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Old 23-12-2009, 14:15   #1
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Re-Fiberglass Old Trimaran in Alaska?

we recantly purchasded a 1970 era horstman trymaran. the boat is in fair shape, it has been sitting drydocked for about 3 years, during that time fresh water got into the amas and rotted an area about 3" by 5'. I have no concerns about the plywood/structural repairs. My questions have to do with refiberglassing the hulls, they are currently 1 layer of glass over 3/8 plywood. I want to add approx 1/4" glass over what is already there to about 2' above the waterline. my ? is what type of materials should I use and what am I getting myself into? I have 2 weeks this summer I can devote to this project

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Old 23-12-2009, 14:32   #2

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I'd think that would be one miserable two weeks. Were you thinking of inverting or glassing overhead? Doing the layups with hull inverted may be feasible in a two week window, but the grinding filling and fairing to any type of smoothness is definately a nontrivial task. You may want to expand that time window quite a bit.

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Old 23-12-2009, 14:38   #3
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And you need to prep the surface first.
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Old 23-12-2009, 17:30   #4
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you want to add a 1/4" thick extra glass? you got be kidding!)
is there something wrong with the glass thats on it now?
is this a D/D boat or sheet ply
call Ed Horstman the designer. you will pay a fee for his help, but in the long run it will be worth it.
by the way it's Trimaran
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Old 23-12-2009, 19:52   #5
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You've got to consider the added weight of that 1/4" of glass. the effects of that are what Polunu was eluding to. My guess is it'd have a serious detrimental effect on the sailing qualities of your boat.
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Old 23-12-2009, 22:31   #6
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Is this to add strength? Check out the unidirectional glass, it can add strength while keeping the weight down (kinda). The down side is it is a real pain to wet down. If this is to keep water out maybe look at the penetrating epoxies, I love Smith's epoxy. I looked around the net for an owners group but couldn't find one, it would be great to see what other Horstmans have done to resolve the "old" ply problem.

You probably already know this:
- if the rot area seems to be about 6 inches in diameter, you will probably dig out more than a foot in diameter of rot.
- I made the mistake of grinding an area down before degreasing it (it was a clean suface) this caused adhesion problems with my new glass. It seems that a small amount of wax residue was ground into the fbg, a simple degreaser will prevent this.

Had a friend that owned a sistership to yours and she was a great cruiser. Have fun sailing her. I hope you are headed for warmer waters
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Old 27-12-2009, 11:01   #7
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Aloha and Welcome aboard!
We all have our opinions on how to make repairs and improvements in our boats. In your case I'd replace the ply that is damaged with marine ply and cover it with the exact same thickness of fiberglass as the rest of the boat using epoxy resin. Start with mat, then cloth, then more mat, then more cloth with the last layer being flush with the rest of the hull and being cloth.
Adding 1/4" of glass all over will just weigh you down. Your hull will be bulletproof but very slow and who can guess when another section of ply will rot or delaminate.
Freshwater is plywood's enemy.
kind regards,
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Old 27-12-2009, 13:40   #8
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Your description made me think of a picture I have. This boat went up on a rocky beach in a blow in Mexico. They just jacked it up right there and went to work. Gotta love ply and epoxy boats....
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Old 27-12-2009, 16:09   #9
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Hi, good luck with the Horstman Tristar, good boats that deserve to be kept going. I think you would be wasting your time and your boat if you attempt to use polyester resin to glass the hulls. Polyester just won't make a good enough bond to the existing fibreglass. Epoxy is far and away the better choice.
From the information I can find your tri is 36 foot LOA, 7,300 lbs displacement at 26 inch draught. I'd guesstimate her main hull wetted surface at around 160 square feet.

You want to glass up to 2' above the waterline, for the purposes of rough calculation say 36' length x 2' wide strip x 2 sides = 144 sq ft. So rough total area main hull = 300 sq ft

Amas rough estimate 30' LOA, wetted surface? I'm going to guess and say area each ama to glass = 30x 2'6"x 2 sides . Very rough guesstimation but will get somewhere near. Therefore each ama = 150 sq ft to glass.

Total area to glass = main hull 300 sq ft + 2 amas 300 sq ft = 600 sq ft.

Assuming epoxy materials :- one layer glass @ 6 oz/ sq ft + resin at same weight/ sq ft = 450lbs.

That's going to give you a layer that's about 0.01" thick. You would need 25 such layers to make your quarter inch layer and they'd weigh
11250lbs, more than the boat could carry. The math doesn't improve much by using thicker heavier glass cloth either, unfortunately. The quarter inch layer would be unnecessarily, way too incredibly strong anyway.

So, it's either fewer layers, patches to make good or remove existing fibreglass and replace with new. What state is the old stuff in? Is it polyester or epoxy? Is it sticking tight all over or detaching in places?

