dinghy design questions

Originally posted by JimC 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.

That's the explanation from people who do know what they are talking about. They may be dumbing it down for the likes of me. Quite clearly the hull form can increase lift, or probably reduce leeway or as we all have similar foils they would all point the same. These design tweaks overcome the limitations that the restricted rules bring. What we have discovered is that when you can get your foils working better you can change the hull form without losing.

Andy

I've sailed scows a lot, and yes, there are days when you slam, but on flatish water, even with the crappy centreboard the Minisail has, the boat actually points as high as anything else if you need it to. Topper and Fireball the same. Better VMG on open water can certainly be had by cracking off a degree or 2, but it goes to show that there is a wide variety of hull designs that will go up wind in similar fashion. In fact, I'd say the rig type has far more influence than hull shape or centreboard on pointing ability, and certainly on VMG.

Pointing ability is dictated by the sum of aero and hydro drag angles (arctan of the lift to drag ratios). So both above and underwater equally important, but probably traditionally more design variance in the aero side of things.

Deep bows have a number of advantages like straighter buttocks and volume distribution (all leading to lower drag), but lift generation would be minimal.

Edited by Peaky - 10 Oct 14 at 10:24am

Originally posted by Peaky Pointing ability is dictated by the sum of aero and hydro drag angles (arctan of the lift to drag ratios). So both above and underwater equally important, but probably traditionally more design variance in the aero side of things. Deep bows have a number of advantages like straighter buttocks and volume distribution (all leading to lower drag), but lift generation would be minimal.

 I also wonder if it;as people confusing the tendancy to trim  to bow in the likes of a N12 or MR  up wind  for  drag  reduction with  some kind of presumption of using the  sharp, deep , fine bow for  extra lift  / rather than optimising lwl / dragging surface area 

it also doesn;t help that  thelike of the N12 and the Merlin have rigs which are / can be  encouraged to optime   sheeting and slot for upwind performance complared to  none development One designs stuck with relatively  wide sheeting  angles and normal sails cut to cope with that  ( also  into the realms of  uber string   rig tweaking etc  vs  set and forget on something like an ent ... )

I was just quoting the designer. I also understand one of the modifications on the Canterbury Tales was to extend the stem, and I doubt that initially had a waterline issue. Mike Jackson tried to take this even further with the fore runner to his final chapter design, though the difficulty handling it ashore was apparently too much.
Interestingly apart from the recent trim tab addition I am not convinced my centreboard is that different from a 70's one. I suspect it is the least developed part of the boat. We don't have the high aspect, very deep boards that you see in other classes, though to have a different board for different conditions seems a step too far, and I expect would be visa sailing rather than cheque book.

Andy