TWL: RE: Duck Speed
Of course the 'down' side of utilizing the feathers would be directly
impacted by the age and rigidity of the feathers used. 'Down' would
certainly improve the heat retention within the bowels of the vessel
(certainly a consideration in northern climes), but imagine the masses of
the fluffy stuff it would take and the maintenance intensiveness of gluing
them one at a time (which one would certainly have to do to ensure the
overlap was sufficient). I guess they could be butted against each other
and caulked between them--that way if there was any expansion during drying,
it would make a heck of a seal. Whoa wait a minute--Seal ! Now there's a
concept! Sealskin!!!!! Why now, now that would certainly work. I'll get
back to you on that.
I was muddling over Paul's feather concept last night and decided (albeit
late tho' the hour was when I arrived at this revelation) that there would
be no way I could maintain the integrity of my displacement hull once I
completed the feather installation because the darn thing would never sink
to the waterline and float. The feathers would certainly add sufficient
bouancy to offset the weight of the General and I would either have to
attach sails (since it would now be heeling one way or t'other) or start
removing stuff, like the cabin or the lazarette or most certainly the canned
stuff my Admiral has stored on board.
To verify this theory, as we must do during experimentation, I went to the
attic and drug down several stored boxes containing foul weather gear I
brought with me from up North (knowing it may someday snow here) and fetched
an old down jacket I used during deer hunting (I say hunting, not
harvesting--hunted a bunch, but never found any) and anyway--that's another
story--took that jacket out back, turned on all the lights around the pool,
strapped the jacket to a plastic chair (known to have floated before) and
tossed it in the pool. Eurika!!!! The chair rode a full two inches higher
in the water than in did before adding the jacket.
Next, my calculating mind went to work on area, mass, and weight. At two
o'clock this morning, I arrived at my conclusion. If I attached the
feathers to my displacement hull up to the waterline and lowered the General
into the water from a sling, it would be repelled by the water at such
force, my boat would hover approximately 1/4 inch above the surface of the
water. Hey! Now I'd have a modified planing hull--imagine the speed!!!
Turning might be the trick though.
Oh well, that brings us back to Sealskin...or banana peels. I'm going to go
get a sliderule--back later!
Regards,
Jim Renforth
M/V General Brock
Valrico, FL
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From: PBrowne900@aol.com [SMTP:PBrowne900@aol.com]
Sent: Sunday, September 26, 1999 6:35 PM
To: trawler-world-list@samurai.com
Subject: TWL: Duck Speed
In a message dated 99-09-23 14:20:36 EDT, you write:
If I chose to go the feathers route to increase my hull speed,
would there
be a down side? If so, what could I expect?
Ahoy there Dick,
A couple of the TWL scientific staff have suggested that the
practical speed
of a trawler can be increased through the addition of feathers. I
must admit
to feeling some degree of responsibility for this, having introduced
the
subject of ducks to the list a while ago. So before you bought a
ton of
feathers for your next bottom job, I thought I should double check.
After
all, the essence of the scientific method is to verify a theory by
experiment.
The first part of my work entailed a few dry dock (dry duck?)
observations.
Tempting a threesome of mallards out of the pond with bread, I
observed their
underwater lines. The main observation was that these ducks were a
full
displacement design, definitely not semi-displacement or planing.
The shape
of their little buttocks, sweeping in rounded lines to their pointed
little
sterns, and their complete lack of squared-off transoms made that
clear.
Placing a ruler on the ground, and observing them when they
re-launched,
allowed me to estimate their waterline length with confidence. I
put it at
11 in, close to Don Dodds' original estimate of a foot.
The second part of my work involved actual speed measurements. To
do this, I
adjusted my sliding door so that the width from frame to frame was
68 inches,
exactly the same as the distance between two porch posts. In this
way I
could sight along two parallel lines formed by the door frames and
posts. I
would wait until a duck swam by, and time how long it took for
him/her to
cover 68 inches. My objective was to observe their practical cruise
speed.
I had no interest in their top speed. I wanted them in trawler
mode.
The wind was calm. The pond was smooth, no chop. I hunkered down
and
waited. The cold, hard weight of my stop watch feel reassuring in
my hand.
It took a bit of patience, but I got some good measurements. I
timed four
ducks. All four were in trawler mode, not rushed, looking around
and
enjoying themselves. They came in at 3.8, 3.9, 3.9, and 4.2 seconds.
A bit of math shows that their speeds were 0.88, 0.86, 0.86, and
0.80 knots,
for an average of 0.85 knots. Taking a waterline length of 11
inches, the
theoretical hull speed for these ducks would be 1.28 knots.
Disappointing
results indeed for fully feathered hulls! They were only cruising
at 0.89
times the square root of their LWL in feet. You can draw your own
conclusions, but I am feel obligated to suggest that the Dodds
Postulation is
seriously flawed.
Now some listees may think to themselves that perhaps old Browne
doesn't have
enough to do, but consider the legal bills that George would face if
a major
boat builder were to launch a new line of feathered trawlers based
on list
advice, only to find that that advice was unsubstantiated. Besides,
it was
raining on and off today - can't work on the boat.
Scientifically yours,
Paul Browne
Boatless in Tampa