[Public-List] Propellers...

[Gordon Laco via Public-List]

Hello friends,

I¹m sorry to reintroduce this topic... But I¹ve changed propellers and
thought I¹d share the experience.

Some of you may recall that I have pontificated about taking a Œdon¹t
change¹ position with regard to the prop supplied by Whitby Boatworks with
the Atomic IV engines many of our boats have.

Well this spring I was thinking about the engine and decided to try a
change.  Last fall¹s ŒMisery Trip¹ reached a crescendo of suffering with a
slog to windward in 40 knot winds and a sharp chop...  We were nearly
stopped a few times, mostly by wave action, but SURPRISE trudged along and I
would say coped better than our companion¹s boats which were all fin keeled
yachts fitted with diesels.    So power delivered to the water wasn¹t the
issue... What I was thinking about was alternator performance and cooling.

Cooling has never been an issue with our engine, particularly since I
replaced the old water pump with the upgrade offered by Moyer.  However I¹ve
been keenly aware that our cruising RPM of about 1000 doesn¹t really spin
things down in the engine compartment fast enough to deliver what the
alternator is theoretically capable of.

I liked the look of the narrowed bladed ŒCampbell¹ props I¹d seen on other
boats, and liked the idea of increasing revs while at least keeping the same
Œpower in the water¹ situation the stock two bladed prop gave us.  So I
ordered the Campbell which they recommend for Alberg 30¹s fitted with Atomic
IV engines with 1:1 transmissions.    The vendor said he was certain what
shaft diameter and taper my boat has... But because I¹m a doubter, I sent
him my old prop for reference.

In due course the new prop came back along with the old one (and he was
right, he did already know the specs).  I couldn¹t wait to try it out.

We installed the new prop as part of my condensed spring outfitting (and no,
I did not do the cap rail job I wrote about earlier.  I got busy with work
which took me away most of April and May so that¹s that on that job for
now).  Eagle eyed Rod saw the shiny new thing and commented ŒI thought you
said...¹     Well I know what I said, but what the heck...

We got SURPRISE into the water and after securing the rig, started up and
started the two hour trip back to our sailing club.  First thing I noticed
was that I seemed to have a lot more power in reverse than before.  The
second thing was that prop walk seemed to have dissappeared... Amazing.

The only negative comment I¹d read about these props on line referred to a
supposed loss of maneuvring power... But I was able to do the usual spin
within her length that SURPRISE normally does.    Motoring out of
Dutchman¹s Cove Marina, I found that our speed at idle was lower, and that¹s
a good thing of course not unexpected because of the finer pitch.  Once out
past the breakwater, we opened the throttle and both Caroline and I were
amazed.  Boat speed climbed to 6.6 knots as usual for full throttle, but
there was no roar and vibration from the engine.  I won¹t say it was as
quiet as electric, but the change from how things were was startling and
dramatic.   We were so quiet at full speed I mistrusted the knotmeter and
fired up the GPS, but it confirmed the speed.  Amazing.

We found our old cruising speed of 5.2 at 1000rpm was now 5.2 at 1400 (this
second RPM was full out open throttle with the old prop). Yes the engine was
spinning faster, but at the same throttle setting and clearly not labouring
quite so hard.   The boat was so quiet we didn¹t feel like we were moving,
so we did the trip at 6+.

So the prop change is rated a total success.  But there was a surprise in
store for us.  Because I was away so much I didn¹t do my usual thorough
recharge of the batteries... We started up after launch on what was left in
the batteries after the Misery Trip and months of winter lay up.   I was
glad there seemed to be enough juice to spin the engine.
Yesterday I decided to connect up the battery charger and run it all day...
But after only moments, the charger was indicating full charge.  I assumed a
problem with the charger but after investigating, realized that the
Œproblem¹ was that the battery bank was indeed fully charged and the
automatic function on the charger was sensing this and shutting off.

How could that be, I thought... Then it occurred to me that the alternator
must have run up the batteries on the trip over from the marina.  In the old
days, the alternator barely kept up with the engine¹s requirements and I¹d
had to charge from shore power periodically.  So it appears that whatever
was in the batteries at launch, the engine itself topped them up in the 90
minute shot over under power (wasn¹t two hours because we galloped home
faster).  

Happy happy.

Gord #426 Surprise