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andymck View Drop Down
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    Posted: 09 Oct 14 at 11:26pm
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.

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Post Options Post Options   Quote zippyRN Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 12:05am
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.

I'd agreewith that , especially given that the N12 and the MR  have long  well developed  centreboards ... 

 the fine deep bow  on the aforementioned lcasses is much more to do with maximisation of Lwl vs Loa  as discussed before  

I'd agree with jim about the wave stuff as well  - i think the optimum bow forms  are probably the extremes here 

either  the fine deep V shaped bow  which pierces the wave   or the scow bow  which where possible rides the wave  - most people who have any significant amount of hours  in scow hull form  boats be they  toppers , scow moths  or fireballs/ tempos   will have  experienced conditions where no matter wht you  do trim wise you just slam slam slam  your way up wind 
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 8:28am
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.
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 9:43am
Originally posted by Rupert

. In fact, I'd say the rig type has far more influence than hull shape or centreboard on pointing ability, and certainly on VMG.

That's highly probable. Even the crudest centreboard is, after all, far closer to a proper foil shape than soft-sailed dinghy rigs, which have a much lower lift/drag ratio and quite possibly a wider variation even between being set well or badly.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 10:23am
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
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Post Options Post Options   Quote zippyRN Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 11:15am
Originally posted by Rupert

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.

I'd agree with that  rupert 

I do likes me some fireball action  ( only sailed  them for a few hours compared to some of the other classes in my log book ) 
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Post Options Post Options   Quote zippyRN Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 11:20am
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 ... )
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 11:29am
Originally posted by zippyRN

I also wonder if it's people confusing the tendency...

I'm sure you're right. Just because one's theory of how something works is incorrect doesn't mean it doesn't work.
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Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 11:50am
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.

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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 14 at 11:58am
I'm sure I saw at some point a comparison of a Finn centreplate and a deep, shaped centreboard, and there was surprisingly little difference in how they behaved. This was then compared with a flat rudder and a shaped one, where the difference was much, much greater.

There was a difference, of course, so boats which have the option will go for the optimum shape, but it could explain why the board is what Andy sees the least change in.
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