Filling transducer holes

Lots of good advice and undoubtedly the method described by West Ssytems will give the strongest and most homogenous repair.
However it is worth remembering that we are talking about blanking off a transducer / seacock hole in the hull not a structuarl repair. How much strength do you think the seacock or transducer contribute to the actual hull laminate in the are of the hole - very little to none is the answer.
Consequently the aim of most people really only needs to be making a durable, waterproof repair - no real need to restore the structural integrity and strength of the hull since you were perfectly happy with the minimally reduced strength when the transducer was in the hole!!!
Obviously if you want full structural strength go with West Systems, otherwise a reasonable taper inside and out together with a plywood plug is pretty adequate, although I would use resin mixed with chopped strand to make a filler rather than a plywood plug.
Polyester resin is good enough although epoxy is certainly better. Remember a large proportion of structural repairs to polyester grp hulls are made using polyester resins after suitable preparation and grinding away of any damaged laminates. If your hull was t-boned and badly damaged the yard would almost certainly be using polyester resin for the repair so if it is ok for large repairs it is good enough for blanking a transducer hole - or am I missing something??
 
Polyester doesn't stick to old grp very well so most repairers will use epoxy although if you do remember in the future polyester doesn't chemically bond with epoxy at all. The reason west & other repairers use the 12to1 method is structual integrity in case of an impact.

Here is a good guide from a professional grp repairer who also use the 12in1 method.

 
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Tammany said:
Polyester doesn't stick to old grp very well so most repairers will use epoxy
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Your video link is talking about structural damage, not the same as getting rid of a small, machine made hole, so the 12 to 1 is more relevant. It's nice to see this professional repairer using polyester resin :)

If making something new with polyester it is best to apply successive layers before the preceding one has fully cured. This give a stronger bond, as it's chemically bonded. Repairing polyester that's fully cured using polyester resin will still give a structurally sound bond. When boats where built before epoxy was used there were lots of structural components that were added to fully cured polyester and they stuck.

The key is in the preparation. As said, removing a transducer isn't a structural repair anyway. I could bash a wooden bung in with a smear of Sika and saw it off flush and it's be no less structurally sound than it is now.
 
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PaulRainbow said:
Your video link is talking about structural damage, not the same as getting rid of a small, machine made hole, so the 12 to 1 is more relevant. It's nice to see this professional repairer using polyester resin :)...
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By the time he cut the bevel, the result was the same as for a machined hole. He used polyester resin because he is going to use gelcoat.
 
nigelmercier said:
By the time he cut the bevel, the result was the same as for a machined hole.
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I will not be cutting such a bevel, it would be insanity to do so for a one inch transducer hole. No matter how badly a repair i make it will not reduce the structural integrity of the hull at all. So long as it holds water it will be no worse than it is now. If i grind back a large area, as in the video, i will have removed a lot of hull material and that will, without any doubt, reduce the hull strength. I then have to effect a repair that not only stops the water getting in but returns the hull integrity to that which it was before i started. I shall make the hole slightly larger and bevel both sides slightly and then repair with CSM and polyester resin.

He used polyester resin because he is going to use gelcoat.
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Nonsense. Polyester gelcoat will bond to epoxy perfectly well.
 
PaulRainbow said:
I will not be cutting such a bevel, it would be insanity to do so for a one inch transducer hole.
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Perhaps if I repeat my post from the previous thread, although I did link to it earlier ...

I recently contacted Gougeon Brothers (West System) as follows:

I have read your document at http://www.westsystem.com/ss/repairing-machined-holes-in-fiberglass/
I have a 1" drilled hole at the bottom of my hull, currently occupied by an unused 3/4" through-hull (skin fitting).
The GRP is about 1" thick at this point, cutting a 12:1 taper will result in a huge area.
Please can you advise the best solution.

Reply:

Ideally, you would grind a bevel from both sides - in and out. This allows you to reduce the bevel to 8:1 so the effective thickness of the laminate becomes 1/2" making the bevel 4" dia. from the edge of the hole on both sides. I wouldn't recommend you go any less on the bevel since this area is a high risk area where failure could be catastrophic.
Bruce Niederer | Senior Tech Advisor
Gougeon Brothers, Inc

Nonsense. Polyester gelcoat will bond to epoxy perfectly well.
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So you didn't watch the videos then.
 
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nigelmercier said:
Perhaps if I repeat my post from the previous thread, although I did link to it earlier ...
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Yes, i saw your post Nigel. That's pretty much my plan.

So you didn't watch the videos then.
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I skimmed through the first couple. My point still stands though, gelcoat will stick to epoxy just as well as it will stick to polyester, if prepped properly (which applies to both of course).

Polyester will bond to fully cured polyester too, just not quite as well as to that which is not fully cured. Part cured is a chemical and mechanical bond, fully cured is a mechanical bond. The same applies to using epoxy though, it's still only a mechanical bond.
 
The boatworkstoday channel is amazing. Co-incidentally, my favourite was when he tested gelcoat on epoxy - https://www.youtube.com/watch?v=kHAbyglpp3M - he found it was fine if memory serves.

Given the choice I'd use Epoxy, especially as a DIYer, but I'd not be concerned if a competent person chose Poly either. I've done some minor repairs with both and generally find epoxy easier and nicer to work with.

I don't agree that filling a transducer hole is a non structural repair. Indeed the boatworks chap defines any repair that has gone through the whole laminate as structural.
 
