AUGUST 19, 2025
DRIFTING OVER THE
FINISH LINE
Another afternoon of discouraging light wind showing on the
flags. As we left the harbor at 5pm,
there was a healthy Northwesterly blowing clear in to the S/F mark. We watched
as the Easterly seemed to build and pushed the Northwesterly further out to
sea. We set an offset mark and called
for course Echo 4. When setting the start
line, trying to anticipate all outcomes with the wind, we set it between square
to the Easterly and square to the Northwesterly if it filled in. Sticking with the Easterly course, as we did,
the line was favored at the S/F end of the line and most boats, that were
fortunate enough to be even in a light breeze started at that end.
Fleet A had a couple of boats that were OCS, but did not
gain much because of the light wind.
Fleet B got off to a clean start with many boats right on the line right
on time. On PAD we were sitting in the
only part of the whole bay with zero wind and were not able to cross the start line for about 30
minutes. It was obvious the Easterly was
not strengthening as the race progressed, so we used regatta hero to announce a
shortened course to end at Blacks. We
also announced the shortened course over the radio.
It was a challenging evening of sailing and I got many
thanks from sailors at the club for shortening the course. I was surprised to see how many boats were able to drift over the finish line.
The track for Fleet A can be reviewed at:
The track for Fleet B can be reviewed at:
 |
| JUST ANOTHER DRIFTER |
PLACE BOAT PHRF ET CORRECTED
TIME
FLEET A:
1 TRUE
LOVE(OCS) 72 20:48 20:06
2 PACIFIC
HIGH 96 26:49 25:53
3 DUET 140 28:05 26:43
4 WATTS
MOORE 150 30:58 29:30
5 ABORIGINAL 33 33:37 33:17
6 ROSIE
(OCS) 162 38:04 36:29
7 ABSOLUTE
25 48 37:38 37:10
8 MAGIC 141 41:49 40:26
9 WIND II 213 45:16 43:11
FLEET B:
1 BIG MAC 222 36:24 34:14
2 ZOOP 144 39:09 37:45
3 TOAD 150 39:16 37:48
4 GOLD RUSH 126 40:38 39:24
5 SIMPATICO 165 44:42 43:05
6 WIND
GODDESS 165 54:47 52:10
ZOOP SCOOP BY PAUL TARA
A HORSE OF A
DIFFERENT COLOR
Big boats are relatively faster in breeze.
Little boats are relatively faster in light air. Why? In breeze, a boat
continually displaces the volume of its hull, creating a bow wave and a stern
wave (the water has to go somewhere, right?) The boat is essentially
“trapped” between the crests of its two waves. The laws of physics state
that wave speed is directly proportional to wave length; the longer the
distance between the crests, the faster the wave travels. (In the open ocean a
tsunami travels at the speed of a commercial airliner.) So, the longer
the boat’s waterline, the faster the “trap” (with the boat in it) travels,
until it reaches the theoretical maximum of the waves, or “hull speed” (1.34 x
square root of the waterline = speed in knots). But, in light air, boats
don’t sail fast enough to make a wave trap. The water has time to
accommodate the boat and just slides by (like molasses, on Tuesday).
Then, skin friction, becomes the critical factor. This can be expressed as
the sail area/wetted surface ratio, a largely mystery number, due to the
difficulty of calculating it without sophisticated design software.
(Homer Lighthall and I once joked that it could be done by weighing the amount
of bottom paint for each boat. Though that really wouldn’t be accurate,
since wetted surface changes with angle of heel.)
Tuesday’s drifter supplied an interesting
example of this in action. In the A Fleet, True Love, a blue Express 37
(PHRF 72), pretty much had her way with Aboriginal, a Sydney 38 (PHRF
33). Both boats got reasonable starts with clear air. But it soon
became apparent that the Express had both speed and height on the Sydney,
forcing her to tack away into less breeze and adverse swells. The Sydney has a
5’ longer waterline and a higher SA/Disp ratio (25.4 vs 22.4). What
gives?
Is PHRF wrong? Nope. It just grades on a curve,
and is based on average speeds on all points of sail. What’s important to
remember is that the Sydney is dragging around 5 feet more boat and a deeper
keel, factors which do her
absolutely no good in light air but make
her fast in a breeze. Plus, that narrow bulb keel is susceptible to stalling at
low speeds.
However, the key factor is that the Sydney
is a one-design with a class legal 105 percent, minimally overlapping jib,
whereas the Express is not, and was using her 150 percent light air
genoa. SA/Disp ratios are calculated using a 100 percent fore-triangle.
Add in that 45 percent more overlap and, voila, True Love is a shorter
but lighter boat, with less wetted surface and more horsepower.
Thank you Paul.
NEXT
TUESDAY IS THE LAST TUESDAY OF THE MONTH WHICH MEANS BARBECUE AT THE CLUB AFTER
THE RACE. BRING YOUR BEST GRILLING FOOD.
EVEN IF YOU DON’T HAVE FOOD TO SHARE SHOW UP FOR THE FESTIVITY, THERE IS
ALWAYS FOOD BEING SHARED.
Barry Keeler
Sailing Pair A Dice
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