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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Sailboat maximum airespeed
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Thread: Sailboat maximum airespeed Reply to Thread
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Topic Review (Newest First)
01-18-2012 11:38 AM
Barquito
Quote:
All of these three choices will reduce healing but also reduce the force attempting to move the boat forward.
I'm not sure I agree with this part of your analysis. With higher wind speed, a reefed sail will produce more force in the forward vector (than a reefed sail in slower wind). So, assuming you can maintain good sail shape, a tripple reefed main and a storm jib in 50k wind will produce a lot of power. The problem is, that it will also produce a lot of heeling moment. There is also is a resistance vector from the wind that increases... OK my head hurts, I am going to fall off and run with the wind.
01-17-2012 09:47 PM
davidpm Patrick
I have experienced the same effect many time. The following is a mental experiment to try.
Your boat is trimmed properly for wind coming from 60 degrees off the bow.
The boat is not moving (lets assume it is held back for some reason) This not moving constraint is not necessary but makes it easier to visualize.
The wind starts low and gradually increases

The wind hitting the sail exerts a force against the mast (the force against the mast is what ultimately moves the boat).
That force is composed of two vectors.
One vector attempts to tip the boat over.
One vector attempts to move the boat forward.
The weight of the keel resists the vector to tip the boat over.
As the wind increases the force to tip the boat will increase.
At some point the healing of the boat will be excessive.
At that point you have two three choices.
Spill the wind by easing the sheets
Reduce sail by reefing
Or do both
All of these three choices will reduce healing but also reduce the force attempting to move the boat forward.
At some point the force moving the boat forward will be so low it will not be enough to overcome all of the forces that exist to keep the boat stationary.

It is pretty obvious that even in perfect conditions on a beam reach with flat seas and steady wind there is a minimum amount of sail area required to got any boat to move at all. IE a clean-ex will not sail a 30 footer.
Also as the wind increases and the sail is reefed nothing improves but lots of things detract from efficiency.
The sail bags (unless you have a hi-tech racing sail)
Your halyard stretches.
A reefed sail is seldom the perfect shape.
The mast bends (can be a good thing but often not.)
Waves and chop builds
currents build
All these things slow you down.

I remember being disappointed about how badly several boats would point when the wind exceeded their sweet spot, usually about 14 knots for Catalina's 25,27,30.
A boat that would point through an arc of 90 degrees in perfect conditions would be hard-pressed to manage 120 if it had to be reefed.

Your experiencing the same thing but instead of pointing it is being manifest as a slowdown.
01-17-2012 09:15 PM
tommays

As it gets towards 40 knots we are pretty over-powered with a #4 jib and a deeply reefed mainsail And it's pretty much time for the storm jib

The biggest issue is the sea state in the picture it was pretty flat due to the wind direction on the sound

I have been in the same wind speed in and area that has the space to build the sea state to the point it just COMPLEATLY beats the crap out of the boat and crew in no particular order
01-17-2012 07:20 PM
casey1999
Quote:
Originally Posted by -OvO- View Post
Time to build a flying vertical wing...
Done:
Sailing Video of the Week - Flying a Sailboat | YachtPals.com
01-17-2012 07:17 PM
-OvO- Time to build a flying vertical wing...
01-17-2012 07:02 PM
GeorgeB Patrick, you need to find a copy of the polar diagram for your boat. This will tell you the maximum speed potential for windspeed, point of sail and sail size. Remember, as a displacement boat, you are constrained on the top end by your theoretical hull speed. I donít know what boats you sail on the Bay, but I have had the experience of going into horizontal stalls a couple of times on light displacement boats where a gust pined us over and we didnít have enough displacement/ momentum to carry forward boatspeed. Wound up getting dragged sideways a little bit. On our family cruiser, we do not have the rail crew to hold the boat upright and the constant feathering and square waves/chop knocks some boat speed off.

Most importantly, where were you sailing and what type of boat? I had to take care of some family business and wasnít able to get out on the Bay. Sounds like I missed a good one.
01-17-2012 05:51 PM
Faster I think the greater hindrances are hydrodynamic drags... low drag multihulls, esp those on foils are going to go much faster than our lead bombs.

Could be those craft (and ice boats) may get a chance to run into the aerodynamic limits, but since we're working in two distinct elements I think the aerodynamic ones won't come into play for the average boat....

This question is probably a good academic one, though, when dealing with extreme winds in the 100 Knt + range...
01-17-2012 05:40 PM
curtcee
Quote:
Originally Posted by casey1999 View Post
That's a good article. Thanks for posting it.

Curtis
01-17-2012 05:01 PM
casey1999 Sailing faster than the wind - Wikipedia, the free encyclopedia
A good link
01-17-2012 04:59 PM
CapnBilll In any point of sail there reaches a point where the forces exerted on the sail needed to further increase boat speed will only blow out a sail.
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