[PCW] 'Sno Dog performance

[D C *Mac* Macdonald]

Hi, Bob.

I have no idea as to why the performance of Henry Clew's
PDQ 34 seems to be so linear.  I am just mathematically
inclined and I noticed an apparent linearity.  I just used a
calculator to check out the extent of linearity and decided
to share it with the group.

I would say that the linearity indicates a happy marriage
of design elements, whether intentional or accidental.

In any event, I would say that the linearity in 'Sno Dog's
performance is highly desirable.

Mac in Oklahoma City



----Original Message Follows----
From: Robert Deering <deering@ak.net>
Reply-To: Power Catamaran List <power-catamaran@lists.samurai.com>
To: 'Power Catamaran List' <power-catamaran@lists.samurai.com>
Subject: Re: [PCW] 'Sno Dog performance
Date: Tue, 01 Aug 2006 20:16:44 -0800

Mac,

I'm wondering what portion of your ratio is a result of the prop
(pitch/dia/cup...) and engine (torque/hp) characteristics as compared to
the hull characteristics?

Is the linearity due to a careful match of hull, engine, and prop?  Or
is it just happenstance?  Or is it maybe just a meaningless number?
Seems to me that this number gives some indication of the performance of
the whole propulsion system (hull/engine/prop) but I'm not sure what to
make of it.

Any insights you can share?

Bob Deering
Juneau Alaska

-----Original Message-----
From: power-catamaran-bounces@lists.samurai.com
[mailto:power-catamaran-bounces@lists.samurai.com] On Behalf Of D C
*Mac* Macdonald
Sent: Tuesday, August 01, 2006 5:12 PM
To: power-catamaran@lists.samurai.com
Subject: Re: [PCW] 'Sno Dog performance

Hi, Henry and all.

I did some calculations from your performance figures
because it appeared to me that the speed/rpm ratio
was surprisingly linear.  I have converted your chart
to SPEED/1000 RPM ratios shown below.  Although not
perfectly linear, they show up much more so than most
boats.  Very interesting indeed.  I know that these don't
translate at all to fuel economy due to the degree of
loading of the engines, it would appear that increasing
speed when it is needed at least won't put you into the
bankruptcy courts!!!

.________________________________.
|    RPM       SPEED      RATIO  |
|  (1000)     (Knots)            |
|________________________________|
|    1.0        4.8        4.80  |
|    1.2        5.6        4.67  |
|    1.4        6.6        4.71  |
|    1.6        7.5        4.69  |
|    1.8        7.8        4.33  |
|    2.0        8.1        4.05  |
|    2.2        8.6        3.91  |
|    2.4        9.2        3.83  |
|    2.6       10.9        4.19  |
|    2.8       12.7        4.54  |
|    3.0       14.5        4.83  |
|    3.2       15.7        4.91  |
|    3.4       17.0        5.00  |
|    3.6       17.9        4.97  |
|    3.8       18.6        4.89  |
|________________________________|

D C "Mac" Macdonald
m/v Another Adventure
Grand Lake - Oklahoma