Subject: Re: [harryproa] Hull Speed
From: "Rob Denney" <proa@iinet.net.au>
Date: 11/9/2006, 8:10 AM
To:
Reply-to:
harryproa@yahoogroups.com.au

G'day,
 
Sorry, this slipped through the net.
 
There does not appear to be a hull speed hump on Rare Bird, nor does it appear to form a displacement wave at 1.34* sqrt of wl which is 7.6 knots.   The windward hull has a length to beam ratio of 10:1 at rest, so I would not expect one.  As the waterline gets finer, so it is less of a problem. 
 
On Elementarry the ww hull is even finer, and lifts out at lower wind speeds.  There does not appear to be any difference in the wave train from 3 people sitting on the windward hull so it is heeled to windward and going 5 knots (hull speed) or the hull just skimming the water at 15 knots. 
 
Neither hull of either boat seems to produce much in the way of waves.  I have not done any theoretical speed calculations so cannot say whether it matches them or not.  I did do a tow test on Harrigami and it had similar drag, up to 12 knots to a 14' planing dinghy, according to Bethwaite's book, and within the limitations of one person reading the scale and steering the tow boat simultaneously.
 
regards,
 
Rob
 
 
----- Original Message -----
From: jjtctaylor
To: harryproa@yahoogroups.com.au
Sent: Friday, November 03, 2006 9:38 AM
Subject: [harryproa] Hull Speed

Rob, ...... or anyone else on the forum...

Ever figure out what is hull speed for an asymmetric proa design ?  Or how the current
mathematical approximations are affected by the difference in hull lengths and underwater
profile ?

Likely the lack of on the water experience and measurement equipment may affect the
possibility of evaluating the issue.  But, was curious if before "Rare Bird" was or is sold off
did any acurate test made to compare predicted versus actual performance?  Same goes
for the elementaries although not sure whether they are displacement, planing or mixed
hull speeds.

JT


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