Thru-hull Hole Problem, Maybe

[GorillaToast]

I have two holes in my hull where failed depth and speed transducers used to be. Neither worked; the wires had been cut by a PO. I removed the old housings, and bought new Raymarine ST-40 system to install. A quick measurement of the holes showed that 2" fittings would work, which is what the new ones are.

I just test fitted one, and found that the old holes are 1/16 - 3/32" too big - the new fitting is very loose in the hole. I'm guessing that the threaded transducer housing should snuggly fit in the 2" hole; maybe not - the old ones fell right out with a couple of taps from a mallet.

Do I need to plug these old holes with epoxy and glass and redrill? If so I'll relocate them (they are just port of the swing keel, in-line with each other and about even, fore to aft, with the keel pivot; not the best location from what the instructions say). Or will I be able to seal around the fittings sufficiantly with Sikaflex or 5200?

Thanks,
Bill

 

[Don S/V ILLusion]

The proper way to re-size the holes is to feather back the glass around the holes and lay new glass building up to the existing hull thickness. Simply plugging or sealing the holes won't provide any strength.

 

[GorillaToast]

The proper way to re-size the holes is to feather back the glass around the holes and lay new glass building up to the existing hull thickness. Simply plugging or sealing the holes won't provide any strength.

Yes, I have several books outlining that process. That was just what I was hoping to avoid by buying new transducers, that btw, I don't really need.

So, are you saying that re-glassing is my only option?

 

[Allan12210]

If the flange portion of the transducer still gives adequate coverage area (overlap) on the outside of the hull, then why not just make a thin ring (bushing) to keep it centered until the sealant you use cures. Does the nut that threads on from the inside also cover adequately to the hull surface? Again, it should be fine with the sealant. I'd consider a bushing made of PVC pipe, or a PVC pipe coupling that will fit the hole and can be sanded or turned to the correct inner diameter. If the transducer is long enough into the interior of the boat you could also use a piece of marine plywood like a seacock has as a backing plate.

 

[s sauer]

If you are saying you have 2-1/16" to 2-3/32" vs the actual 2" diameter of the fittings; what kind of backing do you have in the inside of the hull?
I'd remove the existing (plywood?) backing plate and replace it with new 3/4" thick marine plywood, coated with West System epoxy and also epoxy glue it to the inside of the hull bedded with something like PC-7. I'd then drill the 2" diameter holes thru the plywood and again , coat the inside of the drilled holes and any exposed wood surfaces with 3 coats of West System. Install the fittings with 4200 sealant from the exterior, fully coating the threads and underside of the flanges.

 

[Merlin Clark]

1/16 to 3/32 is a good fit. I wouldn't worry about making it a tighter fit.
I'd use something besides 5200, the future owner that decides to replace that thru hull with a cooling intake for his flux capacitor will thank you.

 

[GorillaToast]

Hmm...Seems to be a pretty wide range of opinions here.

Looks like the most prudent thing to do is to make backer plates.

Btw, I plan to use Sikaflex 291 to bed them.

 

[kloudie1]

I am with Allen on this one.. center the new housing with a bushing.. If the inside nut covers the hole with a pretty good overlap.. (guessing here, but 1/8" or more is probably OK).. then glue it in with a good sealant. If that makes ya nervous, a new fiberglass or ply backing plate under the nut will be fine..

 

[Vic H.]

+1 Allen & Claude.

Vic H.

 

[Merlin Clark]

Might try a bearing shop for that 1/32" or 3/64" wall thickness bushing.

 

[GorillaToast]

With a 3/4" ply backer plate, don't you think an adhesive sealant like Sika 291 or 3M 4200 would be enough to fill the gap? The backer platewill be bedded in thick epoxy, and its hole will provide a tight fit to prevent lateral movement. I suppose I could put a few layers of cloth between the plate and the hull, covering the hole, then drill thru the cured layup and backer plate from the outside.

 

[Vic H.]

