1st big project, bronze thru-hull

Minnesail said:

This is what I'm replacing:

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Correct the issues, and do it right this time, so you don't have to do it all over again. I suggest that each hose deserves its own through hull.

Yeah Minnesail, you do need to fix that. I'd do that as a seachest. For my part, I'd never drill more holes in the boat than I absolutely have to.

Minnesail said:

My first big project on my little boat!

The Catalina 22 was built with a garden-hose style valve glassed directly to the hull for the sink and cockpit drain. I'm replacing it with a bronze thru-hull.

This might be mass overkill for a tiny boat that will be sailing on a tiny lake, but one of my goals with this boat is to learn how to do things The Right Way so I'll have the experience for future, larger boats.

So I've got a printout of Maine Sail's instructions, and a big pile of 1" bronze hardware:

Any tips, tricks, or advice?

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On very bottom of the picture is picture of bronze thru-hull with straight thread.
Usually nut of some sort tightens(this is fancy one) it from the inside. This is all covered with lot of some kind glue to make permanent seal. Then comes ball valve with tapered pipe thread on both side. Question is how this can work straight thread and pipe thread?

Osprey 26 said:

On very bottom of the picture is picture of bronze thru-hull with straight thread.
Usually nut of some sort tightens(this is fancy one) it from the inside. This is all covered with lot of some kind glue to make permanent seal. Then comes ball valve with tapered pipe thread on both side. Question is how this can work straight thread and pipe thread?

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It cannot work well. That is the reason for the flange adaptor shown in the picture. The other proper installation would be a true seacock which has straight threads where it mates with the through hull.

Osprey 26 said:

On very bottom of the picture is picture of bronze thru-hull with straight thread.
Usually nut of some sort tightens(this is fancy one) it from the inside. This is all covered with lot of some kind glue to make permanent seal. Then comes ball valve with tapered pipe thread on both side. Question is how this can work straight thread and pipe thread?

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It is not supposed to work but MANY builders simply choose to IGNORE the safety standards and connect NPT valves to NPS thru-hull fittings..

The proper method, is as shown, with a proper flanged seacock or a Groco flanged adapter which has NPS into the bottom and NPT threads on the top...

Adding that the reason for the NPS thread is that it enables the installer to cut the through hull fitting to the correct length to accommodate the thickness of the hull and backing plate, while the NPT allows the seacock to be tightened down onto the flange.

mitiempo said:

Groco has backing blocks similar to Mainesail's no through bolt method. They don't state what material they are, I guess fiberglass.

From Groco's catalog:

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A few months back I called Groco and asked what material their backing plate was made of. The tech support did not know exactly, but said the material is like a man made plastic plywood. It is not solid and the literature states it can form to non flat surfaces. I am sure you cannot drill and tap the Groco backing plates. The backing plates would only be of use if you plan to through bolt a seacock or Groco adaptor plate. These cannot be used like Maine sail drill and taps the G10 and epoxies to the hull.

casey1999 said:

A few months back I called Groco and asked what material their backing plate was made of. The tech support did not know exactly, but said the material is like a man made plastic plywood. It is not solid and the literature states it can form to non flat surfaces. I am sure you cannot drill and tap the Groco backing plates. The backing plates would only be of use if you plan to through bolt a seacock or Groco adaptor plate. These cannot be used like Maine sail drill and taps the G10 and epoxies to the hull.

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I couldn't find any place that sells them. I thought I could save a step and save having to buy a big hole saw if I could buy a pre-shaped backing plate, but although they're in the catalog I couldn't find any website selling them.

Minnesail said:

I couldn't find any place that sells them. I thought I could save a step and save having to buy a big hole saw if I could buy a pre-shaped backing plate, but although they're in the catalog I couldn't find any website selling them.

