Formula 40 singlehanded trimaran build log

Way back, when Bamboo Bomber was first launched, the board position was set in the "correct" place but we found with the new fangled wing mast, that the "drive" (CoE) of the more efficient rig was further forward than what we would have believed (wing masts do that) ... so shifted the boards back to reduce the weather helm.
Take a look at the high performance day sailing cats, like Tornado for example, boards well aft, as is the setup on the Kurt Hughes F40, which is just an overblown beach cat anyway. High aspect ratio rigs also seem to require this board further aft position. Empirical knowledge, learned the hard way. Fine bows too ... because they can dig and shift CLR forward. The Farriers are not fine bowed. There are no hard and fast rules. Also comparing cats with tris? Different fish. And boards, foils in floats, different again. Foils have to be forward of CLR (actually that is almost a hard, fast rule) - that is unless you enjoy rocking the platform into a down the mine position. But even so, this could be countered by another smaller set of foils further forward.
Warwick, no one wants lee helm ... and although never having been aboard a Hughes F40, I don't believe this boat will have lee helm; he's too experienced to allow this fatal imbalance.

 

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Hughes 40's are both tris, mon capitan..... I like Kurt Hughes vertical foils better than the angled foils of Farrier-at least performance wise.
Gary, look at the two Hughes 40' tri's: the board on the one is way aft but then so is the rig. But the board is closer to the mast on the one with the forward board as well. The amas on boat are in about the same position relative to the main hull.

Link to the one on the left: http://www.multihulldesigns.com/designs_stock/f40shtri.html

 

Of course, F40 is tri, not cat, my mistake. I was mixing up my board position cat experience with Bam Bomb ... but everything still applies. But the F40 Hughes tri is a much leaner machine than the later more cruising version, finer hulls and floats, taller rig, set further aft as you say, still looks correct to me.
Need to ask Kurt, "Hey, Kurt, your F40 theoretically has deathwish lee helm - is that correct?"
I know what the answer will be.

 

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I respect Mr. Hughes as a designer-I know there is a rationale for that board position-I'm just curious what it is.

 

On Ian Farriers boats I believe he is making use of the daggerboard case as part of the compression bulkhead structure which probably influences it's positioning? Not sure there is a right answer just different approaches the French racing tri's rake their daggerboards well back even though they protrude in front of the mast but they are incredibly long thin and high aspect. Maybe they are compensating for changes in the CLR when the main hull is flying? Kurt's F40 as typical of the boats drawn to the rule has a focus on mainsail area with the blade jib as the upwind sail so it's quite mainsail centric as Gary has mentioned even if it's sail area is quite moderate compared to later F40 trimarans with 85' rigs (Kurt drew a 60' rig for this boat). Kurt also favours the deep vertical daggerboard set well back and slightly offset from the centreline on his tomcat racing trimarans

 

Gary, I've been thinking lately about a wingmast built along the same lines as you have suggested in the past it's certainly the way to go in terms of rig simplicity and if sufficiently stiff removes the need for the twin spreader rig. Do you have any experience with building a 60' mast in ply and carbon? I gather similar principles would apply but you would have to step up the laminate schedule.

 

The largest I've done is 15.5m tall by 500mm chord. To build an 18.5m, you could go to a larger chord and more thickness (say 650mm x 190-200mm) so you get your stiffness and strength from the larger depth and cross section wing ... plus you'd need the usual runners, lower shrouds and uni carbon up the mast sides at thickest section. The I beam could be made into a box for extra stiffness, otherwise you could stick to basic ply gauges, just imo, others may disagree, 4 or 5mm and skin with 3 or 4mm. I'd go for the thinner because you have to keep the weight down - and then rely on carbon for its stiffness and strength.
I''m going to build (later, after I get Sid sorted) a new, straight luff wing mast for Groucho (for the new main to fit without creasing at top) but it will be the same, or a little larger, dimensions as the curved upper luff section earlier mast - which has had its day.

 

Gooday all. Gary - I'd be extremely supprised if Kurt would bother answering such a question - I sure wouldn't.

With respect Warwick - listen & you'll learn a heck of a lot - not the smartest question you've ever asked - IMHO & I say this with respect to you & your knowledge - - but - a word of caution here - none the less.

Now blokes - do you care to take a step sideways & go back a bit in time - to then go forward - with more knowledge & information ???

