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

Simple to ask "What cruising catamarans over 10m use Z-boards?"

 

Picture already posted-more details here: New 'Z' board Cruiser-Racer Cat: The North Wind 55 | Catamaran Racing, News & Design http://www.catsailingnews.com/2016/04/a-cat-applied-tech-new-z-board-racer.html

What about the board raise system, curved boards seems to have a smoother framework, and Z as seen in the As do have a special space required in the deck for fully raised?
The boards will end flat over the deck?
GR: We have designed the tightest daggerboard trunk possible, so the way they are positioned is not a problem even for the interior. They do go a bit over the deck but this is something we studied and is not a problem. In the end when sailing, both boards will be down.

 

Nice boat, it's on my list of favs, that's the one Brian mentioned only midgets would be able to get below without banging their head, not enough overlap of roof, surely it must work though

 

I was hoping for actually built hulls.

Well, this is the designer speaking so of course everything "works well" & "not a problem"
No examples have been launched so no owner has yet to make the choice between curved or Z boards.

This special space required in the deck is the key design point as it appears to cut the accommodation up. But we need detail images of the cassette/trunk system to know exactly what the costs are.
This is the best I could find but it is retrofit of an existing hull by Stefano Tachi. Images seem to show that the z-board is not removed completely? But the trunk is massive.
https://2.bp.blogspot.com/-Jn44aOGP...BqpoQ0oemu3x-w/s1600/AclassFLYER-Retrofit.jpg
Catamaran Racing, News & Design: March 2016 http://www.catsailingnews.com/2016/03/

 

Very interesting video of F4 Red Bull )( 46 foot ) trying to go NY to Bermuda.

 

Wet and a lot of work, I bet if you move the mast more to rear of boat you can eliminate some of that downward thrust. Maybe 4 feet or so and balance her well. Keep it simple and lighter.

 

Im not even going to respond further to the Z foil idea- the above pics and other info posted earlier about why its not practical are obvious.

Doug- look at the above pic. Now imagine the hull is not 1ft deep but 8 feet deep, go ahead and draw it if you have to. How on earth are you going to fit that trunk in there allowing for the curvature of the Z part of the foil and the straight sections so that the board can be inserted from above? Go ahead and draw it and then show me how much volume you have left in there for a bathroom or a galley or anything at all! And this occurs at the most useful voluminous part of the hull so ypuve just destroyed your best living space with your decision to use z foils... great idea mate!

 

That F4 hull is not a boat, its a force transfer structure.
Adding 1 m of free board seems necessary but of course now you trigger the negative design spiral where every bit of weight presses you closer to the water which means greater stress etc.
24k with comfort!
What do we need to be comfortable? The 24k is doable but comfort is far far harder.
First step seems to favor relatively thin/deep keels that have low rates of unit displacement. The keels/submerged hulls start looking more like foils so they cut through 75% of expected wave heights (provides comfort) but
they would need active stabilizers to prevent pitching/hobbyhorsing. Control system would need high response speeds and excellent damping to provide comfort. Active stabilization is possible through the rudders only?
Such hulls would have poor light wind performance due to high surface drag but wave friction might be significantly less. And of course the internal space is a problem.

 

Interesting thread, best wishes for your new project.

I am also interested in possibilities to use foils in a 'foil assist' mode. Just a few months ago we saw three remarkable sailing records - round the world single handed, round the world crewed and monohull round the world single handed. Would any of those records have been possible without 'foil assist'? Indeed Thomas Coville's single handed 49 day round the world trip was made in the same boat that in 2004 Olivier De Kersauson used to take the crewed record with a time of 63 days. So, same basic boat but two weeks quicker single handed than fully crewed! - well I suppose he did not need to carry such a weight of provisions! Of course a lot of modifications were made to the boat between those two records and perhaps one of the most significant of the modifications was the addition of 'C' foils for 'foil assist'.

I have been doing numerical analysis (computer programming) to try to evaluate the likely advantage of various foil systems on various types of craft, monohulls, cats and trimarans. So far I have developed software using a 10m trimarn (its actully a rough approximation to the Farrier F32R) as an example base craft, you have to start somewhere, and the foil system I have considered is one of my own concepts based on 'T' foils rather than 'C' foils, but my aim is to extend this study to a range of alternative boat types and foil systems. I have got as far as producing polar performance diagrams for the 10m trimaran with and without my foil system and operating in the 'foil assist' rather than 'flying' mode. A few weeks ago I presented this work to a meeting of the Amateur Yacht Research Society in the UK, since then I have been busy with another boating project, completing a rowing boat which is described somewhere in the thread here "Design a Fast Rowboat". The rowboat needs to be finished for an event at the end of this month, after that I hope to get round to publishing the work I have done so far on foils somewhere on the internet.

