Hull Construction

How our boats are really made, information from the hull builders!

As a result of questions received concerning type of resin and cloth in our boats, Duck Soup’s new area of research for the IOM Compendium is construction. The following brief questionnaire was sent to all the builders we list. Some replies are somewhat brief, and others are very informative such as the answer by Craig Smith for the TS2, and include many editorial comments. I think the information is quite revealing, but I still would rather buy than build. That thought may not be the same for all the sailors, but there are enough of us that want it built for us that we have a very nice selection of boats. The questionnaire and the various answers follow:

What resins do you use, Epoxy, Polyester, or what?
Do you use woven cloth, (standard weave or S glass, or??); or do you use chopped strand mat, or anything else? What weights and layers of cloth do you use in your lay-up?
What curing techniques do you use; any oven curing?
Do you use vacuum bagging?
Are there any other construction techniques you use that you feel are important?
Why do you use your construction methods and materials; what do you think are the advantages as compared to other alternatives?

I was not trying to find out how to make a boat; just the various construction methods and materials that are out there, so I was not asking for any trade secrets!

Some of the builders gave us the cloth weight in grams, so I have given my conversion to ounces, multiplying by .02973 to get from grams per square meter to ounces per square yard. I think that is the right way (I got this factor from Craig Smiths notes) but if I am wrong, tell me, after all what does a duck know about glass cloth!

ADDITIONAL INFORMATION

We have some additional information on resins; one source is our friend Larry Robinson, a member of the Seattle East Coast 12 fleet, who also helped us on the Metallurgy issue, which dealt with the composition of our aluminum masts. He has given us a nice write-up on Epoxy.

Another source is my favorite search engine Google. Go to Google and type in epoxy. The last time I checked Google found 546,000 listings in 0.11 seconds. If you spend only 5 minutes looking at each site, and you keep at it 8 hours per day 7 days per week, we will see you back in a little over 15 years! Trust me, Larry’s info is much more to the point, and you can read it in only a few minutes.

CHINOOK AND CELEBRATION - BOB STERNE

I have been building with polyester for 25 years, and have never seen a problem with "melting" of the boat.
I use polyester resin in my hulls. The kit includes written instructions plus:

Fiberglass hull (polyester resin, 6 oz. and 4 oz. glass woven cloth, clear only, balsa inwhales installed)
Balsa core fiberglass deck (polyester resin, vacuum bagged, woven ‘glass both sides of 1/16th balsa)
Carbon fin (polyester resin, vacuum bagged, bias woven carbon over vertical unidirectional carbon, balsa core)
Fiberglass rudder (polyester resin, vacuum bagged, woven 'glass, balsa core)
Fiberglass keel/mast trunk (epoxy/epoxy tubes, molded to fit fin, made in jig)
Rubber bumper (silicone RTV)
Lead casting

The curing is not specifically addressed in 3.
Vacuum bagging is used as noted in 3.
I use vinyl ester on my Kevlar hulls in other classes, but that is because they are so thin and flexible that they are susceptible to "bruising" in a collision with polyester because the resin will fail before the Kevlar.... this is not a problem on the IOM because the hull is more rigid. Any plastic can melt of course, given enough heat, and all resins once cured are plastic.

DISCO - BRAD GIBSON

I use West System Epoxies. They do have a little higher viscosity than some others on the market, but this is not a big enough problem if preparation is right. The West has fantastic gluing & fairing properties with the addition of their own brand of powder additives.
For lay up I use 1 layer 2.5oz E glass & 2 x layers 3.8 oz S (satin weave) glass. Over time this has shown the best trade off in my hulls between weight & rigidity.
My boats are cured at 50 degrees C for 6 hours from lay up completion.
I do not use gel coat in my boats. Moulds are pre coated with epoxy undercoat prior to lay up. Boats are then gloss coated with 2 pack polyurethane finish for a very durable gloss finish.
I don't believe that there are many big gains to be made in IOM construction with minimum hull weights being quite easily obtainable. I have been familiar with resin systems I am using for over 10 years now & they have never let me down in the past. Best to stay with what you know.

DRUMBEAT - IAN MACLENNAN

We use epoxy resin. It is stronger and more stable than polyester.
We use two layers of 195gm (5.8 oz) S glass in the hull for consistent strength and stability. Carbon cloth and carbon uni directional fiber in the fin and rudder. No chopped strand mat.
The curing is carried out in a controlled environment in an oven.
We now use vacuum bagging, it gives us better resin control and consistent lay up.
Important construction techniques are careful measurement of ingredients together with aggressive quality control and robust packaging. Computer controlled routed moulds. Complete construction, painting and sign writing of hulls.
We think our methods and materials are the best available.

IKON - GRAHAM BANTOCK

We exclusively use epoxy resins.
For hulls we use twill and plain weave E glass cloth as appropriate. For One Metre hulls it is currently 2 plies of 165 gsm (4.9 oz.)
For foils we use plain weave carbon and high modulus uni-directional as appropriate.
Our curing is at room temp elevated a little if necessary.
We do not use vacuum bagging. We use custom made presses for almost all the carbon parts we make (foils) and also for the deck unit, which is common to all our boats. The presses give circa 10 times the pressure of vacuum bagging and therefore much higher fiber volumes.
Our other construction techniques are proprietary!
We have arrived at the methods we use as a result of having tried many and retained the ones, which are best. But we are still seeking improvements. In no particular order the advantages are high repeatability, low weight, high stiffness and strength, high quality of surface finish.

