Formula 40 singlehanded trimaran build log

Geez Corley, new kids, rebuilding an old classic tri, building an ubercool f40 tri, I think youve got too much time on your hands

Keep the updates coming

Cheers
DAVE

 

Thought I'd just post a pic to show what I'm on about re the daggerboard as can be seen in the main hull section if you go for the short board (it's level with the height of the half height case when deployed) you get some adjustment. We will have a standard arrangement for pushing and lifting the board by an up and down haul (the downhaul will come through the daggerboard shroud with a grommet fitted to prevent water coming in and back through a deck fitting to the cockpit. Once the board is up to deck level we can remove it completely if necessary.

 

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This really isn't to your question but that board sure seems a long way aft to me...

 

The board works fine where it's located Kurt reckons he could leave the helm and tend to other parts of the boat when singlehanding with no autopilot engaged the boat just balanced well. We are aiming at building a boat thats not too extreme but has a good turn of speed in light conditions and is manageable by one person hence no massive rig etc should be a nice fast boat but not overpowered. Attached video of Kurt's F40 trimaran "gecko" sailing

 

Gooday 'Corley' - Doug tut - tut - Do wash your mouth out with soap ! ! !

Or maybe the rig is to far forward ??? O.K. & I'll go get my soap also ! !

Corley with the board down - then the top of the board is down in-side the case ??? does that mean you wont be able to wedge (tack) the front of the board to windward by say 4 degrees - - then - over something like 2000 ks - is that not a loss in potential - speed made good - over course distance covered ??

I sure hope the c/b & rudder blades are tapered- in line & the maximum cord is drifted back from the top to the bottom which will reduce drag considerably & point higher with much less wetted surface exposed. Like 30% aft at top & 55% aft at bottom plus also in thickness % ???

Next question - please - What with the substiantial rig developments since the boat was originally designed - is theere some reason not to go for a limited wing-mast section of some kind regardless of how small it might be - - as that would be much more efficient than the video shows ???

Spunky looking boat - in the video - sure hope someone can eventually learn how to tune sails though.

 

Well everything is a compromise Silver Raven, like you I'm not made of money. At some point you have to trust your designer to make the right compromises. I have to make the best of what can be done on a limited budget so we're making do with an updated stock plan. Kurt has a reputation of delivering good performing boats at a moderate cost.

I cant answer your questions on rig as yet as it's not finalised a wingmast may be a possibility or may end up with an aluminium rotating mast if the price is right.

btw we looked at putting a trim tab on the daggerboard but decided to keep things simple, in the end we may lose a bit of vmg but hopefully not too much. Who knows we may do it on daggerboard mk2

 

the space between the mast and the goose-neck! looks like there is even more on Gecko! Traveler though, will it be effective on a broad-reach? no vang. I've found it hard to keep the upper closed and powered-up. btw, dogzilla never sheeted out, the wind is always from the bow for her!

idkfa

 

Theres another line (not pictured) that can be used as a preventer for the boom when sheeted right out. Kurt found in practice he didn't use it or run deep as there was enough apparent wind to make it unnecessary.

 

Doug,
this drawing is taken from the website of Kurt Hughes or from the studyplan. In the real construction drawings the position of the board will be different. Same thing is to the aft rockerline.

Best Regards, Michel

 

Michel, the pictures on the site are just plan pages reduced in size (I have the full planset). Kurt drew the daggerboard there and built the prototype of the boat. He tells me the boat balanced well and I believe him it's a bit discourteous to the designer to carry on in this way fine to question but the numbers have been done the boat built and it works. What comes to mind is a Newick trimaran that was built in the states the builder decided the boards "looked" like they were in the wrong place and put them where he thought they should be. The boat had balance problems until the owner ripped the cases out and put them in their plan position.

 

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Corley, I don't think I was discourteous to the designer in the least. I certainly had no intention of being discourteus nor do I think I was! I've studied sailboat design for 50 years, designed and built a number of boats including a couple of small trimarans and cats myself and it just seemed like a relevant question.

 

Board position looks perfect to me. In stronger winds, when you'd be carrying smaller headsails, weather helm is more pronounced because of wind strength, so the CLR needs to be aft, as it is in plan. With the board further forward, as Doug is suggesting, that's when weather helm rules its ugly head. In lighter winds, with large headsails, the tendency for the bow to blow off, pivoting on the board, is not a problem, doesn't happen ... unless its blowing a gale and you should have reduced up front anyway. Multihulls are mainsail predominant boats, asking for trouble lugging large headsails. All this was found out the hard way in the 1960's. Offwind large sail, you want the bow to pivot downwind anyway, don't want it rounding up. Oooops!

 

Tri designs

Kurt Hughes and Ian Farrier-note daggerboard positions:


Pictures, L to R: 1 & 2 are Kurt Hughes 40 footers. 2 is the newest. Note how much further forward the board is on 2 and on all the Farriers.

click on image:

 

could it be that one designer prefers lee helm and another prefers a neutral balance. So could it be designer preference.

From what I understand you can sail in continuous circles with the Ian Farrier designs with out touching the sheets, I am not sure of the Kurt Hughes designs.

 

Whats striking to me is the different design philosophy on the two Kurt Hughes designs-both 40 footers-very interesting and very different.