Nacra 5.8 based foiling Trimaran

Hi all, I have a Nacra 5.8 hull and rig that I would like to turn into a beach style single handed trimaran, similar to Randy Smyths Sizzor, with the option of adding foils to make it fly.

The plan is to use the Nacra 5.8 as the main hull (I am part way through a bow extension to 6.2m total length, only for looks similar to ETNZ's AC72) and use small planing amas like Sizzor, and hopefully foils. Planned overall beam is in the 5m range (needs to be demountable for trailering) Planning on using the Nacras mast and main sail (possibly add the jib to the equation later) I have some questions for anyone willing to help out:

1 - If I step the mast in the current position (forward beam mount) on the hull it will be approx 3250 aft from the bow, and 2950 forward of the stern, so almost mid way along the hull. Does this sound OK?

2 - Amas I have sketched up are 2.4 m long, approx 300 beam and 350 high, just a scribble so far to guage what looks right. I am planning on a beam spacing of approx 1.2m, but Im not sure where to position the beams and ama relative to the main hull/mast? I have tentatively planned on the forward beam being approx 400 in front of the mast? Does anyone have any opinions/rule on any of this.

3 - Ama and Rudder foils. Will need the forums wisdom and guidance on this aspect

I have attached a simple sketch (please excuse the crudity, I am more a pencil and paper kind of guy) Please note, sketch is not to scale (Main hull shape is fairly accurate as is Amas fore/aft position, but not its shape)

Any help, ideas, knowledge will be greatly appreciated. More questions will come later I am sure Cheers

 

Sounds like a great project! If you're talking about full flying foils you want to design the forward main foils so that they support 80% of the boats weight.
That will affect your rig position IF the vertical strut of those foils is used for lateral resistance. Take a look at the Osprey(below) or the Rave-both were designed that way.
You have to decide if the windward main foil will be wand controlled and/or manually controlled and allowed to produce downforce: that would up the ante structurally. What beam are you leaning toward? IF you use wand controlled main foils AND are ok with the structural loads, the foils will be more efficient with an oversquare beam. Osprey is 18' long and 22' wide and 400lb.
Good Luck!

 

The concern I have with your plan is insufficient diagonal stability. There are two things you lack (or didn't mention) that scissors has -the ability to shift the lee float forward, and an Olympic medalist at the helm. If you are going for fixed akas you would be well advised to go directly to lifting foils at the extremities -the lift and drag of small floats will have you tumbling at speed and breaking the boat before you get to the foils.

 

Dave, if you use planing amas and put the dynamic center of lift where you'll place the main foils, you should be ok in most conditions. That depends also on how the crew will move-staying near the center or going as far to windward(and aft) as possible. "Foil assist" would allow an intermediate configuration that would be very resistant to pitchpole as long as you had one foil in each ama and a rudder t-foil. You wouldn't require altitude control .
The reason my test model uses a lifting foil on the daggerboard is that a small oversquare trimaran develops a hell of a lot of RM-so much that the main hull probably won't fly before you have 15 knots of wind or more. The idea is to use that foil in light air to fly the main hull as soon as boat speed is 5 knots or faster. Then,as speed increases, the daggerboard foil unloads and can produce downforce increasing RM. Aside from flying the main hull early, the advantage of the system is that you have two foils(daggerboard and rudder foils) actively controlling pitch which is twice the anti-pitchpole control of a simple foil assist arrangement with a rudder t-foil and much more control than a system using small ama foils and ama buoyancy only. With this system you can use foil assist on the ama(small foil and the ama doesn't fly) or full flying with a couple of different arrangements.
If I were you, I'd initially go with a rudder t-foil, a manually(or wand) controlled foil on the daggerboard(for flying the main hull early) and relatively small foils on the ama, and a planing ama for sure.
Flying the main hull with the daggerboard foil greatly expands the conditions you can sail in with the main hull in the air, increases pitch resistance dramatically and greatly inceases speed in all conditions, particularly in light to moderate air.

Picture: Frank Bethwaite designed a series of small trimarans using very small planing amas. The ama would not necessarily be in the water when the boat was moving too slowly for the ama to plane and, since the ama is small(and designed to plane) it would begin to do so at fairly low speeds:

 

Im not sure if this is actually acurate or a myth about Scissors folding on water while sailing. I read somewhere (I will search around for it) that Randy only folds Scissors for transport and paddling through narrow openings, but never while sailing. I will look for the article and confirm or deny this. Obviously Randy is an excellent sailor, but I guess at sone stage he was an amateur too. I have been tinkering with boats long enough to expect breakages with a boat like this.

