Through-hull fitment question

[Gene Neill]

My boat's sink drain has a 1 3/8" hole drilled. (I presume the old fitting was metric?) I would like to use this hole as is, if possible.

A 1" Groco thru-hull calls for a 1 5/16" hole, which is 1/16" too big.

Can I get away with it?

 

[justsomeguy]

Can I get away with it?

Is this a test?
I wouldn't get away with it. You probably shouldn't...

 

[Richard19068]

My boat's sink drain has a 1 3/8" hole drilled. (I presume the old fitting was metric?) I would like to use this hole as is, if possible.

A 1" Groco thru-hull calls for a 1 5/16" hole, which is 1/16" too big.

Can I get away with it?

Seems close enough to me but what do I know. I'd call Groco.

 

[Gene Neill]

Seems close enough to me but what do I know. I'd call Groco.

Yup. Might do that tomorrow.

FWIW, I'll be using a proper flanged seacock, backing plates, etc, all to @Maine Sail specs.

 

[Gene Neill]

BTW, I can always go to an 1 1/4" thru hull and just enlarge the hole. It's a few extra bucks, and a much bigger than necessary mushroom head for a sink drain, though. Otherwise, I'll have to fill that hole and drill another one.

 

[dlochner]

There will be a 1/32" gap around the through hull. That is not all that large, a good quality caulk could fill it.

The "right way" to fill a hole is to grind out a 12:1 bevel and then apply layers of glass and fair it. I don't think it is necessary to go that route to fill this small a hole. I'd be inclined to clean the edges of the existing hole to make sure all the caulking is removed and sand the hole with 80 grit. Then fill the hole with thickened epoxy and drill the new hole. This isn't a structural repair and the new through hull will seal the hold, you're just trying to fill in a 1/32nd inch gap around the new through hull.

While it sounds easy to just enlarge the hole to take the next larger diameter through hull, it really isn't that easy. I tried enlarging a hole this year and ended up filling the hole and then redialing it. If there is a reason to go with a larger drain, then go ahead and fill the hole and drill a new one. Either way it is the same job.

 

[BigEasy]

Gene,
I agree with Dave Lochner....you will have a 1/32" gap that will be filled with sealer (3M4200?) and a backing plate and nut on the inside of the hull. I wouldn't hesitate to do it; should be a strong leakproof fitting. However, just so you have "peace of mind," go ahead and give Groco a call to confirm.

 

[Gene Neill]

I'd be inclined to clean the edges of the existing hole to make sure all the caulking is removed and sand the hole with 80 grit. Then fill the hole with thickened epoxy and drill the new hole.

Bingo. I like that. I'll install a very thick G10 backing plate first, then paint the hole with thin epoxy, let it get tacky, then fill it with thickened. Fair it, drill a new hole, done.

Since I get a new hole, I think I can go smaller than the original. I don't think 1" plumbing is necessary for a sink drain, am I right? Will 3/4" do the trick? Maybe 1/2" even? The sink is just foot-pump operated.

 

[dlochner]

Since I get a new hole, I think I can go smaller than the original. I don't think 1" plumbing is necessary for a sink drain, am I right? Will 3/4" do the trick? Maybe 1/2" even? The sink is just foot-pump operated.

How fast do you want the sink to drain? The bigger the hole the faster the drain. You could take an old bucket or a gallon jug and put a ½'" hole in it see how it drains, then a ¾" hole and so forth.

The flange for the through should be larger than the old hole. The reason this repair works is the the compression from the through hull is primarily on the original hull, if the original hole is larger than the flanges the repair is relying on the bond between the thickened epoxy and the hull. I wouldn't be comfortable with that.

 

[jssailem]

the original hole is larger than the flanges the repair is relying on the bond between the thickened epoxy and the hull. I wouldn't be comfortable with that.

Yes if the repair is just epoxy I agree. If the hole is repaired using the 12to1 bevel edge and layering of glass with the epoxy the area of the hole should be as strong as the rest of the hull.
Though this was discussed it does sound like Gene was considering a short cut approach using just backing board and thicken epoxy. I that case Dave’s caution is more than a suggestion, it is a safety issue.

