Filling holes in hull with epoxy barrier coat

[slugchewer]

I'm in the process of replacing all the old, corroded thru-hulls and valves (most of them gate valves) with new ones. The existing valves were bolted all the way through the hull with stainless steel, which is now corroded almost to dust.

The plan is to remove those bolts, fill in the holes in the hull, and lagbolt the new valves into new (epoxy-sealed) plywood backing plates.

I would normally clean out the holes and fill them with poly filler, then gelcoat over, but the bottom had an epoxy barrier put on a few years ago by the previous owner. Can I still use poly filler, or do I need some kind of epoxy putty? Do I need to seal that, or can I just paint over it?

(Another option that was mentioned was just to glass over the existing corroded bolts on the inside, and to leave them in the hull, but I don't like the idea of sealing a bunch of rusted metal in there.)

Cheers!

[Stillraining]

Hmmm...are you doing it this way to avoid messing with the new epoxy barrier coat?

Or is it that the existing bolt pattern/holes wont line up with your new seacock flanges?

I personally dont much care for lag bolts in a potentially wet environment..hard to seal the wood...just MHO.

[slugchewer]

Mostly because the existing bolts are so corroded that they're no good for anything. I don't really want to see it happening again (with through-hull bolts), so I figured sealing it back up and keeping the bolts inside the boat was best.

One other option was to bolt up through the back of the backing plates... takes care of that lag bolt problem (I know what you mean). I'm not sure yet whether they line up -- will have everything together this weekend.

Either way, I guess I'm still curious about filling those holes... any thoughts?

[Stillraining]

I have to admit I have contemplated doing exactly as you described the second time..putting the bolts up through the block only and epoxying the block to the hull forgoing drilling through and having more hull penitrations..BUT..thats not the recommended way of doing it..I think if it were me and the existing hole pattern lined up ,I would reuse the existing holes after cleaning them up and maybe even re drilling them one size larger.

I can relate to the corrosion issue but dont think youll get completely away from it the other way either.

As far as filling the holes most people recommend using thickened epoxy..as it has better secondary adhesion properties...then fair and reapply your barrier coat..No way would I intumb the corroded bolts in the repair no matter which way you go...if they possibly continue corroding they could delaminate your repair from internal pressures..just like a blister does.

Don Casey does a good job of explaning it.
Installing a Seacock by Don Casey

[Maine Sail]

They should have never been stainless in the first place and should have been silicon bronze. Replace them with silicon bronze and they will most likely out last you and the boat. Stainless steel suffers badly from crevice corrosion and does not like a moist oxygen starved environment.

[slugchewer]

Stillraining -- that idea was straight from Groco, who recommended that method of installing them.

halekai36 - absolutely my thoughts. Though, Groco recommended SS, not bronze, despite all my persistent arguing. They pointed out the SS ball in the valve.

At the moment, it looks like I'll do the following:
- remove all old hardware, including corroded SS thru-bolts
- fill existing bolt holes with epoxy filler
- cut out round plywood backing plates and seal with penetrating epoxy
- seal backing plates and thru-hulls to hull with 4200
- bed (bronze!) lag bolts into backing plates with Dolphinite

Sounds crazy but it just might work!

[Maine Sail]

Originally Posted by slugchewer

Stillraining -- that idea was straight from Groco, who recommended that method of installing them.

halekai36 - absolutely my thoughts. Though, Groco recommended SS, not bronze, despite all my persistent arguing. They pointed out the SS ball in the valve.

I don't know who you spoke to at Groco but the balls in the bronze ball valves are NOT stainless steel they are supposed to be chrome plated red brass. I can assure you it took about three phone calls and many folks before I got a straight answer on this. I still don't know why they are not chrome plated bronze but was told it has something to do with the bronze and the chrome plating..?

If you are going to bolt them internally consider laminating solid fiberglass backing plates, not wood, then drill and tap them for some 1/2 inch long bolts and epoxy or glass the backing plates directly to the hull. Both Morris and Hinckley have solid glass where every thru-hull is installed not wood. Why? It lasts for ever, wood does not, and when your paying a minimum of 750k for one of their boats they damn well better..

The proper fix for any hole in the bottom of your boat is a 12:1 taper even on a small bolt hole. They should never just be filled with a "filler".. A 12:1 taper means that the hole is tapered from the center to twelve times the diameter of the original hole then cloth and mat are used to rebuild the lamination schedule.

I'd still through bolt them!

P.S. Can you let me know who you talked to a Groco? I have spent considerable time on the phone with them for a few articles I've written and many of the folks there have no clue. There are some that do but you may have just got one of the clueless ones as bronze seacocks should always be installed with bronze bolts!

For more info on seacocks feel free to read these two articles.

Seacock Installation

Thru-hull and seacock Primer

[sailingdog]

Actually, IIRC it is twelve times the DEPTH of the area being repaired, not the original hole size, since a 4" hole would require you to grind approximately EIGHT FEET of the hull to repair it.

If the fiberglass has a hole four inches in diameter and is five-eighths of an inch thick, you'd need to taper an area about 20" in diameter from the center of the hole—the original four inch hole and an area about eight inches out from that (since a 12:1 taper for 5/8 = 7.5").

Originally Posted by halekai36

The proper fix for any hole in the bottom of your boat is a 12:1 taper even on a small bolt hole. They should never just be filled with a "filler".. A 12:1 taper means that the hole is tapered from the center to twelve times the diameter of the original hole then cloth and mat are used to rebuild the lamination schedule.

From the West Systems site:

Now grind back about 1/8" to 3/16" (depending on how thick the puck is) thickness from the laminate on both sides of the hole on a 12:1 bevel. This will give the beveled area about 5" diameter. Fill the beveled area on both sides with a layered fiberglass patch and epoxy. Once the patches cure, sand them and an area larger than the patch to prep for fairing and finishing. It is especially important to remove all the antifouling paint anywhere epoxy will be applied because epoxy will not stick well to most bottom paints.

[Maine Sail]

Originally Posted by sailingdog

Actually, IIRC it is twelve times the DEPTH of the area being repaired, not the original hole size, since a 4" hole would require you to grind approximately EIGHT FEET of the hull to repair it.

If the fiberglass has a hole four inches in diameter and is five-eighths of an inch thick, you'd need to taper an area about 20" in diameter from the center of the hole—the original four inch hole and an area about eight inches out from that (since a 12:1 taper for 5/8 = 7.5").



From the West Systems site:

Thanks for the proof reading it must have been the wine and beautiful scenery that made me type "hole diameter" instead of "hole depth".

When your sitting on the hook on a remote off shore island with internet cell service and views like the one bellow bad typing can happen..

[pegasus1457]

Originally Posted by slugchewer

I would normally clean out the holes and fill them with poly filler, then gelcoat over, but the bottom had an epoxy barrier put on a few years ago by the previous owner. Can I still use poly filler, or do I need some kind of epoxy putty? Do I need to seal that, or can I just paint over it?

All of the fairing compounds I have tried (3M Filler, Interlux Interfill) strongly recommend overcoating the filled areas below the water line with 4 coats of Interprotect -- before you paint.