Carbon on Ply on Polystyrene

Another option would be to laminate your 5 layers of 3 mm (or equivalent) into a set of Constant Camber panels and forget the other stuff. Eg. Searunner 44 uses panels up to about 16mm thick. Gives you the opportunity of building a 'kit' in a smaller area, and by all accounts any fairing is minimal. Probably no cheaper than building conventional foam/poly though.

IMO Derek Kelsalls ideas (and designs) are well worth exploring. If he ever does another workshop in NZ I'm going to attend just out of interests sake.

 

An update after a few days feedback and reading (and this will change - is a stake in the ground for now).

Some decisions, let's see if they stand up long-term:

No polystyrene core, not even Very High Density. By the way, the cost here in NZ would be NZ$500 for a block 5.4mx1.2mx0.6m

No foam core at all. Instead, two layers of 3mm ply and a final light glass/epoxy layer over frames spaced 600mm apart (22 frames for each hull). Stringers on outside of frames for outer skin. Frames separate inner and outer skins by on average 100mm. Stringers on inside of frames, for the second innermost skin (one layer 4mm ply and a finishing layer of 1.5mm bamboo for the internal skins save for the cabin sole, which will be 4mm/core/4mm.

Total outside area per hull is 90m2. Translates to 32 sheets 8'x4' per skin, or 160kg (plus 20% for epoxy & paint, etc) per skin. All-up weight of two 44' hulls and open deck, unfinished but floating, is around 1.65 tons.

I've weighed a sheet of Gaboon 3mm at 4.5kg, cost is NZ$30. Puts cost of all timber at under NZ$8k. Intending to use epoxy, as in bulk it can be had for NZ$15/litre.

Construction method is sounding like a version of DD's radius chine for plywood. For small-radius areas and smaller sections that require more of a compound curve, will layer up four layers of 1.5mm instead of two of 3mm, or cut fingers.

Have accepted the need for a good amount of fairing, but will get help with this work. Sounds like it is the least liked chore.

I have an idea for pre-building the hull in sections vertically, each section 2.4m high, and then dismantling again (no epoxy, just testing, cutting, bending and shaping the panels and frames), so that I end up building a giant 'kit' in the space my Tornado, trailer, mast etc takes up right now (20' x 20'). I have a 2xcar space to store all the parts in. Thinking, if this works then other builders in suburbia may find it useful.

Final assembly with numbered components (panels, frames, stringers) would need to take one week per hull in a rented space with a small team. 400 hours per hull.

So there it is so far: all-ply, two skins (outer and inner) built in stages using the Radius Chine method.

This is by no means a final decision on how to build. It's a journey still. The hull shape is very similar to the proa Akka - as you can see, the rounded section should be quite a factor in keeping the hull in shape with the inner and outer skins. Beam is 8'.

 

Some of Malcolm Tennants earlier designs (pre the strip plank era) around the 40' mark used 2 or 3 diagonal planked skins totalling 9mm or so with glass on the outside. These were light boats for there size/time, but proven seaworthy. What advantage do you perceive in having two 6mm skins separated by 100mm?

 

Jamez, the outer is 2x3mm and the inner is 4mm (plus the 1.5 bamboo) - so all-up, is 11.5mm versus the 9mm you mention. In fact I may go 3mm on the inside, totalling 10.5mm plus the glass.

The main reason for the cavity (and this was why I was considering poly also) is for temperature. This is not to be a performance vessel, but a liveaboard in what may be some very cold places at times. I'd like to keep the inner hull away from direct cold.

The secondary reason is for the stiffness advantage that two separated layers provides, whether they are filled or not.

I have entertained the idea of filling the space with expanding polyurethane foam after construction is completed, but am concerned that any ingress will be soaked up into that section of foam, requiring excavation. Better to leave it a free space.

Good to hear about the Tennant designs. By the way, I realise that I said DD earlier, and i meant Dudley Dix, not double diagonal. But your reference is useful, thanks.

 

What you propose would most likely work fine... but building it sounds like twice the work of a typical ply boat tho... your basically doing both sides twice, and for 2 hulls!

Secondly, for it to behave like a sandwich 100mm thick, you need a method of tying the inner and outer skins together so they cannot slide laterally - like a phone book when you bend it... the frames and stringers can roll inside the skins, tough problem... would need a minitruss system inside to work...

Building the hulls is bugger all work in the grand scheme of things, its everything that comes after the hulls are joined together that takes most of the time...

Friend of mine pumps out a pair of strip plank cedar hulls in no time, he uses the frame and stringer method with ply paneling to build the deckhouse, sheets the inside ceilings with 4mm ply after running all the wiring etc, then paints it.... all exterior surfaces are sheathed in e-glass and epoxy. Plywood bridgedeck floor etc...

If you want the insulation, build a foam core composite boat and be done with it...

 

This build method uses foam strips and a layer of CF inside and out. Looks pretty straight-forward, no vacuum bagging. This is for a small racing cat - wondering how scalable the method would be?

http://lindahlcompositedesign.weebly.com/lr4-build.html

 

The typical method used for full size boats that require compound curvature, is transverse foam strip planking. Same as teh LR4 build, except screw battens to the frames first before transverse planking it in foam, followed by the laminate etc

The strips of foam can be much wider and thus laid quicker, and you can get away with greater spacing between temporary frames. I personally still find the system very labour intensive tho - you have to do one side of the sandwich a time, and fair both sides afterwards...



If you havnt read my thread yet, i suggest you take a look - im building a 35ft cat in foam sandwich, with only a double garage as a workshop.

