[Alberg30] At4 propulsion and the A30

[CHRIS HARDY]

I would definitely try a larger prop.  Unless my gps ,knot meter, and tach are off
I cruise at 1800 rpm doing around 5.5 knots with a 12x6. I do have an annoying
vibration at that rpm though and will check my alignment this spring.  Chris #296

George Dinwiddie wrote:

> Scott,
>
> You've got a 10x6?  You know that the original prop on an Alberg30
> with an Atimic 4 was a 13x7 two-blade.  That's what I have and it
> seems to work sufficiently well, cruising at 1700 to 1800 rpm.
>
> I know the prop experts say this is too much prop, and a smaller
> prop will let the engine get further up its power curve.  And I
> know they say there's too little tip clearance in the aperture
> and it will cause cavitation.  But in spite of that, it seems to
> work pretty well.
>
> I'd try a bigger prop before moving the engine.
>
>  - George
>
> > Scott said:
> >
> >       Hey- want to throw this out there and hopefully have a response. I, like
> > many others are unsatisfied with the at4 performance in the A30. However the
> > 10k investment with a diesel exchange is not feasible for many. I have
> > recently rebuilt my at4 engine. It purrs, easily serviced and love the
> > simplicity. My present prop is a 10x6-3 blade. Works great at 2000rpm, no
> > sea conditions, clean prop and bottom.  =5KTs. any sea and its back to 4Kts.
> > The 10" wheel really has minimal blade exposure behind the keel. My thought
> > this haul-out was possibly sliding the engine forward some 3" and installing
> > the reduction gear. The question to diesel owners is then.... What  wheel
> > size (prop and pitch) do you have and what shaft RPM do you estimate at
> > cruising engine RPM.   This is to assume that diesel engines have a 2:1
> > ratio. My figure would be a at4 engine running at say 2500 rpm at more up
> > with its 80% efficiency curve, larger blade with more surface for bite. an
> > engine on motor mounts?   any thoughts   Scott   Thanks
>
> --
>  ----------------------------------------------------------------------
>   George Dinwiddie                             gdinwiddie at alberg30.org
>   The gods do not deduct from man's allotted span those hours spent in
>   sailing.                                    http://www.Alberg30.org/
>  ----------------------------------------------------------------------
>
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