sailing conundrum

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nicholas
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sailing conundrum

Post by nicholas » Fri Jan 24, 2014 5:59 pm

Ok i have a flat earth sail and the mast is stayed below the boom which means the boom can swing 360 degrees
Sailing down wind i normally have the boom out at 90 degrees more or less.
In this position the sail is not acting like an aerofoil.
Lets say i let the sail out to 160 degrees (have not tried this yet) it will then act as an aerofoil and in theory
be more efficient .
Will this increase my speed ?
Will there be an unmanageable turning force ?
Has anyone tried this ?

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PhilAyr
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Re: sailing conundrum

Post by PhilAyr » Fri Jan 24, 2014 6:49 pm

Hi Nicholas,

There are plenty more experienced kayak sailors out there than me but in answer to your question I would say no. By sheeting out to 160 degrees in a following wind all you will do is de-power the sail (handy if you get into trouble). When
" running " ie paddling down wind the sail is similar to an umbrella and is being pushed by the wind. The sail acts as an aerofoil in a close reach, beam reach or broad reach. I think that the sail is at its most efficient in a broad reach.

Anyway that is my understanding and I stand to be corrected. I hope I have been of some help.

Phil

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Re: sailing conundrum

Post by pathbrae » Fri Jan 24, 2014 7:10 pm

I'd agree - I suspect it won't take up an aerofoil shape once it gets wind flowing the wrong way and will probably just flog as it spills wind. You also loose wind speed as you'll be taking boat speed away from the wind as soon as you start to move. Wind surfers let the sail fall forward to loose speed and power when running before the wind.
Only way to move a bit faster downwind is to catch more wind. Yachties would be "goose-wing-ing" with jib and main out on opposite sides of the boat (and -- for us poor souls in kayaks - sailing completely blind with no hope of seeing anything in front of them) or sailing with a spinnaker rigged.
Spinnaker on a sea kayak? Handling the sail would be "interesting" but I don't see any reason why it shouldn't work - maybe using your spare splits as a spinnaker pole.......



At least, that's what theory would suggest. The only way to know for sure is to get out and try it. And let us know how it works.
So much sea - so little time to see it.

ruralweb
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Re: sailing conundrum

Post by ruralweb » Fri Jan 24, 2014 7:51 pm

As soon as you let the sail out beyond 90 deg to the wind you will loose power.
Mal

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atakd
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Re: sailing conundrum

Post by atakd » Fri Jan 24, 2014 8:43 pm

A sail acting as an aerofoil generates lift to the windward side. When running, any lift generated will act to slow the boat as the windward side of the sail is towards the stern
Andy

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Douglas Wilcox
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Re: sailing conundrum

Post by Douglas Wilcox » Fri Jan 24, 2014 8:51 pm

Hello Nicholas, the others are correct There is no conundrum. Even if you were travelling in the opposite direction and going up wind, you would not be able to fill the sail with it sheeted at that angle, which would be 20 degrees to the wind. If you were travelling upwind closehauled about 45 degrees to the wind, the sail would be be out a further 20 degrees or so which means the sail would actually need to be about 60 degrees to the wind to work efficiently. The importasnt thing is that fast clean air is flowing over the sail from luff to leach.

In the scenario you describe, you would need to sheet in further to establish any sort of airflow which will be ruduced anyway as you are going down wind. Even if you did establish an airflow over the sail, the lift and power of the sail would not be in line with your direction so you would not go anywhere fast.

If you are going dead down wind and continue to paddle and catch waves you might find the sail will back wind as you accelerate when you catch a wave and the apparent wind changes from behind and moves forward. If it is just an occasional wave then you can just ignore it but if you maintain a high speed downwind, you might need to sheet in to compensate for the apparent wind that your boat speed generates. For fun I usually very broad reach downwind (to maintain the airflow over the sail) rather than run dead down wind and use the sail sheeted at about 90 degrees (in practice, due to the twist in the sai, l I usually have the sail sheeted to about 75 degrees off the direction of the wind when I am running with the wind). In F4-F5 you can travel so fast downwind that you need to have the sail sheeted in a surprising amount.

Douglas

PS you don't need to understand any of this to start having fun with a sail on a kayak.