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Yes I was hoping the same thing. If you want them, just go to the Groco website and look up Groco distributors, they can special order them for you. In any case, they do not look like they would work. In fact, I am really not sure how they can be used. It looks like Groco would expect the installer to use the thru hull itself as the sole method of connecting the seacock to the hull. This backing plate would just distribute to loads on the hull. This would be no different than sticking a piece of plywood under the seacock (or adapter fitting). With the thread inserts, it looks as if Groco is not expecting the installer to through bolt the seacock/adapter plate.

Lots of good advice. The most important issue to me is that...

Every through hull eventually becomes a step or hand hold. If you can grab it and break it, there is too much leverage or there needs to be better support.

Minnesail said:

I couldn't find any place that sells them. I thought I could save a step and save having to buy a big hole saw if I could buy a pre-shaped backing plate, but although they're in the catalog I couldn't find any website selling them.

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There is a fiberglass product I know as 'strong-back' which I believe is 'structural fiberglass' at McMaster-Carr (mcmaster.com) you can get that and fabricate a backing plate for yourself. You may be able to buy something like you want at McMaster, whether or not fiberglass

Multihullgirl said:

There is a fiberglass product I know as 'strong-back' which I believe is 'structural fiberglass' at McMaster-Carr (mcmaster.com) you can get that and fabricate a backing plate for yourself. You may be able to buy something like you want at McMaster, whether or not fiberglass

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Are you talking about G10 (Garolite)? I used that for my thru-hulls; also, got it from McMaster-Carr. Used West Systems 404 mixed into epoxy for the adhesive to the hull. I think that is what people used on other threads on this topic.

Maybe this will be useful: I have used G10 for a number of different things. It is really a hard material. I use a saber saw with fine teeth to rough cut rounded shapes. Then do final shaping using either a sanding disc on the table saw or sanding attachment on the angle grinder. This makes a lot of dust. The dust will coat everything in the shop. I do it outside if using the angle grinder. I rigged up a vacuum attachment for the table saw.

When cutting G-10 on the table saw, I buy cheap plywood blades (fine spaced teeth). They don't last too long. But normally, there are not very many cuts to make.

gbgreen59 said:

I have used G10 for a number of different things. It is really a hard material. I use a saber saw with fine teeth to rough cut rounded shapes. Then do final shaping using either a sanding disc on the table saw or sanding attachment on the angle grinder.

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Yeah, I have a little sheet of G10 that I'm going to use for the backing plate. That stuff seems crazy durable!

So the jigsaw works for round cuts? I was thinking about that, but I'm afraid I wouldn't be able to cut a very neat circle.

The other option is a hole saw, but that means picking up a moderately expensive hole saw that I'd likely only use once or twice.

(It would also mean clearing away the rubble from the corner of my garage so I could get to my drill press, but that's another issue&#8230

I do a rough cut with the sabre saw...outside the line. Then finish shaping by sanding with the tools mentioned above.

I've used the method you mentioned too and work just fine. The really big cutters get pretty expensive, but not that bad. Makes it an easier, less messy job too.

Minnesail said:

Yeah, I have a little sheet of G10 that I'm going to use for the backing plate. That stuff seems crazy durable!

So the jigsaw works for round cuts? I was thinking about that, but I'm afraid I wouldn't be able to cut a very neat circle.

The other option is a hole saw, but that means picking up a moderately expensive hole saw that I'd likely only use once or twice.

(It would also mean clearing away the rubble from the corner of my garage so I could get to my drill press, but that's another issue&#8230

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Bi-metal hole saw. Dig out the drill press. G10 is tough stuff. I used a pulsing technique on drill press to fab several backing plates from 1/2" G10.

WoobaGooba said:

Bi-metal hole saw. Dig out the drill press. G10 is tough stuff. I used a pulsing technique on drill press to fab several backing plates from 1/2" G10.

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I guess that's what I'll do. $40 for a 6" bi-metal hole saw at Home Depot. I'll just have to think of something else to use it for to justify the expense. Oversize checkers set?

I'm really not looking forward to tunneling my way back to the drill press... A winter's worth of procrastination is stacked up in front of it.