 

[RoyS]

You will find that it is very difficult to obtain two flat sealing surfaces when using epoxy between the backing plate and the hull. If the epoxy sets up and then you try to install the thru-hull and seacock and find that the sealing surfaces are not in fact perfectly parallel what are you going to do now? You may be better off using a submersible sealant under the backing plate and assembling the whole thing in one pass. The sealant will fill any misalignment between the backing plate and the hull. Epoxy and G10 requires great care to install correctly.

 

[capta]

If you have a cored hull, I would dig out an inch or so of the core around the hole and fill that with epoxy as you were building up to close the hole for redrilling.

 

[jlp0217]

How fast do you want the sink to drain? The bigger the hole the faster the drain. You could take an old bucket or a gallon jug and put a ½'" hole in it see how it drains, then a ¾" hole and so forth. .

A hole in a bucket is not a fair representation of a sink drain. The limiter is the hose full of air. My head sinks have 1" hoses and through hulls and drain slowly. My galley sink has 1 1/2" and drains well. The head sinks can be made to drain quickly by closing the through hull valve and letting the air in the hose escape into the sink then opening the valve. Water is then sucked out of the sink until air gets sucked into the hose, leaving 1" of water in the sink to drain slowly again.
I'd be tempted to go with the 1 1/4" through hull and hose, and adapt it at the sink.

 

[dlochner]

A hole in a bucket is not a fair representation of a sink drain. The limiter is the hose full of air. My head sinks have 1" hoses and through hulls and drain slowly. My galley sink has 1 1/2" and drains well. The head sinks can be made to drain quickly by closing the through hull valve and letting the air in the hose escape into the sink then opening the valve. Water is then sucked out of the sink until air gets sucked into the hose, leaving 1" of water in the sink to drain slowly again.
I'd be tempted to go with the 1 1/4" through hull and hose, and adapt it at the sink.

I don't disagree and I wasn't suggesting this was the definitive test. It was just a suggestion to get a rough idea and to see the relative effects of different size holes. A more time consuming and expensive test that would approximate real world condition would involve buy lots of parts and setting up the whole test differently.

 

[capta]

A hole in a bucket is not a fair representation of a sink drain. The limiter is the hose full of air. My head sinks have 1" hoses and through hulls and drain slowly. My galley sink has 1 1/2" and drains well. The head sinks can be made to drain quickly by closing the through hull valve and letting the air in the hose escape into the sink then opening the valve. Water is then sucked out of the sink until air gets sucked into the hose, leaving 1" of water in the sink to drain slowly again.
I'd be tempted to go with the 1 1/4" through hull and hose, and adapt it at the sink.

This might help, though backwards. Interesting, at any rate.
But don't forget the water pressure if the thruhullis below the waterline.

 

[NYSail]

I spoke with group today...... they do have a full line of metric fittings..... why not just stay the course.

Greg

 

[Gene Neill]

I spoke with group today...... they do have a full line of metric fittings..... why not just stay the course.

Greg

Group?

 

[Gene Neill]

You will find that it is very difficult to obtain two flat sealing surfaces when using epoxy between the backing plate and the hull. If the epoxy sets up and then you try to install the thru-hull and seacock and find that the sealing surfaces are not in fact perfectly parallel what are you going to do now? You may be better off using a submersible sealant under the backing plate and assembling the whole thing in one pass. The sealant will fill any misalignment between the backing plate and the hull. Epoxy and G10 requires great care to install correctly.

I've been thinking a lot about that. One fitting in particular (I'm doing them all) is actually on a convex surface, which seems even dicier than the aforementioned sink drain and all the others.

My plan is to butter the backing plate with a thick layer of thickened epoxy, place it over the pre-inserted through hull, then thread the seacock onto the though hull and snug it down until the epoxy begins to squeeze out and the flange is seated flat on the backing plate.

I can (and probably will) remove the fittings when the epoxy is not yet at full cure, then put them back in place permanently when it's all set up.

Sound reasonable?

 

[Gene Neill]

The flange for the through should be larger than the old hole. The reason this repair works is the the compression from the through hull is primarily on the original hull, if the original hole is larger than the flanges the repair is relying on the bond between the thickened epoxy and the hull. I wouldn't be comfortable with that.

Agreed.

 

[dlochner]

I can (and probably will) remove the fittings when the epoxy is not yet at full cure, then put them back in place permanently when it's all set up.

Get some mold release wax and wax the threads and the fittings. The epoxy will form threads around the through hull. It will also be easier to remove the through hull later.