polyester resin stitch and glue

James,

I will ask you a real question, HOW MUCH will you use?

One 'can?' You might save a 'c' note - $100. But, is that much money in the overall scheme of building your boat?

wayne

 

Wayne, as you say the chine log runs longitudinally, along the joint between two planks and holds them together in glued construction, just like as the glass tape and an epoxy fillet do in a stitch and glue boat. Personally, I might use temporary fasteners to hold the joint together while the glue sets, or permanent fasteners for a heavily loaded flat bottom to reinforce the glue.

The ribs and stringers question is a bit more complicated, there are several reasons why they are used. I used ribs on a strip-built canoe to provide cross-grain support to the strip planking, because I didn't want to go the usual route of glassing inside and out. Ribs and stringers can be used as hard points, to attach engine bearers or rigging for example. I am currently investigating a new method of construction where either ribs or stringers can be used to provide planking support - I haven't decided which way to go yet. They are often used, particularly in traditional designs, to frame the hull before planking.

I would note that adding ribs and/or stringers to an existing monococque hull design could create hard points that might lead to failure under stress. A minor change to a design is one thing, but each designer has his reasons for using them or excluding them, and unless you understand the designer's logic you shouldn't make structural changes.

 

I am definitely in the epoxy camp in this argument but it is wrong to say that polyester resin cannot be used to reasonable effect in S&G boats (or taped seam boats built in a female mold as many of the earlier ones were). Epoxy was not well known or readily available until the 1960's and S&G was being used with polyester a decade earlier. As said, the early Mirror dinghy was one of the boats that depended on poly for the taped seams. Particularly in England, polyester was used in highly competitive racing dinghys that were lighter and thus more competitive than their molded fiberglass sisters. This was true even in Olympic classes like the Flying Duchman.

Polyester is not a good glue and great care was used to make sure that the gluing surfaces were pristine clean. Even fingerprints were not allowed. When the necessary stringent rules were followed, some very good dinghys were built with polyester S&G that did not fall apart rapidly.

That said, it is very foolish to attempt to save a couple bucks with polyester when the track record of epoxy is way better.

 

Terry

Thanks! That makes it clearer.

wayne

 

Sure you can use polyester, but why would you use an inferior product for such a critical join?

Consider that you will spend many hours building your boat. More than that, you will spend good money on materials. Jeoprdizing the integrity of the boat, after all that work and money makes no sense. unless it is to be a throwaway boat. In that case use the Poly and dont look back. Otherwise get the good stuff. If you must save every penny, do as Steve says and use chine logs and resorcinol or other cheap glue..

 

Tom is correct, though I remember the late 60's and 70's with Flying Dutchman and other polyester sheathed and glued craft in a terrible state, with sheathing peeling off, structural elements broken loose, etc.

Good polyester resin and well refined practices helps, but takes away much of the advantages too. Good polyester is about 2/3's the price of good, discounted epoxy.

So, if you have a project that will need 3 gallons of goo, this is about $150 for epoxy or $100 for polyester. Simply put, you can use the cheapest polyester you can find and save $75 bucks on the project, of course skimping on the very product that will hold things together and keep your socks dry, or . . . just doesn't seem to be a very logical or economical decision to me.

 

3 gallons of epoxy for only $150?! Does that $150 include hardener too? Links please. I just spent $75 per gallon yesterday for Apex epoxy which included hardener and I lucked out because it was local which meant no shipping charges. Even good polyester resin is $38 per gallon locally but of course the cost of catalyst for polyester is almost nothing. Where can I find this $50 per gallon epoxy please?

Thanks

 

I suspect you have to live where Par lives and use as much as he does! I can't remember the prices I paid for epoxy although I can recall what I paid for lumber, fasteners, fittings and marine plywood. No doubt the trauma has wiped it from my mind; of course I am cheap and amnesia can result from severe psychological trauma . . .

 

There are several major epoxy formulators in the USA, you might try a quick search. Raka's 3 gallon kit is about $168, Bateau's epoxy is $163 for 3 gallon kit, Progressive Polymer is $95 for a 1.5 gallon kit (kits include hardener). Look around, these are the full retail prices (which I never pay) or you can continue buying West System, System Three or MAS for a lot more.

 

I checked prices with Bateau, Raka, Surf Supply (and bailed on Progressive because their website gives me a headache) and the thing that kills you if you can't buy locally is the shipping.

I bought a 3 gallon kit of Apex epoxy (with UV) locally yesterday for $162 and that was $50 to $116 LESS than all the other guys I mentioned previously because there was no shipping cost.

So...

-3 gallon kit of epoxy locally: $162
-3 gallons of polyester locally: $118 (including catalyst)

-Difference: 3 gallons of epoxy was $44 more than polyester.

The bottom line is that if you can pick it up locally and the price difference is similar to what I experienced then I would for sure use epoxy.

 

I'm going to unsubscribe: a Canadian can't handle this kind of information . . .

 

I don't even want to post the prices of marine epoxy in Egypt ...... you guys are real lucky ...