Bottom Job questions :: Catamaran Sailboats at TheBeachcats.com

Bottom Job questions

jpr9c

Rank: Lubber

Registered: Jun 15, 2004

Last visit: May 22, 2015

Posts: 6
Posted: May 21, 2015 - 09:15 PM

I've got an older P18 and it's time to do a bottom job. I've been reading here and on the web in general, and I've pretty well decided the right approach is to build up the keel with fiberglass and Polyester Resin, followed with Gel Coat. One hull is fine, but the other is worn down to the glass. I've got a few chips/chunks missing as well. no delamination and the hulls seem quite sound (no punched in spots).

I'm planning to use unwaxed resin and gelcoat, topping the gelcoat with PVA to give a curing seal.

I'm curious what people recommend for a patching resin for filling chipped gelcoat?
MN3

Rank: Master Chief

Registered: Jun 20, 2006

Last visit: Apr 06, 2024

Posts: 7088
Posted: May 21, 2015 - 10:14 PM

i am not an expert but ....

i would spend a little more $ and go with west system ...

order online and its about $60 (http://www.discountmarine…H2ndqV1MUCFdcZgQodaJgA7w) for the epox/starter and pumps - no measuring, totally predictable kick off times - forget the poly

i would plan on using some cloth as well - i would ALSO add filler (http://www.westsystem.com…product-selection-chart/) to add more strenght to the bottom - i personally use mill fiber - http://www.multitechprodu…ed-glass-fibers-1-8-mill when it's on a bottom or rudder (or board)

i also have gotten lazy and don't gel coat in non UV areas (bottoms)

YMMV
jpr9c

Rank: Lubber

Registered: Jun 15, 2004

Last visit: May 22, 2015

Posts: 6
Posted: May 21, 2015 - 10:41 PM

So, from what I've been reading, the west system is an epoxy, which has two issues: first, the original resin is polyester, and second, gelcoat doesn't bond well to epoxy. For an epoxy job, I think I'd do quick-and-dirty and use the marinetex stuff, just to shore up the bottom. Either way, I am planning to add glass fiber.

NB - I've posted an album with some shots.
pbegle

Rank: Mate

Registered: Mar 12, 2003

Last visit: Feb 19, 2021

Posts: 879
Posted: May 21, 2015 - 10:45 PM

+1 on everything MN3 posts. Get a roll of 2" fiberglas tape. This is a I hour job with 4 layers if you flip your hulls over. Gelcoat not necessary. Pete
jpr9c

Rank: Lubber

Registered: Jun 15, 2004

Last visit: May 22, 2015

Posts: 6
Posted: May 21, 2015 - 10:50 PM

So, the hulls are off - boat is completely torn down at this point...I have read many recommendations for the west system stuff. I don't mind the extra expense, but I'd like to not have to do this again anytime soon.
pbegle

Rank: Mate

Registered: Mar 12, 2003

Last visit: Feb 19, 2021

Posts: 879
Posted: May 21, 2015 - 11:57 PM

Palm sand bottoms for about 5-6 ' (5 min), mix one pump of resin & catylst with thickner & fill any voids with spatula (8 min). Mix 2 pumps & paint 6' of bottoms with 2" throwaway brush, lay down 6' of 2" fiberglas tape & wet out with brush. Proceed again with 5', 4', 3' lengths (30 min). Sand next day with palm sander and put finish coat resin on (10 min). Use paper towels to wipe off any rundown on hull sides due to careless work. Advertise locally that now you are expert at hull bottom repair & only charge $300 for the job. Pete
klozhald

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Posted: May 22, 2015 - 02:29 AM

pbegleAdvertise locally that now you are expert at hull bottom repair & only charge $300 for the job. Pete

Pete,
Isn't there beer between the layers?

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Dogboy

Rank: Mate

Registered: Mar 19, 2004

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Posts: 960
Posted: May 22, 2015 - 06:40 AM

Epoxy is good for bonding and structural repairs. A typical bottom job is neither of those.

Since the hulls were originally manufactured using polyester, I would use polyester laminating resin with fiberglass tape. If you do a proper job preparing the surface (sanding thoroughly and wiping with acetone) there should be no adhesion issues with the existing fiberglass. It doesn't make a lot of sense to use a more expensive material (epoxy) for something that is just going to get dragged around and worn off over time anyway. Polyester is less expensive, easier to work with, faster cure time, and more readily accepts gelcoat. Also, if you (or the next owner) ends up needing to do another bottom job in the future, there are not compatibility issues and no guess work about which type of resin needs to be used.

For filling in imperfections, Formula 27 filler works well and cures very quickly.

sm
Edchris177

Rank: Chief

Registered: Nov 26, 2009

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Posted: May 22, 2015 - 12:26 PM

I did exactly what Pete said, on my 20' Mystere, as a rub strip for sliding on/off the seadoo lift. Only difference was I "tacked the 1st foot or so of 2" tape, starting right at the transom.
I then lightly stretched the tape & tacked it every few feet, ending about 1 foot short of the bow. Then went back & wetted the entire length. My hulls are pretty flat, so I did most of the bottom.
Don't attempt to use cut strips from bulk cloth, it will leave a crappy edge, buy 2" cloth, makes it very easy to lay it down. The woven edges leave a bit of a bump, after the resin cures just run a sander with 240 grit over to smooth, then paint a thin sealing layer.
I used the clear hardener, it was the same cost, & made the strip nearly invisible. I mixed the West microfibres, they cure to a white color, fairly easy to sand, & give more wear resistance. Not as durable as colloidal silica, but it's a bitch to sand. Wipe the hull with acetone before application, & it will stick.
Forget Gelcote.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
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jpr9c

Rank: Lubber

Registered: Jun 15, 2004

Last visit: May 22, 2015

Posts: 6
Posted: May 22, 2015 - 01:06 PM

Edchris177Only difference was I "tacked the 1st foot or so of 2" tape, starting right at the transom.

