The revisionist mythology of Wharram

[Basileus]

For foam sandwich Vinylester is a brilliant resin. Faster gell and cure times make for much faster and time efficient building.

How would you compare it to polyester? I think I've mostly used polyester and and that cures pretty quick

 

[redreuben]

How would you compare it to polyester? I think I've mostly used polyester and and that cures pretty quick

It works the same as polyester with an MEKP catalyst but it is more epoxy like in properties.
And no osmosis worries.

 

[fallguy]

Im interested in building a composite Skoota myself but with polyester resin and mostly nidacore. I want to be able to get in and around very shallow areas and the possibilities of rot mixed with the thinness of the plywood and laminate makes me worried about scratches and impacts taking their tole on it and leading the boat to an early grave. Im a super new member so I cant send direct messages yet but Id really like to be able to talk to you in depth some time about building yours.

If you are worried about abrasion, you build the Skoota with a beaching keel.

You don’t use nidacore if you have abrasion concerns. Hole that stuff and you get a wet core.

I used plascore (similar) for the bdeck, but only for its size at 5x10. I regret making a double bottom and the weight added is really enormous. I think an elephant could walk on my bdeck if the cat wouldn’t sink.

 

[Basileus]

If you are worried about abrasion, you build the Skoota with a beaching keel.

You don’t use nidacore if you have abrasion concerns. Hole that stuff and you get a wet core.

I used plascore (similar) for the bdeck, but only for its size at 5x10. I regret making a double bottom and the weight added is really enormous. I think an elephant could walk on my bdeck if the cat wouldn’t sink.

Indeed what I've been increasingly finding is that under the waterline I would need some kind of substantial reinforcement if I used nidacore. I was considering a second, but much thinner layer of more impact resistant core material before the external layup and/or lamenting an extra layer of kevlar below the waterline

 

[redreuben]

Just use a higher density core from 100mm above waterline and below.

 

[cavalier mk2]

Skip the kevlar, if it gets exposed it wicks water and gets heavy. If it is all that complicated solid glass would probably not weigh more, make the outer layer dynel.

 

[redreuben]

Kevlar and other exotics are wasted with polyester, the resin system shatters before the material gets even close to its load limits, again, vinyl ester is a better fit.

 

[rwatson]

Kevlar and other exotics are wasted with polyester, the resin system shatters before the material gets even close to its load limits, again, vinyl ester is a better fit.

Vinyl ester isn't all that much stronger. In any case, for less price, you can add a more glass, and achieve the rated strength needed for the component.
If you engineer a deck for say 2 tonnes, it doesn't matter how strong the resin is, if the engineer has calculated the amount of each resin correctly.

Vinyl V Polyester is about 30% greater cost, and even worse, the Vinyl smell is absolutely shocking to work with. Its like breathing burning plastic.

 

[redreuben]

I love the smell, I think it smells sweet, but your mileage may vary. If your going to consider vinyl ester get numbers from your local supplier, I found when manufacturing spa pools and yachts that VE performed much better with a post cure which needn’t be exceedingly hot or long, again, talk to your supplier. I consider it a medium tech resin for uses where higher performance is desirable but the cost of epoxy can’t be justified.
One area it excels is resistance to osmosis, which is why many boatyards use it as a barrier coat behind the gelcoat, again a post cure boosts this but most yards don’t bother.

 

[gonzo]

Whether you use nidacore or plywood, what matters is to have the correct scantlings and built it with the correct techniques for the material.

 

[rob denney]

Epoxy is not expensive unless you pay for the name on the label. I have just paid $US8.56/kg and $US7.12/kg for infusion and general purpose resin. $US15K for 1,800 kgs/4,000lbs for a 15m/50'ter. The Gen Purpose has a very long outlife, would be fine for vacuuming. Shipping from Aus to the USA would add maybe 10%, but I am sure you could find similar prices in the USA if you looked as the base materials are imported to Aus from Europe

Infusion and vacuum bagging use about half the weight of the fibres in resin. Each kg/lb of resin wets out 2 kgs/lbs of fibre. Hand laminating uses about 1:1, ie the same weight of resin as fibre. To vacuum bag you first hand laminate the resin, then bag it, suck 50% out and throw it away. A wasteful, stressful way to build a boat in this day and age.

The same cores are used for both infusion and bagging.

Infusing vs ply: Infusing a large flat foam/glass panel is cheaper (in most of the world, maybe not in some parts of the USA), easier, lighter and quicker. There is no scarphing, fairing, suiting up to use and sand toxic chemicals and the result is about half the total weight. If you carefully choose the design there is no strongback, building frames or alignment thereof and no planing of stringers, full length filletting and tabbing on your hands and knees or endless sealing of plywood edges. Foam/glass does not rot, does not need ventilation in 'watertight' compartments and is easier to repair.

Yesterday we tested some hand laid samples of 400 gsm glass either side of 10mm 100 kg per cu m recycled PET foam panels. Nothing scientific, some enthusiastic 120 kg/260 lbs Fijian students standing on a sample sitting on a sharp rock. There was barely enough damage to analyse by eye, so they took to it with a hammer. Took a lot of hammering to damage the inner surface enough to destroy the watertightness, and even then it was a crack rather than a hole. After the testing, we cut the single hit samples through the damage. The fibres were still stuck to the core, despite a ~5mm x 30mm (1/4" x 1.25") depression. The structure is sound, but the foam is compressed. The fix would be to bog it, or ignore it. We didn't do any comparisons, but 80 kg PVC foam or plywood with a rigid/brittle resin (most of the 4 or 5:1 epoxies, vinylester and polyester) would not be as tough or as easy to fix.

 

[rwatson]

Puzzled. I understand Infusion is sucking the Epoxy into the dry laminate, but I have never seen 50% of Epoxy sucked out of a wet layup Vacuum Bag process.
I have just been watching wet layup Vacuum bagging on the RAN Yacht build, and there is no excess Epoxy created.

 

[tane]

sounds good, rob, but how do you get the infused flat panels to bend into a "boat-shape"? They are sandwich & very stiff...?

 

[ropf]

but how do you get the infused flat panels to bend into a "boat-shape"? They are sandwich & very stiff...?

Isn't that exactly what Kelsall did with his KSS system - including shapes with round bilges?

OK - round bilges don't work with prefabricated panels.

But think of a Wharram - if you don't buy the prefabricated panels - but perfectly fitting machined parts - put together as easily as Lego... I was extremely impressed with the build photos and videos of the Mana 24 - the kits are worth every penny of extra cost over the raw materials.

I'm neither an expert nor a designer - just a technically minded sailor - and if the Tiki 26 was available as a kit in foam sandwich - I would really consider building one.

That said I still have conclude:
significantly better boats can be built with the same investment of money & labour

A better boat with less cost and work - for my location and style of sailing ... I couldn't found one - but I'm seriously interested to discuss that topic in a separate thread with an experienced Wharram builder and sailor.

 

[redreuben]

Tane, I’d like to see that discussion although similar was done on the better Tiki thread.
As for panels I would leave off the internal skin so you get the moulded finish and glass the internal after joining OR bend the panel to plan shape when moulding.
Flat for transporting curved for onsite.