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Old 29-08-2015, 09:36   #16
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Re: Fiberglassing in hole in thick hull.

If the existing thru hull is not compromised, why not leave it?

Clean it, epoxy a plug in it, be sure the valve inside is serviceable, and inspect it w every haul out.

A lot less work, and no worries that your patch may fail.
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Old 29-08-2015, 09:51   #17
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Re: Fiberglassing in hole in thick hull.

Have any of you seen a movie called "All is Lost"? Sailboat rammed by floating shipping container - sailor does a fiberglass patch mid ocean! Good movie!
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Old 29-08-2015, 10:02   #18
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Re: Fiberglassing in hole in thick hull.

Quote:
Originally Posted by Maka View Post
If the existing thru hull is not compromised, why not leave it?

Clean it, epoxy a plug in it, be sure the valve inside is serviceable, and inspect it w every haul out.

A lot less work, and no worries that your patch may fail.
+1. If it ain't broke, don't break it. That thru hull might come in handy some day.
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Old 29-08-2015, 10:09   #19
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Re: Fiberglassing in hole in thick hull.

If the existing thru hulls are not leaking dont remove them.
Clean them out, epoxy a plug in them, and be sure your in hull fittings and valve are serviceable. Or remove the valve and cap that end.

Inspect both at every haul out.

Keep in mind that any fiberglass patch you make will only have a mechanical bond and NO chemical bond like the rest of your hull.
Don't underestimate the value of that chemical bond.
No patch will be as strong as the original hull is.

This approach is much cheaper, easier, and safer. IMHO.
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Old 29-08-2015, 11:24   #20
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Re: Fiberglassing in hole in thick hull.

Alert!! I have to chime in here. PLEASE please please, if you don't REALLY know the answer to a repair question, SAY it is just your opinion. Bad advice, taken as fact, can be dangerous!
All fiberglass manuals that I have ever read show the "largest" piece of repair glass goes on FIRST!! The longest fibers contact the greatest number of hull fibers, and the rest of the layers bring the strength up to the existing area of the hull. It also works the same if you are installing/replacing a bulkhead.
I was a dealer for a major manufacture that had to replace a whole series of chainplate bulkheads that had been designed correctly but installed wrong at the factory with the small pieces of glass put on first. They started failing fairly quickly.
While it may seem reasonable to "grind out" through several layers of hull, you are actually just making a bigger hole in a perfectly good boat. Hand laid repair glass has about 25% of the peel strength of the original layup, maybe 50% with epoxy, so your patch has to be at least four times the area of the ground out area, which quickly becomes a major repair, and beyond the abilities of most owners.
The "fill the actual hole" repair and a reasonable number of layers over the hole is in most cases the "best" solution. It will be heavier and not look as pretty, but done correctly, fast, easy, and safe on most cruisers.
If you are dealing with a very light and/or cored construction, vacuum bagging, re-coring and such is usually beyond the scope of owner repair.
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Old 29-08-2015, 11:35   #21
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Re: Fiberglassing in hole in thick hull.

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Originally Posted by minaret View Post
Done it that way many many times. Buy a piece of G10 and laminate it together to make your plug. Then grind and glass exterior, grinding at least 1/8" material off and laminating with 2-3 1708. Then slap a fat patch on the interior too. Fair exterior, barrier coat, and paint to match.
Minaret,

What do you think about leaving the through hulls in place as some have suggested?

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Old 29-08-2015, 11:41   #22
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Re: Fiberglassing in hole in thick hull.

What about an hourglass plug. Grind inside and outas tapered into existing glass after removing thruhull. Then layup your fbiberglass in an hourglass fashion all in one layup so you get a good chemical bond between all surfaces. Of course on the inside of the hull you can place a large heavy stitchmatt piece. Then when cured the exterior can be faired and filled as necessary and the inside will need minimal work.

The problem with using plugs of a different material is you essentially have a cored structure. With this method you have only widen the hole just enough to get into good virgin hull and only taper the glass enough to keep the new composite layup strong enough to prevent working out. Kind of a compromise to extreme 20:1 or 12:1 grinds?
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Old 29-08-2015, 12:20   #23
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Re: Fiberglassing in hole in thick hull.

On the very thick hull, it is hard to do any real damage, but the plug and glass, with minimum grinding in or out, seems best. I would limit grinding on the outside as much as possible on any boat unless you were ready to make a major repair. A modest radius (1/2" - 3/4") tapered no more than 1/4 ' in is all that is necessary in most cases. It doesn't have to be very deep either, and I much prefer to make all repairs with epoxy.
On my own, very thin and cored boat, I am installing a "cheap" extra depth sender to fill a 2" hole. It seems the easiest solution. The hole is forward and sort of exposed, my hull is 1 layer of 12oz glass inside and out over 3/4" airex, and a "proper" repair would require cutting out too much interior. It also proves that it doesn't take a whole lot of glass to keep to water out- my boat is quite fast, well used, and 39 years old. It hasn't broken yet.
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Old 29-08-2015, 12:21   #24
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Re: Fiberglassing in hole in thick hull.

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Originally Posted by Lojanica View Post
What about an hourglass plug. Grind inside and outas tapered into existing glass after removing thruhull. Then layup your fbiberglass in an hourglass fashion all in one layup so you get a good chemical bond between all surfaces. Of course on the inside of the hull you can place a large heavy stitchmatt piece. Then when cured the exterior can be faired and filled as necessary and the inside will need minimal work.

