Small trimarans under 20'

Looks the same as the British cat, is it the Firebird ?
Also on YouTube.

 

Very similar righting system as the Firebird but mine is a Gougeon Bros G32.

 

That is a beautiful little trimaran! Love it!

 

Lots of potential but you will have to sort out a few things before you take it out in very strong wind.

I watched your video from day 1 & 2- and obviously you are busy developing the sail plan as you are going along- bigger jib etc. but... I also noticed the following issues that are even more important than the sails.
The leeward shroud becomes completely loose and the jib fore stay falls away under pressure. The lack of fore stay tension will affect the boats ability to beat into the wind.
As it is now some of the components in the design are not stiff enough to deal with the forces you are applying to it. The aluminium "deck" ladder frame is bending- not only because of the righting moment is pushing the leeward ama up- but also because of tension induced by the mast stays and your weight on the back of the ama is twisting the frame.
This is clearly visible in the video from the port side of the boat, if you compare the attitude of the main hull and the amas to the water you will notice that windward ama is riding bow up compared to the leeward ama.
The windward stay is pulling the bow of the ama up and your weight behind the stay is pushing the transom down. This will also explain the lack of stay tension.
Since winter in Sweden is approaching fast you will probably have more time to find and build the required design solutions.
Lastly what type of instrument are you using to record the boat speed? it is brilliant.

 

Home Built Tri.

Hi Troops: I notice I am responding to an old Thread.
I currently sail a Hydra Cat good performer, but at 76 it can be hard work.
I have built a few tri,s so as a shipwright building offers no challenge.
So a mate of mine who also sails tri-s and cats suggested a performance tri.
I came across the WETA tri and went from there ,took me a month to finalise the main hull design and AMA, So after design work went looking on line to see if any similar scenario had been done ,eventually came across the RAIL 19 ,it is so close to my design, I thought well there is always someone done it before.
I finished up at 18' hull sections are similar but I probably have a bit more displacement, performance wise I will not nbe racing on a regular basis but certainly need to be able to stay with the beach cats, our waters here can be fairly lumpy often 15-25 kn breeze and against tide runs it can be fairly lumpy and short.So I probably have a little more freeboard.
Prototype I will build of ply and frp over.
I will see if can photo plans or maybe attach a PDF File.
Shipwright

 

Shipwright,

I would be very interested in photos and plans.
How far along are you on building the boat?

 

Thanks Cholsson,

With more sail area the skinny bow section of the AMA's and main hull will probably struggle to keep the bows above the waves, you should seriously consider extending the trampoline further towards the transom so that you can move your weight further back diagonally across from the lee ama's bow to help balance the power of the bigger spinnaker/genaker.

To a much lesser extend we had similar issues with our beams- there was too little tension in the rig when it was really blowing and by analysing the GoPro footage from a camera that was 2m behind the transom we could see where it was flexing.
Obviously all the components are playing their role in a inter-connected system but the beam at the front of the boat must deal with more loads than the beam at the transom. The beam at the front must transfer at least 2/3 of the righting moment to the rig and hull and it must absorb most of the rigs stay tension depending on where on the ama's the stays are connected.

We added a purchase system to tension the stays while we are sailing so that we could get some data on the rig / beam flex. By measuring how much slack we must take up on the beats we could replicate it on shore, take measurements and work out how to fix it.
Last summer we revised the beams fixing positions on the main hull- which made a big difference but since then more carbon-fibre was added to the beams- we will be trying it out soon.
We aim to remove the pulley system that tensions the stays if we can get to a point where we can see that it is serving little to no purpose.
To sort out a prototypes performance requires a ongoing process of component evolution and redesign- not all of it- just some of it.

 

6.32m Tri

UPCHURCHMR: Thanks for reply. Still finalizing construction drawings.
plan to start build December should launch around June, you may find the hull sections a bit wild, would like to use foils but our areas of sailing have heaps of sandbanks. Should have the main hull lofted next weekend.
hull will be double diagonal 3mm ply 450g 0-90 fabric over.
still sailing catamaran at the moment , hard to stop sailing to start building.
Shipwright

 

6.32m Tri

View attachment Sections-Model.pdf
upchurchmr; see attachment hope it opens ok,should draw some comments.

Shipwright.

 

Any particular reason you are going with double diagonal? Strip plank is easier and gets similar results.

 

A nice start.
Looking forward to seeing the rest.

Actually I also would choose strip planked, just because I'm familiar with the method.
Corley is familiar with double diagonal, so you might think about your answer.

 

Reply

upchurchmr: Thanks for reply, just finished lines for AMA-version 3 There is plenty to think about ,engineering the AMA connecting frame has given me a job.
The Wetta and Searail seem to get away with slide in sockets ,none of it is very large or heavy.
re:strip plank versus diagonal planks,i could go either way but usually the cross planking is lighter.
Keep your feet wet.
Shipwright.

 

tri

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Beautiful!

 

Looks sweet my man !

Cold moulded won't be lighter unless you can get Paulonia ply, since your in Australia, check these guys out, buy boards and cut your own strips.

http://www.paulowniatimber.com.au/marine.php