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size plywood backing for seacocks

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cmckitrick
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USA
116 Posts

Initially Posted - 06/20/2008 : 07:21:21

It looks like I will finally be replacing my gate valves. I am away from my boat right now. Does anyone know off hand the dimensions of plywood backing blocks? Also somone at West Marine told me that you should not use plywood with marelon seacocks due to expanding wood and breaking the seacock. Any thoughts?

Charlie McKitrick
Norwell, MA
Valiant Lady... for now
'81 C 25 SR/FK

Edited by - on

redeye
Master Marine Consultant

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3476 Posts

Response Posted - 06/20/2008 : 08:34:52

Last backing blocks I made were hardwood. Soaked in resin.

Seems like a hardwood plywood soaked in resin would be ideal?

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ClamBeach
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Response Posted - 06/20/2008 : 08:38:22

"not use plywood with marelon seacocks due to expanding wood "

I wouldn't use plywood unless it was epoxy saturated/sealed so it wouldn't take up water.

"It looks like I will finally be replacing my gate valves."

IMHO: Don't get the plastic ones... they requre periodic disassembly and lubrication or they seize up. (Disassembling a through-hull valve is tough to do in the water).

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 06/20/2008 : 09:14:36

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by ClamBeach
 IMHO: Don't get the plastic ones... they requre periodic disassembly and lubrication or they seize up. (Disassembling a through-hull valve is tough to do in the water).<hr height="1" noshade id="quote"></blockquote id="quote">I've heard horror stories about bronze being attacked by stray electrical current in a marina and turning to powder... Plastic should get some teflon lube about once a year. Bronze should be greased.

For backers, how about Starboard (or a plastic cutting board from Walmart)?

Edited by - Dave Bristle on 06/20/2008 09:16:19

tinob
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1883 Posts

Response Posted - 06/20/2008 : 09:25:35

The tu hull replacement package sent to me from CD had in it 1/2" plywood blocks about 5"X5". I don't recall if the wood was treated, but they ( the packagers ) should know what is required and act appropriately. I assume they did.

Val on Calista, # 3936, Patchogue, N.Y.

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redeye
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Response Posted - 06/20/2008 : 10:45:06

I think the standard treatment for many repairwork on the hull fittings is plywood so that it will bend and conform to the hull, and epoxy resin to seal it all up.

My problem is I use epoxy so few times and in such small batches, that I mix a few batches first to make sure it is kicking properly. Mixed wrong and it can be brittle, or not set up properly. It can be a mess before it sets and it is kinda set in stone after it hardens.

With such an important fitting, I'd feel better if it was a bit more straightforward and predictable.

Would the starboard and silicone work?

what about starboard and bedding compound?

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Deric
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408 Posts

Response Posted - 06/21/2008 : 09:54:54

I had the original gate valve and pipe thru hull set up that came with the 78 Cat on my boat when I purchased it. I replaced it all this past winter.

I used Bronze: Groco products. I also used a cutting board for my backing board.

I went to Walmart and bought a Plastic Type cutting board and used that as my backing board. I added epoxy to the hull to create a flat surface to place the plastic cutting board on: drilled a hole into the plastic board not only for the thru-hull pipe, but for also for three bolts that bolted from the outside of the hull into the flange base of my new inline valve set up. I purchased the bronze bolts from Boltdepot.com

Someone on this site recommended the place for the bolts.

The cutting board was another idea someone on this site suggested. it made sense to me because the material will not rot, and it is strong. The backing board's function it to help displace the pressure of the connection over a wider surface area while also provide a smooth platform to secure your fittings.

Something to think about.

Deric

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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4479 Posts

Response Posted - 06/21/2008 : 10:43:01

I would hesitate to use synthetics for an epoxied-in-place backer plate. Epoxy doesn't stick very well to [url="http://en.wikipedia.org/wiki/High_density_polyethene"]HPDE[/url] (Starboard) or [url="http://en.wikipedia.org/wiki/UHMW"]UHMW [/url](cutting boards from wherever). Both are forms of polyethylene, which is specifically called out for caution on the West System website:
<blockquote id="quote">quote:<hr height="1" noshade id="quote"> From [url="http://westsystem.com/webpages/userinfo/manual/index.htm#2.1"]West System website[/url]: Plastic-Adhesion varies. If a plastic is impervious to solvents such as acetone, epoxy generally will not bond to it. Soft, flexible plastics such as polyethylene, polypropylene, nylon, Plexiglas and polycarbonate fall into this category. <hr height="1" noshade id="quote"></blockquote id="quote">

You can purchase marine plywood for this, although it's quite expensive by the sheet. Or you can do as suggested, soak regular plywood in epoxy resin to seal it from exposure to water. I'd probably use hardwood instead of plywood as was also suggested. A 1x6 of Ipe is about $12 or so, and you'll still have 11+ feet of it left over after you're done making your backing plate. However, using tropical hardwoods like Ipe or Teak have their own caveats, you must clean the oils off of them prior to applying epoxy. Acetone works great for this. I've never had a glue joint that I used acetone on first, fail. The converse is not true.

To make epoxy easier to handle, use fillers to thicken it to the consistency of peanut butter so it'll stay in place. For high strength bonding I use West System's 404 filler but all manufacturers have a variety of fillers available. Sorry if this sounds like a commercial for West, but it's what I know and use. There are plenty of other epoxies out there that'll work just as well.

