dinghy design questions

You brought the plusplus Jim? What was it like? Does it need the modifications talked about on the website?

So for waterline length is key for upwind does but does hull shape effect pointing? And how?

What hull shape is fast down wind? If we say in ten knots of breeze.

Originally posted by gbrspratt So for waterline length is key for upwind does but does hull shape effect pointing? And how?

Originally posted by gbrspratt You brought the plusplus Jim? What was it like? Does it need the modifications talked about on the website?

Well, I would say so [grin]

Originally posted by gbrspratt So for waterline length is key for upwind does but does hull shape effect pointing? And how?

Not really in the sense of affecting leeway. Foils are so much more powerful and efficient than the hull. But indirectly, well hull shape affects drag, and drag affects pointing ability.

Originally posted by gbrspratt What hull shape is fast down wind? If we say in ten knots of breeze.

Very hard to make hard or fast rules. But all else being equal a long boat will still be better than a short one unless you can get into a real planing mode with very little wave generation, and there are precious few dinghies that can manage that.

Originally posted by Jim Mitch I always thought Blue Arrow looked interesting.

Certainly interesting. The thing about it though was that it was primarily a rule beating boat but most of the rules it had to beat were unwritten. They had to work up a boat that would meet the Deed of Gift rules (not too difficult), be faster than the Yanks catamaran (pretty challenging) but, when the principle dimensions were put on paper, sight unseenm make the Kiwis and Yanks think it couldn't possibly be faster than the big Kiwi monohull so they'd be allowed to play (very difficult and in the event they failed at that). So it wasn't necessarily the boat they'd have built for maximum speed round a track.

My understanding was that they were not allowed to play, and so with the last of the money they went sailing faster and faster in more and more wind, and then one day... bang.

Edited by JimC - 09 Oct 14 at 8:59pm

[QUOTE=gbrspratt]

So for waterline length is key for upwind does but does hull shape effect pointing? And how?

Scam

Hull shape can be changed to affect pointing ability. N12 and Merlin designs have since the 70's had fine deep bows as they improve upwind performance by giving lift off the bow. The DCB was a big move away from this, the winged rudder helps overcome the need along with the trim tab. This of course is used to overcome other constraints, in boats that are designed to plane downwind, and go at displacement speeds upwind. Of course for a displacement boat I would agree with a u shaped cross section with a banana rocker like the americas cup boats, or look at the modern radio controlled hulls like the 1m britpop. These attempt to reduce wetted area in light winds then go to maximum waterline once healed like the old J's and metre class boats.

Going downwind designs over the last 15 years have also changed. In the N12 wide flat sterns had already been tucked in with the planing surface sometimes more forward. The winged rudders have changed the trim angle again, with the boats planing less bow up. The stern waves have as a result got smaller. It feels more like the way a motor boat planes. Of course the skiffs are different, so again depends on power to weight ratio.

Andy

Originally posted by andymck ...as they improve upwind performance by giving lift off the bow.

Has to be a myth. There's not a chance that the lift/drag you'd get off the hull could contribute anything useful compared to what the foils are doing. The reduced wave impact of a fine deep bow might be another matter. Just because something works doesn't mean people know *why* it works.