Enlarging hole in hull?

[Tally Ho]

I am assembling parts to replace all of the above-the-waterline thru-hulls on my 1988 O’Day 322. The original white plastic one are brittle and ready for replacement.

I have 4 different hose sizes and 4 different “hole” sizes in the hull.

Despite my best attempts to verify the diameter of the threaded body of the new thru-hulls, when they arrived today, only the 1” hose size fits the hole In the hull.

The 2 smaller hose sizes (5/8” and 3/4”) have a hole size the same as the 1” hose size, so I will need to enlarge the holes in the hull for these 5 thru-hulls. The hull is solid glass.

****The question is, what is the best tool or way to enlarge the holes? I can’t imagine I can hold a hole saw in place well without having the arbor to keep it steady. A spade bit probably will bind in the existing hole.... would a step bit be the way to go?

The largest thru-hull for the 1 1/2” scupper drains is actually smaller than the old one...so those holes may have to be reduced...which I assume will mean grinding and glassing them over, then re-drilling. Really didn’t want to do that...

photo 1) all the new ones with their originals
photo 2) 5/8” hose size, but bodies are way different size
photo 3) 3/4” hose size...body larger than original (and same size as 5/8“ and 1” hose sizes)
photo 4) 1 1/2” hose size...body is smaller than the original and may require making the hole in the hull smaller to



==================Notes=================================================
I am ready to order some thru hulls, but want to verify the hole size in the hull...
For example, part # 145708 - 1 1/2 hose size, but what is the size (diameter) of the threaded area or the size of the hole in the hull? The old one is 1.85" (1 7/8").
Part # 145703 - 5/8" hose - what is the thread area/hole size? the one I am replacing is about .785"
Part # 145704 - 3/4" hose - what is the thread area/hole size? (I haven't taken this one out yet).
Part # 145705 - 1" hose - what size is the thread area/hole size? the one I am replacing is about 1.3"

Response============================================
Greg,

It doesn't tell me exactly, but it does tell me what the pipe area size is so I have looked that up and have listed the conversion below.

5/8" hose - 0.84 (this one is listed as 1/2" pipe size)
3/4" hose - 1.05
1" hose - 1.315
1-1/2" hose - 1.9

I think these are real close to what have so you should be fine.
======================================================

Rant over....


Greg

 

[sesmith]

Cut a plug for the hole the right size with your hole saw from a piece of wood. Glue it into the hull (or maybe you could just tape around it and tap it into place). You could also back it up with a piece of wood temporarily glued to the inside of the hull. Use the plug as a pilot for the larger hole saw.

 

[Allan12210]

Here is a link to my post when I enlarged my raw water intake through hull. I used two hole saws; one inside the other to follow the existing hole.

Hunter 34 Owner Modifications and Upgrades

Hunter 34 Owner Modifications and Upgrades

hunter.sailboatowners.com

 

[dlochner]

There are a couple of ways as @sesmith mentioned. The tool to use is a hole saw. If the hull is thin enough, hot gluing a piece of door skin plywood on the inside of the hole will give the pilot drill a place to start. On thicker sections of the hull the pilot bit will need to be longer or gluing a plug in the hole will work. I've used both methods. Another method I recently read about using a tapered plug and driving it into the hole and using it to start the drill.

How much smaller is the 1 ½" through hull? If the flange and the nut are larger than the existing hole, this is not a big deal. Cut a plug that is a little smaller than the diameter of the new through hull. Epoxy the plug into the existing hole with thickened epoxy. Once the epoxy has cured, drill the new hole the proper size. This is such as small area there should be no issue with strength and the new through hull will secure the filled area so there is no danger of it falling out.

It should go without saying, proper preparation for the epoxy and working when the hull is warm enough is essential. Use a structural filler, like cabosil or glass fibers to thicken the epoxy, microballoons would be a poor choice. Or make life easy and use West System SixTen or Total Boat Thixio.

 

[daviddp]

I had a similar problem with my oday. I used Bed-it tape (LOVE IT!) on the inside of the hull to stick a piece of thin luan plywood to the interior, I then drilled from the outside in. ( much easier access with the drill) You only need to get the pilot bit centered of course, I pre-drilled it to just under the hole saw pilot size through the luan and then get a "bite" of out the fiberglass on the outside. Go very slow at the start until you have the hole saw (spend the money on a new saw blade, its worth it) a 1/8" or so into the fiberglass. Clean up was easy with a plastic putty knife and weather is not an issue. Just a thought.

