Canoe lamination?

Can anyone help me number of layers and glass weight? What combination of mat, cloth and roven, etc. This is for a canoe. Thanks.

 

Help would be more forthcoming if you provided enough information to speculate on a laminate schedule. This of course, raises the questions of why you're not using the original designers schedule, or possibly you've made materials conversion without the required knowledge or skills.

What are you building? Method employed? Materials, general dimensions, design goals, etc.

 

Canoe

I'm building a wooden Piroque that I want to use as a mold for an all fiberglass version. I'll be using polyester resin. I work for a large chemical company who makes resin for the boating industry and also have the advice of some of the chemist I work with. I want to know what types and weights glass I should use to make this thing. Thanks.

 

Buy Dave Geer's book "Elements of Boat Strength" and work up the laminate schedules. There's no simple answer, you have to engineer the composite, either by using generic rules (such as Geer's) which typically produce hull shells heavier then they need to be or through structural analyses.

 

A canoe is not any rocket science, anyway not so long we aren't doing any high-tec-light-as-a-bart piece Just take a look how much does same size of gf canoe weight generally and you know how much material was used to it...

 

That's my whole point Teddy, a little research and you're in the ball park.

 

I find the easiest fibreglass for general purpose use is cloth around 200gsm (say 6 oz/sq.m).

For a canoe type hull you can get away with three full layers of this cloth. BUT the skin alone does not make a boat. You need to place some stringers to add stffness. The stringers can be wood, polyurethane foam, PVC tube, aluminium etc.

One design element that is important is that torsional (twisting) rigidity is related to the area enclosed. So an open boat like you are making will have little torsional stiffness unless your stringers or gunwales have some enlosed area. I have used PVC tube for this but make sure you seal off the ends of the tube so they cannot fill with water over time.

I gather your wooden boat will be a male mould. So you will do the skin first and then glass in stringers and maybe some ribs once you release the skin from the mould.

You should aim to do each layup of the skin in one complete piece of cloth. The glass can follow contoured surfaces providing the curvature is smooth.

You can also do layups in quick succession but use fresh mixing containers and applicator for each batch. If you have a small amount of resin that is curing mixed with a fresh batch it will reduce the setting time for the fresh batch. You could also end up with lumps - I guess you should know this.

If you get foam for stiffeners it has to be polyurethane. The polyester resin will dissolve polystyrene foam.

Good Luck - Post some pictures of your progress. If you feel the three layers is too flimsy then you can add a forth after you have done the inside. Just freshen up the cured polyester with some grit and acetone.

You can fair the hull once finished with polyester and micro-bubble mix to make a paste. This is very low density and easily sanded. Once faired you should be able to get some coloured flow coat from your employer for a nice hard finish that will look good and improve life.

Rick W.

 

It depends on the shape of the hull and what strength is gotten from that shape. X amount of glass on a curved, rounded area might work whereas the same amount on a flat area might flex. I made 17.5' canoes, in a female mold, with polyester resin and a laminate schedule of one full layer of 10 oz cloth on the outside, then one full layer of 3/4 oz mat and one full layer of 18oz woven roven on the inside. The bottom had to be reinforced to prevent "oil-canning". Either an extra layer or two of mat was placed under the w.r. or foam ribs were laminated over with mat and cloth. The insides were finished with latex porch and floor enamel as it was cheap, worked very well with a large assortment of colors widely available and it saved a number of extra # of weight compared to gelcoat.

I think that even though I was using polyester resin, the mat could have been either been eliminated or another layer of cloth substituted and weight could have been saved if I was able to laminate it all at once, but in doing it by myself, that was not possible. I was told by my resin supplier that some mfgrs. were laminating up to 7 layers of cloth at one time with no mat, but I don't know what they were building.

If you make the canoe as light as you dare and don't coat the inside with anything, you can then put it in the water and try it out. If any areas need reinforcement, you can then add them. It is a lot easier, cheaper and you end up with a better balanced laminate schedule, if you build light and work up to whats needed and where, as opposed to overbuilding and then having to live with the extra weight forever.

 

Lighter, tighter cloths and multiaxials can be successfully laminated without intervening layers of mat. Where the thin layer of mat between layers becomes important, is when you have heavier cloths, rovings, or heavy stitched fabrics with large, coarse yarns. In these fabrics, the mat is needed to provide some fibre content in what would otherwise be a thick, brittle layer of pure resin between the layers of fabric. The light mat helps to reinforce the bond between the structural fabric layers, reducing the risk of delamination.

As PAR says, there's no shortcut way to estimate the appropriate laminate schedule. Gerr's "Elements" offers a reasonably easy to follow, conservative method for doing the calculations. This method will produce a hull that is slightly on the strong and heavy side; if you want to use lighter scantlings than result from that method, it becomes important to develop a more thorough understanding of the detailed load cases involved.

 

Sam Sam's Layup was typical for what we made and his method of finding out how much is needed by building then adding as needed works great. Cloth to cloth is not very strong, or should I say durable, it fractures easily, then starts to delaminate. Using better stronger resins (polyester and VE) will help, but the resin layer between the two is still a weak point, the fibers of even a 3/4 oz mat makes a big difference, but does add weight.

 

Cloth to cloth bonds are not necessarily weak, except when less then good wetout or contact is permitted. With epoxy laminates you can skip the mat entirely because of the increased peel strength of the resin.

Insure good chemical bonds take place with timely layup and maintain good interlaminate fabric contact with proper technique and procedure.

 

When using vacuum (most any type) cloth to cloth is a little stronger because the the two are consolidated better. In a typical hand laminate the loft of the fabric creates a resin rich layer between them even when layed up at one time, resulting in a weaker layer. This resin rich layer tends to fail when stressed long before the cloth portion will, that's why I went with "durable".
I was just working with a company on this exact problem, the failure of woven fabrics hand laminated back to back with no mat betweem them. They made test panels with several different resins and laminate schedules, these were submitted to a lab for testing. The results showed as the quality of the resin increased, so did the strength (expected), but if you added mat, even 3/4 oz, between the woven products the strength improved measurable (also expected) and the failure was far less dramatic, as in the part was still functional even though is was fractured. They tested stitched farbrics also, with multiple layers of 1708, these were the strongest of the bunch.