[Alberg30] At4 propulsion and the A30

[T. Kevin Blanc]

George is, as ever, practical and pretty much right.

You may want to look into  Indigo's 11 x 7.4 x 3 blade
Atomic 4 prop if you want a three-blader, But
whichever way you look at it, 10x6x3 is too small.

--- George Dinwiddie <gdinwiddie at min.net> wrote:
> Scott,
> 
> You've got a 10x6?  You know that the original prop
> on an Alberg30
> with an Atomic 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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