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Author Topic: Reduced sail plans and heeling force  (Read 2267 times)

tigertiger

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Reduced sail plans and heeling force
« on: April 27, 2007, 06:34:07 PM »

A dumb question.

I have read that you need to have a reduced sail plan because of the heeling forces from wind pressure and the effects of scaling etc.

My question.
If I were to make the sails out of a material that was less wind proof (allowed lots of air to pass through it) this would reduce the wind pressure and heeling forces.
So could I get away with a full sail plan?

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Colin Bishop

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Re: Reduced sail plans and heeling force
« Reply #1 on: April 27, 2007, 06:40:00 PM »

That's an interesting thought tigertiger. In theory it might work but I suspect that with some wind going through the sail and some not it might have an unpredictable effect on the aerodynamics of the sail. Imagine the effect on an aeroplane if the wing was peppered with holes... What sort of material would you use anyway?
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dougal99

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Re: Reduced sail plans and heeling force
« Reply #2 on: April 27, 2007, 06:46:35 PM »

Swiss cheesecloth  ;D ::)
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tigertiger

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Re: Reduced sail plans and heeling force
« Reply #3 on: April 27, 2007, 07:16:43 PM »

Dunno about material.

Regular cotton sheet, instead of downproof cambric.


Scale wise might be a bit thick, but:
Dacron bedsheet, it will billow but lots of air gets through.
Nylon bedsheet.

These are my initial thoughts.
I expect someone has tried before.
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Colin Bishop

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Re: Reduced sail plans and heeling force
« Reply #4 on: April 27, 2007, 07:56:00 PM »

I suppose what you could do is to set up a dummy mast of around the right size and then attach "sails" to it using various materials which you could then test with an electric fan. Some sort of light springing could indicate the pressure on the sail. Should give some indication of what might happen. I've never heard of anyone trying this before although, as you say, someone will probably come up with the goods.
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Welsh_Druid

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Re: Reduced sail plans and heeling force
« Reply #5 on: April 27, 2007, 08:42:14 PM »

Imagine the effect on an aeroplane if the wing was peppered with holes...

Strangely enough that is exactly what is being researched by Loek Boermans at the Technical University of Delft in order to increase the performance of sailplanes (gliders). There are lots of minute holes drilled in the wing surface at the point where the laminar flow becomes turbulent and by sucking the air through these holes 100% laminar flow is achieved with a remarkable reduction in drag and thereby efficiency. Hardly applicable to model boats though  :D

I have couple of scale sailing boats and I have kept the standard set of sails at scale size using sails with fairly normal porosity with no problems. If the wind gets up I simply reduce sail area.(or if its REALLY blowing - just pack up for the day  :-[)

 Full size boats  reduce sail by reefing but it is more convenient with models to simply change to a smaller set of sails. Sail material which is very porous will tend to be very soft also and distort into an inefficient shape too easily.

Don B
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BobF

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Re: Reduced sail plans and heeling force
« Reply #6 on: April 27, 2007, 10:47:03 PM »

Hi all,
Down hill Ski Racers have to have the suits they use checked, to make sure they comply with the amount of wind that can penetrate. Yes I did watch Ski Sunday when I was younger.

Bob
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JayDee

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Re: Reduced sail plans and heeling force
« Reply #7 on: April 27, 2007, 11:19:29 PM »

Hello Tiger,
Reducing the Sail plan by lowering the sails onto the Booms as in full size is the way to go.
This lowers the sails Centre of Effort, which makes the boat "stiffer" in the wind.

Look at a full size boat and you will see the Reefing straps on the lower parts of the sails.
Or, make some sails which are not as high up the masts. as the standard ones.

Better still, stay at Home when its VERY windy !!!.

John.  ;)
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tigertiger

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Re: Reduced sail plans and heeling force
« Reply #8 on: April 28, 2007, 09:07:25 AM »

Hi Jaydee.

I thought your Bluenose was full size  ;D :D ;)
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JayDee

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Re: Reduced sail plans and heeling force
« Reply #9 on: April 28, 2007, 11:03:26 AM »

Hello Tiger,
No, a mere 1/20 of the real thing !!!.
John.
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andywright

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Re: Reduced sail plans and heeling force
« Reply #10 on: May 02, 2007, 08:39:13 AM »

If you use material klike you say, it will probably be stretchy. I would go for a scale sail plan, if its an older style model fit a false keel, nobody will see it when sailing. Have a reduced size sail plan for stronger winds.
Regards Andy
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tobyker

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Re: Reduced sail plans and heeling force
« Reply #11 on: May 12, 2007, 11:22:44 AM »

I wonder. If you used a porous material you might get even more heeling effect, because there would be an area of uniform low pressure on the leeward side of the sail. On another tack, has anyone ever tried a mast with a Handley Page slot in to guide the airflow over the back of the sail?
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malcolmfrary

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Re: Reduced sail plans and heeling force
« Reply #12 on: June 25, 2007, 11:24:55 PM »

Remembering my reading about how to rig yachts, that is exactly what the slot between the fore and main sails does. 
A more porous cloth might well soak water, thus adding weight where it isn't wanted.  A really open weave migh work, but the fibres would have to be impervious to water.  I would go for the false fin and bulb suggested earlier.
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tobyker

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Re: Reduced sail plans and heeling force
« Reply #13 on: June 27, 2007, 08:09:46 PM »

Yup, but the jib is very large compared to the HP slot vanes on a flying machine. I wondered if you could have a really narrow vane (vertical Venetian blind slat?) held off the fwd edge of the mast which would give the slot effect of a jib without the weight and area of one. However given that a staysail is more effective than one set on a spar, maybe its the main we should be getting rid of!. Wanted - one skyhook to hang a forestay from.
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