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

Well that makes mounting the foils on the centerboard problematic as CB is designed/placed+ for leeway control and should be under the mast for strength. Fujin has no separate board but assume that it has adequate lee resistance and resistance to pitching?

 

The C boards on Fujin would have almost ZERO effect on pitching as they are located very close to the LCF. To my eye, the C foils on Fujin would not significantly contribute to lifting the boat either - they are more vertical than anything else so its still very much a displacement boat.

Fujin does however, have horizontal foils on the rudders which are in optimal position to reduce pitching as the moment is the largest at the fore/aft extremities. However the horizontal stabilizers on the rudders of Fujin are not of a large size so their pitch damping effect has a limit.
Many reasons of design compromise for this include;
Keep drag minimal in light conditions,
Keep forces reasonable in fresh conditions to avoid engineering difficulties in the rudder design. Forces here can be extreme if the stabilizer foils are too big and the whole assembly has to rotate for steering etc

See i dont want to build 2 boards into the hulls of a cat for no reason. The potential gains in speed and seakeeping by seperating the leeway foils from the lifting foils and their ability to be retracted as conditions change, have yet to be satisfied by any other previous design - including Fujin or any other foil assist catamaran to date.

 

OK, so C foils facing inboard with 50% displacement wt lift and a single centerboard for lee resistance. For reference, floor is 1.26m wide and ht over floor is 2.06 m
Probably your hull section fwd would be somewhat tighter

 

yes - that is essentially what i have shown already - im just not convinced on the single centerboard in nacelle idea yet. That discussion has taken place on another thread some 30pages already - no need to cover it again here - its an option but im not convinced either way on that.
This image of the Mod70 phaedo 3 shows the longitudinal separation between leeway board and lifting foils. This configuration has proven fastest in ocean racing sailing and its only been deployed on trimarans to date- hopefully we can change that

 

Otherwise - the approach taken by Biekers design of Fujin- to simply leave all pitch damping for the rudders and solve those engineering problems. Then, the main foils can revert back to combined lift and leeway, why not move to uptip foils instead of C foils? This render shows uptip foils exiting just above the static waterline - in this way they are free from marine growth problems both in the trunk and on the boards once retracted, are vertical, dont impinge too negatively on the interior space, and damage survivability is better if exiting above static waterline. When the boat is pressed, they would exit slightly below waterline. They could be positioned such that they lift the boat with a slight bow up trim if the CoG of the boat and rig forces are accurately accounted for, ideally with rake control of both the rudders and boards.

 

You'll lose a bit with the free surface effect but as the support is straight and vertical, foil depth is not a problem.
Solves a lot of the problems particularly with internal space but is not removable from the top.
At some point you'll have to decide how much lift you want and at what speed.
Skyak? noted earlier that if its only partial foiling the keel should be v-shaped to soften re-entry.

 

I don't know how to design this interior. We are so far apart in our visions lol ... just to show you, even with a reduced size custom fridge and freezer you have a little less than 2 feet of space in the galley. That would drive me crazy, it's driving me crazy just looking at it.

I think if I was going to build a boat like this I would make it one level, put a bench for the aft bed, put a bench to set a hot plate and small sink. I would build a custom freezer fridge under this bench because a regular fridge won't fit. As it is, I had to move the foil tighter to the hull but you still need the cassette.

The two entry benches would be really small 14" max or just get rid of them, who is going to use them anyway, you will be outside most of the time otherwise in bed. I would wall off a space forward for the head and add some open racks to store non perishable goods. That's it, keep it to bare minimum.

 

I have a question on the rudder foil, does that pull downward? If so, I think I would do it the same way power boats by adjusting trim at the stern. Make the rudder foil bigger or have another foil maybe a bit bigger which can be raised when you don't need it. I wouldn't put it in a cassette, it would pivot down.

 

for Jorgepease: First impression is to replace the inboard bench with a counter and the refrigerator top is placed at eye height over the counter.
the inboard bevel in the coachroof seems rather large. Possible make the inboard bevel much smaller to provide a touch more internal space?
Is there enough space inboard of the door for a wet locker?

 

can get rid of that bevel completely actually, it does no good. Is this what you mean about fridge, put it on counter? I think a custom cooler box, can be up like this, would be best for this boat. Get the most storage space possible out of it rather than rectangles.

 

Yes - fridge and freezer up on the counter top imboard side is where i had them in my concept. They sell pigeon pair units like this in the big department stores for approx $350aud each here. Custom fridge units are way too $$$!
You need to keep roof line tall enough to fit them like that- my original coach roof had just enough space for them...
First thing closest stairs can be simple seating - no need for benches there... fold down bunk perhaps?

 

how asymmetrical is the hull at hip height - standing in the galley? Here is the SIG 45 for reference

 

About this assymetric...

The raised floor level you can see is the galley section midship.
The floor width hull skin to hull skin is 1.48m at this level.
The height floor to ceiling in this area is 2.05m - plenty of room for benchtop fridge and freezer which are 850mm tall and sit on the 900mm bench height. No bending over to get things from the fridge!

 

The inboard hull appears really too straight. There is space but only at 1.7 m above the floor?
where does the keel shoe end and the developed panels start?
1.48 cm is tight but you knew that already.
One trick to give the feeling of more space is to provide a kickspace 20 cm deep under the cabinets.

edit: typical 90 litre fridge is 48cm deep and door swings 56 cm so over 1 m projection when fully open.
How deep is the bridgedeck where it meets the hull? The bottom side is 90cm or 1 m from WL but not sure about the top surface.

 

The entire topsides is developable from the round bilge area- thats why it looks dead straight in the section plane. The panel itself is a contant warp from verical at the stem to the angle you see in the section planes.
The join from shoe to topsides is at the approximate DWL or slightly above so that the boot striping will cover the joined area. The round bilge area is all antifouled and the level of fairing perfection is not critical.