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[sjoormen]

At work we had bit of a fight over this: At what angle should be wind blowing to sailing boat with bermuda sails that would allow highest speed( faster than wind is blowing)
I looked at wikipedia, and it seemed somewhat logical, but is there simpler answer avaliable
Thanks in advance
http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind
 

[CJ1]

Often, a bermudan rigged monohull boat sails fastest when the wind is on the beam or slightly behind it. The boat designer will have a polar diagram for their boat to show exactly where this is.


Not many boats can sail faster than the wind is blowing and when they do, they then generate an apparent wind which becomes forward of the beam. So another answer to your question is that!


Lester Gilbert explains it well on his model boat website.


http://www.onemetre.net/design/VPP/PoorVPP.htm


A polar diagram looks like this:

[rickles23]

Hi,
 
Try 59.23 knot average with a 62.53 peak by Sailrocket a purpose built yacht.
 
Regards

[sjoormen]

So if I understand correctly it is possible but rare with usual boats and much faster speed could only be achieved with only few boats, which are built with that purpose in mind.

[rickles23]

Hi,
 
It depends on whether you want speed or comfort.
 
The faster you go in a boat the more uncomfortable it is and you don't have the essentials like toilets or cooking or even a drinkies cabinet.
 
Regards

[sjoormen]

Hi again,
 Well we were discusing only speed, or in which direction- regarding to wind- to sail, that max speed for boat could be reached. I have no sailing experiences whatsoever, so I thought I might ask here .

[CJ1]

So, in that case the simple answer is, for those boats that are designed to do it, the wind needs to be from the side.
Chris

[Colin Bishop]

As stated in one of the posts above, a beam reach is usually the fastest point of sail for a given boat. Some more explanation here: http://www.sailnet.com/forums/learning-sail/85744-why-beam-reach-near-fastest-point-sail.html
However the fastest speed a boat will actually go on a beam reach will be determined by the relative power of the sails against the boat's weight and hydrodynamic qualities. That is why the America Cup catamarans go so fast - there is hardly any boat in the water at full speed and they are literally almost flying.
 
Colin

[sjoormen]

Thanks, You cleared some thinks for me

[NFMike]

From the polar diagram above and my own feeling from sailing some years ago I think the fastest speeds are sailing a bit closer to the wind than beam on. Also a fast boat (ie. one that planes) makes its own wind to some extent so I'd expect the 'best' angles to be different for something like that as compared to a slower displacement boat.

[dreadnought72]

Hi Plague.

I think it only feels it.

Taking the above polar diagram as an example, and using the "20kt" wind speed setting, I've eyeballed (ang) and (vel) for the heading of the boat and the velocity it achieves, over water. These are listed below.

We know a moving boat causes an apparent wind from the addition of two vectors: boat speed and wind speed. This apparent windspeed (vapp) is listed from calculation, below, and it peaks in strength (as we'd imagine it might) at about 45 degrees from the wind.

However, you can also calculate the angle of this new apparent wind (beta), relative to the boat, and plot the difference in this angle from the angle that a stationary boat would feel (diff).

Job done.

ang  vel  vapp  beta  diff
  0  0.0  20.0   0.0   0.0
 10  0.0  20.0  10.0   0.0
 20  0.0  20.0  20.0   0.0
 30  6.1  25.5  23.1   6.9
 40  6.9  25.7  30.1   9.9
 50  7.3  25.3  37.2  12.8
 60  7.7  24.8  44.4  15.6
 70  7.8  23.8  52.1  17.9
 80  7.8  22.7  60.2  19.8
 90  7.5  21.4  69.4  20.6
100  7.2  20.0  79.3  20.7
110  7.2  18.8  88.9  21.1
120  7.1  17.6  99.5  20.5
130  7.1  16.4 110.6  19.4
140  7.1  15.3 122.6  17.4
150  7.1  14.3 135.6  14.4
160  7.1  13.5 149.7  10.3
170  7.1  13.1 164.6   5.4
180  7.0  13.0 180.0   0.0
Note the diff peaks in that area of a beam reach to a broad reach between a (true) angle of about 90 and 120 degrees. In my dinghy sailing experience, this is the point at which you can most easily plane a boat - not quite exceeding wind speed for a small dinghy, but getting pretty close, and certainly exceeding the hull speed. And it's here you really notice you have to harden the sheets towards a close reach: all the effects of that greater diff.

So what's fastest? Big vapp or big diff?

For a sail-powered craft you might think that the more wind the merrier, more energy = more speed, and therefore sailing into the wind is best. But sailing into the wind, especially in a small boat, is hard work. You're fighting waves, have to be totally in control of heading angle - any luff losses power instantly - and in cases of upwind sailing the hydrodynamic qualities of the centreboard are more critical.

I'm going to bet - and especially at model sizes and for displacement hulls - a beam reach to broad reach will always get you maximum speeds, and you'll be sailing with the sheets heading for close reach or close hauled.

Andy

[malcolmfrary]

http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind


Chapter and verse, and enough footnotes to create even more confusion.