[Public-List] Public-List Digest, Vol 3380, Issue 1

[SNCSoft via Public-List]

Hello Gord,

Interested to try out three blades propeller from Indigo Electronics?

http://www.atomic4.com/propeller.html

I have spare one laying around. :-)

Serguei
#602



> Message: 3
> Date: Mon, 28 Nov 2016 10:30:13 -0500
> From: Gordon Laco via Public-List <public-list at lists.alberg30.org>
> To: <mpcbi at aol.com>,    <public-list at lists.alberg30.org>
> Subject: Re: [Public-List] Propellers...
> Message-ID: <D461B7B5.2E0A3%mainstay at csolve.net>
> Content-Type: text/plain;       charset="UTF-8"
>
> Good day friends,
>
> Here's my report on the first season using the Campbell 'Sailor' propeller.
>
> First, the 'Before' report.
>
> Surprise is an apres hull #400 boat, with the usual two bladed prop, 13"
> diameter, 7" pitch.  Our Atomic IV engine has the usual direct 1:1
> transmission (so prop RPM = engine RPM)
>
> What I liked about this set up was the following:
>
> - superior 'grunt' when maneuvring... I liked the trememdous power the
> engine delivered when making tight turns, stopping the boat with reverse
> power (reversing in general)
> - when idling at 600 rpm in gear, the boat moved at about 2knots which was
> useful for maneauvring.
> - maximum speed in flat water was about 6.7knots, which was excellent given
> the hull characteristics of the Alberg 30
> - headwinds made little difference in top speed
> - towing our heavy Boston Whaler 'Squall' sailing dinghy knocked about
> 1knot
> off speed, but we figured that was acceptable.
> - fuel economy seemed to be about the 1 gallon per hour published as normal
> for the Atomic IV
>
> What I didn't like:
>
> - the boat's economical cruising speed was 5.2 knots, which we achieved at
> about 1000 RPM... Which is too slow for the alternator to produce a useful
> return
> - flat out full throttle was about 1400 rpm, better for the alternator but
> gulping fuel, and cooling was not optimimum.
>
> What I wanted to achieve...
>
> - I wanted the engine to spin up closer to it's rated 'normal' operating
> RPM
> to improve the output of the alternator and cooling systems
> - I was intrigued by the promise of 'more horsepower in the water' given
> that at 1000 rpm the Atomic IV is only delivering a small fraction of it's
> rated 30 hp.
> - I was also intrigued by the promise of a lower engine sound level (it was
> already nice, particularly when compared to a diesel) better 'grunt' when
> pushing against a head sea or wind, and towing, as promised with three
> blades vs two.
>
> What we observed this past summer.  The Campbell Sailor supplied was the
> 11"
> diameter 5" pitch they recommend for direct drive Atomic IV's for the
> Alberg
> 30.
>
> First the good.
>
> - the engine was so quiet even at full throttle, I disbelieved the knot
> meter and double checked it with the GPS and a timed run.  The engine is
> significantly quieter and smoother with the Campbell Sailor prop
> - RPM rose as promised.  Flat out is about 1800rpm, we get 5.5 knots at
> 1400.
> - the engine ran cooler, more in the temp range recommended for the Atomic
> IV engine.
>
> And the not so good...
>
> - there was a definite decrease in what I call 'grunt' when maneavring in
> close quarters.  The Alberg 30 is particularly good with regard to using
> the
> engine to spin her in her length but where response was immediate with the
> old prop, with this one I had to wait for the engine rpm to 'spool up'
> before feeling the kick...and the kick was less.  Not good.
> - power in reverse was about the same.
> - top speed even at the higher RPM was about half or 3/4 of a knot lower
> than with the old prop.  Not good.
> - head wind and seas, and towing the dink had a dramatic effect on speed,
> much worse than before. Not good.
> - fuel ecomomy, even when not towing and in flat windless conditions, was
> much worse.  I had hoped that despite the higher rpm, since the engine was
> not labour as it seemed to be before, that fuel consumption might be the
> same or better, but it was not.
>
> And now some good news...
>
> I made a detailed report to Kelsey at Campbell Props... He is well informed
> with regard to the various factors affecting propeller performance.  We
> discussed pitch adjustment, but settled on increasing the prop diameter and
> leaving the pitch the same as a cure.   We agreed that it seemed my issue
> was excess slip, and increasing the prop diameter by 1" (thereby increasing
> blade area) would lower slip and hopefully offer me the cure I'm looking
> for.
>
> He was prompt and cheerful about offering me a new prop, even offering me
> the new prop before sending the old one back to him.  Because I couldn't
> comfortably change the prop till the boat was hauled for the winter, I
> thanked him and suggested that if he sent me the new one after I'd sent him
> back the old one that would be quite fine.
>
> Surprise came out of the water last week, so I've pulled the prop and will
> be sending the D11xP5 three blade Sailor back to him today.  I can't wait
> to
> try out the D12xP5.
>
> If that doesn't work, I could always do what Bob Crinion in Nova Scotia
> did... Remove 1" from the diameter of the stock 2 blade D13xP7 thereby
> achieving the RPM increase he sought.  I didn't discuss noise with him when
> I visited his boat last spring, but since the tip clearance is a little
> better I expect his 12" diameter prop is a little quieter, although it'll
> still have the thump that is inevitable with two blade props (this is
> caused
> by lack of water flow when the blades are lined up with the stern post.
> Three or more bladed props don't develop this because two or more blades
> are
> always in clean water flow and pushing...)
>
> Cheers -
>
> Gord Surprise #426
>
> I can't wait to try the new one out.
>
>
>