I would say that so far I have been leaning towards a trimaran rather than a catamaran as the basis for utilising 'foil assist'. At least part of the thinking behind this is to do with skin friction drag which is a significant part of the hydro drag for any craft that is carrying even part of its weight on displacement hulls. A trimaran achieves its lowest skin friction drag when upright with both floats only just touching the water (With cruising in mind I am ignoring the possiblity of sailing a trimaran on one float only), whereas a catamaran achieves its lowest skin friction drag when heeled so that the lee hull is fully loaded and the windward hull is lightly loaded. If you have a foil assist system lifting the lee hull you are pushing a trimaran towards the low skin friction condition, whereas on a catamaran you are pushing it towards the high skin friction condition. Ideally I would envisage a foil assist system lifting the lee hull of a trimaran clear of the water, or almost clear of the water, so that the remainder of the weight not carried on foils is carried mainly or entirely by the centre hull. At this stage in my studies the above is just guesswork - I have not got as far as a comparative numerical analysis for cats and tris but that is definitely on my 'to do' list. Maybe I am overestimating the importance of skin friction in which case a catamaran such as you have drawn could be a somewhat lighter and simpler platform.

As I said, I have my own ideas for 'foil assist' which are based on 'T' foils rather than 'C' foils, but if you prefer 'C' foils than I would sugest a possible alternative way to retract them as sketched below - i.e. a pivoting rather than sliding arrangement. I am not saying that this is better than the sliding system you have drawn, I can see advantages and dissadvantages both ways, but it might be worth considering.

The advantages of a pivoting arrangement are:

• Less prone to impact damage and less risk of consequent hull damage
• Probably simpler foil actuation and less friction in actuation.
• Does not require flared outer topsides. I think you have drawn hulls with flared outer topsides to accommodate 'C' foils. Vertical or near vertical outer topsides would have the advantage of minimising overal beam for any given hull centreline spacing which I would have thought is quite a big advantage. Also, highly flaired outer topsides could make fendering tricky when alongside quaysides or rafted with other yachts.

The disadvantages of a pivoting system:

• Drag of long slot in hull, possibly requiring flexible flaps to cover the slot, as is done on racing dinghies.
• Only really works fully retracted or fully deployed, although I suspect thats how 'foil assist' should be opperated. Up to a certain speed a displacement hull offers a better L/D than a foil, so any foil deployment is counterproductive, above that speed even carrying just a small part of craft weight on foils is an advantage, so I suspect that the foils should either be fully retracted or should be fully extended.

From the point of view of intrusion into the accommodation I dont think there is a lot in it, but on a large craft the pivoting arrangement could possibly be installed entirely under the cabin sole while still allowing full headroom.

I dont agree with those who say that you need a more comprehensive SOR - you have told us how many people will be on the boat and what they are expecting of the boat, surely that is all that is needed. I would say that the size range possibly needs to be narrowed down - there is quite a big difference in cost and build time between a 12m cat and a 15m cat.

 

Thanks for your reply Mr Perry.

The main reason im considering a catamaran as opposed to a trimaran is due to useable volume in 2 hulls rather than just the center hull of a tri. For a cruising boat, the cat has proven most successful and they also have proven more marketable with greater resale value om the used market. Ive no desirr to undertake such an expensive project without some reasonable assurance that it will be worth something when im finished with it. Tris havnt enjoyed the same level of success in this regard.

Your pivoting arrangement is something i had not considered before. It will need some thought time as to any practicality and maintenance issues when used on a cruising boat.
Yet another type of system could be a horizontal sliding type such as that of the DSS system. I doubt there would be sufficient hull beam to accomodate it tho- would need to make some calculations with foil area and aspect ratio considerations. Inevitably it would probably end up of a reasonably low aspect to be able to fit within the hull beam.
Im considering building a model. First with just the straight boards as a traditional catamaran and measure its performance. Then after thats done, add the additional lifting foils for foil assist mode and again measure its performance to compare. Ive got to be reasonably convinced before going this far however...

 

Latest renderings showing cabin and perhaps a small hardtop sunroof done in a NACA section to minimize drag, off of which a good set of clears or vinyl canvas could be supported from when at anchor or cruising in light conditions to provide a large shady area. Roll them up to go racing etc.

 

Looks like a speedster. Light weight of around 3500 kg?

 

Probably 4 tonne lightship as a guess - i havnt done a detailed weight analysis yet but i will get that soon. My last boat i designed i was within 200kg from design calculated weight to actual built weight... i have better data this time so i should get very close...

 

would be nice NOT to have to use 100kg of CF and 100 kg of epoxy - say 3,800 kg Project 38?
Did this last yesterday

 

10.7 meter beam? That's wider than mine?