Building a replacement CB for an old DS1

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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 23, 2020 6:20 pm

Also... while I’m asking :
If I don’t go through any structural layers and just need to seal what I’ve sanded and re-paint, what product is recommended for that purpose (sewing and re-painting bare Fiberglas) and how much thickness should I allow?
I’ll do the research too... but if there’s a no-brained answer it would be good to know.
J
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Aug 23, 2020 8:56 pm

For painting a CB on a boat that is dry sailed, you can use a lot of different paints. Neither epoxy nor gelcoat seem particularly difficult substrates.

My favorite of the moment is Petit EasyPoxy. It takes a bit of time to cure, but then is really tough. Which is something you want, because the board will rub against the trunk opening. But you may have to let the paint really cure before reinstalling and first use. Another paint I've used is SystemThree's WR LPU. (Single component, but with an optional "cross-linker" for the last coat). Cures to a really tough finish, but may be sensitive to good surface prep. I've tried it on a rudder to good effect, but had mixed results using it on the hull; the rudder flexes less, that could be a difference and it's smaller, so I may have had more consistent surface prep. In principle the LPU cures faster and would end up higher on the abrasion resistance. Polyurethanes can cure really tough that way, but the EasyPoxy isn't bad, once cured.

In some ways you'll get everyone to tout the paints they've used - none of us has really had a chance to try widely different products that are still on the market.

I painted a racing stripe on one of my boats with spray paint. The results were interesting: the primer I used adheres like barnacles, however, it may have been not as compatible with the top coats, as they scrape off way to easily (the stripe is at the edge of the hull and comes in contact with docks etc.). That primer (if I could only recollect the brand) would be a painless way to seal a CB. So, the answer is, there isn't any obvious answer and you never know . . .
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Re: Building a replacement CB for an old DS1

Postby jboright » Sat Aug 29, 2020 2:25 pm

Some developments on the tight-fitting CB issue...

I've taken out the CB and have started grinding it down to get it t fit more easily. I'm still wondering if the trouble is that the CB is too thick (perhaps it had/has a small crack and water is leaking in and causing it to swell?) or if the trunk is too narrow (perhaps a botched trunk re-build in the past?).

I've checked the lip of the trunk and it is flush to the interior.... so just grinding down the lip isn't going to fix it. I did notice that the inside surfaces seem flat, but taper to a smaller width deeper in the trunk (towards the top if it was upright). Is that to be expected? I've been grinding down the CB with a belt sander just bit at a time and it certainly is helping. The question now is how far to go. I was hoping to be able to simply seal it (product still TBD) when I got to the right thickness... assuming I hadn't gone far enough to compromise it structurally. I'd rather not add glass If I don't have to, but will if I need to. So another question is what to use to seal it? Is gel coat the right stuff? Is there an epoxy-sealant that might be simpler?
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Re: Building a replacement CB for an old DS1

Postby jboright » Sat Aug 29, 2020 2:57 pm

Thanks Greenlake for the thoughts on products... I didn't see your reply until just now (had to go to p2 of this thread!).

I'll check out the products you spoke of... I'm assuming that the existing surface of the CB is gel coat... but I don't really know. Is there a no-brainer way to determine what my original surface is/was? And does it make a difference in what to apply over it?
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Re: Building a replacement CB for an old DS1

Postby jboright » Sat Aug 29, 2020 4:58 pm

Greenlake, wondering what kind of prep you did when using SystemThree's WR LPU. Did you use their primer too (SilverTip Yacht Primer)? If not, what would you do for surface prep?
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sat Aug 29, 2020 5:18 pm

I did not use their primer - and I wonder if I should have. But fact is, I didn't, based on some remark that it can be applied directly on top of neat epoxy and I did apply a coat of epoxy. However, If you sand after that final coat, you may possibly sand through in some spots, and then using the primer would probably be the safer choice. I wonder whether that was something that happened when I did my hull with it, because I have some areas where there were problems and other areas were totally fine.

The CB trunk is supposed to taper. For one, the CB (or at least an ideally shaped one) would taper from about 1/3 past the leading edge. The other, more direct reason for this is the CB trunk was laid up in a mold and if the insides weren't tapered it would be that much harder to get it to release.
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 30, 2020 12:40 am

OK. Thanks GL and good to know.
I've gone ahead and ordered SystemThree's WR LPU and their primer too... (not available anyplace near me as far as I can tell). It'll be a while before it gets to me and my dilemma is that I want to go sailing NOW... What happens f I use the CB as-is? Bare fiberglas and sanded (probably) gel-coat? Will I inflict irreparable damage to the CB? Any quick and dirty way to seal the CB (guessing that any damage would be from water infiltration) and get on the water a few more times before the product arrives?
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Aug 30, 2020 3:41 am

Neither bare laminate nor gelcoat should let water pass. Laminate that doesn't have any damage should also not act like a sponge, for example. However, if kept underwater for a long time, you'll find that neither is 100% waterproof. So, if your CB doesn't have any pinholes / cracks that lead deeper into the board, I'd cautiously suggest you might be able to drysail it for a bit (but then be extra sure it's dried out completely before adding epoxy or paint). You'll have to be the judge of that, as it's impossible to determine anything with certainty from afar.

The one method for a quick seal would be a coating of neat laminating epoxy, but I assume that would also be among the stuff you've ordered.
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 30, 2020 10:50 am

Thanks GL! Sorry for the newbie question... but can you elaborate on what is meant by "neat laminating epoxy"? Might such a product be found at Lowe's or Home Depot or even West Marine (shudder)?
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Aug 30, 2020 11:49 am

Never mind GL. I think I have it figured... 'laminate epoxy' = the epoxy one would use for laminate (i.e. fiberglass) work, and 'neat' meaning just the epoxy... no fiber mesh. And it sounds like I should be able to find something like that at West Marine.
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Aug 30, 2020 1:57 pm

You're well on your way figuring out the lingo.

Any epoxy you'll want to paint in due course, but for a CB the UV exposure should be limited enough that you can wait.
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Sep 06, 2020 12:25 pm

Now that my CB is out and I'm grinding away to thin it out... I've also read some of the other threads about the benefits of producing a true(ish) foil shaped CB. So I'm working towards that too... What is the best tool/method of measuring the thickness of the CB at different spots. Is there a recommendation for a specific kind of caliper to use?
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Sep 06, 2020 7:04 pm

Create a template that shows the curve you are trying to achieve (this may not be the ideal curve, as you would have to sand through laminate to get there from a stock CB). You can then make sure each half comes equally up to that curve.
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Re: Building a replacement CB for an old DS1

Postby jboright » Sun Sep 06, 2020 7:21 pm

Aha! Glad I asked... good idea!

Thanks GL!
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Re: Building a replacement CB for an old DS1

Postby GreenLake » Sun Sep 06, 2020 7:25 pm

You can use "high strength marine filler" from 3M to build up the CB near the leading edge (to allow it's profile to be nearly circular at the front) and to add a bit of a V at the tail. The high strength filler is good for work where it will end up a bit "proud'" of the original surface.

If you sand though the laminate on your CB, you'll have to sand some more and replace the laminate by new layup, otherwise you compromise the strength. The strength in these structures is in the "skin" not the "core".
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