[Public-List] Southbound ICW trip over

Tue Nov 8 07:19:54 PST 2016

Kurt,
 Your almost certainly have at least a 2:1 reduction gear, so your
performance is reasonable.  If this is so, you are spinning your 13.5 x 11
prop at 1100 RPM and going 5 knots .
  You may have hull or prop fouling adding to your drag, or perhaps you
need more engine tuning  to get full torque performance out of the Volvo.

 One design point for the A30 is the original 2-blade 13" D x 7" P ,
matched to an Atomic 4 direct drive.
This combination generates 6.2 kt  at about 1800 RPM  (engine and prop) and
an estimated 16 HP

With my Beta 16 and 2:1 gear  and the same prop, I get 6.2 kt  at 3500
engine RPM (max rated and governed), 1750 prop RPM, 16 HP.
The results are very similar, but wIth the Atomic 4 I was hitting the
torque limit of the engine at wide-open throttle, while with the Beta 16 I
am hitting the RPM limit.

If I were to pitch this prop higher, and/or add a third blade, and/or make
the blades wider,  I could get hull-speed thrust at a lower RPM, and the
torque would be higher to deliver the same 16 HP
This could possibly be a better operating point (RPM and HP or RPM and
Torqe) for the engine in calm water.

If the drag went up due to wind and waves, towing or fouling, the higher
pitch  (or 3-blade ) prop might be a clearly better fit.

Mike
Rinn Duin #272

On Mon, Nov 7, 2016 at 6:14 PM, Kurt R via Public-List <
public-list at lists.alberg30.org> wrote:

> It's a Volvo Penta Model 2002 (that's not the year), 2 cylinder 18hp,
> operating RPM's recommended 2200-2800, max 3200. Above 2200rpm, there is
> not a relative speed increase for the extra noise/work; another inch of
> pitch would add on 200RPM and more top-end speed with it. I think the PO
> had no idea because the engine wouldn't really run smoothly above
> 17-1800RPM due to the fuel contamination, and he probably only really used
> it to get on/off dock anyway.
>
> On Mon, Nov 7, 2016 at 6:06 PM, Rolph and Joan Townshend <
> joanrolph4 at gmail.com> wrote:
>
> > What engine do you have? With the Atomic 4 you should be getting 6.5 - 7
> > kts at 1700 rpm.There is never need to go beyond 1700. Ever
> >  Towney
> >
> > On Mon, Nov 7, 2016 at 5:52 PM, Kurt R via Public-List <
> > public-list at lists.alberg30.org> wrote:
> >
> >> Came in Friday making as high as 8.3mph SOG (motor, tide, and tailwind)
> >> for
> >> the last few miles of bringing #429, nee "Sundance", to her new home in
> >> Georgetown, SC, from Fleets Bay, VA.
> >> Total trip distance according to GPS was 496 miles, tho it was a bit
> more
> >> than that as GPS was not always on the first few days. Underway 10 days
> >> and
> >> 3.5 hours port-to-port.
> >> Due to Dismal still being closed, came via Chesapeake canal/Coinjock
> >> route,
> >> with the exception of one offshore leg between Morehead and Masonboro
> >> Inlet, NC.
> >> Went "astump" briefly in VA while circling for a draw bridge, and also
> >> found bottom for 10 minutes or so in the notorious Shallotte Inlet of
> NC.
> >> Had fuel issues the first 5 days which came to a conclusion when I
> >> jury-rigged a jerry can in the cockpit and gravity fed the engine from
> >> that
> >> instead. This allowed for much better and higher-speed running engine
> >> (first 5 days speed average was 3.3 kts @1700rpm max). I think the
> inboard
> >> tank must never have been cleaned since 1970, as I never was able to fit
> >> in
> >> more than 4.5 gals fuel. Jerry can rig allowed me to up revs to 2200 and
> >> speed to 5 or 5.5mph, still low but considerably better.
> >> Documentation shows the prop as being 13.68" diam with an 11" pitch,
> and I
> >> think that is wrong, and the reason for the slow speeds. Under sail I
> was
> >> able to do better than engine speeds even in light air. Didn't get much
> of
> >> that, but thoroughly enjoyed every moment of it. She sails every bit as
> >> nimbly and able as my Ariel.
> >> Let the projects begin...
> >> Kurt
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