Stiff Finns

Moving to a different thread, I've heard before that Finns need to be "flexible" in waves. I'm not sure we are talking old GRP Firefly flexible here, but a controlled amount. Stiff boats have been tried and proved slower. And a class that is willing to spend the cost of a small car on developing mast and sail combos is hardly likely to care about cost, is it?

Are there any other classes where this could be true?

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

I realise that no one here is likely to believe the wisdom from the Finn sailors, builders and gurus, even after more than 60 years of development.

So, heres an extract from Y&Y's own Jeremy Evans test of a Finn (FYI carbon can only be used for local re-inforcement for reasons of costs in the Finn class so I am not sure about the Pusan Olympics boats but I know that they are very stiff).

Advantages in modern construction don’t

necessarily include the fanciest materials. Hyundai

built an all-carbon fleet for the Pusan Olympics

which proved uncompetitive elsewhere. A totally

rigid carbon Finn does not flex and will

consequently pound and go slowly through waves.

By comparison the Devoti Finn is moulded in

fibreglass laminates using vinylester resin, with a

deck and bow area that are very flexible — you can

feel things moving, which is quite weird on such

an apparently solid, heavyweight boat. The

construction of the Devoti Finn has been designed

to absorb maximum wave impact, allowing this

unusual dinghy to power ahead with the ‘nothing

can stop me’ feel of a racing keelboat.

Edited by rodney

The reason is possibly this, but I´m just an amateur. Best bet is to consult
Frank Bethwaite and others.

Having a "stiff" mast as in the Finn, which is set more or less within a
frame dependent upon crew weight for you to choose, by the class rules(?
Lukiepie Walker) and possibly an advantage for the boat under other
conditions, all other things being equal, makes the rig with a stiff hull
rock over the waves, and consequently slow down. If the energy of wave
impact is transfered to either a flexible mast or a softer, more giving hull,
the result is the mast or hull gives, enabling a smooth run over the wave
without braking and the energy is then dissipated to the wave out the
back of the boat as it clears the wave and goes into the next trough
(more or less). That´s why the Devoti Finn hull IMHO has its flex
characteristics.

Personally, I'd sooner have a flexible ("automatic") mast and stiff hull than
a stiff mast and flexible hull though, one of the reasons being that you
can tune the rig characteristics to suit the average conditions at the time,
but you can´t tune the hull of a boat. Don´t know whether this is just
bull, but there's my ha'penny's worth.



Edited by Slippery Jim

I know very little about Finns, but at a guess, as soon as you are talking about an unstayed rig, then surely hull stiffness becomes quite academic?  At a guess, stiff hulls are not about the boat not "deforming" as it hits waves (as the boat is up and down and all over the place anyway), surely it's all about the rig staying exactly how you want it, no forestay sag, and that power going straight into the boat?  Take away the standing rigging and replace it with a "soft" rig like a Finns, and I could see that a bit of give would be a very good thing.   And the Finn is not exactly a seakindly shape...it's very blunt by modern standards!

I've sailed my missus' Europe quite a lot, especially in a blow, and it's just like a little Finn.  I'm still trying to get my head round the whole "everything works in reverse" rig settings etc, but I do wonder how much stiffness is added to the hull when the main in cranked in hard with the boom on the deck going upwind.  I'm amusingly too big for it but it's a good laugh in a blow, and I imaging it's a very technical boat and very hard to sail well (slight threadjack, sorry)