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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Topic: dinghy design questions
    Posted: 08 Oct 14 at 11:49am
There are other compromises too. An IC is about the fastest thing there is upwind when there's room to stretch it's legs, but the long thin boat does not roll tack well or indeed tack fast at all, and on a river may easily be beaten by a National 12.

Edited by JimC - 08 Oct 14 at 11:52am
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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: 08 Oct 14 at 11:55am
These are not the straightforward answers that the OP was hoping to get, but they do serve to illustrate why one boat will win one day, and another in different conditions.

Cue Grumph and the usual PY debate.  Confused
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 11:56am
I read the OP as meaning clear water, perfect conditions. Otherwise, I'll bet on a Firefly against a 49er in no wind.
Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
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Post Options Post Options   Quote fish n ships Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 12:24pm
I certainly struggled to beat a mirror on restricted water in light winds in my Dart 15...
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Post Options Post Options   Quote JohnJack Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 12:30pm
How would we be measuring upwind speed. Two boats doing the same velocity upwind may have the same speed but different VMG's towards a point. Therefore one will be technically going quicker. 
If for example you took the wind angle out of the equation and kept both at the same TWA, then it wouldn't be fair as one boat wouldn't be fully close hauled.
Pointing ability must be effected by hull shape to a certain extent.

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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 12:48pm
I've had what I think is the answer doodled alongside my original drawings for the V2 before I started down the planing hull route.

Trouble is I've run out of space, cash and bread knife goodwill when it comes to anything further boat shaped littering up Fuller Towers.

If someone would be kind enough to make me a half decent offer to take version 1 off my hands, I could start version two, this time it would be suitable both for the lake and the sea, but wether I could make it light enough out of wood, I don't yet know, but it's still on the cards, V3 will one day hopefully do the job.

Basically with wave piercing instead of planing surfaces, but the same concept and minimal wetted surface when static with a bloody big gap of nothing in the middle, this time that will flood if it goes over.
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 12:53pm
Originally posted by JohnJack

How would we be measuring upwind speed. Two boats doing the same velocity upwind may have the same speed but different VMG's towards a point. Therefore one will be technically going quicker. 
If for example you took the wind angle out of the equation and kept both at the same TWA, then it wouldn't be fair as one boat wouldn't be fully close hauled.
Pointing ability must be effected by hull shape to a certain extent.



Upwind means upwind. Put the 2 boats togather - which one reaches point B first. Angles don't matter, VMG does.
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JimC View Drop Down
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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 12:58pm
Its probably fairer to say that pointing ability is affected by drag and speed.

Its damn complicated, but lets say you have a rig that will set at 15 degrees to the the apparent wind. The pointing angle will be directly affected by speed: because the apparent wind comes back with speed through the water then the faster the boat goes the lower the boat will point: if the boat is stationary the sails will set just fine with the boat pointing only 15 degrees off the true wind, but as soon as it starts moving at all then the apparent wind will come back and the boat will have to bear away a little to get the sails to fill. So that's one factor: the ability of the sails to fill with wind.
The second one is power: the sails may be full of wind, but can they generate enough power to move the boat along when sheeted in that tight? That's where the drag of rig and hull come in. If you look at, say, a modern International Canoe the jib will be sheeted in astonishingly closely compared to something like an Albacore. That's because the boat has such a low lift/drag ratio that it will move upwind with the sails sheeted like that. You could sheet in the sails on an Albacore that close too, and it would sail, and point higher than a Canoe, but because the lift/drag is so much worse it would sail very very slowly, and you're better off sheeting the jib out a bit and pointing lower, but with more power.
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Post Options Post Options   Quote boatshed Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 1:15pm
Originally posted by JimC

You could sheet in the sails on an Albacore that close too  but  it would sail very very slowly


An Albacore ?  Surely some mistake ?
Steve
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Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 14 at 1:47pm
Originally posted by iGRF

I've had what I think is the answer doodled alongside my original drawings for the V2 before I started down the planing hull route. 
[...]
Basically with wave piercing instead of planing surfaces, but the same concept and minimal wetted surface when static with a bloody big gap of nothing in the middle, this time that will flood if it goes over.

We need to see drawings of this masterpiece-in-the-making.
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