Haddock
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Re: sailing conundrum

Post by Haddock » Fri Jan 24, 2014 9:08 pm

atakd wrote:A sail acting as an aerofoil generates lift to the windward side. When running, any lift generated will act to slow the boat as the windward side of the sail is towards the stern
Err...would politely suggest that is the wrong way round. Lift is generated on the leeward side of a sail acting as an aerofoil.

There is a slight gain to be had by having some flow over the sail when running but 160deg would be a bit excessive!. Lasers and other single sail boats will sail with the boom at 90deg but the boat pointing 10 or 15 degrees away from dead downwind: http://fleet20.blogspot.no/2011/11/down ... y-lee.html

However it's a very slight gain on a racing dinghy so whether you'd notice any difference with a kayak sail I'm not sure? The strongest wind is usually higher up (particularly when taking about the first metre or two above the surface) so sheeting the sail in a little may present the upper sail a bit more squarely to the wind as I'd guess when the boom is 90deg on a Flat Earth sail then the upper sail twists further forward than this? Potentially letting the sail twist a bit more than usual and then sheeting in to about 75deg and sailing with the flow reversed (from leech to mast) is the fastest option but probably overthinking it for a kayak sail!

flat earth sails
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Re: sailing conundrum

Post by flat earth sails » Fri Jan 24, 2014 9:23 pm

I can recommend the last comment , Just get out there and do it sum times its best not to bog yourself down with theories and over analize things .
The newer generation of sails are cut to have a broder range to them , their set so there's no fiddling around with tensioning out halls ect... We wont to keep it simple its a sea kayak after all their cut so there's a happy medium for reaching and running , that is when we travel across the wind (reaching) with the wind from behind the faster way to sail and when we are traveling directly down wind , I really bother with taking its faster just to paddle (we are in a kayak )
The twist Douglas mentioned is permanently set in the sail in basic terms it makes the sail shape more forgiving wen we have a bluet of air hit the sail.
Some of you are probably thinking why don't you make them with adjustment so we can adjust tensions twist ect.."....
The design has gon the full sercel I made sails with jeeps of adjustment and found that most kayak sailors didn't bother yousing it , a lot realised that it was to complicated on eneything more than 10kns of wind and those who liked the ability where never happy with the results .
Sume thing s to consider.
We are paddling a sea kayak, we generally like paddling kayaks becos their simple lite crafts so why over complicate what we like in a kayak with a sail that has to much complication ?
The hole design philosophy is not to detract from the kayak , its a kayak that you sum times sail, not a sail boat that you sum times paddle
The stays are below the boom for two reasons , when where reaching the sail keeps a better shape if the stays aren't touching the sail and if things get to Henry just let the sheet go and all the wind is of the sail. With dingy sailing you tern into the wind for your safe position, in a kayak its harder to tern into the wind with a sail , so you tern the sail into the wind ferst.
Just to re entreat the most important comments , don't over think things and don't choke your sail !

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Douglas Wilcox
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Re: sailing conundrum

Post by Douglas Wilcox » Fri Jan 24, 2014 10:03 pm

Haddock>
There is a slight gain to be had by having some flow over the sail when running but 160deg would be a bit excessive!. Lasers and other single sail boats will sail with the boom at 90deg but the boat pointing 10 or 15 degrees away from dead downwind: http://fleet20.blogspot.no/2011/11/down ... y-lee.html
Hi Haddock, as a Laser sailor myself since 1975 I have tried paddle sailing by the lee but it does not work well on a sea kayak fitted with a flat earth sail. Maybe this is because a Laser has a very tight leech compared with the Flat Earth sail, I don't know. What I do know is that when you start sailing by the lee it is much more difficult to paddle sail in balance and so hold your course. You find yourself needing to apply more steering strokes. (What happens is that the bow wants to turn away from the side the sail is sheeted on.) I find if I am on a run and am having difficulty holding a course, I simply gybe the sail which fixes the problem. (Which is caused by paddle sailing by the lee.)

Again, for paddle sailing beginners, you don't need to know any of this to get started having fun paddle sailing. Neither Phil nor Tony in our group had ever sailed before taking up paddle sailing. However, they were both hooked on their first outing!

Douglas

Haddock
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Re: sailing conundrum

Post by Haddock » Fri Jan 24, 2014 10:14 pm

Yes, you're probably right on that Douglas. It takes practice and precise handling in a dinghy where you have a large rudder and the option of moving your weight around to steer much more aggressively. In a kayaks the difficulty probably outweighs any small gain in speed.

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