In article s.com,
llid says...

"Jessica B" wrote in message
...
On Thu, 24 Mar 2011 05:39:14 +0700, Bruce in Bangkok
wrote:

On Mon, 21 Mar 2011 20:35:30 -0500, CaveLamb
wrote:

Jessica B wrote:

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.



But how MUCH longer does the waterline get?
Seldom more than a few inches at most.

As for the other, it's called current.
And if you are going against it, slower than the current is running,
you go backwards...
What fun, huh?


The long overhangs was a relic of one of the old racing rules that
penalized long waterlines. So, the crafty people built a boat with a
very short waterline and sailed it heeled and had a effective
waterline much longer then what was measured for handy cap rating.

Current is only a real help in the few instances where it always runs
the same way. The more usual conditions have it going one way for a
half a day and the other way for the other half. Net help = Zero.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

At first someone claimed that the waterline difference would be tiny.
I found to be what seems a recent photo where that's not the case, and
now you're claiming it's a relic? I don't get that. Either it can be a
factor or it can't be.

Yes, I get that current is only a real help in a few instances. What
about the gulf stream example? I don't think that changes direction
does it?



The Gulf Stream proper always sets the same direction. The only thing that
can and does change is the loop currents which are eddies off the sides that
gyre around and can even set in the opposite direction of that in the axis
of the Stream.

Bruce is often confused. He's even confused about the tides in my part of
the world and probably in his part of the world as well. There are two high
tides and two low tides a day here. That means in areas where there is a
tidal flow the current switches approximately every six hours - not twice a
day as Bruce said.

Furthermore, his conclusion about net help = zero is also flawed for a
couple of reason. 1) off soundings (in deep water) there are no tidal
currents as they are a shallow water phenomena. 2) an experienced sailor
departs and arrives 'on the tide' which means with a favorable tidal current
(astern) so there can be significant gains especially in real parts of the
sailing world where there are diurnal tides (two highs and two lows a day).
Bruce is talking about semi-diurnal tides. He thinks pretty much like your
typical lubber, I'm afraid.

I'm afraid you've got dirurnal and semi-diurnal tides mixed up. It is
semi-diurnal tides that have two highs and two lows per day. Diurnal
tides have only a single high and low in a day.

"Atlantic Ocean (in Atlantic Ocean: Tides)
....of the Atlantic tide are influenced by a combination of complex
factors, which include coastline features, seafloor topography, and wind
and current patterns. By far the most prevalent tidal type is
semidiurnal, which is characterized by two high and two low tides per
tidal day (lasting about 24 hours and 50 minutes). Semidiurnal tides
occur along the entire eastern margin of the Atlantic and..."

http://www.britannica.com/EBchecked/...midiurnal-tide


"The geometric relationship of moon and Sun to locations on the Earth's
surface results in creation of three different types of tides. In parts
of the northern Gulf of Mexico and Southeast Asia, tides have one high
and one low water per tidal day (Figure 8r-4). These tides are called
diurnal tides."


Here on the West Coast we get mixed tides:

"Many parts of the world experience mixed tides where successive high-
water and low-water stands differ appreciably (Figure 8r-6). In these
tides, we have a higher high water and lower high water as well as
higher low water and lower low water. The tides around west coast of
Canada and the United States are of this type."

http://www.physicalgeography.net/fundamentals/8r.html





Bruce is also misinformed about the great ocean currents (of which the Gulf
Stream is a notable example) most of which always set in the same direction
day in and day out, year in and year out. The changing tides don't affect
these currents or affect them very little; they most certainly don't affect
the direction of flow.

Your instincts are good, Jessica B. Don't let Bruce pull the wool over your
eyes.


Mark Borgerson