Small trimaran with Tornado/Nacra 5.8 center hull

[revintage]

Got the idea to make use of some of my beachcat parts and planning a trimaran project to be sailed 2023.

Will use an old Panthercraft Tornado hull as aka and a pair of fresh Nacra 5.5 hulls as akas. Length 6.1m, beam 4.5m with upwind SA 22.35 sqm. The Tornado hull is the one to be modified as it is in bad shape and anyway needs to be reinforced and repaired. The Nara hulls must not be modified at all. Rudder on center hull and daggerboards in the Nacras.

The main beam pockets on all three hulls will be used inline and the center rear pocket will be moved 15cm forward to line up with the Nacra hulls. All hulls has the same height at the main beam pocket. Image shows the hulls lined up around the main beam and to scale.

Question is, how should the amas be placed heightwise in relation to the aka and also if the amas eventually should be rotated somewhat bows up?

 

[Doug Halsey]

A good starting point would be to raise the amas up (without rotating) until they are just barely clear of the fully-loaded waterline at 0° heel angle. That way you will never be dragging the windward hull around while sailing.

I suspect that once you have gone through that exercise, you will conclude that your total weight is excessive and the aka will be too deeply immersed.

I considered building something along those lines back in the middle 80's after I was given most of an old abandoned Tornado, but decided the aka was heavier than I could easily manage by myself for assembling & disassembling on the beach.

 

[revintage]

Thanks Doug,
Taking your advice in account, it ends up in a quite high adjusted DWL, together with a rather odd looking creature. As my idea is to use a dolphinstriker on the main beam the one with straight beams is my option. When using daggerboards, this will probably also be the one to go for.

 

[revintage]

This would be the case with the hulls level. Maybe place the akas 10 cm higher, or no at all, instead of 25cm? This would make things so much easier on the practical side.
Question is if it is worth the effort to place the akas higher in a suboptimal design? This is anyway something I had fantasies about, to use at the lake house, to be used together with family members, to make them understand the beauty of multihull sailing.

 

[Corley]

I like the idea but can't help but think the 5.5 hulls may be too heavy for a performance boat as floats. The tornado main hull is reasonably light on displacement now consider you are adding say 120kg? for hull weights for the 5.5. Yes some will say the floats will carry some displacement which they do but once your windward float is levered out it's weight is effectively added to your displacement

I'd look at buying Kurt Hughes TMS20 trimaran stock plans and building his floats or just contact him and see if he would sell you just the float design pages. I'm sure they would be lighter and more suitable than 5.5 hulls and just use the Tornado main hull centreboard for lateral resistance. If you consider your illustration of the heeled waterline the weight of the windward hull will be depressing the centre hull unless the 5.5 hull has enough displacement to lever the main hull out as you are hanging 50kg to windward.

I think subtleties in terms of weight matter alot at this size and could be the difference between an acceptably performing or poor performing boat. The displacement is going to be tough to get right the Kurt Hughes design has about 400kg of displacement and weighs about 200kg which sounds about right.

You add a bit of weight with beach cat hulls as they are designed for beach abuse and have daggerboard cases fitted which is imo parasitic weight on a simple boat. Kurt Hughes Multihull Design - Catamarans and Trimarans for Cruising and Charter http://www.multihulldesigns.com/designs_stock/daysail/20_tri.htm

 

[oldmulti]

Revintage. Another approach may be to use the Nacra hulls with a purpose built main hull. This will allow the float position to be pushed forward moving the float center of buoyancy to be ahead of the main hull center of buoyancy allowing more power reaching etc. Also the crossbeam positions are not controlled by the main hull crossbeam slots. If you are going to have to repair the Tornado main hull it may be simpler to build a new one. Just a suggestion.

 

[revintage]

Thanks for your advices, Corley and oldmulti.
I am building this the year after next, from leftovers in my stash, two other projects to finish before this one. Have rig, sails(selftacking jib and asymmetric), hulls, aluminium tubing for beams, and every small part needed. Will not invest in any new items, only epoxy, glass and carbon to adapt and repair the crappy center hull. As earlier mentioned, it will only be used at my lake house with flat water and in winds below 20 knots. I imagine it could be a good ride single handed.
So this is just about combining the items in the best way possible. The Tornado hull could absolutely be moved rearwards if that helps.
One could also look at the imagined tri, as a Nacra 5.5 widened to 4.5m instead of 2.6m but with a higher rig and a few more sqm SA and added stability due to the center hull. The added weight will not be more 60kg and no trapezes will be needed.

 

[Corley]

Keep us up to date, I'd love to see how your project progresses.

 

[revintage]

Thanks Corley!
Plenty of time to plan, as I at the moment am fully occupied getting my "Aerow" foiler project ready this spring.
Checked out Kurt Hughes site and got the idea to add a "sea-sole" as on the 16" daysailer, though.
Will come back and try new ideas on you.

 

[revintage]

Maybe a little to far out, but I was recently offered a pair of skeg hulls for the former ISAF Youth catamaran Sirena/Nacra SL 16 at a very low price. I checked them and they where no beauties but very stiff, estimated the weight to 35-40kg.

By using them, I could keep the widened 5.5 platform almost intact and only borrow the F18 rig from it. No daggerbords to break, but maybe an optional T-centerboard? Very low bouyancy bows, though.

How lousy would these hulls be for a mini, leisure tri?

 

[Russell Brown]

The original Tremolino used Hobie 16 hulls for ama's and a Hobie 16 rig. Have you sailed on one? I think it's a remarkable sailboat and very hard to beat with a Hobie 16, so I'd say those hulls could work fine as ama's. Being shorter, they would put less load on the connective structure than longer hulls. I don't know about drag from the skegs.

 

[revintage]

Thanks for all info. About the Tremolino they seem to have a large aka daggerboard. My idea, but probably a little to optimistic, was to get rid of the daggerboard.
Anyway I have been Google researching and also remember what oldmulti said. I guess the akas ideally should be moved to have all sterns at close to the same line.
Should look like this, where I have aligned the beginning of the waterline, if I have understood it right?

 

[oldmulti]

Revintage. Aligning the bows at the waterlines should work to allow more float buoyancy forward for better reaching etc. The Nacra 5.5 hulls would be faster but I can understand not wanting dagger boards on a fun trimaran. This could be a real fun project.

 

[upchurchmr]

Use a centerboard or dagger board on the main hull
I once was sailing a Tornado (old/ well used) in light wind against Hobie16's (to weather).
Easily outsailing them, then they started pulling up to me.
Found that one of 2 centerboards had floated up.
With one board instead of two, the Hobie 16s were beating me.

Align the stems, raise the ama's above the water when setting idle.
Have fun.
What is your proposed beam?
Do you intend to be able to sail with the main hull out of the water? Higher wind speed.

If you are extensively repairing the Tornado hull, consider adding 1/2"+ of foam and glassing to get increased volume in the hull. I know you said no extras, but.......

You might calculate the volume of the Nacra hulls, decide what you need to fly the main hull, then decide if you could shorten the height of the amas to get the volume you need, with less weight.

When repairing the tornado hull, check to see if the foam in the deck is waterlogged. I destroyed a hull, thinking it was extensively delaminated. The only area that had an issue was the deck where fittings were bolted in.
The foam was not sealed well from the factory where fittings were bolted into the deck.
I wasted an almost perfect set of hulls. Which could have been repaired - for casual sailing.

 

[trip the light fandango]

I would be tempted to make the centre hull wider by cutting it down the middle and adding a fine wedge shape. good luck, interesting project.