[Public-List] Engine Power Loss

Wed Sep 12 08:35:26 PDT 2007

Gord - I think this is a good way to look at it.  Most ships have prop
and engine tuned for max efficiency at somewhere below the "hull speed".
Tugboats are and interesting exception because they have to be efficient
at very low to zero speed - they are generally qualified by a "bollard
pull" test against a dynamometer at the pier.

My tach has been busted all season, but from memory I agree, I get 6.5
knots at much less than 2000 RPM. 

Mike
Rinn Duin #272

-----Original Message-----
From: public-list-bounces at lists.alberg30.org
[mailto:public-list-bounces at lists.alberg30.org] On Behalf Of Gordon Laco
Sent: Wednesday, September 12, 2007 11:20 AM
To: Alberg 30 Public List -- open to all
Subject: Re: [Public-List] Engine Power Loss

I agree - I was thinking the same thing.  FYI SURPRISE gets about 6.5 at
about 1400 rpm; I have never tried revving up to full power at the
jetty.
If you have a slightly heavier pitch on your prop your revs will show a
little lower at full throttle as the boat comes up against the
steepening resistance curve due to that old 1.4 x the square root of
your effective waterline length.  At rest, and with the water flow past
the prop not being what it might be while moving fast, the 'slippage'
will be greater possibly allowing the revs to go up as the efficiency of
the prop drops a little.

Mike - am I on track with that reasoning?

Gord #426

> You may get 2000 RPM at the dock straining against the docklines, but 
> since the prop is more efficient when the boat is moving forward, it 
> absorbs the maximum power of the engine at lower RPM.
> 
> 
> What's your speed at 1200 RPM underway?
> 
> 
> Mike Meinhold / Naval Architect / SAIC
> 4321 Collington Road, Suite 250, Bowie, MD 20716
> Office: (301) 352-4734  Cell : 410 271 5394 
> Michael.j.meinhold at saic.com
> 
> 
> -----Original Message-----
> From: public-list-bounces at lists.alberg30.org
> [mailto:public-list-bounces at lists.alberg30.org] On Behalf Of Cole, 
> Andrew L
> Sent: Wednesday, September 12, 2007 7:48 AM
> To: public-list at lists.alberg30.org
> Subject: Re: [Public-List] Engine Power Loss
> 
> Brian,
> 
> It is puzzling that you can get power in gear at the dock, but not 
> underway.
> 
> This may be directly or indirectly a fuel quality issue.
> 
> If you have a fuel filter, yank the element and see if it's all full 
> of crud.  The ethanol gas in particular does not get along well with 
> water and will go bad quickly.  That can gum up your carb., or worse, 
> stick a valve.  If the filter is crud-filled, drain the tank, get a 
> better sealed filler cap, change the filter element and re-fill the
tank.
> 
> If you have access to a compression tester, check each of the 
> cylinders to ensure you don't have a stuck valve.  These low
compression 4cyl.
> engines will run well enough on two cylinders to fool a mechanic into 
> thinking it's running normally unless he puts load on it.  If you 
> don't have a compression tester, you may be able to see the valves 
> through the spark plug holes, if so, you can check to see that each is

> moving up and down on each pair of revolutions.
> 
> If you're lucky, neither is the case, but you may as well check to 
> eliminate possible causes.
> 
> Andrew Cole
> Andante - 152
> 
>> When the transmission is in forward, neutral and reverse at the dock 
>> I
> get about 2000 RPM.
>> However when I leave the dock I cannot get the RPM's over 1200 in
> forward.
> 
>> Brian - Putachieside - 496
> 
> Cole, Andrew L
> Admitted in Maryland, Virginia & Florida One Corporate Center
> 10451 Mill Run Circle, Suite 1000
> Baltimore MD 21117
> 
> 
> tel: 410 581-7408
> fax: (410) 581-7410
> mob: (410) 206-3577
> 
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