OCKA, COCKATOO, RAGE - JEFF BYERLEY

I use Epoxy resin.
Use inner and outer layer of 100gm (3.0 oz.) satin weave, and a middle layer of 190 gm (5.6 oz.) plain weave.
Cure lay-up for 10 hrs at 50 deg C (122 deg F)
I do not use vacuum bagging.
Undercoat is used as 1st coat in lay-up, and 2-pack paint used for finishing, which allows a greater color range.
I cannot think of any great advantages in my methods.

TORNADO 250 - MICKY PETERSEN

I use Epoxy resin.
I use standard woven cloth. My molds are the hull and deck halves. The hull gets a 0.75 oz layer, plus (2) 6.0 oz layers plus a strip about 12" wide of 6.0 oz around the fin area to reinforce the hull there. The deck gets a 0.75 oz layer, plus (2) 2.4 oz layers, plus (3) 12" strips of 6.0 oz around the fin area to reinforce the deck in that area. I reinforce the deck with a 1/4" dowel along the gunnel, and then I glue the two halves together.
Since it is pretty warm in Texas, especially in the summer, I use what I have available. I don’t seem to need an oven for curing. Sometimes it is too hot to lay up the fiberglass in the garage, because the Epoxy sets in no time, so I have to bring it inside the air conditioned house to do the lay up. In the Winter I bring the molds into the house and let them cure under a heating vent. I leave the fiberglass in the mold for about 4 days.
I would like to use vacuum bagging, but it is too expensive.
There is no particular one technique that I find important. It is the sum of all, plus the layout. I spent many weeks figuring out the best deck layout and technique so that the sailor could access everything easily and quickly between heats.

TS2 - CRAIG SMITH

I use SP systems’ Ampreg 22 epoxy laminating resin. I used to use Ampreg 20 but the new formula is meant to be, "not such a health risk", although it is a bit more viscous and a little more difficult to use. I use the super slow hardener, which gives a very long working time of two to three hours depending on the ambient temperature. Lately I have been experimenting with other epoxies in an attempt to find a cheaper alternative, the Ampreg is great but it is quite expensive.
I use a modified E glass (woven cloth, crows foot), on the hull and deck. On the hull, three layers of 3.3oz (105gms) and then one layer of 5.5oz (185gms) around the load areas. On the deck, one layer of 3.3 and one layer of 5.5oz and extra on the load areas.
I cure the Ampreg 22 as per the manufacturer’s specs. After the initial cure, I post cure for 16 hours at 45-50c (113-122f). It is quite a modest temperature obtainable by any simple methods. I could post cure it at 80c (176f), which would save a considerable amount of time, but my polyester moulds would break down from thermal fatigue a lot quicker.
I do not find vacuum bagging necessary as the minimum weight of the One Metre is very obtainable without having to go to all the trouble of bagging and all the set up that goes along with that.
I cure the resin in a controlled environment using a PID temperature controller. The PID controller is able to keep the temperature within .1C and also makes it possible to ramp up the temperature a bit at a time if necessary. In the boat I use timber inwales (inner gunwales) as I find it fast and easy to glue them in after the boat is dry and out of the oven. I use gaboon ply backing pieces wherever there are fittings screwed through the deck of the boat.
I am a boat builder by trade and I was trained in the old school of boat building, I also have the fortune of being trained in the new materials and methods that this day and age demands. I use epoxy glass as it gives good weight to stiffness and also good weight to strength. It is a little more difficult to get a planked timber or plywood boat down to weight. Although it is possible it does take a bit more time and care.

The only problem I see with epoxy glass is it is not all that easy for the average person to knock a boat up as it generally requires a mould and a lot of time to make that mould. The advantage that I have found with epoxy over polyester (and everyone has an opinion on this you need only ask) is that the epoxy tends to be tougher and resists cracking and fracturing in the event of a collision. Polyester expands and contracts more than epoxy with temperature fluctuations although I have found that epoxy is more prone to relax and sag at higher temperatures than polyester. This can be overcome to a certain degree by curing the epoxy at a higher temperature.

Epoxy by nature is far better glue and sticks to thing better. I hope that doesn't sound too “layman” but it is as simple as that. So it is tougher, it is less likely to crack, as it will flex further before it breaks and it sticks better.

Now for the disadvantages of epoxy. It kills you faster, although it doesn't smell like it would.

I personally find epoxy harder to use and it takes me 2-3 times longer to lay up an epoxy boat than if I use polyester. The main problem is that most fiberglass cloth won't wet out as easily with epoxy as it will with polyester or vinyl ester.

Epoxy is more difficult to get out of your brushes and because it tends to be more viscous it drags hairs out of the brush on a regular basis and deposits them on the job (I hate that). It is generally more expensive and it is more critical on the mix and the drying temperature, but apart from that it is great stuff.

I join the boat and deck at the sheer line as opposed to joining it down the center. I think the shape of the TS-2 made me go that way, and also that is how I used to build full size boats, so I feel it's a bit more natural for me to build a boat that way.

Back to Top

Where to go now?

[ Home ] [ Up ] [ Epoxy ]