On Sun, 13 Sep 2015 11:47:17 -0400, Wayne.B
wrote:

On Sat, 12 Sep 2015 14:24:12 -0600, Paul Cassel
wrote:

On 9/12/2015 1:04 PM, Wayne.B wrote:


Heading 150°T, with a resulting COG of 140°T, we were on a beam reach - the
fastest point of sail - and thrilled with our progress. Depending on which
of our speed indicators you believe, we were making 9.8-12.0 knots STW.
Approaching the edge of the Gulf stream meant we had a slight current
against us, but we still averaged more than 7 knots SOG, despite an apparent
wind of under 10 knots.


oops. My previous message which I tried to recall was wrong. The formula
for hull speed is (sqrt Lwl)*1.34 yielding a hull speed for you of about
8.5 kts. I still think either 9.8 kts much less 12 kts unrealistic and
both demand a calibration, but the embarrassment is mine.


===

I'm guessing that he might have been quoting SOG from a GPS and
getting some boost from the Gulf Stream. My old Cal-34 used to exceed
hull speed under sail fairly frequently however. It's not an absolute
limit, just a point where you need a lot more power to start climbing
the bow wave.

Going up and down the Malacca Straits there can be a pretty strong
tidal current and it isn't unusual to read a speed of, maybe 4 K
through the water on the log and a SOG of 1 K on the GPS. Or zero
through the water and 3 or 4 K SOG, for that matter :-)
--
Cheers,

Bruce