Message-Id: <199711191257.HAA48132@onlink4.onlink.net>
From: "John Winters" <jwinters@onlink.net>
To: <baidarka@lists.intelenet.net>
Subject: Re: Skin Boat and Hard-shell
Date: Wed, 19 Nov 1997 06:38:59 -0500
Stefano wrote;
(SNIP)
>
> A long list of failures is available a very high levels with this
> approach. Quoting John Dowd, an american cup sindicate was truely
> embarassed when discovering through tank testing that their project was
> performing better when reversing that on any other point!
This story is cute but not necessarily indicative of anything but the
ignorance of the designer and the fatuousness of the man who thought it was
significant. Michel showed that wavemaking resistance will be identical
for a body moving through a fluid regardless of which end is forward. (back
at the turn of the century) What changes is the resistance to waves (not
tested in this instance) the controllability (also not tested in the
instance) and the form resistance (not a variable because the factors
affecting form drag were almost identical regardless of the direction of
travel in this instance. Like so many things, it is fatuous to draw
conclusions about an event unless you have more complete information.
> Now that is extreme, and numbers can truely work to compare processes
> and in our case design.
What the test proved was that Michel was correct. Isn't it nice how science
works? It is always interesting that the failures of scientific efforts are
so humorous but all those trial and error mistakes get neatly shoved under
the carpet..
>
> But we can use and develop also INDICATORS. This means that looking at a
> boat design, an experienced paddler can TELL although with approximation
> (just like through models) how it will perform, and some times come very
> close to reality.
Let me tell you a true story. Some years back we built two canoes from the
same mold and of the same construction. One was red with wood trim the
other was white with aluminum trim. We then told a group of expert paddlers
that there were differences in hull shape and that we wanted them to test
the boats and tell us which they thought was the better boat.
Surprise. The red boat was judged to be the fastest and most responsive.
similar tests have been tried in all manner of platforms. So much for the
vaunted accuracy of the personal opinion of experts. It has gotten so the
expert paddlers don't even want to participate in my tests anymore because
it is so embarrassing.
>
> BWL, block coefficient, wetted surface are all INDICATORS.
No, the are quantifications of shape.
>
> Maybe we just need to add to the list FLEXIBILITY OF HULL as an
> indicator of performance in rough seas and try to devise a system to
> calculate its influence.
This is exactly what we many researchers have been trying to do. The
difference here is that they don't have the answer first. Indeed, this is
the difference between the spiritual approach versus the scientific
approach. The one has answers, the other has questions.
>
> I know a chap that designs professionally olimpic row boats (eights and
> the like)
>
> He builds 1/5 scale models, in scale also for weight and all other
> parameters, then drags the models off a long pole mounted sideways on a
> catamaran so that the drag of the cat does not affect the model. Then he
> measures RESISTANCE of the models with a sensitive dinamometer which
> can appreciate differences in grams (fractions of ounces) and gets
> results.
>
> You would be amazed at how these test brake current knowledge ideas and
> design shapes, namely in the appendixes drag which seems to be a
> critical issue.
Your friend is doing what hydrodynamicists have been doing for centuries. I
am looking forward to his results. As the designer of some Gold medal
winning rowing shells I am always interested in new discoveries.
>
> Bu the way, the italian team has done pretty well in rowing in the past
> decades...
As has the Canadian team.