Open source 12-15m high performance/semi-cruising catamaran design

Back stay at each corner- not adjustable tho. Shrouds well imboard of the outer deck edge... IIRC it was a masthead rig not fractional but it did have an inner forstay - which my father added at some point. Old school hey...

There was 2 boards originally, got broken and eventually deleted due to leaking cases. In the end there was no boards. We sailed quite sideways but it was still ok due to the assyemtric hulls - just like a giant hobie rhe hulls had a sharp bottom edge flat outer and rouded inner - just like a scaled up hobie hull.

Single 20hp outboard was a real pita trying to maneuver it in a blow. Id definitely go for 2x20hp in a new design being discussed here.

 

You have seen the 53ft Fujin? It has twin c boards and appears to work quite well. Deck arrangement is non-standard
edit: some design details Bieker on Fujin http://sailish.com/index.php/2017/03/29/biekeronfujin/ lots of attention given to chines
Bieker 53 - Exciting high performance cruiser - Cruisers & Sailing Forums http://www.cruisersforum.com/forums/f48/bieker-53-exciting-high-performance-cruiser-144229.html


32 KNOTS? Scroll down to see a group of highly stressed sailors.
B53 Catamaran http://biekerboats.com/project/fujin/

 

Pretty impressive, and with about 1000 extra pounds of people on board.

 

Equally impressive $3.5 million price tag.
World’s Fastest Cruising Catamaran Launched in STX - ALL AT SEA http://www.allatsea.net/gold-coast-yachts-launches-one-of-worlds-fastest-cruising-cats/
Have not been able to find displacement of the boat.

 

I wonder why the center nacelle?

 

Does provide significant strength to the fwd longeron.
Does provide standing headroom in the cuddy but then it extends completely aft -- would love to get on board and poke around. This is 95% racer (?) so slamming is not a significant issue as it is flying one hull most of the time. Down wind the foils should hold it up.

 

32 knots is what my little skiff will do, must be a thrill to do that in seas.

I read what happened to Wahoo in that link, how do you skimp on the rudder post, pretty bad call

 

Yes fujin is an impressive boat.
However for the price its very unimpressive. I think the boat design started here could compete with it, for a fraction of the price and equally livable interior spaces by the looks of it.

Going from glass on foam with carbon beams to full carbon will only save you about 200kgs or the weight of 2 crew.
Theres better weight savings to be had by throwing away the diesel engines!
Fujins rating is 1.3xx btw according to heinekin regatta results page.

 

Couple of things:
1) Suspect the mainsail on the Sig at 30 knots cost more than the 10 grand you are looking at. And the deck gear, ropes and headsails are probably a couple of steps up from your price bracket as well.
2) Strip planking the hull shoe with foam is hard work. You either need an almost complete mould as the foam bends when you try to fair it or you put uni on both sides (one side is not much better than none), then sand half of it off in the fairing process. You then either painstakingly fill every screw hole and gap so you can infuse it, or you lay it up by hand. Either way, it then has to be faired. Then the other side has to be done. Then the other hull.
3) It is unlikely the join between shoe and sides and sides and deck will be accurate, so you will have to trim them, then butt join and glass them, then fair in the glass. On a 12m/40'ter, this is ~200 m/670' of tabbing, probably 2-3 layers of cloth each side which are all wet out and laid by hand, after you have painstakingly cut them, or paid for someone else to do so. Plus the stems and the transoms. This is not quick or light boat building.
4) Putting a floor into a round bilge hull is unpleasant as you are on your knees.
5) The round bilge and floor means the topsides are higher than necessary to get headroom. The weight and windage of this more than offsets the small wetted surface gains from the round hull over a flat bottom.
6) Manipulating a full length single panel side will be hard work (floppy), exacerbated if it needs to be removed and trimmed. A developable panel should not have any extra reinforcing, bulkhead landings, cut outs for windows and hatches, variation of core thickness or local beefing up of the laminate for fittings etc or else it will not bend evenly.

