[Alberg30] small engines

[Forhan, Thomas]

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Dick, 

I'll make a friendly suggestion that your boat may be overpowered or have a
prop pitch problem, based on the information you have posted.

Your BD722 is rated 20hp at 3600 RPM, and 18.5 at 3000rpm. 3000 RPM is 80%
of the max rated HP, and 80% is the usual speed diesels are supposed to work
at for best performance and longevity. I don't have a Beta performance
chart, but it is probably similar to the Westerbeke Kubota conversion,
http://www.westerbeke.com/Engines/20B-TWO/Technical.htm , which suggests at
that 2000 rpm, when you reach full hull speed, you are probably getting
something like 11-12hp out of the engine. (I also see that Westerbeke
recommends a prop that will allow you to run the engine at 3500-3600 rpm.
Will your engine do this?) 

I know that the idea of "extra power" is appealing, but I never felt my 10hp
Volvo in a 7500 lb boat was inadequate in four years of fulltime cruising. 

My personal thoughts are still the smaller engine 14hp Kubota, that would
work closer to the recommended engine speeds. This would be combined with a
maxiprop to maximize the HP you do have onboard getting into the water, both
in forward and reverse. Also, when I look at a typical diesel fuel
consumption curve, say http://www.yanmar.com/FRAMES45.HTM, I do not see that
you are significantly reducing fuel consumption with a larger engine
operating at 2000 rpm. 

So for long distance, full time cruising I would expect the smaller Kubota
to last longer, use less fuel, and do just as good a job as the larger
engine. Finally, as I mentioned earlier, another killer of diesel engines in
cruising boats is operating at very low power settings to take care of
"hotel" loads- charging batteries and refrigeration systems. With identical
hotel loads, the smaller engine will have to carry a greater burden, and
that is, ironically, good for the engine.

Tom F.
Calliope #287 (overpowered with an Atomic 4)



> -----Original Message-----
> From: Dick Filinich [mailto:daf at mobiletel.com]
> Sent: Monday, November 06, 2000 10:34 PM
> To: public-list at alberg30.org
> Subject: [Alberg30] small engines
> 
> 
>   
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> John:John the 13.5 h.p is the z482e,I have the d722e 20.5 
> h.p.My engine
> has three cylinders,and three inches longer than the 13.5 and 28 lbs
> heavier,but 100 # or so lighter than the atomic 4 I pulled 
> out.I cruise
> at 2000 rpm and if I recall right on my gps 5.3 kts ?At 2400 
> the exhaust
> pipe is under water,pushed by 12x6 two bladed prop.What else.  Dick
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