Taking down to fiberglass

[Cadence]

Originally Posted by GrahamHO

50*f is around 10*c and a little on the cool side. It will cure OK but take a lot longer. When you are building up several laminations, you don't want the previous layer to be cured before you apply the next one so 50*f won't matter.
When one layer is still tacky you should apply the next. Then when you want it all to "go off" you can apply some gentle heat with a hair dryer moving it around for some time.
I've just finished laminating some glass onto end grain balsa to make new washboards. After I finished rolling the first layer until it was smooth, I immediately applied the second layer while the first was still wet. Then after I rolled that one I applied peel ply and rolled that. The temp was around 18*c 65* f and I didn't need heat.

I don't think he needs to worry as much about the laminate as the bonding to the existing hull, at temps that low.?

[Terra Nova]

You can use heat lamps to help cure.

[GrahamHO]

Originally Posted by Cadence

I don't think he needs to worry as much about the laminate as the bonding to the existing hull, at temps that low.?

I usually seek advice from my local WEST supplier (who manufacture in NZ under licence) They are always happy to give help with anything I'm not sure about. Personally I would be happy about the bond to the hull as long as it's prepared correctly, after applying some help with a hair dryer hot air gun or other source. It could take an hour or two moving it around without overheating. It might be possible to have an oil filled electric heater or two nearby, with some screens taped onto the hull to keep the heat in. There are also gas fired blow heaters that would certainly warm things up if they can be used at a safe distance.

Epoxy does cure more strongly with the correct temperatures.

However it's best to contact a WEST supplier who can in turn contact the manufacturer if they are not sure.

[reed1v]

If you grind down to almost make a hole in the boat, you got a dangerous patch situation: i.e. popping patches as boat flexes. Need to make a patch inside and out so it will not pop off. Should never go down to the roving if possible. Fiberglass works by having all the strands interlinked. Patches on the other hand are structurally inferior. that is why pros do beveled patches inside and out to give a mechanical hold on the hull if all else fails(and it will, given time).

[Scot McPherson]

That's interesting, I did this according to instructions here as well as reading some gougan brothers about patching cracks/holes in your boat.

I however do agree with your assessment that a "plug" on only one side could in theory pop out, and that to patch from both sides makes the single piece plug span the hull material on both sides.

Perhaps I'll grind down some more so the crack is 1 inch wide so I can laminate on both sides. This way if the plug started to delaminates from the out hull, the inner part of the plug would at least hold it in place. Or short of that, just bulking up on the inside laminations so if the plug pops out, there is still a 1/4 inch more material behind it.


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[Cadence]

Originally Posted by reed1v

If you grind down to almost make a hole in the boat, you got a dangerous patch situation: i.e. popping patches as boat flexes. Need to make a patch inside and out so it will not pop off. Should never go down to the roving if possible. Fiberglass works by having all the strands interlinked. Patches on the other hand are structurally inferior. that is why pros do beveled patches inside and out to give a mechanical hold on the hull if all else fails(and it will, given time).

[minaret]

Originally Posted by Scot McPherson

That's interesting, I did this according to instructions here as well as reading some gougan brothers about patching cracks/holes in your boat.

I however do agree with your assessment that a "plug" on only one side could in theory pop out, and that to patch from both sides makes the single piece plug span the hull material on both sides.

Perhaps I'll grind down some more so the crack is 1 inch wide so I can laminate on both sides. This way if the plug started to delaminates from the out hull, the inner part of the plug would at least hold it in place. Or short of that, just bulking up on the inside laminations so if the plug pops out, there is still a 1/4 inch more material behind it.


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You are getting some misleading amateur advice. There are far more important considerations than this, and laying a big patch on the back is likely to create as many problems as it solves. I've said it here many times, your primary concern is carefully matching the original construction. What do you think happens if you put in a patch that is twice as stiff as the surrounding hull material? The surrounding hull will flex more heavily than the patch, putting high loads on the bonding surface. A backing patch that is not fully tapered will exacerbate this. You are already using epoxy instead of poly, biax to replace chop matt. Your patch will be much stiffer than the original laminate. If you add a backing patch as well, your repair area will be dramatically overbuilt. This is not a good thing, as it will put high loads exactly where you don't want them. A really good pro repair will match products at each layer of the laminate schedule, providing a surface which distributes load evenly throughout when flexed. This means poly or vinylester resin, and matching each ply for fiber continuity.

[Scot McPherson]

Well isn't that part of why you taper your patch across several inches per thickness of the hull? This is kind of like scarfing sort of so the load is spread across a larger area, and also so any differential between hardnesses is graduated somewhat.


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[reed1v]

Originally Posted by Scot McPherson

Well isn't that part of why you taper your patch across several inches per thickness of the hull? This is kind of like scarfing sort of so the load is spread across a larger area, and also so any differential between hardnesses is graduated somewhat.


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Yes it is. However tapering on one side with a shallow depression is different than when you have a through hole to patch, especially if it is larger than a penny. Remember, if your cruising and meet real heavy weather, your hull will twist well beyond what you would expect: sides will oil can, bottom will flex, and the bow will twist. It also heats up the hull. Day sailors and sheltered bay sailors need not bother, but open ocean, long distance sailors really need to take notice.

[minaret]

Originally Posted by Scot McPherson

Well isn't that part of why you taper your patch across several inches per thickness of the hull? This is kind of like scarfing sort of so the load is spread across a larger area, and also so any differential between hardnesses is graduated somewhat.


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Try taking a standard 2x4, and put in a 20:1 scarf in the middle, scarfed both ways, almost all the way through, just like your repair. Do one with 2x4 scrap and one with a piece if oak or ash, to represent your dissimilar material repair. Then bend both until they break. Record where the break was and how far you bent it before breaking. Compare to a 2x4 with no repair in it. The. You will understand.

[model 10]

Originally Posted by minaret

A really good pro repair will match products at each layer of the laminate schedule, providing a surface which distributes load evenly throughout when flexed. This means poly or vinylester resin, and matching each ply for fiber continuity.

See this is why we should have some sort of regulatory agency. If everybody did it right, things would be so much better.

[Scot McPherson]

Yeah I understand the principles well enough. I am just going based on recommendations made by those i believe many people respect, both on this forum as well as the gougan brothers of west systems and boatus (which is also a boaters insurance company as well as a boater's AAA), and others, including my engineer neighbor who is also an old salty sailor.


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[minaret]

Originally Posted by Scot McPherson

Yeah I understand the principles well enough. I am just going based on recommendations made by those i believe many people respect, both on this forum as well as the gougan brothers of west systems and boatus (which is also a boaters insurance company as well as a boater's AAA), and others, including my engineer neighbor who is also an old salty sailor.


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Well if you're only taking advice from respected people, that throws me right out the door!

[Scot McPherson]

Hehe, I am not saying that at all. Not saying anyone is wrong, just explaining how I began this journey, and also explaining although I am by no means an engineer I am an engineer type of person, I understand how epoxy works, mechanical adhesion, and why patching from both sides can make sense.


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[Terra Nova]

Originally Posted by Guy

See this is why we should have some sort of regulatory agency...

We don't need no steenking badges.