Once again, good luck. I wouldn't mind a restoration project like that myself.

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Old 27-12-2009, 16:54   #10
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Welcome aboard, there's a lot of good advice here which you can accept blindly, trust but verify, or run screaming for the exits. The fun part is figuring what's what.

My two cents worth is this: Keep it light, doubly so if it's a multihull. Learn to use epoxy instead of polyester, you will be happier ten years from now, even if you can't figure out what all the fuss is about. Don't stray too far from the designer's plans. There are an awful lot of "modified" designs that eventually never see another owner. Have lots of fun doing this. It will be a memorable part of your life, though not nearly as much fun as sailing it when you've completed the repairs.
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Old 27-12-2009, 18:03   #11
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Yes, by all means.....remember...."It's a pleasure boat"
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Old 30-12-2009, 19:43   #12
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Tristar 36

Go to Ed,s site , print out an order form, order Trimaran Catamaran Construction. With your order form send whatever questions you want to ask. Leave a space below each question for him to write his answer. A 1/4 inch of glass over wood will be too much, I will have to look at my scantlings but I think he calls for one layer of 7oz, there should be two layers of 3/16, or 1/4 ply and not just one layer. I will be starting a tristar 31 around feb, it will be in foam and there wont be 1/4 inch of glass anywhere except the keel. The book will be a good tool to have on your boat, good luck rick.
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Old 30-12-2009, 20:14   #13
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Great Idea! Why did I not think of this?......I have The "Trimaran Construction" Book and two copies of "Foam Fiberglass Sandwich Construction" Everything is is in unused condition. Unmarked or buggered at all. Shoot me a msg. on the Private mode if you want them.....:-)
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Old 30-12-2009, 21:39   #14
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First off, before you do this... go ahead and get some whole sale accounts lined up. You are talking about 900 bucks easy worth of glass, probably close to double that in resin if you go name brand. A 60 dollar case of gloves, 2 dozen 4 dollar paint rollers, 25 2 dollar 5 quart mixing buckets, 1 good full face respirator (pushing 160...) 150 bucks in sand paper, 5 or 6 white suits, 5 gallons easy of acetone...

Forget about using mat (you'll just hate life...) or doing a 1/4 inch layup out of 6 ounce finish cloth.

For hand laid glass, you are going to have 50% of the weight of the layup in the glass... 50% in resin. As everybody else has stated... you want to use epoxy.

1/4 inch is overkill in all aspects, but the fastest and strongest layup for the money will result from using biaxial glass. 17 ounces per yard, with 3/4 ounce per square foot of mat stitched to the back. This is pretty much the industry standard called "1708" it is strong enough to tab in bulkheads, and do whatever you want it to... but not such huge bundles of glass that you can't get a fair surface over it for paint, like roving.

2 layers = 3/16th. 4 layers = 1/4. I think 2 layers is a gracious plenty for the under belly of a plywood boat, particularly one that has been sheathed since the 70's to no ill effect.

The last roll I bought was just over 600 dollars, 220lbs of the stuff including tax.

You could go without the mat backing to save weight and resin, but its not as readily available. You really want the mat on the first layer to get better adhesion, but then again with epoxy it isn't "really necessary."

What you will need to do, is remove all the bottom paint. Down to the glass. For speed sand blasting is the fastest. Failing that, get a 7 or 8 inch grinder and a box of norton hard sanding discs around 36 grit. Or if you are loaded, spring for the extra cash and get your grubby hands on some Norton Blue Mag 7 inch paper in around the same grit.

Don't ask questions, just go buy one... It's a Makita 9227 Circular Polisher that you want. The speed is adjustable so you can dial them back if you run into bottom paint that wants to melt and turn to bubble gum... and they are light weight for working over head. You will need a hard black plastic backing pads for the Norton hard paper discs, or a foam backing pad for sticky discs if you go with the Blue Mag. Don't waste your time with hook and loop pads, 5 inch orbital sanders... you have a lot of boat to do, and 2 weeks to do it in. While you can hold 20 pound grinder overhead for 2 days straight, it sucks, i've done it... you can't get a smooth finish with a 7,000 rpm monster that has an on off switch when you go to fair her. Save yourself the trouble.

Once you have the bottom paint free, get a sharp sharp sharp set of scissors. I have a pair of Gingher pinking shears that make life easy... around 30 bucks, or you can spring for the hundred and something ones that are made for cutting glass.

Once you have your scissors, build a work bench and a roller so you can slide a piece of pipe through the roll and unroll the fabric without it dragging in the dirt.