 

[Tally Ho]

Thanks all for the tips and suggestions. It looks like the hole saw, with a thin piece of something glued over the existing hole is the best idea. The idea of pounding a tapered plug into the hole also promising....maybe the best idea.

Thanks for all of the great ideas! I feel less worried about it with those good suggestions.

@dlochner - For the 1 1/2”, the new one is about 1.5”. The one that came out is 1.85”. So pretty far off. But the OD of the nuts are about the same size...so maybe it will fit...but there is about a 1/2“ difference in the size if the heads...a lot of that is in the difference in the size of the flange...

I will take it out to the boat this week and see how things look.



Thanks again for all of the great suggestions!

Really appreciated.

Greg

 

[Charlie Jones s/v Tehani]

Here is a link to my post when I enlarged my raw water intake through hull. I used two hole saws; one inside the other to follow the existing hole.

Hunter 34 Owner Modifications and Upgrades

Hunter 34 Owner Modifications and Upgrades

hunter.sailboatowners.com

This will be the quickest and easiest way. I've done it several times

 

[dlochner]

Thanks all for the tips and suggestions. It looks like the hole saw, with a thin piece of something glued over the existing hole is the best idea. The idea of pounding a tapered plug into the hole also promising....maybe the best idea.

Thanks for all of the great ideas! I feel less worried about it with those good suggestions.

@dlochner - For the 1 1/2”, the new one is about 1.5”. The one that came out is 1.85”. So pretty far off. But the OD of the nuts are about the same size...so maybe it will fit...but there is about a 1/2“ difference in the size if the heads...a lot of that is in the difference in the size of the flange...

I will take it out to the boat this week and see how things look.

View attachment 188640 View attachment 188641 View attachment 188642

Thanks again for all of the great suggestions!

Really appreciated.

Greg

Greg,

I think you will be fine with just filling in around a plug. The .35 inch difference will be evenly divided, so the there will only be about 1/6" gap all around. That will be sealed with caulk and held in place with compression from the through hull. When the through hull is installed, the threads will be caulked and the nut should be caulked too. The caulk will seal the sides of the hole and lock the nut into place.

If you want a bit of belt and suspenders, epoxy in the plug as I suggested earlier and then lay a layer of glass on the inside of the hull that overlaps the hole by an inch or so. That would help seal the seam between the epoxy plug and the hull. You could also grind down the gelcoat around the hull and add a layer of glass on the outside too.

 

[Tally Ho]

Greg,

I think you will be fine with just filling in around a plug. The .35 inch difference will be evenly divided, so the there will only be about 1/6" gap all around. That will be sealed with caulk and held in place with compression from the through hull. When the through hull is installed, the threads will be caulked and the nut should be caulked too. The caulk will seal the sides of the hole and lock the nut into place.

If you want a bit of belt and suspenders, epoxy in the plug as I suggested earlier and then lay a layer of glass on the inside of the hull that overlaps the hole by an inch or so. That would help seal the seam between the epoxy plug and the hull. You could also grind down the gelcoat around the hull and add a layer of glass on the outside too.

Thanks. I will get a good look later this week and see how the thru-hull looks in the hole. This is above the waterline, but under water when motoring as the boat squats in the water.

Greg

 

[Richard19068]

For the 1 1/2”, the new one is about 1.5”. The one that came out is 1.85”. So pretty far off. But the OD of the nuts are about the same size...so maybe it will fit...but there is about a 1/2“ difference in the size if the heads...a lot of that is in the difference in the size of the flange...

Tally Ho,

The threaded portion of the 1-1/2" mushroom to hose barb thru hull from Marelon looks like it has an od of 1.850".
Perhaps you could get the Marelon item for that hole and not have to worry about size difference.

What brand did you get?

 

[Capt jgw]

If you're going up from one hole size to another, get one of the hole saw kits where a smaller bit will fit inside the bigger one. Put both on the arbor and the smaller one will protrude enough to hold the larger one in place. Works well, I've done it a few times. If the hole is just "a little bit" too small, a rotary file or a sanding drum in a drill motor run around the inside of the hole will open it up. I've done that too.

