# Tornado to performance trimaran conversion

Discussion in 'Multihulls' started by tamkvaitis, Nov 18, 2009.

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### tamkvaitissailor/amateur designer

I have a clasic Tornado catamaran with GRP hulls. Because we do not have serious Tornado racing we are sailing it for fun. As the sailing season have ended I started thinking about converting my Tornado into Trimaran. I am thinking about realy narow but high center hull with no room for storage or sleeping, L/B ratio between 20-30.

I think this would increase boat performance in strongers winds - trimaran would be almost twice as wide as original.

In lighter wind's the performance could be increased by adding aditional sail area (adding a genoa etc.).

Increased height of beams should also increase the performance in chopy waters.

could you share your thoughts about displacement of hulls. My Idea is to design the boat to almost fly the center hull, but I am not quite sure if tornado hull has enough boyancy to do so.

Any thoughts on this idea? Maybe you know somebody who has done similar projects?

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### DarthCluinSenior Member

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### tamkvaitissailor/amateur designer

I did some calculations. Tornado's standart (design) weight is 170kg, Crew weight is 75x2, so single tornado hull's sailing buoyancy is 320 kg. I guess that I could build a center hull, beams etc. within 100-150 kg range. So My tris weight should be about 300kg with crew weight tris displacement should be about 450kg (counting that it will be sailed double handed).So best buoyancy distribution should be: 320 kg on leeward ama and 130 kg on the main hull.
with this buoyancy distribution I get that righting moment with two crew would be about, 1100 kgm (I am thinking about 5m width) while standart tornado has only about 780 kgm. Thinking that 780kg. for tornado rig is optimal righting moment I get that buoyancy will be distributed: ~240kg on leeward ama and 210 kg on main hull.

Am I going the right way with my math?

4. ### Chris OstlindPrevious Member

Yes, you are going in the right direction. There are some fairly important considerations, though beyond the math and its feasibility indicators.

The height (freeboard) of the Tornado hulls will keep the aka beams very close to the water no matter what angle of heel you sail. The typical tubes you see on boats of this type will likely create extra drag and hamper the performance of the boat. You can build some aka beams with a nice graceful arc to them and minimize the beam exposure to the point of dragging water only when the complete ama hull is submerged.

Or... you can confine the sailing to protected bodies of water that are near flat and not be concerned too much about the beams hitting the water.

If this boat is a day sailor only, then affixing the aka beams will be fairly simple to figure out. There's no need to be concerned about a beam running through the cabin area, as there probably won't be a cabin to speak of.

If the boat is going to have a cabin for overnighting, etc., then the beam issue will need to be very carefully accomodated to keep the intrusion to a minimum.

Or... you can go to folding beams, or easily demountable beams, as a strategy for the design.

There are lots of little relationships that have to be juggled to a final solution in order to make this work well. Keeping the weight down is probably going to be your biggest obstacle, but it can be done.

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### tamkvaitissailor/amateur designer

I am thinking about arc'ed beams, or some kind of spacer between Tornado hull and the beam. Price and weight will guide me.

My Idea is to split the beams into 4 separate parts. So They will be about 3m. long thus easier to transport or cary. Boat won't have any interior space, so beams going through hull is not a problem for me.

I am thinking about water stays. I am interested will water stay will influence more than aditional weight in stronger beams.

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### bill broomeSenior Member

make the main hull wide enough for 2 berths, head to head. it will make little or no difference to speed but will make the boat much more useful. there is no guarantee this boat will go faster than a tornado, so be prepared for camp-cruising as well.

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### elliottJunior Member

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### tamkvaitissailor/amateur designer

My goal is not to make it faster. I want to keep it as fast as tornado is, but gain more stability and safety. At the moment it looks like that because of increased weight and weted area it will be slower in small winds. But in stronger winds it should be faster because of increased righting moment and added buoancy it shuold be safer.

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### tamkvaitissailor/amateur designer

I did a sketch. I used A trinardo delft ship file, so you can see a lot of similarities, but basic concept has changed. Main hull became narrower and longer.

LOA: 7.00 m
BOA: 5.00 m
full Disp: 450 kg

P.S. My computer started crashing, so sorry for unremoved layers from trinardo and poor image quality better images will be published soon.

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### tamkvaitissailor/amateur designer

more renders:

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### TinkersailorJunior Member

why not just put some big racks on your tornado and turbo the hell out of the rig for light air?

looks like your design will be heeled way over before the center hull lifts. and i think you need to move the t hulls forward.

Gona have to put some straight bows on those hulls to make em look right.

Leigh

Leigh

12. Joined: Aug 2005
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### tamkvaitissailor/amateur designer

So, tornado trimaran conversion is still in idea stage, simply amount of man hours needed is not available at the moment.

Although we are planing to do a slight face lift to our tornado catamaran this winter, as it involves, sanding old paint down and a lot of fairing and painting afterwards, I started to wonder about extending the standard tornado bows, so it would be more similar to modern catamaran bow shape. The idea would be that this decreases entry angle, so less drag and less pitching.
So first question, would this make any tangible gains in performance?

Second question is what is the best way to extend the bows? Idea at the moment is to add a layer of foam to existing bows, shape it in desired way and cover it with several layers of fiberglass. Is this aproach feasable?

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### teamvmgSenior Member

Take a fast boat, double the weight of it to make it go faster?

Go and get a sport rig!

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### tamkvaitissailor/amateur designer

well my estimations are that weight would increase by 5-10 kg, so nothing close to doubling weight

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### Steve WSenior Member

I think he must have been refering to the trimaran conversion, if plumbing the bows adds 5 - 10kg that should be offset buy the extra displacement you will gain and the extra waterline length wont hurt, lots of older cats have had this done. Go for it.

Steve.

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