[Public-List] hull speed

[Mike Lehman]

The formula for the speed of a displacement hull is the square root LWL x 
hull factor based on design (in the Albergs' case I believe this to be 1.34)

4.66 x 1.34 = 6.2 knots

So....you could install a turbo-charged v-8 and a huge prop...but you will 
still only achieve 6.2. The standard prop for the A30 with an Atomic 4 is 
2-blade 13x7 RH. With this prop the engine achieves 1400 RPM at hull speed. 
If you look at the power curve for the Atomic 4 that is about 10 HP.  If you 
switch to a 3-blade prop, it will be smoother because you will always have 
one blade cutting but it will not increase the boat speed. A 3-blade prop 
may be smaller in diameter (a good thing since it reduces prop wash and 
noise against the hull) but the pitch would have to be adjusted. The best 
way to determine this is to contact Michigan Wheel because they have a 'prop 
calculator' to determine pitch and diameter based on boat type and engine 
type. You may need to provide them with the power curve for your engine. 
This should not be a guessing game, you'll never get it right.


-----Original Message----- 
From: Jeffrey
Sent: Monday, November 14, 2011 6:45 PM
To: gewhite at crosslink.net ; Alberg 30 Public List -- open to all
Subject: Re: [Public-List] hull speed

Gordon,

With respect, I don't think it is possible to power an A30 hull to 7-8
knots. Hull Speed is somewhere around 6.2 knots. My 20hp can power the boat
to just over 6 knots at max rpm, but the noise and fuel consumption is
wicked. I've hit 7 knots and more for very brief periods of time under sail
when hit with a gust, but never under power. These speeds clocked with GPS.

-jeff

On Mon, Nov 14, 2011 at 5:46 PM, gordon white <gewhite at crosslink.net> wrote:

>   I'm not sure what "hull speed" is for the Alberg 30, but when
> clean-bottomed, I get 7-8 knots (on the knot meter) at full power with my
> diesel. I know, I need to time myself two ways between known points, but
> I'm not sure how accurate the daymarkers are located on a chart.... At
> those speeds it's really churning (obviously not planing)
>  - Gordon White, Brigadoon II
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-- 
Jeffrey Fongemie
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