[Paddlewise] Loading

Ralph wrote;
(SNIP)

>Which brings up the question of payloads and how accurate they are.  The
>Klepper single claims 550 pound payload!!!  Can that really be?  I know
>it can carry a lot, but that figure is a lot too!
>
>I suppose payload limits may be a matter of how much freeboard you feel
>comfortable with and whether you want to supplement it by wearing a
>snorkel :-)
This business of payloads presents a problem because few designers actually
design around a payload and few builders actually publish realistic load
ranges. By "realistic load range" I mean a load range at which the boat
will be safe and still perform as intended. I know of no easy answers but
in an effort to provide some simple guidelines I studied the boats in my
database and compared paddler perceptions with displacement.
Hardly science but this is what resulted.
It seemed that good paddlers could notice (in a crude way) a change in
performance within a range of +/- 5%. My reading into Psychokinetics
suggests that I was overly optimistic).
Using this as a base and recognising that a whole lot of measurements might
not be available or convenient I created a table based on this information
and a form factor called the "Fatness ratio". The fatness ratio is the
volume of displacement divided by (0.1* waterline length)^3. Since the
performance range seemed to fall within fatness ratios of 0.95 and 1.6 I
set those as range limits leading to the following table;

WL Length        12     13     14     15      16     17
Low limit          105    133   166   205     249   298
High Limit        176    224   280   345     419   503

Of course, you all will recognise that boats don't become instant water
pigs when outside the range. It could be called a "fuzzy" range. I don't
pretend that this guarantees anything but it might be a useful guide where
nothing else exists. There was a short article that went with the table
(and a graph of the table but you all have spreadsheet programs and can
make up your own graph labelling it "John Winters' Absurd Theory of
Loading").
Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/





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