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To Hull to Thru Hull Replacement

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jackfuller
1st Mate

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USA
29 Posts

Initially Posted - 08/31/2005 : 16:14:41

I'm replacing my to-hull with a thru hull (under the galley). Any suggestions about correcting the angle that the thru hull makes as it comes out the bottom? I've seen a fairing block used on a Morgan I had. What kind of wood and how to attach it to the hull? Epoxy, 5200.? Maybe it would be best to plug the current hole and hole drill another at the proper angle for a thru hull. How to plug the current hole?
Thanks,
Jack '79 C25

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Dave Laux
Captain

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318 Posts

Response Posted - 08/31/2005 : 19:23:53

The to hull you have now must be ground off altogether. This will leave you with a hole that is much smaller than the thru hull will need. When you expand it to fit the thru hull the of ange will disappear.
You can use a wood, ususally plywood , spacer backing block to help to add stifness to the hull skin. Its usually wood cause if it leaks a little the wood will swell and seal itself. However with modern sealants, 3M 101 or 5200, a plastic ring works fine to.
Be prepared to cut the thru hull down so that everything fits with no extra threaded body between the lock nut and the valve. Better get a sea valve with a large flange and cut the thru hull to fit.
I like the Forespar marelon fittings, valve MF 849, thru hull CF251, and tailpiece CF252, all x pipe size.
Dave

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thaind
Navigator

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Canada
145 Posts

Response Posted - 08/31/2005 : 22:10:24

When I did this last spring I used a Forstner bit the same size as the fitting. I shaped a piece of 2" stock to outside hull shape, bored a hole through it on my drill press, hot-melt glued it over the undersized to-hull hole and used it an allignment jig to drill the new hole. When finished there realy wasn't much of the volcano left inside and ground/reemed square with through-hull fitting and sealed all with 3M. I didn't find any need for a spacer, but if I had would likely have used some high density plastic. The hot melt came off easily, but this was before bottom coating. Good luck.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 09/01/2005 : 07:48:30

While relocating and installing a new knotmeter thru-hull, I found that when I dry fitted the assembly, the outside flange was flush to the hull, but the inside flange nut was only making contact on one side with the other side more than a 1/4" from the inner hull.

To fix this problem, I used a hockey puck size ring the P.O. made from epoxy as a backing for the old knotmeter. I formed the bottom of this ring to follow the contour of the inner hull while leaving the top flush so the flange nut would sit flat. Not only did I have to taper this ring, I also had to put a curve in it to make it sit right.

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jackfuller
1st Mate

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USA
29 Posts

Response Posted - 09/01/2005 : 10:53:54

Thanks for the wonderful HELP!!!!
We just bought an '89 30' Hunter and I can't find anywhere near the web resources that I have here and with a Morgan we used to have.
Jack

(Yes, the 25 will be for sale as soon as I finish some fixer upper things. We are in Eastern VA on the West side of the Bay.)

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ronrryan
Admiral

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USA
561 Posts

Response Posted - 09/01/2005 : 12:46:26

Have done this job on a couple occasions. Used to take a circle of ply or whatever fit nicely, butter well with marinetex and apply until dry (suitable plastic taped on outside of hull) then you can drill through as appropriate from without, and also throughbolt the pad if you like. Makes a neat and strong application, and the marinetex provides the proper curvature for the inner hull, also a neat fillet looks nice and strengthens everything. Good luck, Ron Orion srsk #2343 SW FL

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Happy D
Admiral

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921 Posts

Response Posted - 09/02/2005 : 08:28:47

I used the Forespar [url="http://www.forespar.com/onlineCatalog/44-Marelon.shtml"]Intergrated [/url]assemblies. The web page shows OEM only, but I called them and they sold me whatever I wanted. I talk to an engineer there and he e-mailed me the installation instructiions.
To make the hole larger and to correct the alignment, I just used a [url="http://www.northerntool.com/images/product/images/170966_med.gif"]rotary file[/url] in my electric drill and cut the hole proper. It was real easy. I sealed the edge of the fiberglass hole with unthickened epoxy so the water doesn't get to the polyester laminate.
Forespar is an excellent company to deal with.
Dan
http://home.wmis.net/%7Edhapp/through.hull.html

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