Thanks for the posts Doug and Skyak, I am thinking along the lines of some of Gary Baigents designs, Im not very familiar with wands etc. But am very keen to look into this aswell

Cheers

 

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I think if I ever get to build a fullsize version of my tri I'd go with manual control of the main foil flap because I think it would be fun. And if you use a TNZ type foil on the ama or some version of a surface piercing foil or combo's like Gary's then you wouldn't need a wand but would still have early takeoff of the main hull and flying(or not) of the ama. Way too much fun anyway you look at it.....

 

I don't know for sure how he sails, but the construction of scissors is consistent with folded sailing. If Randy only wanted to fold for transport he went to a lot of unnecessary trouble constructing a design with proper kinematics for movement underway. I meant no slight to your sailing abilities, just wanted to make a joke. Great project recycling old race hardware into a fast challenging new boat. I look forward to updates.

 

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Dave, this is second hand but maybe the guy knows what he is talking about as far as Randy's "scissoring" with his boat: http://www.boatdesign.net/forums/multihulls/randy-smyths-trimaran-37078.html post 15.

 

Ive started shaping the bow extensions. Happy with the initial shape, but still need to add some more foam in places and refine the shaping, before glassing and final fairing.

I was watching some videos of Doug Halsey "Broomstick" foiler. That is the sort of thing I am aiming for. Can I still use the Nacra daggerboard in the main hull for windward pointing/tacking, and simple fixed foils in the amas (fixed fore/aft, but still need to be raised for beaching/launching like a daggerboard) Wands and other control devices just look a bit to complicated to my simple mind

What sort of shape foils would work best? ETNZ curved L's? C's? J's? Simple angles straight foils? Any help would be appreciated

 

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That really looks good!! Sure you can use the Nacra daggerboard unless you come up with a better solution. That whats really cool: if you get the CG right so your main foils lift about 80% of the boats weight you can try anything! Experiment, if it doesn't work build another that may.
Too bad I haven't got the model sailing yet but I will soon and that will tell a lot about whether my version of the TNZ foil concept will work on a trimaran-the beauty is that altitude control is automatic. But so is a surface piercing foil or Dougs "V" foil. The TNZ foil is a bit like a "V" foil as is my ama foil. You can try one of Gary's foils or all of the above over time. My personal favorite is my version of the TNZ foil-if I can prove it works on the model because of its simplicity and automatic altitude control IF it works like I hope it will.
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Pictures,L to R--1-my ama foil inspired by TNZ and others, 2) Flying Phantom foil, 3) Hydros foil.
Background: The Flying Phantom foil is similar to Groupamas foil which is similar to the TNZ foil. Very stable because of the "UPTIP" that forms a sort of "V". The Hydros( Oracle had some foils similar to Hydros-less "uptip"-and less stable than TNZ) foil was faster than Groupama but so unstable(required constant adjustment of the angle of incidence) that Groupama was the winner in the C Class. TNZ, Groupama, and Hydros foils were used as single main foils and therefore were required to not only provide vertical lift but all the lateral resistance for the boat. The princible on which these foils were based is "leeway coupling" where leeway was essential in controlling altitude.* Manual changes to the angle of incidence of the foil was required but is less on a foil with the "V" uptip. My foil design, if it works, will only require one angle of incidence adjustment thruout the speed range, which means ,after I get used to it, I should be able to set the foil for the particular conditions I find on any one day. Unless I'm wrong(!) But thats my idea of what an ama lifting foil(for full flying) should do: no wands, no constant adjustment, retractable, automatic altitude control.
I hate to bring it up again, but when you do some calculations on your boat you will see how much RM a tri is capable of and maybe my idea of the daggerboard foil, manually controlled will make more sense - without it you may not fly the main hull until it's quite windy when with it you fly the main hull in light, moderate and heavy air. Unless, of course you use a full flying system like Doug Halsey's . Good Luck-I hope this stuff helps you.
* Read Tom Speers explanation of how this works here: http://www.boatdesign.net/forums/hy...r-design-foil-assist-full-flying-40894-4.html post49 Dave, check out this whole thread. It's got a lot of info including the Specs of "Broomstick".

PS- the Groupama and Hydros foils pictures were taken from Freds hydrofoil site: ( http://foils.wordpress.com/ )

 

Skip the original dagger anytime you plan to have ama foils in the water. The ama foils need the side pressure to work properly. If you could pull off a set of uptip L or J style foils that are the hottest item in cat foiling, you would be at the cutting edge of non-active (no flaps, wands or feelers) foiling. If you just want to foil, a traditional V or an L that comes real close to a V will probably be a lot friendlier.

 

Dave, check out the foils on the 19' Exocet trimaran-5th boat in the slideshow here: http://www.perspective-design.com/

 

Progress?

Any progress on this project?

 

Be careful with weight. On a beach tri it's very important. Good luck! I hope to hear soon on how this is going!

 

foiling trimaran

And an update on my end: in my last post I didn't know whether UptiP foils would work well on a trimaran-well they work perfectly!
So how's your project coming?