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Steve Clark View Drop Down
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Posts: 38 		Post Options Post Options   Quote Steve Clark Quote  Post ReplyReply Direct Link To This Post Topic: Stiff Finns
    Posted: 02 Jan 10 at 8:23pm

 I owned Vanguard and we built the fastest Finns until 1992.  The "softness" that is referred to is a lack of torsional stiffness between the hiking area and the mast step. The hull, and how the mast step is supported is part of the rig dynamic and has a pretty profound effect how the boat responds to gusts. We had a formula that worked pretty well,  the mast step structure was springier athwartship than fore and aft. 

The bottom of the hull was a pretty massive laminate with lots of stringers and was stiff by any standard. The Finn is a pretty heavy boat, but the maintaining the tolerances required to achieve a minimum gyradius, aft LCG and low VCG were a challenge. They weren't easy boats to build to the standard expected by Olympians and the business was made more difficult by the fact that they stayed competitive for so long.

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charlie w View Drop Down
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Posts: 84 		Post Options Post Options   Quote charlie w Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 10 at 11:57pm

Hooray Grf. glad that you are back again - everyone must be delighted.

Hope that we will be seeing your Alto at the Battle of the Classes.  You can start with us if you like.

Chas
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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 10 at 11:12pm
So, a sad arse Finn wouldn't go any faster however light you make it or
efficient you make the rig, all the time there is no shape, on that
'quadrant board thingy'.

Short answer if you want a faster Finn give the centreboard some
shaping, then make it light and stiff, the shaping would have to be
designed around how fast it will eventually go through the water. My
guess is, the reason the sad arse Flexi Finns are working is probably
down to the fact they need all the waterline length they have in the water
all the time and making them light and stiff would bounce them up and
down more. Or they derive lift off the curved hull surface which only
works at slow speeds.

Best solution?

Can them, they're old dross sailed by rich not very bright folk who know
no better, or poor bloody Olympic types forced to use them.


But then that's probably what the D1 is all about and poor Olympians will
have another 'K9' to use instead wether they want it or not.

Edited by G.R.F.
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Lukepiewalker View Drop Down
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Posts: 1341 		Post Options Post Options   Quote Lukepiewalker Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 10 at 5:43pm
Finns have a quadrant board made of alloy with limited shaping, so mostly a flat plate.

Edited by Lukepiewalker
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The Moo View Drop Down
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Posts: 809 		Post Options Post Options   Quote The Moo Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 10 at 4:03pm
A glass of red taken whilst gazing at Big Wave Dave's Avatar makes the whole stiffness versus flexible Finn Hull issue so much more understandable.

BTW GRF What is a no foil centreplate?
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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 01 Jan 10 at 3:48pm
Does the Finn still have that silly no foil centreplate?

If so, there probably lies the answer to this conundrum.
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rodney View Drop Down
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Posts: 915 		Post Options Post Options   Quote rodney Quote  Post ReplyReply Direct Link To This Post Posted: 29 Dec 09 at 1:29pm
Originally posted by KennyR

Of course if anybody belives they know better than 50 years of olympic driven development, they should build a new design and go prove it.

Thanks Kenny all agreed except it's more like 60 years of development and over the years massive investment.  If anyone could build a Finn that's stiff and faster than the current design concepts, as pioneered and applied by Devoti, they could get rich very quickly - we know the answer I think

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KennyR View Drop Down
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Posts: 52 		Post Options Post Options   Quote KennyR Quote  Post ReplyReply Direct Link To This Post Posted: 29 Dec 09 at 12:49pm

Everybody is missing the critical 'what stiffness are we talking about' question. Remember the rigs are unstayed so there isn't  the huge boat folding loads on these things. The best finns have alwyas been soft torsionally up front but stiff in the sag/hogging/Fore-aft direction and stiff torsionally from the centreboard aft. It's been known for years that this was that case, from the soft Bruder boats in the 60's onwards. One one trick in vanguards, was to remove the front ring bulkhead by the bow and grind off the underdeck stringers to soften the deck. You could push the deck rings up and down one inch on these fast old boats. The effect was you could use a stiff mast with the stiff [F/A] hull and the hull torsional siftness made the whole thing work. It took Tim Tavinor years to get a design to beat the old simple flexible vanguards and end up with the Devoti. Prior to Devotis it was very common for really really beaten up looking '76-'78 vanguards to still be winning gold cups in the early 90's, 15 years or so later.

Carbon like boats have been tried. There was a kevlar Nomex taylor or two around and I think the Hyundia boats were similarly stiff. Both were absolute dogs in anything but very flat water and have been described as being like being in a land rover with stiff suspension. Certainly copming off the startline in a chop the vanguard / devotis are visably quicker than any of the super stiff boats. As for the comment that the Finn is not a sea worthy hull shape, I do remember that Mr Bethwaite commenting on th efact ot went so fast was largely due to the very fine entry angle of the bow. I may be wrong, but I think the Devotis also flex inwards, narrowing entry as your bow hits a big wave sometimes.

Of course if anybody belives they know better than 50 years of olympic driven development, they should build a new design and go prove it.
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Lukepiewalker View Drop Down
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Posts: 1341 		Post Options Post Options   Quote Lukepiewalker Quote  Post ReplyReply Direct Link To This Post Posted: 26 Dec 09 at 9:17pm
Maders not much seen outside of Germany these days. Devoti very much have a lock at the top of the fleet, not many willing to take the plunge on something different, although Pata are in the vicinity with the B4 (which comes in two different foredeck stiffnesses). Wilke are building Epoxy finns (epoxy is allowed), and Ben trialled one before the Olympics but went back to his 2004 Devoti (he may have had a new Devoti on trial too but don't quote me on it) and the Wilkes haven't made a massive impact. Hitechsailing have just come out with a new boat (Vinylester) which I know not much about at all. And there is a builder in Brazil building from Pata moulds and one in America (Jibetech) aiming for the more affordable end of the market.
Anyhoo, on the stiffness front you essentially have to forget everything you know about boats. We have a freestanding rig, a big sail, and a heavy hull. The nearest would be a Laser which doesn't have as big a rig, or as heavy a hull. People have suggested a Carbon hull would undoubtedly be faster, and it would. Until you put the lead in... The key thing we have to remember is we are not dealing with an unconstrained system. You have constraints on weight, rig design, weight distribution, and foil shape which all affect your decision making in a way most other classes don't have to worry about. And the stiffness is not a recent invention, it goes pretty much all the way back to the start. It was an issue with wooden hulls, it was an issue with double floors and so forth all the way through eternity...
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Posts: 102 		Post Options Post Options   Quote Flick-Flock Quote  Post ReplyReply Direct Link To This Post Posted: 26 Dec 09 at 9:15pm
Originally posted by asterix

Energy used to flex the boat is surely lost and therefore unavailable to
drive the boat forwards?


The way i see it, the reason the flex seems to work in waves is basically the opposite to this.

Some of the waves energy is used to flex the boat, and therefore isnt used to stop the boat dead in its tracks.
So a bit of a shock absorber
Obviously you'd have to engeneer it in such a way that the rigs power wasnt used to bend the boat.

I think....
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