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Rise Of The Ok etc

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Rupert View Drop Down
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Topic: Rise Of The Ok etc
    Posted: 03 Oct 14 at 3:08pm
I think you have to teleport to get to the other side on your boat, Jim.
Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
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Bootscooter View Drop Down
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Post Options Post Options   Quote Bootscooter Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 14 at 7:31pm
The OK is an awesome boat, and one that teaches you so much about how rigs work. BTW, there's more space boom-to-floor in an OK than a Laser.
I love mine and can't wait to get started on refurbing my REALLY old one - it's going to be a rocket when done!
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iiitick View Drop Down
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Post Options Post Options   Quote iiitick Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 14 at 7:42pm
Originally posted by iiitick

You have Byte for lightweights.......Finn for heavyweights and a whole load of classes in between available for 'average' sailors. Tastes wax and wane and new boats inject themselves into the system causing damage to similar classes. Niche boats like OK survive but will vary in numbers as time goes by.

D Zero will damage many classes but the niche boats will soldier on.

Radials may be more common World wide but Byte is more suitable. You wont get many 8 stone ladies surviving what they survived at Calshot in a Radial. Hence my comment.
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Medway Maniac View Drop Down
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 14 at 10:54pm
Originally posted by JimC

Originally posted by Medway Maniac

And do you really think raising the boom to make the boat accessible to old men and novices while sacrificing efficiency to induced drag is progress?

What makes you think that having an 18inch gap under the boom is significantly better than having a 30 inch one?
I like Dan's point about lowering the centre of effort more than my observation about induced drag, but I can't accept your reasoning, Jim.



No way that's an 18" inch gap between the bottom of the boom and the deck at the mast (where it matters most, as you know); more like 5" or 6".  And there's a deck flush with the gunwales beneath the boom.  Whereas on the Aero:



Put it another way, if you were running a wind tunnel test with the foils with those sorts of ratios of gap to floor:span, would you be happy there was no end-plate effect in either case?  I'd say there would be an effect with both rigs, but considerably more with the OK.  Marchaj recorded a 10% improvement in L/D by moving a Finn sail from 10" to 6" above the floor.
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Post Options Post Options   Quote Blue One Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 14 at 12:48am
But how much of that 10 % is theoretical, and how much is real when sailing in all the ever changing conditions that happen in a race? Also what percentage is the increased drag of a higher boom in the total drag of the boat and sailor? And if an average sailor is more comfortable and quicker though the tack with a boat with a higher boom does this also out way the theoretical advantage?It's like bikes, a manufacturer will tell you it's new bike is 10 % more aerodynamic, but a bike is less than 1 % of the total drag of the bike and rider. So what do good riders do, go in a wind tunnel and get tested and this is where it gets messy. His best aerodynamic position, might not be fastest on the road, because it's too uncomfortable. Most of these things are a compromise.

Edited by Blue One - 04 Oct 14 at 12:50am
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mongrel View Drop Down
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Post Options Post Options   Quote mongrel Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 14 at 5:35am
I think the end plate effect between the boom and deck is limited. It may look worth while in a wind tunnel, but in the real world, its acknowledged that there's not a great deal of wind between the water level and 1 metre above it. So unless you've got a metre of freeboard its probably better to give yourself a bit more room beneath the boom for ease of handling. 
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Daniel Holman View Drop Down
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Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 14 at 7:54am
Originally posted by mongrel

I think the end plate effect between the boom and deck is limited. It may look worth while in a wind tunnel, but in the real world, its acknowledged that there's not a great deal of wind between the water level and 1 metre above it. So unless you've got a metre of freeboard its probably better to give yourself a bit more room beneath the boom for ease of handling. 


How come my hat always gets blown off then?
Accept wind gradient in the light stuff but it scrubs sown to sea pretty well in any breeze else you wouldn't be able to see it on the water.
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Medway Maniac View Drop Down
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 14 at 8:42am
Good point about the hat, Dan, mine does too! And of course it's in windy weather that L/D becomes most important, when you want max. thrust/heeling moment.

Blue One, I share your scepticism about manufacturers bike tests. Results depend on how they weight yaw, the wheels they fit and whether the dummy's legs are pedalling. Nonetheless, measurable improvements have been made, meaning you cover a set distance faster and/or use less energy, so an aero frame is handy if you have a flat stage.

Likewise I'm sceptical about claims made for small-area, high aspect boards in, say, the 505 class. There are so many other, major contributors to drag upwind - hull hydrodynamic and aero - and high-aspect foils stall more easily. Nonetheless, I'd be loath to risk turning up at a 5-oh worlds with a large area, low aspect board.

That 10% gain was experimentally measured, not merely theoretical, and the difference between Aero and OK is greater than that. We've had testimony from two people that the OK has plenty of room under the boom, too, so I find it hard to see any advance in the Aero rig over that of the OK, quite the contrary in fact.
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Daniel Holman View Drop Down
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Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 14 at 8:50am
The size of foils on most boats is such that you can get out of tacks relatively easily - so when you are applying max righting moment but are only doing 2 or 3 kts, the whole lot doesn't stall.
The flip side of this is that especially for the quicker boats like 505s that can do approaching 9kts upwind in breeze, that they are working at very low lift coefficients, and are therefore carrying around a lot more WSA than they need to.
A high aspect foil is working at its best at about 4 deg AOA - best compromise between reducing induced without having too much frictional drag.
About 6 years ago the 14 class gravitated to skinnier foils, so daggers went from 280 chord to 220, rudders from 220 to 170 chord, so a fairly large change. I reckon that it made a minute an hour or more difference depending on breeze. And makes you have to get good at tacking / downspeed manoeuvres!!
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Post Options Post Options   Quote sawman Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 14 at 9:11am
I have always had a soft spot for the OK, I actively sought some when I jumped out of open circuit 2 man boat racing - but for some reason I ended up with a Vareo (with which I never really gelled) 

If my daughter gets fed up sailing the miracle with me and I cant persuade her little brother that sailing is better than rugby I will probably scratch that itch
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