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  Topic Review (Newest First)
06-15-2007 10:52 PM
sailingdog Ah... I see... I normally do it on the backing plate as well, so that there is an o-ring between the plate and the flange.
06-15-2007 10:43 PM
Maine Sail
S. Dog

Look very closely at the picture with the sealant on the flange and you can see that I did countersink the holes slightly before installing the seacock. Good thinking but I was already there....
06-15-2007 05:22 PM
sailingdog Very nice...

I would have countersunk the fastener holes slightly, as that allows the sealant to fill in the countersink area and form an o-ring of sorts.
06-15-2007 02:24 PM
Maine Sail
I had a few questions..

I had a few questions posed to me via private message and thought I give the full low down of my backing plates.

I laminated a 2 foot wide by 3 feet long fiberglass board on a sheet of waxed glass using alternating cloth and woven roving with the outer 3 layers being cloth on each side. I built it up to 5/8 of an inch thick and then used a 6 inch hole saw in my drill press to cut out the "donut hole" backing plates. I then roughed up the hull, the rough side of the backing plates and the edges with a drill and a brass brush. I like the brash brush with a drill because it leaves nice deep scars in the surface for the fiberglass to bond to.

Once everything was preped I mixed up some fiberglass "structural kitty hair" and slathered the backing plate and the hull. I then stuck a bolt through the guide hole for the hole saw and climbed out of the boat with a block of wood and a large washer, centered the backing plate in the hole before it kicked then tightened the nut and bolt to give it a solid fit. I then climbed back into the boat and had enough time to feather the edges of the structural filler to the edges of the backing plate for a nice tapered feather.

I then used Sikaflex 292 as my sealant of choice to put everything back together with..

06-05-2007 10:13 AM
Maine Sail
This page may help..

This page may help clarify that these are indeed called adapters and are designed to be used in the manner I described above..

Flanged Adapters:

06-05-2007 07:29 AM
sailingdog Halekai-

Those are not really adapters but are designed for use with standpipes or manifolds IIRC..
06-05-2007 07:14 AM
Maine Sail
Having done this job..

On at least seven boats I can tell you with 100% certainty that there is NO safe way, diver or not, to replace a sea **** or a through hull while the boat is in the water. You probably could replace a ball valve that was threaded onto a through hull though but this is not safe in the first palce. The sea **** is designed to accept the through hull without the nut. How for instance do you clean up the hull exterior and remove all the old 5200 and apply the new 4200 to the mushroom head while under water? How do you dry fit the sea **** and the through hull to drill the bolt holes for the sea ****? How do you counter sink the holes? My drill is not water proof.....

The female end of the sea **** has the same straight threads as the through hull and is made to thread into it. You will also need a step wrench to tighten the through hulls into the sea **** after you have applied copious amounts of 4200...


"I'm not sure I have room for the flanged seacock (near motor mount and not much clearance.), if not is there a thread adapter to get to the type of thread on the ball valve. FYI, it's almost under the engine with exactly zero chance of anything ever rolling, sliding, falling, dropping, or otherwise moving into / onto it."

If you don't have the space you need a flanged adapter. They are the two flanges, one stainless and one bronze, pictured in the link at the top left of the larger photo. They allow you to mount the flange like a sea **** then put a 90 degree bronze elbow and a bronze ball valve. The difference between a flanged adapter and a through hull is that the flanged adapter is straight thread on the female side and NPT on the top side! Plus the flange is through bolted to the hull for safety. Hamilton Marine does stock these adapters but they are not shown in the on-line catalog. Call them they do stock them! Marine Supplies

Picture of flanged adapter for tight spaces:
Untitled Document
06-05-2007 05:27 AM
Idiens SD is right, haul the boat.

But if you are a diver, you could do all the work underwater (one way or another).

Start by jamming a bung in the through-hull from the outside and see if the gate valve still works when you take the hose off it. Open it and see if the bung works. Then see if you can get the gate valve off the through-hull. Pray that the bung holds, that the through-hull doesn't turn and break its seal. Maybe you will be lucky, but keep your diving gear on, just in case.

If you are tidal waters, and are quick, you could try drying out somewhere suitable.
06-04-2007 10:08 PM
Originally Posted by kjsailingSpring
Is there a relatively safe way to install these below the waterline while the boat is in the water? Probably a silly question but I'm too cheap to take the boat out but the insurance company says "get it done!"
Good way to sink the boat... and you won't even be covered by insurance... hmm... that's a really good idea. Haul the boat and do it properly.
06-04-2007 09:56 PM
Installing in the water

Is there a relatively safe way to install these below the waterline while the boat is in the water? Probably a silly question but I'm too cheap to take the boat out but the insurance company says "get it done!"
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