[Public-List] Propellors

[Gordon Laco]

Hello Marcelo - 

The new prop is a Campbell;  performance motoring ahead is better… revs are up a couple hundred RPM so the cooling and charging systems work better… but reverse is much worse.   I think the later is due to the blades being ‘cupped’ slightly to improve thrust but when in reverse this brings the cavitation threshold lower.

It’s not a problem now that I’m used to it, but the first time I was using reverse to manoeuvre it was a bit of a shock.

The two blade prop was superb in reverse… I could use the prop walk effect to aide manoeuvring and thrust in reverse was very strong.

Gordon Laco
www.gordonlaco.com




> On Jun 24, 2019, at 9:29 AM, Marcelo D. Gentinetta via Public-List <public-list at lists.alberg30.org> wrote:
> 
> Hi Gordon,
> Is your new prop an Indigo brand? How does she maneuver in reverse or when stopping the boat?
> 
>> On Jun 24, 2019, at 7:27 AM, Gordon Laco via Public-List <public-list at lists.alberg30.org> wrote:
>> 
>> So there I was, yakking it up with a friend about how pleased I am with my new prop… besides the performance I commented how much quieter the boat is under power with the narrow three blader we have now than she was with the stock two blade one she came out of Whitby Boatworks with… and which she had fitted to her for all of the previous 49 years of service.
>> 
>> My friend asked me what pitch and diameter the old prop was.  I’d forgotten so I took it off my book shelf where it is now an ornament.   What did I discover?  The damned shaft hole is off-centre.   Yes, the prop was made with the shaft hole off-centre.   Crazy.  Well no wonder the new prop is ‘quieter’.    Three blades are of course smoother than two due to at least two blades always in clear flow whereas with a two blade prop the whole thing is blanketed by the sternpost twice per rotation… but off centre…. that must really have made whatever was inherent in the thing worse.
>> 
>> Onwards…
>> 
>> Gordon Laco
>> Surprise #426
>> 
>> 
>> 
>> 
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