Regarding mixing epoxy wrong. Most manufacturers make metering pumps for dispensing from their cans of resin & catalyst. If you don't use metering pumps, you can buy [url="http://www.hobbylinc.com/htm/nhp/nhp215.htm?source=froogle"]small plastic shot glasses that are also measuring cups[/url]. I found a bunch of them at Target I think. They come in very handy for the 5:1 mix ratio that my epoxy uses. You must be very careful with the ratios when using epoxy or you won't get a good cure. This isn't so true with other resin/catalyst combos like vinylester or polyester & MEKP.

Good luck, take pictures and show us what you did.

Edited by - delliottg on 06/21/2008 10:56:22

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 06/21/2008 : 10:52:59

5" x 5" x 1/2" plywood impregnated with epoxy isn't going to bend to conform any more than plastic... bedding is important. Equally important is rounding the corners and edges so you don't get extreme point-pressure against the hull.

Edited by - on

Deric
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408 Posts

Response Posted - 06/21/2008 : 19:47:06

Dave,

I appreciate your sharing of knowledge regarding the epoxy and polyethylene issue. Knowing this may cause adhesion issues, I shall be sure to check the epoxy adhesion to my cutting board often. I suspect that the three bronze bolts, in addition to the valve pipe threaded to the inline ball valvebase, is securing the pressure plate in place; the base is merely spreading the load over a wider surface area against the inside of the hull. My backing plate is approximately 5 inches.

Here is a link to the Groco setup I used. Maybe it is something others may find helpful.

http://www.groco.net/08-scks-valves/08-ibvf-1.htm

Dave, thanks for sharing. I love learning from this site.

Deric

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delliottg
Former Mainsheet C250 Tech Editor

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4479 Posts

Response Posted - 06/21/2008 : 21:42:29

Deric,
I think you're in reasonably good shape as long as you understand that you're more using the epoxy as a filler to conform to the shape of your hull than as an adhesive. With the bolts and pipe threads keeping it in place, loss of adhesion isn't as big of a deal as it might be otherwise. Plus the epoxy should stick just fine to the fiberglass on the inside of the hull.

Edited by - on

cmckitrick
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116 Posts

Response Posted - 06/23/2008 : 10:46:10

Hi all. I ended up using the highest grade marine plywood that money can buy. Probobly overkill but thats what I did. Needless to say I have a lot left over. We ended up cutting trangular shapes with rounded edges that fir the base of the flange. I used 3/4" marelon seacocks for the ones under the v birth and stove and a bronze 1 1/2" for the head discharge. The only reason I used bronze was that my local West Marine was out of marelon. I sort of wanted bronze anyway because I like their look. I know they are more maintainance not to mention the sticker shock. We used 5200 sealant. A very experienced friend helped me. This is not something I would have attempted myself although now I probobly could. It is such a relief to be rid of those rusty gate valves. Especially when the one in the v berth practically fell out by looking at it.. I will try and get pics if people are interested. Its a thing of beauty. If anyone in my area needs marine grade plywood let me know.

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redeye
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Response Posted - 06/23/2008 : 11:39:57

I wanted to find a way to change mine without using epoxy resin but I could not figure out a way to keep water out of the backing blocks. Did you use your sealant all over the backing plywood?

Thanks...

Edited by - on

cmckitrick
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116 Posts

Response Posted - 06/23/2008 : 18:37:36

Yes we covered the plywood with it.

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redeye
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Response Posted - 06/24/2008 : 09:18:58

Thank you.. that sounds like a lot more fun than epoxy!

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JohnP
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1520 Posts

Response Posted - 06/24/2008 : 09:59:06

Ray,

You may change your opinion of epoxy if you take advantage of the West System with their resin pump and hardener pump and the little and big pamphlets that explain all the details. The methods are worked out VERY WELL. I bought their 80-something page booklet.It's easy, and so useful for some things, like this kind of backing plate.

I had used epoxy for years before on household items, by squeezing tubes, or pushing syringes, and those methods are so poorly controlled in comparison to the West System with pumps and thickeners and temperature info guides.

My 2 cents.

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delliottg
Former Mainsheet C250 Tech Editor

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4479 Posts

Response Posted - 06/24/2008 : 11:02:47

Given the chance, I'd rather work with epoxy any day than sealant. It's much easier to control IMHO. Sealant gets EVERYWHERE, epoxy stays reasonably well where you put it if you've prepared it properly.

Edited by - delliottg on 06/24/2008 11:29:50

redeye
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Response Posted - 06/24/2008 : 11:52:20

Yepper... I've used epoxy and glass for years. Stinks. Works well but I don't like it. Hard to beat for below the waterline though.

I've used bedding compounds and 100% silicone for above the waterline and both are the bomb...

I think the Catalina is one of my first boats that was laid up so well that I did not have a patch on it somewhere...Kitty Hair ya know...

May I live to see the day we hafta use carbon fiber!

I've never used 5200 sealant, but it sounds like something I'd like to look into.

thanks..

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Deric
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408 Posts

Response Posted - 06/25/2008 : 08:23:02

Hello Folks,

I took an after picture of the work I performed on the thru-hull. I mentioned in a previous message on this thread that I had used a cutting board material.

Note: two pictures below. One picture displays the original 1978 gatevalve connected to a pipe that was glassed into the hull. Another picture displays a new bronze valve with a flange base whereby three bronze bolts secure it to the hull. I used epoxy to form a level base so that the cutting board could be mounted; between the hull and the flange base.

Pictures often tell the story.

Deric

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redeye
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Response Posted - 06/25/2008 : 08:51:59

That is amazing how scary the original to-hulls looked. They did work for a long time. The new one looks great.

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