The revisionist mythology of Wharram

It's many years since I did a vac layup and I didn't measure the waste. However, it is difficult to wet out cloth at better than 1:1. A good vac bag will be similar to a good infusion, which is 1:2, so half the resin gets wasted.

Tane,
Harryproas bend the table to get the curve for and aft and use fillets in the mould for the chine. You could also use the same thickness foam as you do ply. The bend characteristics (although not the torture potential) will be similar, but you will need the same number of frames and stringers. Or, you could use a boat design which does not have more curvature than the panels can provide, which is what we did on the 3 ton 24m/80' cargo proa prototype. Ugly, but effective and quick.

ropf,
Derek used flat panels and made a series of cuts in the bottom which then needed glassing and fairing. Clever, but hard work.

 

That's not how it works. You apply enough resin to get a close to optimal resin percentage, and apply the vacuum. There is no excessive waste.
Its not like you wet out the cloth until its dripping, and then apply the vacuum.

how much resin use， in resin infusion process http://www.talkcomposites.com/20873/how-much-resin-use%EF%BC%8C-in-resin-infusion-process

 

If you calculate the amount of resin that will end up in the vacuumed laminate, there will be be dry patches in the laminate prior to applying the vacuum. Otherwise, hand laminates would not need to be vac bagged.

If these dry areas are in the layer under the bag, they may get wet out, but I would not bet on it, especially for any areas not in line with the flow path to the pump.

In the Ran video, he wet out all the laminate (not 'dripping', but I'd bet he was over 50/50 resin/fibre judging by the amount that soaked into the dry laminate as it was applied). We did not see the finished absorbent layer. If he had one, and it was full of resin, the excess would be in the job. ie not 2:1 fibre:resin.

The 'Talk Composites" reference is for infusion, not vac bagging. And does not come up with a fixed number due to not defining the variables, and using resin intensive infusion techniques on small parts.

Best way to understand all this is to get some gramme level scales, a cheap infusion/vacuum pump and do some samples.

 

Very helpful info, which resin did you use for that test? I assume the epoxy you mentioned. Is it some particularly less brittle kind?

 

It is less brittle, but we chose it primarily for it's long outlife and simple 2:1 mix ratio. I was prepared to sacrifice some mechanical properties for this, but it is fine (better than fine in terms of toughness) for the jobs we are doing. It is a formulation from Hiltour in Gosford Australia. They also produce the Compset range which is what we use for infusion. Not sure if they sell less than drum size, but they have a few distributors around the place.

 

Toughness is underrated. It is a property that seldon gets mentioned in sales, probably because strength is the property that seems more important in popular view.

 

In the 70s ithe mixing ratio of Araldite 106 (IIRC..) & its hardener HV 253 U (again iirc..) could be varied slightly tochange the properties: harder & better weather/water resistance to more flexible & less durable against environmental effects

 

Absolutely. Weird really as the fibres take a lot more load than the resin can.

Tane, you can still do this with most epoxies, but I would not recommend it. It is a function of insufficient cure due to not enough hardener to connect to all the resin.

 

CIBA had it in the specs: hardener ratio from-to (it would never occur to me to experiment with the ratio without the say of the manufacturer, least of all as I did the beams of my Wharram then.)
The dispensing pumps of the Gurit Epoxi I am currently using are not totally correct, they dispense a little more hardener (I run out of the hardener canister before the resin), so now I have taken to weighing with the electronic scale.

 

Not uncommon. The first thing to do with new pumps is to get 2 identical containers and pump 5 hardeners into one and 1 into the other (or whatever the ratio is). Repeat occasionally, but keep the pumps clean. It is usually the hardener which gums up. Fortunately, many hardeners wash off in warm water (no soap) so they are easy to clean. If weighing, read the instructions as most resin are heavier per volume than most hardeners, so 5:1 by volume, may not be 5;1 by weight.

 

In the case of West Systems at least, either is OK, or they provide an alternate ratio.

The mixing ratios for West System epoxy depend on the type of resin and hardener being used:

• 105 Resin and 205 or 206 Hardener: Mix five parts resin with one part hardener by volume or weight
• 105 Resin and 207 or 209 Hardener: Mix three parts resin with one part hardener by volume, or 3.5 parts resin with one part hardener by weight

 

Not sure where your info came from, but The WEST System data page https://www.westsystem.com/app/uploads/2022/09/105_205-207-Combined.pdf shows the attached for 105/205. This aligns with the resin having a specific gravity of 1.15 and the hardener 0.98

 

When the Wharrams prototyped the Mana 24 kit boat didn’t they use a “Green” epoxy ?
Anyone have any experience ?

And I think we are in new thread territory

 

The 2:1 system I referred to above is "41% bio carbon", apparently the highest in Aus. I have no idea what this means (maybe 41% of what would normally be fossil fuels sourced is bio sourced?) , but it is 'certified in Europe'. There is so much greenwashing happening that I am dubious about all such claims.

 

Irrespective of those weights, the instructions from West Systems manual


You can see here that you can use the Ratio by Weight OR Volume, unless you are using Special Clear, or Extra Slow Hardener.

Dispensing and Mixing | WEST SYSTEM Epoxy https://www.westsystem.com/instruction/epoxy-basics/dispensing-and-mixing/#:~:text=Dispensing%20without%20Mini%20Pumps%20(Weight,resin%20with%20one%20part%20hardener.