Walk down the boat and measure off the pieces you need. Roughly... Do not try to wrap the underside of the boat at her ends if she tapers, as you won't be able to get the glass to curve forward. Looking from the top it will do this ///// as you lay your pieces to the underside. Not a bad thing, but where she starts to splay out, you get a wrinkle and then have to fight gravity to go up the other side. Sucks!

The glory of fiberglass, is that for all intents once you surpass the width of the bevel needed to attach new material it quits caring that it's not one continious piece. Fossilized snot is amazing stuff, but steel is real.

Anyway... you want to build thickness and stagger the seams. So... the easiest way to do that is to cut a piece that is 25 inches wide, and drapes from the waterline to the bottom of the keel. Then you cut the next 50 inches wide, and let it overlap the full 25 inches... and the next 50 inch peice butts right up against the hump.

Why run up and down instead of side to side? If you are doing this overhead, there is a trick...

First, you'll want a plywood table with a piece of polyethelene sheet stapled over it. Take a 5 quart mixing bucket with lines on it so you can mix by volume. Mix your resin out of 5 gallon drums filled about half full so they are easy to pour. Now, take the cheapest paint roller frame and candy stripe 1/4 inch nap roller cover and pour the resin onto the cloth, rolling it around. Once wet out, roll it up on a PVC pipe long enough to extend out each side about a foot. Walk the roll over to the boat with paint roller in hand, roll resin onto the boat hull where the cloth is going to go.

Have a friend on the other side of the PVC pipe, grab a big plastic squeedgee, unroll the first 6 or 8 inches, push the air out of it. Unroll about a foot, work the air out from under it... Then ditch the pipe (carefully to keep it off the ground.) Have one guy work the air out and get it all stuck down, then roll it with an air roller while the other guy wets out the next piece. Get the aluminum air rollers, the plastic ones are shot the first time the resin kicks on them. Aluminum you can burn them off with a propane torch.

While your time window is still there and the glass is still green where you started... mix up a few batches of microballoons and a cabosil. It should spread about like heavy whipped cream, go back and coat your seams and fill in the weave of the cloth.

Keep on going... When you get done put in a big honking tab that goes 6 inches or a foot up each side of the keel and make this stretch your 1/4 inch thick so if you want to ground out... there is a lot there before you get to wood.

After your microballons set up, grab an bunch of 7 inch soft sanding pads for stick on sand paper and walk down the hull with 60 grit. If you sand up and down rather than walking left to right with the sander you won't put any scars that won't fair out with a screed... A screed is a piece of sheet metal with a straight flat edge. Go to the hardware store and get a 25 or so inch sheet rock taping knife and use that to spread the ballons on nice and thin. You drag this one up and down and let it feather out the low spots.

2 guys should be able to grind the bottom in 2 days. Each ama should take about a day to glass and microballoon. If you can wait until the temperature will let you use a tropical hardener you will be rewarded when you go to microballon her, and when you get to the sunny side of the boat you'll have as much working time as you need.

If you can beg an air compressor... its a sweet thing to be able to blow the glass dust off every half hour or so. Also, when grinding a lot overhead, they making cheap cotton spray socks for painting cars... it'll keep most of the dust out of your scalp and ears. Wear earplugs... grinders are in the territory of permanant hearing damage!

Dang, I think I just wrote you a book... but in any case, have fun with it.

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Old 02-01-2010, 06:53   #15
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Interesting post, Zach. I've never used the 17oz biaxial you describe, sounds good stuff and something I will certainly look at using in the future. My previous post describing the arithmetic of glassing used 6oz cloth just as an example. I was trying to show the basic problem of the weights involved not trying to suggest 25 layers of 6oz as any kind of feasible method.
Problem is, even using a heavy duty biaxial, the weight problem doesn't get much better. Did I get my estimate of area to be glassed wrong? Still seems to me that though my estimate of 600 sq feet is indeniably a crude and quick one, if wrong it probably errs on the low side. So here's another estimate for weight based on biaxial glass, West system 737 15 oz biaxial without mat and WEST 738 22 oz (15oz biaxial with 3/4 oz mat). I'm using WEST as an example because they give accurate figures for hand lay up thicknesses. I'm not sure about the estimate of 2 layers 17 oz equals 3/16th or 0.1875".

Weight 600 sq ft 15oz biaxial = 600 x (15 glass + 15 resin) = 1125lbs
Layer thickness = 0.033 inch

Weight 600 sq ft 22oz biaxial with mat = 600 x (22 + 22) = 1650 lbs
Layer thickness = 0.04 inch

Design displacement Tristar 36 = 7300 lbs

1 layer 15 oz biaxial 0.033" thick =15% displacement
1 layer 22 oz biaxial with mat 0.4" thick = 22.6% displacement

It seems to me adding that much weight is going to cause problems. Anyone with more expertise got some input?

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