The problem with using plugs of a different material is you essentially have a cored structure. With this method you have only widen the hole just enough to get into good virgin hull and only taper the glass enough to keep the new composite layup strong enough to prevent working out. Kind of a compromise to extreme 20:1 or 12:1 grinds?

" hourglass fashion all in one layup so you get a good chemical bond between all surfaces."

Not so. You only have a chemical bond on the surfaces of your patch. You will NOT have a chemical bond between the patch and the cured existing hull, where you want it most.

Bruceb and I are in agreement in his post regarding patching holes.

My opinion is that removing the thru hull fitting creates a worse hole than the one you already have, which is a planned and properly created hole.
But if you do remove it, follow Bruceb's advice, along with others here who post similar solutions.
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Old 29-08-2015, 13:44   #25
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Re: Fiberglassing in hole in thick hull.

You're probably right. Another way I've seen it done is a big plank bolted into the hull as a backer with the screw heads countersunk exteriorly then filled and faired. The plank is glassed and bolted into place or (5200). Then the fiberglass layup is performed from the outside. The screw holes are separated from the thru hull hole by a large margin.
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Old 29-08-2015, 14:35   #26
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Re: Fiberglassing in hole in thick hull.

Probably the most "secure" "repair" would be a rubber plug (like a transom plug on a skiff) secured from the inside I am not suggesting it, just saying. A 2" hole shouldn't! have much movement in a thick hull, and the rubber would take up any flex that happened.
Unless the hole is very near the end of some inner hull structure like keel support frames, (and it should not be) the flex across the hole is about nill. The hardest boats to repair are the thin ones, like a trailable 22' for instance. Often their bottoms are trampoline- like flexible and then they have trailer bunk loading also. Holes of any kind can start a stress crack so repairs have to be spread over a large area to be safe.
Not that it is not correct, but I am not much in favor of combining wood and fiberglass in hulls. If the glass repair is proper, the wood is unnecessary, and in my experience, wood in a glass hull ALWAYS rots eventually. Using any sealant that sets with an acid chemistry (like most silicone) creates an acidic area against the wood that is an ideal place for rot to start. If the wood rots at all, you are back to depending on the glass repair.
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Old 29-08-2015, 15:42   #27
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Re: Fiberglassing in hole in thick hull.

Quote:
Originally Posted by Maka View Post
If the existing thru hulls are not leaking dont remove them.
Clean them out, epoxy a plug in them, and be sure your in hull fittings and valve are serviceable. Or remove the valve and cap that end.

Inspect both at every haul out.

Keep in mind that any fiberglass patch you make will only have a mechanical bond and NO chemical bond like the rest of your hull.
Don't underestimate the value of that chemical bond.
No patch will be as strong as the original hull is.

This approach is much cheaper, easier, and safer. IMHO.
So that is what I did with my two thru-hulls. I removed the valve and capped them, which can be done while the boat is in the water too by the way, if you don't mind snorkeling around your boat and pushing in a soft plug. However, I did not epoxy a plug in. That seems too tough to undo in the event I want to use the thru-hull again. Once capped I just filled the fitting with silicone to keep stuff from growing in there. HOWEVER there is a caveat with this technique. The fitting and capped end are still there, sticking up, inside the boat, exposed, and vulnerable if smashed by some heavy weight falling on it while sailing. We had a sad case many years ago of a Cal 24 disappearing on a fairly rough day in the Santa Barbara Channel. The boat was later snagged by a fishing net in deep water many miles away. The theory was a heavy object had fallen on a thru-hull and they took on a lot of water, and lost their electrical, before they realized there was a problem. Before they could find the leak the boat sank. To this day I scrutinize thru-hulls (on any boat!) and keep a PLB and a waterproof handheld VHF. So anyway, most folks protect the area around thru-hulls but one that is capped may get forgotten or ignored.
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Old 29-08-2015, 15:43   #28
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Re: Fiberglassing in hole in thick hull.

These kinds of discussions are great because you learn a lot. There are many ways to approach the problem and by having people discuss people find a good solution. Also if somebody's in a far off location these ideas can be applied in those situations.

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Old 29-08-2015, 16:02   #29
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Re: Fiberglassing in hole in thick hull.

Quote:
Originally Posted by Maka View Post
If the existing thru hull is not compromised, why not leave it?

Clean it, epoxy a plug in it, be sure the valve inside is serviceable, and inspect it w every haul out.

A lot less work, and no worries that your patch may fail.
I agree with this. Based on the data from the OP, Anything you do will be at least as strong as the port you removed. 1-1/2 inch is massively thick. Even if the port is removed, glass cleaned up & dry & back-filled with epoxy and chopped glass it will likely never be an issue. You could even laminate a patch over the inside.
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Old 29-08-2015, 17:47   #30
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Re: Fiberglassing in hole in thick hull.

Just to provide some perspective on all this.

If all you did was the very very simplest plug - take the thru hull out, clean the hole surfaces and glue in a round disk the same thickness as the hull (of fiberglass or G10) with epoxy, with no/zero cloth layers inside or outside and no tapering at all. You would have a shear strength of very roughly around 10,000lbs (surface area x typical epoxy lap shear strength) - eg that plug would have to get directly hit by a 10,000lb push to break the bond, and that might well fracture the surrounding fiberglass rather than pop the plug (depends on the quality of the fiberglass - remember the hull is polyester and your new bond is epoxy).

Now if you did that plug and then added a 12" diameter inside patch you move the bond strength up into the 100,000's lbs and the hull will most definitely fracture before the plug pops out.

That's an extremely simple analysis, does not account for dynamic (shock) force, but suggests basically whatever you do will be 'strong enough' so long as you make a nice clean bond.
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