 

[Tally Ho]

Thanks @Richard19068,

I am not sure what brand the are...I ordered them here on SBO.

I picked them as a cost-effective compromise between bronze/sst or marelon and the cheapest plastic ones.
They are fiber-reinforced and have a sst cap that I hope cuts down on UV damage.

Greg

 

[Tally Ho]

If you're going up from one home size to another, hey one of the home saw kits where a smaller but will got inside the bigger one. Put both on the arbor and the smaller one will protrude enough to hold the larger one on place. Works well, I've done it a few times. If the hole is just "a little bit" too small, a rotary file or a sanding drum in a drill motor run around the inside of the hole will open it up. I've done that too.

Thanks for that. Others have suggested that approach. I was trying to visualize the 2 sizes together...and I think I see what you mean.

I will get out to the boat this week and see how much each size needs to be enlarged.

The good news is that 3 of the different hose sizes will have the same sized hole in the hull, so only need one hole saw for all of those.


Greg

 

[dlochner]

Thanks. I will get a good look later this week and see how the thru-hull looks in the hole. This is above the waterline, but under water when motoring as the boat squats in the water.

Greg

This is good. With the through hull above the water line hydrostatic pressure is not an issue. Water pressure while motoring won't be that much and it will be intermittent. You could probably get away with filling the void with 3M 4200 or 4000, but I wouldn't do that, I'd go with the thickened epoxy.

 

[Tally Ho]

This is good. With the through hull above the water line hydrostatic pressure is not an issue. Water pressure while motoring won't be that much and it will be intermittent. You could probably get away with filling the void with 3M 4200 or 4000, but I wouldn't do that, I'd go with the thickened epoxy.

Thanks Dave. I am sure I will get it fixed right. I sure appreciate the solid advice.

Greg

 

[RoyS]

You could go with a larger through hull and seacock, then reduce to the hose barb size with a threaded bronze reducer inside. Expensive, but certain success.

 

[MikeHoncho]

I didn’t read the whole thread so apologies if Simone already said it but get one of these to enlarge the hole with a hole saw
Starrett KA19-N"Oops" Arbor, Hole Enlargement Arbor Starrett KA19-N"Oops" Arbor, Hole Enlargement Arbor: Amazon.com: Industrial & Scientific
The inner bit is the existing size and it is your guide while the outer is the new size. I used it several times and worked great.

 

[Tally Ho]

You could go with a larger through hull and seacock, then reduce to the hose barb size with a threaded bronze reducer inside. Expensive, but certain success.

I could do that, but this is an above-the-waterline scupper drain. So it seems like over-kill to me.

Thanks,

Greg

 

[Tally Ho]

I didn’t read the whole thread so apologies if Simone already said it but get one of these to enlarge the hole with a hole saw
Starrett KA19-N"Oops" Arbor, Hole Enlargement Arbor Starrett KA19-N"Oops" Arbor, Hole Enlargement Arbor: Amazon.com: Industrial & Scientific
The inner bit is the existing size and it is your guide while the outer is the new size. I used it several times and worked great.

That certainly would work.

I went out to the boat this morning, and was able to enlarge the holes for the smaller size thru-hulls using the wooden plug idea suggested by @dlochner. It worked very well, and was simple solution (often the best kind) using stuff I already had at the boat.

I fit the 1 1/2” thru hull into its hole, which is a bit too large. The backing nut fits good, but there is precious little of the mushroom flange making contact with the exterior hull. I am going to think about this for a while, take the 2nd one out and see how the new one fits...it is too cold to do much with epoxy, so I have some time to think about this issue.

But for now, the smaller ones are in place thanks to the great ideas for enlarging the holes in the hull. I haven’t bed any of them yet as it is too cold to apply Sikaflex, but I am very confident in all but the 1 1/2“ thru-hulls, but will come up with a solution before spring.




Thanks everyone for the very good ideas to enlarging the holes...

Greg

 

[jssailem]

Make a 'Note to Self' Greg... Do not sit boat in water till all of the thru hulls are checked for caulking. You know how we all get when it comes to spring and the chance to splash is suggested.