Fastest dinghy?

Originally posted by Phil eltringham Simon, Re: boards. Windsurfers are an interesting point as when the plane they are barely in contact with the surface of the water and so the rules about righting arms do not really apply, the same can be said to some extent of planing craft, but it still works as an analogy that is sufficent for this discussion (Bethwaite discribes it better than I could).  Have you noticed that board sailers at speed have the rig heeled over significantly to windward?  This is what supports the riders weight.  On a dinghy sailed upright the two main componants of the force produced by the sail are along the centre line of the hull and across it, both horizontally.  With a rig canted this far to windward the force that would be heeling the board to leward is now pointing up as well as across the board.  This vertical componant supports the riders weight and also lifts the board out of the water.  The other plus point is that the force to leward is reduced and so a smaller foil is needed to keep the board in a straight line (also less drag).  The thing to remember about boards is that they are inherently less efficient that a dinghy and have allredy reached their top speed to within 2 knots (i guess).  Their limiting factor is infact the air resistance of the rider.  What allows them to seem faster is that they can go out in far windier conditions.  Most board records have been set doing only a small fraction more than the true windspeed, whereas the records set by multihulls have been set at more than twice the windspeed.

Sorry Phil, can I disagree with a lot of the above?

1) The windward rake of sailboard rigs is generally accepted (by those who do well in them) to have very little effect. In fact, in boards with smaller rigs (Mistral) people spend a lot of time trying to keep the rig dead upright. Even in Formula (12.5m2 sail) you can see sailors often trying to keep the rig as upright as possible, sometimes to the point where they hang off the uphaul line.

Jim Drake, the guy who invented both the original Windsurfer and the modern wideboard, is (quite literally) a retired rocket scientist. He says that rake should be no more than 15 degrees, and that does not create much upward force.

If you look at pics of top windsurfers, you'll generally see the rig is close to upright. OK, there's a bit of windward rake, but in any wind that's the only way you can stop from blowing straight over. And of course it's easy to get more windward rake. If it was efficient, sailors would lean back until their backs dragged. That provides heaps of upward force, in a breeze you can basically lift the board straight out of the water.

But you don't - basically you want force to move you forward, not up. The  reduction in wavemaking and wetted drag is not worth the loss in volved in directing sail force up rather than forward.

You can see this in a Mistral fleet - compared to boats they go best downwind, when the mast is upright (from side to side, it's raked aft).

2) Boards are not innefficient. That's just a common misconception. Yeah, Frank Bethwaite says it but he has admitted to me he's never really looked at course-racing boards. We were going to do some work on it for his new book but then we had strained relations for a while over a Tasar class matter.

The course racing  boards are really efficient in all conditions. The Lechner (3.9m round-bottomed raceboard) using a 7.3 or 7.4m sail is faster than a Moth (OK, shorter but with an 8m sail and similar weight 'cause the Lechner is a One Design with a heavy 18kg hull, and waterline length is only about 3.75m IIRC) around a triangle even in about 5 knots. Surprisingly the Moth seems faster on a reach in the light but the LEchner is fully competitive upwind (very similar height, just a fraction lower) and faster on the square. That's in flat water, the board would be superior in chop I believe. That's the guy who was 5th & 6th Aussie in the last 2 board nats IIRC to the world's best two Moths (the Thorpes). That's without the board pumping.

In a stronger wind, say 10 knots, the Mistral is fully competitive with an International Canoe (both Mistral and IC were 3rd in the nats, the Mistral guy was also 3rd in 29er worlds) )upwind. Downwind on a square it's no contest if the board pumps and in a breeze but I think it would be close with the board not pumping in the light.

In stronger winds still, the boards really start to move. The Mistral is faster downwind than a Hobie, in a big breeze faster than an A Class or F 18 cat. The FW boards seem to be fully competitive on squares with an 18 or the national Tornado champ (wioth kite) and they are very, very close to the pace upwoind as well.

That's incredible efficiency in any terms for such a small bit of kit. So the idea that they are crude but controllable is very common but wrong - no 12' OD  with a 7.4m sail that is normally quicker than an IC could be called innefficient!

hi,

 

Um i wouldnt be able to get to many races around the country but as i am only 14 (is this too young for one) maybe once i had some experience i may be able to go to the races then! But if they can keep up with laser 4k's they must be pretty good and what sort of wind speed do you need to get out on the wire??

 

 I have little experience of trapeze boats but would this boat be far too hard for me too manage??

 

Thanks

Ok Thanks very much thats really helpful!

I have been speaking to people and they suggest for me a good fun cheap boat may be the international contender.

 

Is this a good fast boat to sail or is it rubbish bearing in mind i love speed??

 

Thanks

 

No doubt a Vortex sailor will chime in with a defence but in my limited experience they are very fast on a close reach in a 4 or 5 but otherwise rather a disappointment.  They don't point, don't go downwind very fast and work well in a limited wind range.

The RS300 mentioned above,on the other hand, has a wide range of winds in which it performs well. Its fast upwind, extremely fast for a non trapeze boat on a reach but a demanding boat to sail especially in strong winds and I'm told even more so in waves.  Strangely it hasn't really caught on.

Wave Rider - the vortex is reasonably fast in a straight line but crap in anything less than a F4-5, it doesn't point and has nowhere near enough sail area given its weight and righting moment. I've not seen one with a kite up yet but I'd imagine they're more entertaining.

The best thing you can buy for that money is an RS300. Far more challenging, bloody quick on all aspects of the course, better made and you will learn a lot more, much faster than in a Vortex. Okay the 300 is slower in a straight line, but it's a lot more fun to sail.

As for the skiff comparison? The Vortex wouldn't see which way it went!