Thru Hulls above the water line

[britinusa]

I have read Maine's excellent article about installing thru hulls and watched a dozen utube how toos and they all seem to say the same except one.

The backing plate should be thru bolted from outside the hull.

But what about above the waterline thru-hulls?

On Eximius, none of the thru hulls (above or below the waterline) appear to have shut off valves that are bolted to a backing plate, they all appear to be just screwed onto the threaded part of the thru hull itself, although there appears to be a retaining nut on the inside of the hull that is either glassed in or is sealed with something like 3M 5200 (guessing)

So the thru hull from the Anchor locker looks the same as the engine intake thru hull, or pretty close.

I have to cut a new thru hull into the side of the V-berth about the same height as the anchor locker thru hull.

Not too happy about drilling 4 holes through the hull, one for the thru hull and 3 for the bolts for the sea cock.

So I was thinking about following Maines process except not drilling the 3 holes through the hull.

Then, with the bolts in place in the backing plate, gluing the plate in place.

When cured, mount the sea cock onto the backing plate and screw the thru hull into place with sealant around the flange and outside most threads.

Am I way out on this one?

Any links to show how to do this would be welcomed, as always 

Thanks.

Paul

[ghebbns]

Hi Paul,

I faced the same dilemma as you and did exactly as you suggest.  I found a few websites that gave some information on this:

http://www.pbase.com/mainecruising/backing_blocks
http://www.raggedsails.com/replacing-through-hull-and-seacock/

Hope this helps,

Greg

[Jon W]

There is also a video by Forespar on how to install Marelon flanged sea cocks. Mine were installed similar to the video. The backing plate is bonded to the hull, and the sea cock is attached to a backing plate with SST screws from inside the hull only. No bolts/screws from the outside. Photo attached showing the raw water inlet sea cock and backing plate as an example.

Jon W.

[britinusa]

Thanks Greg, I had seen the other (bolts through hull) method on Mainesails site. His explanation on the studs threaded into the backing plate is a great review of the process.

Jon, that Forespar video was the only 'one' that showed bolts through the backing plate. There were a bunch of issues with that description, so I'm glad that Greg pointed me to Mainesail's other description.

Thanks Guys.

Paul

[Jon W]

The Forespar video I saw does not talk about using bolts, he says to use screws through the seacock flange holes into the backing plate after the thru hull and seacock are tightened together.

There is a follow on video from someone else that says to use screws or bolts through the backing plate instead of the approach Mainesail recommends. Of these two I would follow Mainesails site.

Jon W.

[britinusa]

Already working on the Mainesail method  - cut off bolts.

Paul