SailNet Community - View Single Post - Why is beam reach (or near to it) the fastest point of sail?
 View Single Post
Old 04-04-2012
Senior Member

Join Date: Nov 2007
Location: SF Bay area
Posts: 1,940
Thanks: 9
Thanked 7 Times in 6 Posts
Rep Power: 10

Re: Why is beam reach (or near to it) the fastest point of sail?

Quote:
Originally Posted by brehm62 View Post
No, you seem to be getting confused about relative versus true wind. If the water is stationary and the wind is 5 knots then the true wind is 5 knots. If the water is moving at 5 knots and the wind is stationary but the boat is moving with the current then the true wind is still 5 knots.

True wind is with regard to the water (because that is what the boat is sailing in).
Relative wind is with regard to the boat.
These two are not the same.
I guess I could be completely wrong. I'm pretty sure that true wind is relative to the land, and apparent wind is relative to the boat.

Quote:
Let's say the wind is blowing out of the north at 10 mph.
Now, let's say you are on a beam reach traveling east at 10 mph.
The apparent wind is 14.14 mph out of the north east.
So, lets make some naive assumptions.

When we started we couldn't sail directly north because that would have been into the wind. But now with the relative wind out of the NE we should be able to turn straight north and have the wind at 45 degrees and keep sailing, right?

No. That would clearly be impossible since the true wind doesn't change.
You're arguing something I never said. I never suggested that apparent wind would remain constant if the boat alters course or speed. Such a claim never came up in this thread, by me or anybody else.

Quote:
To be honest I find it somewhat amusing that you would suggest that energy is related to relative wind rather than true wind. That would be a pretty obvious violation of conservation of energy.
I'm glad you're amused. It's a pretty pedantic point, and I stand by my words. If you want to argue it, maybe let's do it in another thread without further sidetracking this one. Since you agree that force is relative, just pretend I said "force" in that paragraph.

s/v Laelia - 1978 Pearson 365 ketch