Like kelsalls method, there is much time to be saved if you can complete both sides of the sandwich laminates in 1 shot, and get a finished surface that doesnt need to be faired on at least 1 side. The catch is with a flat mold, you cant do compound curvature, only single curvature or developable panels. Eliminating all the secondary bonding would be my next improvement, as all the filleting, taping and joining is very time consuming, not to mention rather expensive - all that epoxy and tape adds up. Id consider making a full mold out of MDF next time, direct female molding, and infuse the whole boat in 1 shot... i think it would be a better way to go if only i had the space/workshop/shed to do it in...

 

I think you are making a mountain out of a moe-hole , (or should that be a mole-hill )----anyway we built the 42 ft "Bagatelle" hulls out of 5/8th" Klegicell, coated with F/glass set in polyester resin. The 4 X 8 ft sheets were used whole in the hull mid sections, and ripped into less wide strips toward the more curved sections at the ends, becoming very thin strips at the buttocks. No need for expensive epoxy at that stage. No need for expensive carbon cloth either. This was not an Americas Cup catamaran but an Ocean Going Cat. The Klegicell was very stiff and had to be heated in order to bend it down from the keel to the gunnels. We made a simple 2X4 wood frame with two horizontal beams over which to bend the foam pieces while they were heated by standard radiant heat bars from above. Worked a treat. The foam eased into the required bends as we applied careful downward pressure on the end of the sheet.
The mould was the frames from the plan, stood upon a strongback, --less the thickness of the 3/4"stringers, which were screwed on from end to end, then checked that all was fair.
Holes were drilled in the stringers and the foam was held on by coarse screws through the holes from the inside. We took boxes of cocktail sticks and cut them in half on the band saw, using the half sticks to fair the edges of the foam pieces, pushing the sticks in with a nail punch. We filled the edge gaps with a resin/ phenolic microballoon mix, smoothed down with a putty knife and then smoothed down the joins with a sanding block. No great amount of fairing was necessary.
The hulls were then glassd with 10 oz cloth and resin.
When all was cured the screws were removed and the hulls were turned over and supported in cradles cut from MDF using the frame patterns. The hulls were then glassed on the insides and the frames glued in place with epoxy.
After that the remainder of the construction went ahead as planned. The wing deck was built separately in the same way, and was offered up between the hulls as the boat was assembled. The whole thing was very straight forward, simple, light weight and strong. The foam sandwich was great insulation.

 

Any progress?

Wayne

 

Given what is possible with CAD these days, and 3D cutters, it would seem to be perfectly feasible to cut a female plug from a compounded 'block' of styrofoam (XPS for preference) and then lay a thickish layer of resin/fairing mix on the foam, and use the cutter again to 'fair' the resin.

Light sand and then a final spray coat of self-levelling paint, a bit of polishing, and there's your mould.

'Course, building the 40' long frame to attach the cutter head to might be a bit tricky.....and require a laser level....

But if you were planning to build multiple hulls, say for a 'formula' or One Design, this might make sense. And the XPS would only need to be in the final layer - the majority of the block could be cheap recycled building industry EPS foam....and building a *female* mould it would be a bit like building a cuppla block walls with a gap between them, and fillijng inthe bottom with more blocks......vacuum out the swarf as the cutter head moved down towards the keel.....if you used pregressively smaller cutters, and finsihed with essentially a tiny circular sanding disc, the foam would be well finished and spot on accurate.

Vacuum infused laminates onto gelcoat laid into the female mould and you'd get a faired hull in one operation, especially if you used peel ply as the final laminate.

And for cats only need one mould. Tris would need one for the main and one for amas.

'Course, it wouldn't be 'cheap'......

Just out of curiousity, recalling something OS7 said somewhere about how the Bucc 24 was built from ply panels with attached stringers, tortured into shape, could not something similar be done with XPS foam with glass vacuum infused to it on the flat (much easier to do) and then the panels tortured into shape, or does that run the risk of delaminating....???

Remember, I am a student, I know nothing....just askin', is all....

Personally I think the simplest, quickest and cheapest method is probably the multi-chine flat panels onto a temporary strongback. As people like Ray Kendrick have demonstrated this can produced a nice shape with a near rounded profile, and no doubt adding panels could produce a closer approximation of a full curve.

And again, the panels can be laminated on the flat and bent onto the strongback.

Sure, you then still have to fair the exterior, but if you've peel ply'd the foam sheets first, they'll be near perfectly faired already, and youll only need to do the chines after taping them.

At least, that's how it looks to me from Ray's Scarab plans......

But again, I know nothing......*1st Yr apprentice*, OK, so be gentle....

 

I don't know of any CNC mills large enough to do an entire hull mold here in Australia... Do you know of one? Only one i now of is in europe... But yes it certainly sounds feasible... I built my boat from infused flat panels and you can let the panels fair themselves when you torture them into shape. The problem occurs afterwards when you tape them together, you have a raised edge the thickness of the tape which needs to be feathered out.... So even tho the panels are fair, you still have to do some fairing regardless before the paint will go on nice and perfect. You can setup rebated edges for the tape, but setting this up around complex shapes and curves is time consuming also, probably easier to just fair it out the old fashioned way, but straight edges ae easy enough to setup and worth doing...

 

Oracle chose their carbon fiber for the AC because they did not have to paint it. They were saving on the weight of the paint.

Then again, they were paying top dollar for really good craftsmen to put it all together ....

I wonder how far along Cutaway got?

 

There are facilities to do this in the US see Greg Lynn's GF42 project the hull halves are being CNC cut into a female mold out of foam blocks pretty interesting stuff.

http://www.boatdesign.net/forums/multihulls/gf42-trimaran-design-47747.html