Epoxy vs. Vinylester vs. Polyester in production Catamarans

[Parmenter]

Originally Posted by dennisail

Outremer 49.

I find it amusing that many of these builders claim the usage of carbon fibre.

I was under the impression that this a huge waste of money in anything less than an epoxy build because the polyester resin is by far the weakest link failing way before the carbon gets to its yield strength.

[cwjohm]

Epoxy is expensive, but I always thought vinylester was fairly close to polyester in price.

I checked with suppliers this morning

Polyesters
Advantages:
Easy to use
Lowest cost of resins available ($2/kg)
Disadvantages:
Only moderate mechanical properties
High styrene emissions in open moulds
High cure shrinkage Limited range of working times
Vinylesters
Advantages:
Very high chemical/environmental resistance
Higher mechanical properties than polyesters
Disadvantages:
Postcure generally required for high properties
High styrene content
Higher cost than polyesters ($4/kg)
High cure shrinkage
Epoxies
Advantages:
High mechanical and thermal properties
High water resistance
Long working times available
Temperature resistance can be up to 140°C wet / 220°C dry
Low cure shrinkage
Disadvantages:
More expensive than vinylesters ($10/kg)
Critical mixing
Corrosive handling

[Stumble]

This gets complicated quickly, since price/pound is a poor measure of how it works out in the end.

Epoxy is about 5% lighter by volume than polyester
Epoxy also allows a properly designed structure to eliminate 10-15% of the volume of laminate because it is so much stronger.

Put together this means you could very well end up using substantially less epoxy by volume compared to a polyester boat! but at a substantial price increase for the hull. But you save substantially in the weight department as well.

The fun part is that by reducing weight you can further reduce the structual elements because there is less mass to worry about, and momentum is reduced because of the reduced weight...

Basically it becomes a beneficial spiral that all works to reduce boat weight, and forces incurred. But at a cost premium.


How much the premium is really depends on the design, and the redesign (to take advantage of the better materials), and how much of the total boat weight is concentrated in the structure. A stripped down racer will notice a much higher weight reduction by percentage than a long distance cruiser.



Then there are other issues...
Epoxy and vinyl construction don't require a barrier coat since they are naturally water impregnable. Which can save substantially over the life of the boat.

Gel coat doesn't stick to epoxy (tho epoxy will stick to gel coat) which raises issues with repairs down the road.


Frankly this is a huge issue, and if there was a clear winner the other two would disappear from the market. My preference is for epoxy boats, but there is a limited number out there.

[44'cruisingcat]

Originally Posted by Sand crab

5. Epoxy is not tolerant of sloppy mixing at all. A minor variance and the goo ain't gonna go and you are screwed.
6. To build a strong enough poly boat you just keep layering resin and glass To build a strong light epoxy boat you have to get the mix right and use the minimum of glass to achieve the strength needed. There is little room for error. Many epoxies benefit from heat curing also and that's a big oven to slide that cat into.

I keep reading how accurately epoxy has to be mixed. Yet to me it's very easy to mix ratios like 4:1 or 5:1, which most epoxies seem to be. I've mixed about 1000 kg of epoxy over the past few years (I always do it by weight) and have NEVER had a batch fail to cure. Not one. Ever. (I've had a couple exotherm out of control though, if I've mixed too big a batch on too hot a day....)

I'd have thought getting right the very small amounts of catalyst the ester resins require would be more critical.

"You have to use the minimum of glass etc...." well no. If you want the absolute OPTIMUM weight yeah, but you can use more glass and just make the boat stronger, just like with any resin.

[Redreuben]

The reason poly is still king is price, buyers want quantity over quality so poly wins.
If I was building from a female mould as in a production boat (my old job) a VE skin would be my absolute minimal requirement.
But I would go for an all VE construction of hull, deck and structurals and haggle hard for a decent deal, not a rip off.

Building a one off, epoxy all the way because it can be engineered that way from the start, every gram saved at construction adds to the useable payload without killing the performance.
You gets what you pays for.

[colemj]

Originally Posted by 44'cruisingcat

I can't see these figures being correct. For a start, the hull/deck structure is only about a third (or less) of the overall cost. And the resin is only a fraction of the hull/deck cost.

Epoxy is expensive, but I always thought vinylester was fairly close to polyester in price.

When getting a quote from a production boat manufacturer, I image some of the cost differential is due to price breaks on volume purchases. If they are getting polyester very cheap because of volume, then ordering a relatively small amount of epoxy could be that much more expensive for them.

Or it could just be increasing margins by marketing.

Catalyst ratio in polyester is not very important like in epoxy. Epoxy is a chemical reaction and the proportions must be exact. Neither half of those chemicals will cure by themselves, and mixing them together produces a completely different product. Like all chemical reactions, heat is a catalyst, so that is why it can kick uncontrollably at times. But get the proportions of chemicals wrong and the reaction does not complete to the expected properties.

This is in relation to the epoxies used in building boats - some other types of epoxies are catalyzed reactions to themselves and are similar to polyester in that regard.

Polyester is a catalyzed reaction and the amount of catalyst changes the rate of the reaction. The polyester will react without catalyst, but the reaction time is long (ever had some old gelcoat resin go solid?) - the styrene helps keep it in solution and prevent it from reacting. There is no chemical reaction producing a separate new product like in epoxy.

Add a small amount of catalyst and you have a long time to work with it. Add a larger amount and you will have a hard reaction within minutes. This is a very useful and convenient property of polyester compared to epoxy.

Mark

[geoleo]

Outremers are the world 'class' in using polyester -flex but don't break-