What'd you tack it with?

Edchris177My hulls are pretty flat, so I did most of the bottom. Don't attempt to use cut strips from bulk cloth, it will leave a crappy edge, buy 2" cloth, makes it very easy to lay it down.

My hulls are not flat at all - pretty sharp keel actually - but I was planning on using 2" strips.

Edchris177I mixed the West microfibres, they cure to a white color, fairly easy to sand, & give more wear resistance. Not as durable as colloidal silica, but it's a bitch to sand. Wipe the hull with acetone before application, & it will stick.

Just to be clear: mix the microfibres into the resin? I gather you also used Epoxy?

Edchris177Forget Gelcote.

Heh...this seems to be the universal advice. My hulls have the original, fairly oxidized gelcoat. I can wet sand and then use rubbing compound to clean them up I suppose. I'd like to fill the gelcoat scrapes as well...looks like the Evercoat Formula 27 or West 404?
Edchris177

Rank: Chief

Registered: Nov 26, 2009

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Posted: May 22, 2015 - 01:48 PM

QuoteWhat'd you tack it with?

Resin. Tacking down the 1st two feet gave enough adhesion that I could lightly stretch another 3-4', then while holding it in place, paint some resin on, then continue down the keel. Pete did a 6' section,(then added shorter layers on top), I did mostly the entire keel. With a sharp keel, the entire bottom isn't required,as only the lower portion wears, Pete's way is it for your boat.

QuoteJust to be clear: mix the microfibres into the resin?

Yes, but that is the last step before application. Mix resin/hardener, then add microfibre til you get the consistency you want. I used 403.
Everything you need to know is here;
http://www.westsystem.com/ss/the-105-system/

Edited by Edchris177 on May 22, 2015 - 01:50 PM.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--
jpr9c

Rank: Lubber

Registered: Jun 15, 2004

Last visit: May 22, 2015

Posts: 6
Posted: May 22, 2015 - 02:57 PM

A final question for you West System Epoxy advocates: let's say I bail on gelcoating (about which I'm not really excited): what color do you wind up with from the Finish coat of the West Epoxy? The hulls are (were originally) white, and I believe that after I sand off the oxidation and apply polishing compound, I'll be back to pretty much white. I don't need an *exact* match, but I really want it to be close ...I don't want to be driving the Bondo Boat.
Edchris177

Rank: Chief

Registered: Nov 26, 2009

Last visit: Apr 10, 2024

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Posted: May 22, 2015 - 04:07 PM

If you use the clear hardener, the fix will come out clear, allowing the "white" to show though.
If you have ground the bottom down through the gelcote, whatever color shows through is what the final will be.
Unless you have ground the sides of the hull through, anything showing will be on the very bottom of the hull & no one will notice.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
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Dogboy

Rank: Mate

Registered: Mar 19, 2004

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Posts: 960
Posted: May 22, 2015 - 04:19 PM

It might start out clear, but if you don't overcoat the epoxy, the UV will eventually cause it to turn yellow.

Polyester (or vinylester) resin is really the appropriate material for this job.

sm
jpr9c

Rank: Lubber

Registered: Jun 15, 2004

Last visit: May 22, 2015

Posts: 6
Posted: May 22, 2015 - 04:59 PM

DogboyPolyester (or vinylester) resin is really the appropriate material for this job.

Most of what I've read suggests this is the case. I really am not all that intimidated by the extra time required for polyester.

So, on spraying gelcoat...what do you recommend? If I get a laminating poly resin, will a finish gelcoat be sufficient as a "mold release" (vapor/02 block?) to cure the laminating resin? I've found a wiki/blog from a guy who sprayed PVA on top of his non-waxed gelcoat to provide the curing layer...this is an appealing option, preferable to contamination with paraffin.
Edchris177

Rank: Chief

Registered: Nov 26, 2009

Last visit: Apr 10, 2024

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Posted: May 23, 2015 - 11:45 AM

QuoteI don't need an *exact* match, but I really want it to be close ...I don't want to be driving the Bondo Boat.

We don't get as much sun as Florida, but in 2 years the Clear hardener is still perfectly clear.
The other thing to remember, you are only using 2" tape. That means 1" on each side of center, actually less because your keel is not a knife edge.
I would spend zero time trying to get a close match, it is not noticeable from 10' away.

--
Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
--
MN3

Rank: Master Chief

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Posts: 7088
Posted: May 25, 2015 - 08:44 AM

QuoteSo, from what I've been reading, the West System is an epoxy, which has two issues: first, the original resin is polyester, and second, gelcoat doesn't bond well to epoxy.

west systems is an epoxy but gelcoat does bond well with it - that is a good reason to use west over a cheaper epoxy
just realize there is no chemical bond between dried epoxy (or poly/vinylester) after they are cured - it is a physical bond only

PS you could do an entire bottom job in gelcoat only ... it would be fine, but it would wear down faster