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

I know, i know lol
Will it float- i have no doubt. Will she float upright - yes, until its been flipped over and then NO!

But past experience of similar boats tells me its going to be between 4 and 5 tonnes lightship. All depends on how much junk or lack thereof we decide to load it down with...

 

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Below is the 32' TF 10 by Morrelli and Melvin with fully retractable"Z"boards which are, in essence, surface piercing foils that can be left down all the time while sailing. On this boat they are very deep because it is a full foiler. But in your application they could be designed to draw much less water and still be retractable and effective for foil assist.

 

Yes doug - i know about the retractable Z foils on boats like that - the problem is how are you going to make that work on a hull which has accommodation inside of it? The boards of this boat are located right in the main living space and the keel to deck height in this area is about 8 feet.

So please explain to me how you achieve retractable Z boards whilst working within this space?

 

You're the designer-I imagine if you worked at it you could make them work with no more(and probably a lot less) problem than you would have with "C" foils! See post 17 and do a bit of research and you might figure it out. They are probably the best foil for your type of boat given what you've said early on.

 

Talking to you is like listening to a broken record doug - you keep repeating yourself ad nauseam yet do not offer any solution to the issue i keep raising about these. I would love to use these type of boards if i could make them work with the accommodation space! I said from the beginning that the size of the trunks that these would require destroys the interior space which precluded their inclusion. Now if you can figure out a way around this - then show me is what im asking.

In case the problem with these is not understood - the bend in the board requires a large trunk athwarthship so that it may pass through the entire hull and be withdrawn from the top. A trunk of this size pretty much closes off the entire interior of the hull meaning you can no longer walk through it! Again, if im mistaken, please show me a solution!

 

true that. along those lines, has any video shown that Catana 59' with c-foil assist actually doing some thing exciting? Like partial foiling with significant heave damping? The main impression is sheer weight.

 

One needs to appreciate marketing use of features VS actual utility of features... theres no way a heavy boat like that will see much benefit from this type of thing. Its like putting reverse bows on a lagoon 50 to reduce windage - its a marketing thing rather than actual utility.
The closest thing put in the water to date would be the bieker 53 Fujin. So far it has proven quite quick but id say this is due to the relatively light weight and powerful rig. Looking at the angle and curvature of the C boards i doubt they are getting much lift from them - maybe 15%?

 

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I took 20 minutes ,a piece of notebook paper with your hull section traced off an early post, a piece of tracing paper and made a "Z" foil work with room enough for a person to walk along side the trunk! 20 minutes! You simply have not tried this-you're just wrong about a "large trunk athwartship" being required! All you need is a drawing of the hull section and a piece of tracing paper to get the basic parameters correct. Would take you less than an hour. If I get time in the next few days I'll draw it out larger and take sequential pictures to show you that it works. But you could do it with very little investment in time.
PS-how much lift do you want from two immersed "Z" foils as a % of what displacement and at what speed?

 

A scan will suffice.

 

Actually - i think doug might be right... esp with the slant of the outer hull topsides, provided the angled tip of the board is not too long- then it could work with an offset companion way... drawings later- have to run...

 

I dont know how you can make this work Doug - this is what ive come up with. The opening is 6 feet tall and 2 feet wide at the top - really stuffs up the internal space to fit a trunk like this. If i curved the upper section i might be able to make it better - unsure yet, WIP... IF you know how to make this work, please share...

 

Whats the big rectangular thing that the foil is leaning against? On my sketch the foil trunk is all the way on the inboard side of the hull assuming a flat deck as originally drawn. If the rectangular thing can't be moved my idea won't work-otherwise it works very well.

 

The rectangular thing is the doorway through the bulkhead so you can walk through the hull... to do this you have to be a contortionist wearing a helmet so you can bang your head against the trunk case as you clamber through your half million dollar cruising cat...

 

That is the passage way under the board case.
A rough play around with the sketch shows that if the board is moved inboard as you suggest then the elbow section cuts the internal space below knee level to basically nothing. You do get clear head room. The other points are that its very likely that the board will jam in both directions and the volume of water in the case is significant.