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Old 08-08-2012, 12:36   #1
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Thru-Hull / Seacock Install Questions

Going to be installing a Thru-Hull Raw Water Intake and Bronze Seacock with a 6"x6" G10/FR4 Backing Plate in the bilge of my Fiberglass hulled Skipjack Runabout. I've never done any work like this but from what I've gleaned from this and other sites, think I have a decent idea of how to do the install properly but still have a few questions.

On prepping the mounting spot in the bilge, what would be the correct process/procedure?

Since it's a fairly small job, I was considering using West System's G/flex 650 Epoxy kit to bond the backing plate in place. Is this a good choice for my application or should I use their Six10 Epoxy Adhesive instead? If the G/flex product is adequate, would the small kit (4oz Epoxy/4oz Hardener) be enough for my 6x6 inch plate or should I get two kits or a bigger 16oz kit?

Thanks - David
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Old 08-08-2012, 12:56   #2
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Re: Thru-Hull/Seacock install questions

I would just use a sealant like 3M 5200 and do it at the time you put the thru hull in. put enough in there that it squeezes out when you tighten the assembly. or use a product like Boat Life caulk. Always nice to rough up the surface a bit first.... especially if you have shiny smooth gel coat in there. If just exposed glass mat/roving, probably not necessary if clean. If oily greasy, clean all that off with acetone etc.
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Old 08-08-2012, 13:12   #3
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Re: Thru-Hull/Seacock install questions

4200 might be better if you ever want to be able to unthread the nut in the future.

Most hulls are thick enough where you dont need a backing plate for a new thruhull fitting.
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Old 08-08-2012, 14:32   #4
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Re: Thru-Hull/Seacock install questions

David is correct. Use 4200 from 3M. Do not use 5200. Make sure surfaces are clean and smooth. Use denatured alcohol on a rag to clean up / smooth out after applying for professional look. Instead of backing plate install washer to spread load.
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Old 08-08-2012, 14:37   #5
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Re: Thru-Hull/Seacock install questions

Quote:
Originally Posted by David M View Post
4200 might be better if you ever want to be able to unthread the nut in the future.

Most hulls are thick enough where you dont need a backing plate for a new thruhull fitting.
Unthreading a nut of any metal type or size will not be an issue with 5200. removing wood from fiberglass might! at any rate any good sealant will work.
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Old 08-08-2012, 17:46   #6
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Re: Thru-Hull/Seacock install questions

One reason I was inclined towards using the backing plate was to avoid drilling three more holes in the hull for the Seacock flange bolts. I was going to do it as shown in the following link - scroll down to "Seacocks/Thruhulls/Backing Plates". BTW - I have a full tube of 3M 4200 Fast Cure - that would be plenty strong enough to bond the backing plate in place?

http://www.lizardheadone.com/Plumbing.html
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Old 09-08-2012, 05:53   #7
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Re: Thru-Hull/Seacock install questions

See ABYC H-27, Through-Hull Fittings and Drain Plugs ➥ http://www.marinesurveyorschool.org/...in%20plugs.pdf

And ➥ http://www.groco.net/SVC-MAN-07/Sec4/PDF/IBV-FBV-TB.pdf

And ➥ Replacing Thru-Hulls and Seacocks Photo Gallery by Compass Marine at pbase.com

And ➥ BoatUS - BoatTech - Installing a Seacock by Don Casey
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Old 09-08-2012, 06:06   #8
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The backing plate is important for compression, it's not optional
--We like glass epoxied to the hull as you recommend
--5200 is fine and won't make removal impossible (one of its few good uses in my opinion is underwater fittings)
--thru bolting the backing plate is the correct technique. It really makes for a stronger installation and take the stress off the threads; the drawings from Casey's link from a previous post show it clearly

If you aren't comfortable with this hire a pro... It's an area I'd hate to skimp on.

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Old 09-08-2012, 19:09   #9
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Re: Thru-Hull/Seacock install questions

My original reason for wanting to install a Thru-hull Raw Water fitting and Seacock was to try to circumvent an overheating issue I am having with the raw water pickup/cooling circuit in my Volvo-Penta 280 Outdrive but I've figured out what the problem is and have decided to fix it properly.

A $6 plastic bushing commonly referred to as the Pivot Tube Bushing (p/n 11 in this diagram) is evidently worn, damaged, or missing. It is allowing the Pivot Tube or Steering Knuckle shown in the same diagram as p/n 22 to move/oscillate, causing damage to the Hose Connection Gasket p/n 28, causing air to enter the cooling water flow when up on plane, resulting in the overheat issue.

To fix the problem, the outdrive must be removed and partially disassembled. Taking the boat in next week to have the work done properly instead of trying to circumvent the problem by installing a Thru-hull pickup. Will have other maintenance items (Bellows, U-joints, Bearings, etc.) checked/replaced that are accessible when the drive is off as a precaution. Even though I really can't afford it right now, might as well fix it right or you know it will damned well cost a lot more down the way.

Thanks to all that have replied trying to help - you have a great Community here.
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Old 12-08-2012, 15:02   #10
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Re: Thru-Hull / Seacock Install Questions

Two reasons for a backing plate:
1. make a thicker area on the hull for the valve to mount in
2. spread the stress form the valve onto the hull

The method I'm using is laying up alternating layers of 2 oz mat and 10 oz roving starting (at 45 degrees) with a very large patch and each layer smaller until I build up to the thickness I disire. If you want a 6 inch backing plate maybe start with a 10 inch patch

1. 100 % bonded to the hull with no need for adhesives
2. NO hard spots on the hull, as there would be with a plate, as the patch is tapered out to a single layer

When you're finished with the patch drill your hole and apply the adhesive/ bedding to set your valve in.

Anyway, just my 3 cents on the issue.
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Old 12-08-2012, 19:09   #11
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Re: Thru-Hull/Seacock install questions

Quote:
Originally Posted by Skipjack20 View Post
My original reason for wanting to install a Thru-hull Raw Water fitting and Seacock was to try to circumvent an overheating issue I am having with the raw water pickup/cooling circuit in my Volvo-Penta 280 Outdrive but I've figured out what the problem is and have decided to fix it properly.

A $6 plastic bushing commonly referred to as the Pivot Tube Bushing (p/n 11 in this diagram) is evidently worn, damaged, or missing. It is allowing the Pivot Tube or Steering Knuckle shown in the same diagram as p/n 22 to move/oscillate, causing damage to the Hose Connection Gasket p/n 28, causing air to enter the cooling water flow when up on plane, resulting in the overheat issue.

To fix the problem, the outdrive must be removed and partially disassembled. Taking the boat in next week to have the work done properly instead of trying to circumvent the problem by installing a Thru-hull pickup. Will have other maintenance items (Bellows, U-joints, Bearings, etc.) checked/replaced that are accessible when the drive is off as a precaution. Even though I really can't afford it right now, might as well fix it right or you know it will damned well cost a lot more down the way.

Thanks to all that have replied trying to help - you have a great Community here.
Yeah, why do they want to suck cooling water through the outdrive anyway? never did figure that out... do they try to cool the outdrive as well as the engine? anyone know?
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