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Question about points of sail / apparent wind
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Author:  bmdumr [ Wed May 14, 2014 7:10 pm ]
Post subject:  Question about points of sail / apparent wind
I'm new to sailing and my Hobie 16 and have a question about points of sail, and apparent wind. As I understand it a beam reach at 90 degrees to the true wind should be the fastest point of sail. First stop, correct me if I'm wrong here.

My question is, as you build speed and the apparent wind shifts toward the bow, does that eventually make you on a close hauled, and as such you end up trimming the sails for being close hauled? For simplicity, let's say the wind is steady, doesn't change direction and the boat heading isn't changed.

Thanks in advance for my potentially confusing question.
Author:  mmiller [ Thu May 15, 2014 10:48 am ]
Post subject:  Re: Question about points of sail / apparent wind
Yes, as you increase speed, the apparent wind angle shifts forward which would cause you to either bear away or sheet the sails in more to keep the sails properly trimmed.
Author:  bmdumr [ Thu May 15, 2014 11:21 am ]
Post subject:  Re: Question about points of sail / apparent wind
mmiller wrote:
Yes, as you increase speed, the apparent wind angle shifts forward which would cause you to either bear away or sheet the sails in more to keep the sails properly trimmed.

Thanks Matt! You have confirmed what I thought. This is the fastest (ground speed) way to sail, correct? I'm also guessing the heeling force becomes greater as you approach a close reach.
Author:  ronholm [ Thu May 15, 2014 11:31 am ]
Post subject:  Re: Question about points of sail / apparent wind
This help any?


Image
Author:  bmdumr [ Thu May 15, 2014 11:35 am ]
Post subject:  Re: Question about points of sail / apparent wind
ronholm wrote:
This help any?

Thanks ronholm, never seen this illustrated with this sense of humor before :lol:
Author:  mmiller [ Thu May 15, 2014 12:38 pm ]
Post subject:  Re: Question about points of sail / apparent wind
Yes, fastest is beam to broad reach.

Travel the main out at least to the foot strap I'd think. If you are sheeted tight on the main and are having to sheet out to limit heel, travel out a bit more.

Flat to windward hull just kissing the surface is fast.
Author:  ronholm [ Fri May 16, 2014 5:59 pm ]
Post subject:  Re: Question about points of sail / apparent wind
I'll try and see if I can figure out how to pull some polar diagrams out of my GPS data this weekend..

Up to a 15mph breeze I bet the top speed is found closer to beam reaching... Conditions above that (20 mph + breeze) I'll bet you can max out at closer to a broad reach as you begin to use the crew weight combined with the bouncy of often both bows to keep it upright. Even with the extra wetted surface area I am certain more speed is found this way.. At least it sure feels like it. :mrgreen:
Author:  bmdumr [ Wed May 21, 2014 8:41 pm ]
Post subject:  Re: Question about points of sail / apparent wind
ronholm wrote:
I'll try and see if I can figure out how to pull some polar diagrams out of my GPS data this weekend..

Up to a 15mph breeze I bet the top speed is found closer to beam reaching... Conditions above that (20 mph + breeze) I'll bet you can max out at closer to a broad reach as you begin to use the crew weight combined with the bouncy of often both bows to keep it upright. Even with the extra wetted surface area I am certain more speed is found this way.. At least it sure feels like it. :mrgreen:


Ronholm, any luck on the speed data? Super cool if you did!
Author:  rehmbo [ Thu May 22, 2014 5:50 am ]
Post subject:  Re: Question about points of sail / apparent wind
Here's something you may find interesting
Image

In the diagram, the Hobie 16 would be similar to the old style Tornado (without a spinnaker)

What's labelled as the 18 ft skiff would be similar to an F16 or F18 with spinnaker

The 1/2 ton and 1 ton would be those miserably slow things you have to weave around :P

You can see on a beam and broad reach, the non-spin cats do pretty darn well.

One last point on reading the diagram - the distance from the center point to the line is your speed. If you extrapolate up or down to the horizontal line, that is your velocity made good (VMG is generally the portion of speed directly upwind or downwind on a windward leeward race course). Note that your fastest point of sail upwind is probably a bit further off the wind than you might imagine. While you're sails might be drawing properly at 35 or 40° true wind angle, it's not until you crack off to 45° or a bit more that you get your best VMG. This is called footing, and from what I've been told, boats like the H16, H17, and 18 do this very well.
Author:  rehmbo [ Thu May 22, 2014 6:13 am ]
Post subject:  Re: Question about points of sail / apparent wind
Found this one too. Not sure of the source.

Image

Should be noted that the curves change as a function of wind speed. Ideally you'd have plots at 5, 10, 15, and 20 knots so you would know exactly which point of sail is fastest at each wind speed.
Author:  Johnny Wildcat [ Thu May 22, 2014 6:18 am ]
Post subject:  Re: Question about points of sail / apparent wind
Nice graphs Jeff 8) I can usually tell how fast I'm going by the sounds my boat makes. It roars like a jet when I'm going really fast.

John B.
Hobie Wild Cat
USA 413
Author:  rehmbo [ Fri May 23, 2014 12:08 pm ]
Post subject:  Re: Question about points of sail / apparent wind
You're right! Helps me know where you are on the course ;-)
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