9mm gaboon ply (4.3 kgs/sq m) with 200 gsm/6 oz glass (600 gsm) one side and 3 coats of epoxy (400 gsm) the other will weigh ~5.3 kgs per sq m.
10mm 80 kgs per cu m foam (800 gsm), with 1 layer of 400 gsm cloth each side (2 kgs per sq m) will weigh ~2.8 kgs per sq m. In a lot of places the laminate could be reduced. In a few, it would probably be increased.
If the foam laminate is infused, the weight (and resin) saved will be about 0.8 kgs per sq m, so the end result (2 kgs per sq m) is less than half the weight of the ply.
Both will require the same frames and stringers. If the foam was increased to 12 or 15 mm thick (1.2 kgs per sq m), there would be no need for stringers and non structural frames.
There will be less effort and near zero waste with the foam boat as it is easier to carry, shape and join. If you use foam in a non tortured ply boat, you could cut the foam to shape (no waste from scarphing or puzzle cutting) and make the full length panels with peel plied glass on both sides, then glue the panels to the stringers and frames and tape them. Or, glass the inside, assemble them and glass the outside, which may be less hassle than tabbing and fairing the joins.
Both of which are more work than the Harry method
(Intelligent Infusion) in which simple, single curvature, self aligning, non shiny moulds are used to one shot infuse 2 half hulls with rebated lap joins. Bond the bulkheads into one half, glue the other half on. No strongback, setting up frames, fairing, grinding of glass and little contact with epoxy. Include window, beam, hatch and mast cutouts in the infusion to reduce the fit out work.
The cost of foam in Australia is lower than decent ply. Chinese foam, glass, carbon and infusion material are 50% less than locally, probably less again in the USA. Buy resin by the drum from a manufacturer (Dow, Shell, etc), not a retailer (WEST, System Three, etc) and sell any that is left over. I pay $US8/kg ($US32 per gallon) for general purpose epoxy, a bit more for infusion.
Some other considerations for discussion:
•Most rot in plywood boats starts at a screw hole. The rest in unvented or inadequately coated areas. One screw every 300mm/12" along the six unclampable edges on a double chine hull on an 8m (26'4") cat is ~400 screws, and a bunch more for the stringers and frames. If they are left in, each hole should be epoxied before the screw goes in. If removed, each hole should have epoxy filler injected in it.
•The same double chine boat will require 200 m of filletting/tabbing to cover the chines and gunwhales, some of which will be on your knees or upside down. And another 100m around the bulkheads. At least half of it will need fairing.
•There are a lot of consumables (tacky tape, vac bag, infusion medium, perforated plastic, peel ply, tubing) with infusion. Minimise it by using scored foam (no medium or perf plastic required) and reusing old vac bags over the job so the same bag can be used multiple times. The volume of the waste is high, the weight is less than the resin you will save.
•A home built carbon mast is probably cheaper than a bought alloy one (second hand beats both) and no more difficult to build than the rest of the boat. It will be about 60% the weight, which may not be a lot on a 26'ter, but will definitely reduce the pitching.
•Unstayed masts on cruising multis are far easier to sail and cause less crew stress than stayed masts, not least because it is simple to fit a fail safe floating fuse that trips the sheet when the hull leaves the water (either capsizing or pitchpoling) regardless of the wind angle and whether the sheet is cleated, in a self tailer or wrapped around your foot.
•2 masts (schooner or biplane) with no extras may be more expensive (second mast, boom and sail versus headsails, spinnakers, forebeam, seagull striker, winches, furlers and tracks) but remove the need to go on the foredeck, except to enjoy the sun.
•A wishbone boom is cheaper, safer and less effort than a traveller.
•Daggerboards and fixed rudders cause grief. It is usually lighter and simpler to make them kick up.
•Deck sweeping headsails and steering positions which limit vision ahead and to leeward are like driving a car with half the windscreen and the passenger's window blacked out.
•Length is safety. Not only in reality, but in perception. If the crew feels safe, they will be much more relaxed and able to deal with problems. Unless there is a reason not to (build space, marina fees, trailering), make the boat as long as you can. The extensions (and perhaps the hulls) can be narrower and lower and if they are kept empty will add little to the cost or overall weight. Keep the same rig, width and pay load. Top and average speed will increase and the motion will be better. Light air performance will suffer if the wetted surface increases, but reducing the overall weight using the suggestions above will more than compensate.
•A showroom finish will take longer than any other part of the build. If cost is an issue, a coat of high build over a peel ply surface and house paint will get you sailing for a lot less money than weeks of hard labour turning expensive toxic chemicals to dust.
•Two boats of similar size and type and built with similar materials, will weigh similar amounts, take similar time to build, have similar payloads and similar performance, regardless of what the study plans say.
Re Harrys:
Thanks for the compliments.
The
EX40 has been redrawn for a client (interesting guy, he's experimenting with including his solar cells in the deck infusion) who wanted a bit more room. It has become 43'. An updated 40'ter will be up 'soon' although the basic boat is the same as the one on the web page. The layout is easily customised (including the toilet in the lee hull, which is where I would put it) to suit whatever you want, as long as the hatches, beams and masts aren't moved without consultation.
Building hours for the
C50 are based on the time it took us to build one of the cedar 50'ters and the fact that infusion is far quicker. Judging by the time it is taking the current builders, they may be exaggerated, although all the builders are amateurs, learning as they go and working when they can, so exact hours are hard to track.
We will be building one, maybe 2 of these in Fiji ($US8 per hour labour, $US1,500 per week overheads, $US37,000 for the composite materials incl masts) later this year.
The costs, weights, time, waste (aiming for zero due to our plastic recycling operation) and carbon footprint will all be recorded. The build will be video'ed, so stay tuned. Meanwhile, for the reasons mentioned above and others, I'm confident the build time will be significantly less than that of a similar size boat built with conventional techniques. And far less physical.