With a 3/4" ply backer plate, don't you think an adhesive sealant like Sika 291 or 3M 4200 would be enough to fill the gap? The backer platewill be bedded in thick epoxy, and its hole will provide a tight fit to prevent lateral movement. I suppose I could put a few layers of cloth between the plate and the hull, covering the hole, then drill thru the cured layup and backer plate from the outside.

In my opinion, that sounds fine, There are always a number of ways to solve a problem. I think you have a good solution here.

Vic H.

 

[GorillaToast]

Well, On To Plan B

The installation instructions for the transducers, say that wood should not be used as backer plates because it can swell and crack the plastic housings.

So, I'm looking at some 12" X 12" X 1/2" polyester sheet from Grainger. The problem is that there is a ridge that bisects the holes. It is a flat shelf that seems to run the length of the hull. The plywood blocks I originally made as backers rocked a little on it, so I hollowed them out a bit. I could do the same to the polyester sheet, but I'm concerned that with the hollow on the underside I could get gaps when bedding them that would leak.

That puts me back to square one. I guess it's time to learn how to do the 12:1 grinding and layup work. Just scares me, because the hull is only 3/8ths thick in this area. West Systems suggests making a thin puck by pouring some epoxy into a cup and letting it cure, break it out of the cup, put it in the hole with a waxed backer on the outside, then laminate over it. I think finding a paper cup that's exactly 2-1/8" dia. is unlikely.

What if I taped waxed paper under a flexible backer on the outside, then poured epoxy into the holes, then laminated with mat and cloth on the inside of the hull?

 

[FourPoints]

I would go with you backing plate plan. Fill the little gap with thicked west systems, or attach the backing plate with a healthy glob of 5200 (it's the transducer that may need to come out later, not the backing plate). Either way I think your chances for a leak are about zero.

 

[Bill Roosa]

Build a dam of cardboard in the place you want the backer plate. You can hold the pieces in place with duct-tape. Inset a tube the size of the hole in the hole and then pore thickened epoxy inside. You could get rid of the slop in the hole at the same time if you can seal the external crack with more duct-tape. will probably require some grinding on the outside to fair the hull but you will have a built in backing plate.
Duct-tape, the universal solution to common problems ;-)

 

[Vic H.]

I have two holes in my hull where failed depth and speed transducers used to be. Neither worked; the wires had been cut by a PO. I removed the old housings, and bought new Raymarine ST-40 system to install. A quick measurement of the holes showed that 2" fittings would work, which is what the new ones are.

I just test fitted one, and found that the old holes are 1/16 - 3/32" too big - the new fitting is very loose in the hole. I'm guessing that the threaded transducer housing should snuggly fit in the 2" hole; maybe not - the old ones fell right out with a couple of taps from a mallet.

Do I need to plug these old holes with epoxy and glass and redrill? If so I'll relocate them (they are just port of the swing keel, in-line with each other and about even, fore to aft, with the keel pivot; not the best location from what the instructions say). Or will I be able to seal around the fittings sufficiantly with Sikaflex or 5200?

Thanks,
Bill

Bill, if I understand correctly, you have a hole thats 1/16"-3/32" larger Diameter than the transducer shaft, correct? That's only 1/32"-3/64" between shaft and hole edge, correct? If yes, Im my opinion ONLY, were not talking much slop here. I would use sealant and install per instructions and be done. Use a method to keep shaft centered in hole. Only my opinion, but were not talking a big "Mismatch" here. You have to do what make you comfortable, just my 2 cents worth.

Vic H.

 

[GorillaToast]

Thanks to everyone for their advice on this project. I won't tell you which method I went with. I wouldn't want anyone to feel slighted.

Edit:

I added a picture, plus one of the repair to the inside of the hull where the waste holding tank used to sit. It had delaminated down to the roving, and the tabbing to the pan had broken away.

The project is done now, so while greatly appreciated, any more advice will be ignored.

Thanks,
Bill