Formula 40 singlehanded trimaran build log

It's a beam core as in this case the carbon and glass laminates do the work. There is also an endgrain balsa option but I'd prefer not to use it.

 

Check the plans Corely, if the core section between the balsa and cedar is the same no worries, but if the cedar section is smaller it is being counted on to do some of the work. If so I'd bounce the plans around for other opinions. That said if there is no difference the cedar will give some strength that the balsa won't.

 

Western Red Cedar is pretty common in cross beams at least in Oz. The boat I sailed back from Port Lincoln to Melbourne a Chris White 46 catamaran used WRC strip plank beams. At least some of the Schionning designed catamarans have too as well as many custom one offs.

I'd expect the WRC fibres to do some structural work in addition to be a core or else it wouldn't be an efficient use of material. Kurt has a minimum psi number on his plans for the WRC so I intend to get my wood tested to see it complies, I'll be shocked if it isn't above the nominated figure. Kurt suggested not to bother and that any reasonable quality WRC should be fine.

On the racing trimaran Balina Ian Johnston calculated the strength of the long grain balsa as a contributor to longitudinal strength. It worked well and Balina was 2 tonne when launched and fully compliant with the Cat1 safety requirements of the time.

 

You guys are just making do because it's hard to get Douglas fir or Sitka spruce over there

It all adds up to the ultimate strength for sure. Newick tended to use fir and ash at times in beams with a ply shear web. If Kurt said not to bother checking test it twice !!

Cheers

 

There is no real comparison to the balsa in the plans as it's end grain contour type core. I prefer the WRC as it should sit fair over the mold stations and hopefully require less fairing.

 

Whats the hardwood commonly used in older Australian fibro houses? Its a reddish colour, quite heavy and seems very strong. You cant even hammer nails into it when its as old as the house is. Just wondering if its of any use for boat building as I have saved quite a bit. I thought maybe for daggerboards...

 

I agree, scarphing to length with 10-1 ratio minimum should ease the hard spots and be stronger than the balsa.

 

As a general rule hardwood isn't much good on a multihull where weight is a consideration. The exception to that rule is hardwood plywoods like gaboon which are superior to softwood plywoods in use. I've seen some nice traditional monohulls use it extensively but they were more burdensome than performance boats with weight being less of a concern.

A good use for it in a multihull context might be to cut a veneer from your timber for use on a saloon table or for wood trim somewhere on your boat.

 

Cheers, so too heavy for anything other than decoration. I can confirm its very heavy! But also seems amazingly strong, but maybe not for its weight.

 

kinda have to take each woods failure tendencies into account as well. balsa just snaps outright, walnut, teak type are strong but split for miles down grain when it fails. pine cedar and such can split but won't go for miles every time. A good point of reference is a 2x4 of either bamboo or oak(yes I know bamboo doesn't come in 2x4 but...) take each and bend till the ends touch, oak is stronger but it'll snap like a twig, bamboo touches and comes back, but try to make a bridge from it and see what happens. now see what you have to "actually" build and adjust weight to strength accordingly.

Barry

 

on top of that todays green woods are just not stable at great thickness. Im constantly making custom ply with my choice of veneer to match thicker flat materials. plus with lotta stairs and steps and such I make, I can easily build in curves.

Barry

 

I found this extract from Meade Gougeon on the structural scantling of the F40 trimaran Adrenalin interesting. They used WRC and unidirectional carbon across the grain in her construction.

https://books.google.com.au/books?i...age&q=trimaran adrenalin construction&f=false

 

They also used fir in the appropriate places. WoodenBoat Magazine did a great article on Adrenalin's build back in the day, I'm trying to find my copy to send the date.

 

I had my WRC resawn by a local company that specializes in recycled timber (Shiver me timbers in Clayton). The plans call for 12mm I had them cut to 13mm to allow some scope for sanding the roughsawn surface. I plan to rip the resawn timber into strips on my table saw to different widths to best accommodate the various curves that are required around the front fairing face of the beam.

 

I made a strip planked balsa 14 metre wing mast many years ago. There was no I beam just the 12mm or so balsa with glass skin both sides. But when we were primitively hoisting the mast up using a tree with block hung from a branch, one of the helpers had earlier and emphatically recommended we should double purchase the rope and tackle to ease the lifting problems ... except the crappy rope we were using spun round on itself and wound up locking solid, mast half up. Then the mast pivoted round sideways on the bearing and then lay there like a bow under great tension and comprssion - with no arrow ... and then snapped just below the hounds. I vowed never to listen to advice from that turkey ever again. Single purchse would have worked fine, just some strength required to hoist. I knew that from the beginning. Anyway I later cleaned up the break and then gave the shortened mast to a friend with an altered Jim Young 24 foot catamaran. Worked well on that boat.
Why am I telling you this silly story? Because the planked balsa can do the job well, that is, if not below waterline. I remember Ian Johnstone used planked balsa above WL (cedar below) on his Crowther 40.