After watching a 5900 kg x 18.3 mtr long x 18.3 mtr wide tri - fully air-borne - I'm very reluctant to say very much about anything - I'm sure not in Nigel Irene's league - not in a million years nor Sean & the boys sailing BP-3

Gary a thicker wing is not necessarily heavier - except by very few % - that also applies to a longer - fore/aft section as well. IMHO It's a trade-off of sorts. Lets envisage a 700 mm - fore/aft by 166 mm thick (at the base) - now let us have a single take-off point for the 2 side stays & the forestay - located - center-front approx 13.5 mtrs up in a 18.5 mtr tall rig (3/4 rig) allowing the top 1/4 to bend-off & bend aft - automatically - controlled entirely by the wind. ie - it's the 'nut' on the helm - that usually slows the boat down - - (which comes-off as 1 piece & seperates into two (1 to each hull for a cat & stays as 1 for a tri) - - then add 'running backstays' (if you must) only if you're going to run extra front-sails. Yes no ???

Just like c/b(s) & rudder(s) - a wing-mast needs to have a graduated aft max thickness (maybe at 30% aft at the bottom - drifting aft to something close to 50% at the top) - that is to say - an in-line taper in both directions - - A foil is a foil - is a foil - is a foil - difference being only the 'sg' between water & air - nothing more. Yes/no ???

O.K. chaps - do you want me to continue - or am I just full of bla bla yaddi yaddi ??? Ciao for now, james

 

Wing Mast

Corley,
For what it's worth I think it would make a great mast to combine:

-Mast made in two halves using ply. Both sections are formed over internal bulkheads and the join between both halves is two flat sheets bonded together ie the internal I beam is two ply sheets.
-A front edge which ends at the widest part of the mast and a back section which starts at the widest part of the mast.
-Ideal if the I beam would also be at the centre of area of the mast section this places some contstraints on mast profile vs laminate schedule this is a good thing.
-Internal web in saturated ply @45/45 (big material waste?)
-saturated ply skin @45/45 (big material waste?)
-cheap carbon uni used at 0deg and local reinforcements at 90deg- 50K carbon uni tow gives a lot of stiffness per $.
-Maybe some 45/45 biax over the top in glass

If you have the section details and a rig drawing it's not rocket science to engineer with carbon added the ply is not actually going to add much stiffness so you could just base engineering on carbon used in laminate.

I have built a carbon wing mast @11m (no ply) it did fail but along the way learned a lot about what to do and what not to do and a way to engineer based around existing section.

Alex

 

CofE vs CofLr

Gooday, Hi there eveyone. Lots of great info in this discussion - so far.

'Oooops' bloke (great observation) AND - YES I LIKE IT. Tnx - Gassa !

Not with standing the above. I do agree with you Gary - others may as well.

Suggest all of us understand the real value of the - difference - "vive-la de difference" - that is between the static & dynamic - CofE's & CoFlr - which is of course a huge difference & moves about depending on the changes in Effect of the hydro & aero - dynamics of - sailing.

Whilst Corley is correct 'you have to trust the designer' or you would be building another design - now would you not - Yes ! ! - I still do wonder in what winds Kurt has sailed the 'proto-type' in - ??? - how big & confused the sea-state was & what strength was the wind ??? The answers do in NO way have anything to do with where the above discussion goes IMHO.

AS the 'sea-state' builds & the wind gets above 'Beaufort 6' (#6 = 24 kts wind = 3 to 4 mtr - Probable wave height) to say nothing of the 'sea-swell' height or sequence - which is a large - stability factor - the sail-trim will move the CofE considerably aft (or you'll be totally - out of controll).

Doug - in all fairness (not usually my high suite) A KH 40' ocean racing tri - has as much to do with a Farrier - race-toy tri - as a 12 Mtr mono has to do with an AC 45' or 72' I M H O ???

 

Guys just a minor query, mast with such large chords, do not bend visibly fore-aft? 18.5/0.65 = 28, less than 50, a column, where as 18.5/0.2=92.5 can. tks idkfa

 

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James, USA 17 had no daggerboard in the main hull and developed all its lateral resistance from the ama boards-note the fore and aft position of the board:

click on image- way forward, huh?

 

James and Gary, yes I do have a lot to learn, this is one of reasons I am using the forum. What meant by lee helm and neutral helm was just as a preference deference, and I could have written weather helm instead.

When I was last involved with boats they had a much lower aspect rig in the mid eighties, at that stage I was losing interest.

What effect does the amount of the under water section forward of the centerboard have on the dynamic balance of a boat and center of lateral resistance.

 

Gooday Doug. Yes - c/b's in amas - way forward & also the wing is raked aft a considerable distance (that's always been my preference - for several reasons). I also not the the foren-sail is very very large & quite long on the foot - effecting the balance & necessity for the foils to be so far forward. Yes/no ???

Great pic - for this discussion - thanks mate. Ciao, james

 

Gooday 'idkfa' Bend less yes - but they do bend - in real terms. A wing 11.75 x .36 - carried up to 7.5 mtrs - then tapered - bends off by .2 in 25 to 30 kts, can be made to 'self-feather' & bends aft as well - all automatically controlled by the wind pressure on the wing.

Thanks for your comments. Ciao, james