Re: Filippi carbon fin


Rob wrote:
I think you make adjustments to the turning capabilities of different
boats and their fins, just as you get to feel the way different boats
run in different parts of the stroke. Doing this may be more important
than changing fins, or maybe a person is supposed to do both.

In the fall of 04 I went from a Vespoli Matrix 27 to an Empacher C12.
VERY different boats.

The Vespoi had lots of rocker and was relatively beamy. It looked like
a boat to carry a sack of potatoes in but I was very fast in it. It
turned on a dime (or did it turn on a shilling?), lively at the catch,
much up and down with the bowball through the stroke. Coaches hate
this and think it signifies bad rowing--often it does of course.

The Empacher wants to go straight as is well known. At first it felt
dead at the catch; now I wouldn't say that. I've developed an earlier
power curve, partly in response to the boat (partly just better
rowing). If the Empacher isn't perky at the catch it's obviously
making up for that later on in the run of the boat. It's narrower in
the beam than the Vespoli, and the hull is conspicuously wider forward
of the cockpit.

I've been encouraged by many talented rowers to put a different fin on
it (or cut a triangle out of the existing fin, so that there's less fin
impeding the turn). But after awhile you get to know what to expect
and I'm really not sure I want to fiddle with anything now.

A bigger difference in the two boats is that the Empacher is very
stable in chop. I love the Empacher, make no mistake, but I don't
think one boat is faster than the other. I mean that!

I know I've strayed from the fin discussion but I want to bolster my
argument that the physics is all good, and all true, but our adaptation
to fins and the rest of our boats is a very important factor, too.
"It's not the chariot."

The paste below is back in the technical vein, from my good friend
Carlo Zezza, top 70+ sculler & great guy.

It's all aroma until the fin gets wet. Instead of
theory, need to try
different sizes and shapes, and see which goes best
for which conditions.

Here are some observations based on trial-and-error:

-- What's ideal for course racing isn't ideal for
head racing, and vice
versa.

-- it's easy to make a fin for course racing (just
needs to keep you
straight)

-- but hard to make a fin for head racing. The fin
needs to turn easily
("stall") but recover laminar flow quickly when side
pressure is released,
i.e. the boat stops yawing instantly when the oars
come out of the water.
Flat plates are poor for recovering laminar flow, a
foil section is much
better (NASAsmasa, it just needs to look right, with
no knife edges)

-- continuing from the preceding, the fin is high in
the water at the finish
when yaw recovery is needed: The foil section needs
to continue fairly deep
below the hull into undisturbed water, especially if
the fin is mounted way
aft

-- behavior in cross winds can be a major factor on
some courses (e.g. the
last 0.5k of the Schuylkill downstream). Ideally the
boat won't weather***
either way in a crosswind, i.e. crosswinds will just
drift the boat
sideways. Depends on fin size and location. Only
way to find out is to put
the fin on the boat and go looking for a stiff
crosswind

Logic says that forward mounted fins (King boats)
need to be bigger, and
small changes make less difference. If the fin is
far back (my Resolute)
the fin can be smaller with less wetted surface, but
small changes make a
big difference. Really.

That's my two-bits worth,

Aloha,

Carlo


I too made the Vespoli-to-Empacher transition (with a brief diversion
to Hudson) and my experience parallels Rob's, I agree with all of the
above, and have a few details to add:

(1) hulls with more inherent directional stability are probably less
sensitive to changes in skeg size than hulls that tend to wander more
(but thanks for continuing to use the stock skeg as that gives me at
least a prayer of beating you, Rob)
(2) a friend worked for Resolute and owns the Resolute HW 1x prototype.
It originally had THREE skeg boxes in it so they could test different
skeg locations. Even builders that do intensive design engineering
have to resort to empirical tests for some things.
(3) in agreement with Carlo's thoughts, this friend uses a larger skeg
for sprints and a smaller one for head racing

.

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