Formula 40 singlehanded trimaran build log

I've chatted to Ian Johnston about his balsa strip plank a number of times, interesting stuff. He thinks the weight targets for this boat are reasonable given that Bullfrog was dead on 2 tonne when launched in Cat1 configuration. I'll be happy if I hit that target, it should be possible if I'm careful with my build. Bullfrog was also more boat with considerably larger surface areas in the main hull. Too bad she is such a mess these days with all that cruising structure added on.

 

Bother option might be plane 1/2 mm off one side then leave extra to allow vigorous shaping and sanding on outside. You could hog 1/2mm of Wrc in seconds with sander. Nother thought, wonder what alternating Wrc and balsa would end up like on something? I know right off top you'd have to take care in sanding so one wouldn't end up sanding flutes in softer balsa, bigger block would allege some of that I suppose.


Barry

 

The WRC wont need much sanding more just a quick going over of any high points by hand so it's ready for the carbon uni and off axis glass lamination. If you were to use long grain balsa it would need to be somewhat thicker due to it's lower material properties. Durakore gets around that issue to a degree by having an outer timber veneer on the upper and lower face and the balsa core set into an endgrain position to make the best of its good points.

 

Get out the grinder

When I worked with Shaun Arber he used a 7 inch sander polisher with 24 grit on it to go over the cedar hull. I used 24 or 40 grit as well. Be careful and keep it flat but there will be lots of glue around between the cedar planks and you won't be wanting to try and sand it off by hand. New, clean discs and a careful attitude will clean the hull up in an hour or so.

Then you can go over it with something. I like going over the hull with a rusty piece of angle iron, about 3 metres long, that curves a little. The rusty bits stay on on the high spots and I can take them off with a plane or judicious use of the sander polisher. Keep going till it slides all over the hull nicely.

Dick Newick recommended cedar that was about 15mm for a 12mm hull skin so you could get into it with your sander

cheers

Phil

 

Weight is a problem which is why I don't want too much extra thickness on the strips they should lay fair over the mould and I have some thoughts on using a thin batten to shape the non slumping thickened structural epoxy over the joins between the strips to minimize sanding. I'll probably do just a few strips at a time. I think it's feasible but will test out the idea over a small area first to see how it goes.

 

That's why it's handy to have triangle stock handy, flip.it around for either bullnose shapes or fairing in undercuts to.lessen filler needed. Your right on thickness, I didn't think that thought through! Haha as for heavy glue spots that's where playing cards some in handy. Have a stack handy and pull off all extra, with a deck ya just grab wipe throw it out, as you go. And if you don't wanna sand then yeah! Have it.planed smooth as ya cab both sides, excess wipes off better that way as well.


Barry

 

Don't worry about the epoxy.

No kidding Owen - it will take about half an hour to clean up the glue. As to glue, remember that the cross grain strength of cedar is still less than epoxy filler. So you glue it together with microballoons NOT silica powder.

It sands off in a flash. Clean it up as you go but it takes no time at all to sand. But DON"T use glue or the sanding will be harder.

I like the idea of getting the cedar thicker and then fairing it first. Then fairing the hull after glassing is easier. The best way is to use a female mould and put in the internal laminate and bulkheads BEFORE you lift it off the mould. Then the hull is beautifully solid when you glass and fair the outside. On a male mould we glass and fair the outside whilst the inside can still move with moisture changes AND then you wrack the hull when you turn it right way up.

As to stripping - you can go dry and oush the filler in gaps or do it as you go. In some ways the bast way is to butter up short lengths and butt join the planks instead of scarfing them full length beforehand. The butts take compression fine and the tension is fine if the planks are not too wide. This enables the single handed builder to stack planks quickly with epoxy on them - you just need to keep the ends from flinging around the place. Lots of little plywood scraps are useful

Give me a ring if you want to talk hull building.

cheers

Phil

 

I finally sourced enough WRC at an affordable price to complete the beams. It needs a resaw and laminating up to thickness but thems the breaks.

 

awesome!



Barry

 

A while since I managed to do much on this project but today I dropped the mainsail down to my local sailmaker Hooper Sails. Overall it's in good condition and the sail material is not delaminated but lots of the glued seams that hold the sail together are coming apart. It will be resewn along those joins and at the very least I should be able to get a good delivery sail out of it. A replacement will be somewhere around 20k AUD so it's a handy thing to have. The sails that came with the mast are a mixed bag, two jibs that are pretty worn a staysail in good nick and a near new masthead spinnaker and a Code Zero type drifter so a pretty good sail wardrobe overall.

 

Way to go Corley, even the small steps add up. I can relate to this as a while back I picked up a Farrier main for almost free, largely for the carbon fiber battens as a recut looks virtually impossible. The stitching held but there is the odd bit of mold in the laminate for a unique camo look.

 

Thanks Cav, Moving right along in so many ways on this project. I often ruefully chuckle at my optimism at the start of this thread as everything has taken so much longer than my predictions. I've nearly accrued all the ply and a couple of drums of epoxy for the CM build plus all the vacuum bag accessories and pump. I now have a site to build that is undercover and large enough for me to fully assemble the platform. It all makes pretty boring reading the organisational side of things I guess but is an essential step on a large project.

 

Yes the better you are prepared the smoother things go. When people ask about progress seeing a stack of supplies isn't what they expect but the devil also lives in rounding up the details let alone building them. I make a realist estimate of time then times it by 3.

 

I've been chatting with Kurt lately on the main hull design. He suggested that more stowage space would be handy so the general idea now is to build the floats in CM and the main hull in vertical foam strip. That way a more aesthetic shape can be achieved where the topsides flare (or bulge) outwards. It will probably be something like the main hull of the concept for Phil Stegall: Trimaran Projects and Multihull News: Kurt Hughes 40' racing trimaran concept for Phil Stegall http://trimaranproject.blogspot.com.au/2016/08/kurt-hughes-40-racing-trimaran-concept.html

 

We've discussed building in just a tiny bit more displacement in the main hull. Cat 1 requirements demand a certain amount of tankage for fuel and water that just wouldn't quite fit in the previous design displacement. It's not going to be much extra probably somewhere around 250-300kg at DWL, hoping to keep the lightship weight in a similar ballpark of around 1800kg.