The platen pressing prepreg method of producing the duflex panels is very good, the structural mechanical properties are excellent. Its the cosmetic properties of the panel that i have a problem with - they need extra work which is not nessesary with infused panels off a table. This extra work (and resin = weight + cost) offsets some of the time savings achieved by using it in the first place...44c wrote:The kit for our Oram 44C was about $65k. Not including furniture. I doubt your boat would have run to $70k even with the furniture.groper wrote:The problem with duflex is that the surface quality is poor (pinholes etc) and i dont like the idea of a balsa cored boat. Balsa has brilliant mechanical properties, but boats being boats means inevitably water will get in somewhere somehow someday... for this reason i prefer foam. The total materials cost for my boat shell is looking like going a touch over $40k as i have just about everything i need to finish the boat on hand. This is only glass reinforcements, infusion consumables, resin and foam. A duflex kit for this size boat probably would have been around $70k including furniture, so there is a considerable money saving.
The reason Duflex has pinholes is because it has extremely good glass/resin ratios. Every drop of excess resin is squeezed out. Because hydraulic presses are used, pressures available are far higher than can be achieved with infusion, where pressures are limited to around 0.8 of an atmosphere, or around 10 psi. Pulling deeper vacuum than this risks "boiling" the resin.
The weave on Duflex is easily filled - just a squeegee of a runny glue mix.
I disagree that water ingress is inevitable. There are balsa cored boats 30 and 40 years old still in perfect condition. And many of the early boats used polyester resins, which are nowhere near as good as modern epoxies.
Not knocking your methods or the job you're doing, which is excellent. Just that some of your comments about other materials needed correction IMO.
Your point on infusion vacuum pressure is not complete. Polyester and vinylester resins do need the vacuum pressure reduced a touch to prevent boiling of the styrene. Epoxy resin does not contain any volatiles and as such can be infused at 100% vacuum - the gauge pressure i typically see on my infusions is -101kpa as my boat is 100% epoxy laminates, although i have done some vinylester stuff aswell and have observed the resin boiling in the catch pot if the vacuum is too strong. Absolute vacuum at sealevel is -101.3kpa btw, so im 30mbar off absolute. I have measured and weighed individual components which make up the test samples of the panels i have produced. By measuring carefully the before and after weights, of foam, resin, cloth, resin absorption in the surface of the foam etc, i end up with a 68-70% fibre volume fraction in my laminates - which is considered very good even by commercial standards. Due to the different densities of fibre VS resin (fibre being heavier per unit volume), this equates very closely to half the weight of resin to fibre in the laminate - and i get this with no pinholes or extra filling required afterwards - its ready to start painting.
Compare this to a hand layup, i typically use equal weights of fibre and resin to get the job done. At the end of the build, this adds up to ALOT more resin, something like and entire 200KG drum more... a drum of epoxy costs around $3500 - this pays for all the infusion consumables used with money left over, plus your boat is 200kgs lighter - so infusion will actually save you money compared to a hand layed build - which contradicts another misconception floating around... what im saying is, infusion is not expensive provided you shop for your consumables wisely.
Back to the balsa thing, if your a perfect builder- then sure, you will never see water ingress into your balsa... but how perfect are you? I know myself well enough not to trust my perfection