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post #1 of 7 Old 10-05-2008 Thread Starter
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seacock backing plates

When I service some of my seacocks this spring on my CD30, Im want to change some of the backing plates which are currently made of plywood and 20 years old. Theyre ok but it looks like its time.
Ive seen photos on this site of beautifully made new wood ones of marine ply, epoxied and varnished. But Ive also read suggestions of using fiberglass sheet material, which to me seems bomb proof and not really more expensive or laborious. Checking the MSC website, I see FRP sheets, 4x4x0.5 inch thick for about $350 (smallest size available) but on the same page is G10/FR4 (I dont know what those number mean) sheets, 2x2x0.5 for about $53. The latter are called glass reinforced epoxy. Its seems cheaper per square foot, involves less left over material, and maybe better because its epoxy, (stronger? and as or more compatible with epoxy for gluing to hull) Anybody know anything about one sheet material over the other or if the whole non wood plate idea has any downside?
Do most of you thru bolt your seacocks or does anybody accept the idea of lag bolting to the backing plate from the inside only (would need to be a wood plate I imagine) in order to keep penetrations to a minimum?
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post #2 of 7 Old 10-05-2008
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re

This is a good question. I dont believe in the long run one wins over the other, there are to many other thing that play a part. I have found in my yachts that the plastic decking (used for docks) seems to hold up well but if your bildge is dry, Good old timber will last longer then the safety check interval (check being at the owners disgression). I allways pull and rebed when I do every other bottom job but this is overkill. As far as the thru bolting gos, I have not done it in a long time.. Hope this gives you some help.

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post #3 of 7 Old 10-05-2008
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You really don't want wood backing plates... you're much better off with fiberglass or composite ones. You can make your own fiberglass backing plates pretty easily yourself, with epoxy and fiberglass cloth.

Either the FRP or G10 material will work and either will bond quite nicely to the interior of your hull.

Ideally, the through-hull flange should be through-bolted, and isn't much of a leak risk if properly done. If you have a cored hull, you really need to make sure you pot the holes properly.

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post #4 of 7 Old 10-05-2008
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You really don't want wood backing plates... you're much better off with fiberglass or composite ones.
Fiberglass or composite backing plates have been around what for the last 5 minutes ? Just one more way to spend extra money when you don't need to. Wood backing plates have been used on fiberglass boats since the 1960's. I have never heard of a failure if looked after under the normal course of maintenance. Even the OP states his wood backing plates are "ok" after 20 years of use. Sometimes we don't need to fix something with something new if the old one or way isn't broken.

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post #5 of 7 Old 10-05-2008 Thread Starter
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I guess the key is the statement "IF looked after in the normal course of maintainence." While I enjoy doing maintainence, Im always looking for the best way to do it as well as a way to minimize it as long as that doesnt involve compromise.
I was thinking that using a composite for a small cost (maybe $5 per plate) would save the time and expense involved with epoxy and paint or varnish in turning plywood into a water impervious material.
It seems that what we think of as traditional ways of doing things were all once new ideas.
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post #6 of 7 Old 10-05-2008
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I look at it..

Having been involved in many, many surveys and having been on and in the bilges of lots of boats, both power and sail, I can assure you that what I've seen is good cause to not use wood. Its why I don't.

On almost every single boat we've come across at least one or two backing plates that are rotted and or punky, and on the way out. Perhaps 55-60%+ of the wood backing plates I've stuck a meter or an Awl to have been bad.

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Fiberglass or composite backing plates have been around what for the last 5 minutes ?
Actually there are many yards in Maine that have been doing and offering this for years! It is not new by any means. Up here a fiberglass backing plate is nothing in expense when you have a 20-30k varnish bill each year..? Also most of the top Maine builders have been using solid glass where seacocks and thru-hulls penetrate for a loooooong time.


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Just one more way to spend extra money when you don't need to.
Ummm have you priced marine ply lately?? I can make a 2X2 solid sheet of fiberglass in about 20-30 minutes and for a comparable cost to marine ply.


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Wood backing plates have been used on fiberglass boats since the 1960's. I have never heard of a failure if looked after under the normal course of maintenance.
And I have yet to meet even a DIY owner who takes a meter or an Awl to his backing plates to actually check them. I have seen many that still appear fine to the naked eye but that are very wet and if you poke the Awl in the right location you'll find wood softer than Balsa..


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Even the OP states his wood backing plates are "ok" after 20 years of use. Sometimes we don't need to fix something with something new if the old one or way isn't broken.

This is not surprising as Cape Dory normally used Spartan bronze seacocks that are through bolted thus giving more integrity and less flex induced into seacock the system. I have seen direct corelation of dry wood backing plates to the level of install meaning I've see more wet backing plates on boats with only a thru-hull with a valve screwed to it than I have with boats that have flanged seacocks and through bolts or lags into the backing plate.

Here is a photo of one of my home made, hand laminated backing block sheets. Easy, permanent and it will last as long as your hull.



As always feel free to read these for more information and photos:

Seacock & Thru-Hull Primer/Pre Information (LINK)


Replacing Thru-Hulls and Seacocks (LINK)

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Last edited by Maine Sail; 10-05-2008 at 09:21 PM.
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post #7 of 7 Old 10-05-2008
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Ours were wood and some were seeping so we replaced them with fiberglass.


Twenty years from now you will be more disappointed by the things y%^&*.....oh never mind. 90% of the people on sailing forums already use that as their signature! I'm not a conformist.
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