My suggestion would be to make the hulls using Intelligent Infusion. INTELLIGENT INFUSION – Harryproa http://harryproa.com/?p=1845 A simple, self aligning half mould of the hull and decks, built with flat sheet material, with bog or polystyrene inserts to make the rounds at deck and chine. The join down the centreline of the keel and the deck are straight lines so a Z or male/female join can be included in the infusion, meaning only gluing is required to join them. All the slow and fiddly parts of the fit out are included in the infusion so there is no secondary laminating, filling and fairing required. Almost all the work is done at waist level, including fitting the bulkheads, bunks, etc. The time savings are immense, the work is almost completely clean (there is little or no cutting or grinding of cured laminate, all the foam and glass are cut dry and the pieces for the first half become templates for the other three halves) and the cost and weight savings are significant. On the downside, the panels are only curved in one direction (apart from the compound curves along the chines and gunwhale) so may need thicker foam or more support. This is unlikely with all the furniture etc in your hulls.

Up on Stands,
That foil set up makes sense for a cruiser. I'd add a fuse so that if the board kicks up, the foil slides off the bottom of the board. Otherwise, it will rip the board out of the hull. Plus a string so you can retrieve it and a board that is accessible so you can replace the foil without having to get in the water or haul out. Only worry is that if it was in the centre of the boat, it would not do much for the righting moment. Be nice, but complicated to cant the board to leeward to get around this.

 

true that. Split the bottom lift foil into P&S and mount each on their own board. Yes, the foils would need to pop off if the board hits anything.
The foils develop lift so if the downhaul setting line is released the foil should slide up the board to the surface whereupon the board is swung fwd and up to stow. The boards swing fwd 80 degrees but aft only 30 degrees or so. I do not like indenting the bridgedeck to accommodate the boards.

 

I think the whole construction of a smaller cut up design is way more difficult than long open same level planes however if one wants to eek every ounce of weight savings out of the design, then more work is needed.

Edited
I got 34 inches headroom above a thin mattress by raising the bridgedeck. The mattress was dropped so it had to be cut down a bit. I Raised the BD to the height of the first step so you only have one step going forward. I left the wing or whatever you call it at the current height.

The aft bench and an under bimini bench which can be an extension of your deck panel are now at standard seating height.

Inside I made the steps going down to aft cabin a curve so as to occupy less space. Allows a pretty good size bench in that room and another across the hull, not shown, but the extra height means an extra step coming down so it's going to be almost vertical ladder type thing entering the hulls.

It's all got to be polished up but it's almost livable ))

 

C-board but facing outboard. There is a external bracket under the waterline that holds the board in place against the hull. Above the waterline, the board runs thru a case in cross-beam.

 

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"C" board as drawn facing outboard is a bad idea(very draggy) : you would have high pressure on the top side(due to leeway) and low pressure on the bottom-just exactly the opposite of what you want. The only way an outward facing board works well is if it doesn't develop lateral resistance and does develop vertical lift.

Outboard foil on Q23. red =flight waterline:

 

Thanks for the input.
Design brief for this project is not full foiling. Partial support with lateral resistance and pitch damping.
This board has non-uniform aerofoil X-section. Other solutions possible to meet SOR but this is design meant to stimulate ideas. Consider what benefits are possible re. potential problems.
For example, with the board up there is good clearance to the deck and the foil end is away from center of the boat.
I feel that the center of lift should be as outboard as possible.
Of course, if Groper is happy with the Fujin arrangement that's it then.

 

Dougs comments are correct - and this is why you dont see the C board curved the other way on other boats. The C boards used on all the big racing trimarans and Fujin are a proven system which works - hard to argue against that.
The problem with Fujins arrangement is that the boards are located very aft so that they are in the correct position for leeway. If you look at the design of fujin, the boards are aft of the mast. Im trying to get the lifting foils a bit further forward than this to counteract the rig driving force which tries to trim the boat bow down on a hard reach. Further forward will also increase the pitch damping as the moment is larger to the LCF pitch axis. This is whole reason i considered 2 boards per hull despite the extra hassle/weight/cost.
If you look at the big trimarans - they position the C foils forward of the mast for the above reasons - they actually raise the bows clear of the water as they get powered up and faster and rise up slightly onto those C foils with a slight bow up trim... exactly what you want when the seastate is picking up with the wind