[Public-list] Cockpit coamings.

[Jonathan Whittingham]

JOHN GRAVES wrote:

>Jonathan,
>My cockpit coaming split in the same place. Mine is made of solid mahogany. I don't know if it is original or not. I plan to replace it in the future but I haven't decided of what material.
>What have you found in high quality marine plywoods? I work at a container port and I have noticed around the container maintainence area a really heavy duty industrial plywood that they use to repair the floors of containers. It looks to be really strong. It has to be very strong because they have to withstand the weight of the cargo that can be many tons and the weight of the forklifts rolling in and out loading and unloading. It is also exposed to being soaked down by seas at times. When I get a chance I'm going to try to track down the source for this material. I am going to have to replace the bulkhead between the V-berth and the head and gearlocker. The one with the main beam over it that supports the mast. I want to use something that is bomb proof because the support of the mast is one of the most critical part of a sailboat.
>John (Trelawney #15)
>  ----- Original Message ----- 
>  From: Jonathan Whittingham<mailto:whittle at shaw.ca> 
>  To: Alberg 30 Public List -- open to all<mailto:public-list at alberg30.org> 
>  Sent: Wednesday, December 21, 2005 8:29 PM
>  Subject: Re: [Public-list] Cockpit coamings.
>  
>

 Dear John,
              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 
>  >
>  >
>  >
>  >
>  > _______________________________________________
>  > These businesses support your Association:
>  > http://www.alberg30.org/store/A30supporters.html<http://www.alberg30.org/store/A30supporters.html>
>  > Please support them.
>  > _______________________________________________
>  > Public-list mailing list
>  > Public-list at alberg30.org<mailto:Public-list at alberg30.org>
>  > http://alberg30.org/mailman/listinfo/public-list<http://alberg30.org/mailman/listinfo/public-list>
>  >
>  >
>
>
>  _______________________________________________
>  These businesses support your Association:
>  http://www.alberg30.org/store/A30supporters.html<http://www.alberg30.org/store/A30supporters.html>
>  Please support them.
>  _______________________________________________
>  Public-list mailing list
>  Public-list at alberg30.org<mailto:Public-list at alberg30.org>
>  http://alberg30.org/mailman/listinfo/public-list<http://alberg30.org/mailman/listinfo/public-list>
>_______________________________________________
>These businesses support your Association:
>http://www.alberg30.org/store/A30supporters.html
>Please support them.
>_______________________________________________
>Public-list mailing list
>Public-list at alberg30.org
>http://alberg30.org/mailman/listinfo/public-list
>
>
>  
>



 1135226740.0