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 Post subject: Pedal Sailing into wind
PostPosted: Wed May 10, 2017 2:54 pm 
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Pedaling while sailing is recommended by Hobie kayak sailkit brochures... I don't know what the Islander manual says. I dislike the "impurity" of pedal sailing just as much as motor sailing a bigger boat, but I have to admit it helps. Especially when close to the wind and with wave resistance.

It bothered me why it works. Why can you enter parts of the upwind zone (shown in red below) without **luffing** the sail? I believe it is because you are not only pedaling the hull but overcoming sail drag, where magic things can happen to the force vectors (on third picture).

Image Image

By the way, it is interesting that max sail lift supposedly comes from letting bits of stalling occur at the front and back of the sail. Of course Hobie's sailkit for inflatables doesn't have that stalling at the leading edge because there is a mast sleeve pocket rather than a furling roller :) Anyway let's look at the diagram below being pushed 30% by sailpower and additionally 70% by pedaling.

Image

1) The true wind vT remains the same but boat speed vB rises from pedaling, and thus makes apparent wind vA stronger and angled more straight in.

2) The sail has to be pulled in which rotates the red Lift Drag rectangle clockwise. The resulting total force fT goes dangerously near the lateral direction fLAT where the boat wants to stop and only drift sideways.

3) But wait, your pedals are overcoming most of sail drag D, whose shortening rotates total force fT back counterclockwise, so there is still some resultant forward force fR (= sail "go power"). You don't overcome all the sail drag, because it is still working to pull beyond your pedal speed.

Also the stronger apparent wind vA gives more sail lift L which strengthens and rotates the total force fT into a helpful forward direction. But without pedaling this would be cancelled out by a rise in sail drag D.

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PostPosted: Thu May 11, 2017 12:50 am 
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On reflection I had to correct my terms above. When I wrote about stalling in the red zone, I meant the sail going all wiggly like the boat diagrammed straight to windward... "luffing" must be the term.

Anyway I think Hobie kayak sails are uniquely resistant to luffing their sails when very close hauled, like when pedal sailing. We have a fixed point sheet anchor (ring or block) in the stern instead of a wide traveler. Probably every other boat I have sailed could not pull the sail in tight because of wide lateral movement of a sheet block, and on top of that a loose boom vang (sort of a luff preventer). The traveler allows better sail shape at typical points of sail. Even when motor sailing in a large trimaran, we could not sail very close hauled due to wide traveler (also due to wind catching drag of it's huge upward heaving deck).

Therefore, if luffing sails aren't much concern, then efficient sails like fusioneng's TI wing sail and my inflatable's sail can work at amazingly tight angles to the wind if pedals overcome sail drag. It's not that the drag is so much, but the lift angle gets so sideways that there isn't much forward component left to counter the drag. But you appreciate it when pedaling. I guess pedaling can also help a lot on a beam reach or more downwind in order to make up for the boomless sail's taco shape. But a close reach is perfect for my sail and needs no pedaling.

I'm not sure if furlable sails behave the same way; I believe they may trade off Fred Flintstone airfoil quality for the advantage of spilling wind or furling :) My inflatable sailkit may play Russian roulette with being overpowered, but the mast is stayed and I believe sail has a 3d orangepeel shaped airfoil cut vs the rollable flat. It even seems to pull me a bit pedaling straight to windward, when the puffs vary and fill the front of the sail on alternating sides... pop, pop, pop. The unstayed furlable masts not only bend the sails strangely, but would seem to interfere with the airflow on one tack at sail's critical frontmost leeward area.

P.S. Intuition may suggest that pedaling not only overcomes sail drag, but reduces leeway. But logic suggests that may be an illusion due to pedaling reducing the leeway ANGLE, but no reason it would reduce ABSOLUTE leeway distance loss? Probably leeway loss is constant in distance per minute, and pedaling only helps in the sense it can shorten your time exposed to leeway.

P.P.S. to any inflatable sailors on pulling overpowered sail down. I'm not one who could stand at sea to take down the mast, but I believe I can detach the left shroud while kneeling and swing the mast forward. Then slide mast back where the top and bottom anchors of front shrouds are together and roll. Leave 2 feet of slack in front shroud and thread the mast base thru rear bungees on right side. Wrap remaining sail on the bundle now slung along your starboard side, and pedal home? I also have a paddle lanyard which can loop over sail bundle without defeating paddle use.

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PostPosted: Tue Jun 20, 2017 12:53 pm 
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Daft ... wow! New to sailing and the sailing of my Tandem Oasis. The math and concepts discussed are over my head. But the Sail/furling kit coupled with the pedals/rudder make for a fun and easy newbie experience.


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