"Jessica B" wrote in message
...
On Thu, 17 Mar 2011 13:07:57 -0400, "Wilbur Hubbard"
wrote:

"Bruce in Bangkok" wrote in message
. ..
On Wed, 16 Mar 2011 16:02:48 -0700, Jessica B
wrote:
snip


Ok... so if you have boat that'll go 10 mph and the reverse tide is
pulling you at 5 mph vs. you have a boat that'll only go 5 mph....

You are still looking at speeds in excess of what the "normal"
cruising boat is capable of sustaining for any cruise.


No Jessica is NOT. For example, my fast, blue water yacht, "Cut the
Mustard"
made a passage from Mobile Bay to Egmont Key (Tampa Bay). The time from
sea
buoy to sea buoy was 36 hours. The distance was 300 miles.

300 divided by 36 = 8.3 mph average! The LWL of my fine yacht is 22 feet.
Theoretical hull speed is only about seven knots. But, as you can see, the
theory doesn't always describe fact. So, Jessica is not talking speeds in
excess of normal. If my small yacht can average 8.3mph then imagine the
speeds a fast sailing yacht with a LWL of forty feet could average.

Now, Bruce, if you had ever sailed a real fast cruising boat and not that
big fat rotten old tub you live at the dock in you might have gotten
around
the world in half the time it took you just to get to Thailand.


Wilbur Hubbard


Hmmm... well, I looked up theoretical boat speed... 1.34 x the root of
LWL. But, I read that when the boat leans (heels) then the LWL would
get longer, so the theoretical speed would go up right? Also, what
about the water moving. If it's going in the same direction, then that
would decrease the time you spend traveling.


Ding, ding, ding!! You are correct, Jessica B (I guess the B stands for
'Brilliant'. But, it won't go up much as the multiplier is the square root
of the extra distance.

And, yes, currents can and do make a significant difference. Consider a
sailboat with a theoretical hull speed of five knots sailing north in the
axis of the Gulf Stream. Let's say it has a fair wind and is doing five
knots through the water. Now, the current in the axis sets north about 3-4
knots so that boat sailing north could well have a speed over the ground of
8-9 knots and if this keeps up for 24 hours the benefit of the current is
very apparent. So, unlike the motor heads who just plow through the water.
willy-nilly, full speed ahead and damn the torpedoes, ignoring the affects
of wind and current, a sailboat captain must be more aware and more
intelligent of all factors affecting course made good.

Wilbur Hubbard