Mainsail Trim

DArcy

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Feb 11, 2017
1,690
Islander Freeport 36 Ottawa
I was watching this video of the American Magic training boat. This is the boat being used to train for the AC75 foiling monohulls being used in the next America's Cup. This boat is an engineering marvel, I can't imagine the hours going into the AC75 design and development. The thing that really struck me was how loose the foot of the main is. This seems to be the norm for them at all points of sail, even when the boom is on center-line - look at around 3:45 in the video. Makes me re-think mainsail trim. Also, watch how much the traveler moves, constant trimming.
Anyway, these are very impressive boats and sailors. Should be a fun event when they scale up to 75 feet.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
The thing that really struck me was how loose the foot of the main is. This seems to be the norm for them at all points of sail, even when the boom is on center-line - look at around 3:45 in the video. Makes me re-think mainsail trim.
It’s because its like no mainsail you’ve ever seen before. It’s not a rigid wingsail from previous AC boats (fast but a logistical nightmare in harbor), not a regular softsail like your boat has.

It’s a DUAL paneled soft wing mainsail, with two sail cloths controlled by separate outhauls, and the aero-mast as the leading edge. Note the 3-dimentionality in the picture below. It’s also VERY high aspect, with much more breeze at the top. Notice all the tell-tail sets running across the sail every 5 feet, on both sides. There are class limits on what part of the sail can be controlled for shape, and what part is fixed. They go for max power by shaping the both sizes of the ‘wing’ to get maximum efficiently.

AND - This is a very competitive event. Lots of secrecy. This vid will be poured over by the other teams. I doubt they show perfect ANYTHING. But they are flying. Brave new world.

C64B69B0-C03F-4C05-A3BB-86E7553179BA.jpeg
 
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walt

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Jun 1, 2007
3,511
Macgregor 26S Hobie TI Ridgway Colorado
I dont know what the rules are for a boat like that.. but it sure looks like to me that the traveler is under servo computer control. Ie, artificial intelligence is measuring all sorts of things and generating control and its doing things fairly quick.

I also wonder about the foils. Remember the Tri Foiler (link below). The front foils had a control system where some sort of float followed the water surface and mechanically altered the foil angle of attack.

When I tried to look up any info on computer control of the foils for these modern foiling boats, I could not find much.. but I also didn't look very long.

All that computer control takes power which I thought would mean either you charge batteries before sailing or you would see guys pedaling like crazy to generate power used for controlling everything.

What are the rules regarding how the boats are controlled (sails and foils) and the energy and power that makes that possible?

 

DArcy

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Feb 11, 2017
1,690
Islander Freeport 36 Ottawa
It’s a DUAL paneled soft wing mainsail, with two sail cloths controlled by separate outhauls, and the aero-mast as the leading edge.
Thanks for pointing this out Jackdaw. This seems like a more practical approach than the rigid wingsail, I wonder how they compare for efficiency. Hmm, and cost. Just wondering if any of this will trickle down to us common folk.
Do you suppose that would be class legal on a C&C27? ;)
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Thanks for pointing this out Jackdaw. This seems like a more practical approach than the rigid wingsail, I wonder how they compare for efficiency. Hmm, and cost. Just wondering if any of this will trickle down to us common folk.
Do you suppose that would be class legal on a C&C27? ;)
I think I remember the designer at North saying it was like 7% more efficient (a big deal) than a single panel soft sail, but nowhere near as a efficient as a hard sail, which you can control as two parts.
 
May 17, 2004
5,026
Beneteau Oceanis 37 Havre de Grace
That is a remarkable amount of draft. I would've guessed they would trim for a flatter shape for less drag given the apparent wind speeds they're working at. Maybe that's a result of the dual sails, or maybe it's part of the deception.
 

walt

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Jun 1, 2007
3,511
Macgregor 26S Hobie TI Ridgway Colorado