Fiberglass coaching welcomed

[Delta Riverat]

That thing is just waiting for a log to bust it off clean.

 

[Comodave]

That thing is just waiting for a log to bust it off clean.

Agree, especially if the fairing block is wood.

 

[slowgoesit]

I'm doing that exact same thing to my boat in June haul-out. We're putting in two transducers, which need to be same distance back on hull. We currently have two with large fairing blocks. Haven't decided if I am going to remove both yet, or keep the one working one as a spare with an inexpensive backup fathometer, or remove both, fill both in, and relocate the new transducers farther forward on the hull . . . .

Here's the rub. Our hull is 2" thick. 1/2" of fiberglass on either side of 1" of hard airex foam core.
Based on what I've read here, the 1/2" thickness on either side is the deciding factor of how far to fair, rather than taking into account the additional 1" of the core material, correct? If this is correct, I'm looking at 12:1, a half inch thick outer layer yields a 6" fair, correct?

I would assume the 1" of the core could be filled with matting, or do I need to go 1" down with the fair, and fair out 12" around the hole?

 

[DDW]

How big are the holes? For small holes, I would grind both sides about 1/2 the laminate thickness at a 12:1. Fill the hole with a scrap of Airex (or really any hard foam core). Then glass up both sides back to the original surface. Small holes are not a structural issues, however you want to make sure than the foam core is very well sealed from water ingress. A full structural repair would have you grind to a 12:1 on the total skin thickness. If the holes were 8" diameter, I'd do that, but for 1 or 2 inches, not necessary.

The original holes should habe had the core rebated and backfilled with epoxy, or better yet the core in the area removed before the second skin was laminated. That might change what you do. If the core was removes before lamination, then you have a single skin laminate.

1/2" skins on 1" core is a very solidly built hull.

 

[Comodave]

First make sure the core isn’t compromised around the hole. Hopefully the person that installed the transducer sealed the core properly. If each side is 1/2” thick I would fair out the hole on a 12:1 or 6” on each side of the hole. And on each side of the hull. It is easy to do once you start so why not go the full distance and make it right. As to the core, assuming it is good, I would cut a piece the same thickness of the original core and the diameter of the hole. I would epoxy it in place with thickened epoxy after grinding but before glassing.

 

[Greg QS]

Yes I would recommend removing. You can always put in a sea cock and plug it. If you do not want to do the fiberglass work.

After my run up from Florida to north Jersey, I pulled the boat. Had a weird looking penetration in the bottom of the boat. Turned out to be a snapped off , Old unused, depth sounder. It was not mentioned in the survey, but did not look like a fresh break. I was pretty pissed it was missed. Thank god someone put it in with 5200 and it had a flange on the inside with a couple small no8 screws . So a snap off can Absolutely happen!

 

[CharlieO.]

Yes I would recommend removing. You can always put in a sea cock and plug it. If you do not want to do the fiberglass work.

After my run up from Florida to north Jersey, I pulled the boat. Had a weird looking penetration in the bottom of the boat. Turned out to be a snapped off , Old unused, depth sounder. It was not mentioned in the survey, but did not look like a fresh break. I was pretty pissed it was missed. Thank god someone put it in with 5200 and it had a flange on the inside with a couple small no8 screws . So a snap off can Absolutely happen!

I did consider just putting another seacock in, but I already have an extra one from a previous generator and a couple underwater discharges that currently are not plumbed.

Also did consider putting a new thru hull transducer in, but I already have an in hull and a transom mount and didn't see the need.

Anyway I think the fiberglass work should be pretty straightforward and I look forward to getting it done.

 

[Greg QS]

It is . I have done a lot of it. When doing the glass on the outside upside down, Gravity is not your friend. As the glass heats up the patch will fall off because the resin thins out with the heat. Take a 2x4 with an appropriate size piece of plywood on the end. Wrap the plywood in heavy plastic. Use it as a wedge to the ground to hold up the multi layer patch.

 

[Greg QS]

I generally use Epoxy for these type of repairs. Mainly because I am doing the work in the north east, early year, and you cannot use standard resins below 40 deg. The epoxy is better for lower temps with the fast hardeners. Stay away from a blushing epoxy. New epoxies are non blushing, Meaning no washing in-between layers. No reason to all all that extra work. If you forget to wash your layers will not stick.

 

[CharlieO.]

I do have the new resin epoxy resin and the faster hardener. Should be in the 50's this weekend in the yard.

 

[Greg QS]

Good luck . use the support. You will think all is good and then will find your patch on the ground , or worse , cured and 1/2 hanging off the boat. You don't have to as why i know that. Do You? And don't forget the plastic bag either, unless you want the block of plywood to become part of the boat.

 

[Gdavid]

As a general rule, many boat yards use epoxy below the waterline to ensure adhesion, it is inherently resistant to osmosis and you don't have to worry about getting gelcoat to stick to it. For repairs above the waterline, many shops prefer vinylester because you can work faster with it than epoxy, it is a good compromise in strenght between polyester and epoxy and also, gelcoat will adhere better to it than it will to epoxy. There are products to help gelcoat bond to epoxy, but in most cases, if a repair needs a fine finish above it and is laid up in epoxy, the boat will be refinished in paint.

That said, I am 20 years removed from doing fiberglass work in a boatyard so that may be outdated observations.

 

[psneeld]

As a general rule, many boat yards use epoxy below the waterline to ensure adhesion, it is inherently resistant to osmosis and you don't have to worry about getting gelcoat to stick to it. For repairs above the waterline, many shops prefer vinylester because you can work faster with it than epoxy, it is a good compromise in strenght between polyester and epoxy and also, gelcoat will adhere better to it than it will to epoxy. There are products to help gelcoat bond to epoxy, but in most cases, if a repair needs a fine finish above it and is laid up in epoxy, the boat will be refinished in paint.

That said, I am 20 years removed from doing fiberglass work in a boatyard so that may be outdated observations.

Till a few years back that was still pretty accurate where I was.