Re: [Paddlewise] Pro's and Con's of the "Swede Form"

----Original Message-----
From: John Winters <735769_at_ican.net>
To: 'Paddlewise' <paddlewise_at_lists.intelenet.net>
Date: Saturday, May 29, 1999 7:38 AM
Subject: Re: [Paddlewise] Pro's and Con's of the "Swede Form"


I wrote:
>>If the waves are only the result of drag forces rather than a contributor
>as
>>well how come we don't get the same drag in a uniform fluid (such as
>>underwater). And why does the imposition of another interface between
>>different densities of water (such as fresh water overlaying salt water)
>>create wave at this interface and add more drag to a hull?

John responded:
>The wave making resistance is the net fore and aft force acting on the hull
>due to fluid pressures acting normally on all parts of the hull. When a
>body travels at or near the surface the variation in pressure causes waves
>that alter the pressure distribution and the resultant manifests itself in
>wave making drag as seen in the waves created.

I'm still having trouble seeing this.There still must be an altered pressure
distribution underwater (but without creating any waves) and there is no
"wave" drag then. One of the reasons submarines can be so fast. If the waves
created alter that pressure distribution in some other way and cause drag
(as you seem to have said) that would seem to indicate that the waves
(altered pressure distribution) was causing the drag.

<Snip>
John wrote:
>Yes, I read similar comments and still have trouble with the "climb"
>business. On a purely logical basis how you can climb something you create
>continuously for, as observation of a boat getting up on a plane show
>reveals the bow wave gets smaller as the boat rises. if you climb it it
>should remain until you get to the top (how can you climb something that
>just keeps getting smaller and if so are you climbing or is the bow wave
>just getting smaller

Okay, at some point for speed to get higher the boat must climb higher (and
also out of that even deeper hole it sank into (due to Bernoulli). As it
climbs higher the bow wave is reduced because there is less draft pushing
through the water. This reduces the part of the total drag that is due to
wave creation. So while technically one may not be climbing over the bow
crest it still looks to me that we had to climb out of the wave trough as
well as the hole in the water that was just due to the boats displacement.
This acceleration vertically requires energy (which my water-skier jumping
off the pier didn't have to do) so there is additional energy expended
climbing--beyond the considerable energy needed to maintain the elevation
against the pull of gravity once you get up there.
Anybody have any problems with that explanation?

Matt Broze
www.marinerkayaks.com


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