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Cutting a bevel only applies if you intend to laminate GRP to effect the repair. It is far simpler and just as effective to epoxy in a plug of the original material.
 
So many of you still seem to be missing the message.

I have a small hole in the hull, it currently has a rather degraded looking transducer in it.

If i remove the transducer, no matter what i stick in the resulting hole or how i stick it in, it won't further affect the structural integrity of the hull.

My repair needs to be watertight and be sound enough so as not to fall out.

If i make the hole slightly larger and slightly bevel the hull on both sides i have a good clean surface, to which polyester resin will adhere perfectly well. The centre of the hole will be filled with chopped strand and resin, with some layers of CSM mat and resin on both sides. This will give me a roughly cotton reel/yoyo shaped plug of solid glass strand and resin, mechanically bonded to freshly uncovered GRP.

It won't leak, you wouldn't be able to knock it out with a hammer and by not grinding large areas of good hull away i will not have further reduced hull strength/integrity.

This is not a structural repair, in that it is not being done to return any strength to a weakened laminate. The hole is already there, my repair will be stronger than a plastic transducer. A structural repair would be where something punched a hole in the laminate. It would then be a hole surrounded by weakened laminate, you would need to grind back a large area to be certain of removing the damage and to return the weakened hull to full strength.

Polyester resin will mechanically bond to fully cured polyester layup. It isn't as strong as the chemical and mechanical bond the you get with wet on wet layup, but is perfectly strong enough for the application.

Polyester gelcoat will adhere to epoxy.
 
A couple questions to those who have repaired holes in their boats.

What type of resin did you use ?

What type of mat did you use ?
 
I've used both West Epoxy and SP Gurit 106 - usually with their micro balloons. I've never used any mat for filling machined holes - the epoxy is either coated with gelcoat or marine epoxy filler.
 
PaulRainbow said:
A couple questions to those who have repaired holes in their boats.

What type of resin did you use ?

What type of mat did you use ?
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I've used West epoxy resin and hardener.

I've used woven and/or chopped strand matting.

I've always ground a nice shallow bevel and used varying sizes of matting to build up the layers. Its stronger that way.
 
PaulRainbow said:
A couple questions to those who have repaired holes in their boats.

What type of resin did you use ?

What type of mat did you use ?
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West epoxy and 600g biaxial glass cloth. (IIRC I slightly thickened the resin)

Original hole size 2¼" diam ( BallHed outlet)

Chamfered only on the outside but started with a single layer on the inside laid up against a layer of peel ply supported by a pad of thick polythene and some closed cell foam taped to the outside.

Followed West's suggested procedure for the actual repair starting with a circle the diameter of the entire repair progressing though decreasing sizes until the final piece was the approx size of the original hole.


Used epoxy for max strength of bond to original GRP and waterproofness without gelcoat.
 
PaulRainbow said:
So many of you still seem to be missing the message.
I have a small hole in the hull, it currently has a rather degraded looking transducer in it.
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It's not that I don't get it - my (and I guess others) opinion just differs. I do agree the repair beats a degraded fitting.

If i remove the transducer, no matter what i stick in the resulting hole or how i stick it in, it won't further affect the structural integrity of the hull.

My repair needs to be watertight and be sound enough so as not to fall out.
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On a hull I'd define it as a structural repair if it might compromise the primary purpose of the structure - to keep water out. I think that's the difference in definition that's causing confusion as I think we have a few people on the thread using each definition.

If i make the hole slightly larger and slightly bevel the hull on both sides i have a good clean surface, to which polyester resin will adhere perfectly well. The centre of the hole will be filled with chopped strand and resin, with some layers of CSM mat and resin on both sides. This will give me a roughly cotton reel/yoyo shaped plug of solid glass strand and resin, mechanically bonded to freshly uncovered GRP.

It won't leak, you wouldn't be able to knock it out with a hammer and by not grinding large areas of good hull away i will not have further reduced hull strength/integrity.

This is not a structural repair, in that it is not being done to return any strength to a weakened laminate.
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It's not about the strength of the laminate around the hole and that isn't why I personally would see this as a structural repair. The plug might survive a hammer blow, but will it survive if the laminate flexes due to say a grounding or a collision? If I understand correctly, that's the purpose of the 12:1 ratio, to ensure that the repair flexes with the hull without breaking the adhesive bond.

You are happy it would survive. I think it might not, and that it might fracture or flex and pop out, defeating the water tight integrity of the structure, so I'd do the repair with the 12:1.

To each their own.
 
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oakleyb said:
I've been quoted £750 to glass over 3 transducer holes
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Holy cow I'm in the wrong job. I could fill 12 holes in a day then have the rest of the month off!

Its totally DIY'able. Bit more tricky if you have a cored hull.

I'd recommend a read of the fibreglass boat repair book by alan f vaitses. Probably worth owning to be honest with you!

You can use polyester or epoxy. But would recommend some epoxy paint over the outside of the area when its done.

The 'professionally ' installed bow thruster tunnel on my boat has blisters in the fairing because it was done poorly with little regard to keeping the lamenate waterproofed.

I'm going to have to chop it out and redo it at some stage.
 
yachtorion said:
On a hull I'd define it as a structural repair if it might compromise the primary purpose of the structure - to keep water out. I think that's the difference in definition that's causing confusion as I think we have a few people on the thread using each definition.
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I agree, we might be using different versions of "structural". My version is that if it doesn't reduce the strength of the hull, it isn't structural.

I obviously appreciate it has to keep the water out :)

I'll take a few pics as i go and post them when i'm done.
 
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