpit coamings. This would 
be no more than two or three inches high. It would also be a convenient 
fixing point for a pair of removable backrests that I have in mind. I 
agree that moving the "box" forward of the winch footprint might 
possibly increase the chance of water entering although I am not 
entirely convinced. I have only had the rail in the water a couple of 
times, didn't much care for it and am pretty vigilant at not allowing it 
to happen. Have you tried a reef? he asks jokingly. Sorry, couldn't 
resist. When I have had the green water running along the rail none has 
ever caught on the winch box and shlooped into the cockpit. I imagine 
that if I were heeled that far to let that happen, I may very well not 
be in the cockpit at that moment and a lot wetter with bigger problems 
than a bit of overspray.
   I am wavering on the plywood/solid wood debate. Does anyone have 
experience with Makore as a marine hardwood? Regards Jonathan

>  
>
>>              To be honest,I have not researched that far yet. However,
>>I am assuming, perhaps naively, that what separates a regular
>>"construction" plywood and a certified "marine plywood" is:
>>    1. the quality and type of wood material. i.e. a wood,such as
>>Mahogany that is better able to resist moisture damage than, say,
>>hemlock or fir.Also that the veneers are solid or, at least, properly
>>patched.
>>    2. That the glue used is water resistant. This reminds me of an old
>>debate about the pros and cons about using epoxies or UF109. The epoxy
>>clan insisted that the UF109 would not withstand more than twenty
>>minutes of "boiling water". The debate came to a rapid halt with the
>>charmingly deceptive question" Are you planning to boil your boat?"
>>    My thinking is to create a box, perhaps six or so inches deep, with
>>a plywood coaming forming the inner wall. This box will be nicely
>>tapered from front to back( alright,alright, bow to stern), running most
>>of the length of the coaming. I would then cut out storage cubbies on
>>the cockpit side for rope storage etc,. I would then perhaps top the
>>whole thing with a solid piece of Mahogany that would be a covering
>>board, again nicely shaped and probably tapered outward and downward to
>>shed water. This top plate would sweep right around the back and meet
>>the coaming on the other side. I believe this will be very strong and
>>will also provide function and, in my opinion, improved visual form. For
>>the winches I would provide solid blocks inside the boxes, bolted right
>>through the deck, as they are already.. With this new design, one could
>>actually sit on the coamings without feeling that ones bum was being cut
>>in half!. Water would also be less likely to seep in behind the coaming
>>half round strip and into the cockpit and so on.
>>        My real question to the group is how effective epoxy is over a
>>stable medium such as plywood really is. What experience have people
>>had. I plan to use fibreglass matting . There are many boats out there
>>that use a fibreglass over wood application. What is the problem?
>>Regards Jonathan.
>>
>>
>>    
>>
>>> Tom S. wrote:
>>>
>>> > Plywood coamings?
>>> > Ouch!
>>> >
>>> > tom s
>>>
>>>
>>>    Well, I knew that I would get some negative response to the
>>> suggestion below. Fair enough. However I would really appreciate an
>>> expanded  argument regarding the use of high quality plywoods,
>>> especially if the coamings are finely edged and epoxied. My contention
>>> is that the existing design of the coamings is flawed in that the
>>> bending stresses encourage the splitting of the tailing section if
>>> sideways pressure is inadvertantly applied, which is precisely what has
>>> happened to mine. I would propose further heresy by attaching the tail
>>> ends to a cross piece of timber, which would be bolted to the deck area
>>> immediately behind the rear cockpit, thus protecting the timber from any
>>> side pressure stress. Perhaps,Tom, you could advise as to whether your
>>> "Ouch!" is relevant to form or function? Or both, perhaps. If so, I
>>> would much appreciate further elucidation on the matter. Regards Jonathan.
>>>
>>> >
>>> > Jonathan Whittingham wrote:
>>> >
>>> >>    2. I am considering rebuilding the coamings out of marine grade
>>> >> plywood
>>> >
>>> >
>>> >
>>> >
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