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Prop testing
Prop Testing done, I hope! So I
have a boat that is finally finished after two plus years of sanding
grinding, laminating and all that nasty stuff. Now for some fun, wrong! The
props , the final little detail was still to be resolved. It ain't easy
doing this from scratch if you have to buy the props you test. My first
attempt was just to follow someone's else's advice, which is not easy for me
if they can't or don't explain their ideas. My first set were 15 1/4"
X 21" three blade PowerTech!'s that only lasted one half of
an offshore trip before they spun. My GPS was down, so data wasn't produced
but the boat felt good with these props. Unfortunately spinning
both hubs and the resulting 12 hours idling back sort of eliminated these
from my list. Thank goodness ,the weather was good!
This ultimately resulted in my having a falling out with my prop guru, who
is a respected drag racer and does props for a number of professional
kingfish tournament guys. I had a really big argument with the * CUSTOMER
SERVICE* guy at POWERTECH! about a "restocking fee" for
the spun props.
Next, on to the TURBO Props. I bought a set of 14 1/2" X 21"
three blade Turbo Vectors. By now I had decided that my guru was wrong about
the big diameter props and thought these would be great. They weren't, at
least for my boat. They didn't spin their hubs and top speed looked good but after
a couple of trips I realized that they weren't getting the bite that was needed.
The boat was not responsive to engine trim and did not run level without some
serious trim tab and motor trimmed under. My new prop dealer, Bo's Propeller
in Port Vincent LA, has been helpful an we decided to try four blade Turbo
Ultima's.The results were dramatic and not what the rules of
thumb predicted, but this has river testing. Faster top end and more
WOT rpm with four blades, go figure.
Back to back tests at Bo's shop conveniently located on the river resulted
in the following:
Turbo Vector TurboUltima
3 blade
4 blade
14 1/2" X 21"
14 1/4" X 21"
3500 RPM
30.9 MPH
35 MPH
4000RPM
41
MPH
N/A
4200RPM
43
MPH
45 MPH
5500RPM(WOT)
55 MPH
5550RPM(WOT)
57 MPH
Basically the lightly loaded river cruising mileage maxs out at 2.2 MPG and gets 2.0 MPG
at 4200. But when normally loaded the offshore the mileage has not been better than about 1.8 and more
often runs in the 1.6-1.7 range. I hope to improve the offshore mileage but
that my not be possible. I am not sure, but the four blades may have hurt the
mileage somewhat.
With the three blades Turbo's the boat had a tendency to porpoise at cruise
speeds in smooth water. This happened when I trimmed out for better
efficiently. The four blades may have helped this a little bit but efficient
cruising is still a balance between porpoising at high trim out or smooth
running at lesser trim and efficiency. Offshore, the trim out will be less and
2 mpg will probably not be achieved unless I am very light. After the about
results I raised the motors up two notches and now they plus 5".
This has not increased the speed but the boat feels good and once on a plane
the motors can be trimmed way out and they stay hooked up. The above tests were done
with 100 gallons fuel out of 200 possible, three on board. I would guess
that with two on board and maybe 20-30 gallons fuel it will do close to 60MPH
but those conditions are not real world and just the stuff for magazine tests.
I was avoiding four blades because I thought the three blades would be more efficient and
I thought the four blades was just for big heavy battleships. This shows that
rules of thumb are just that. The
improvement in speeds were noticeable at all RPM's including, surprise!, top
speed.
The original set of POWERTECH!'s that spun had a really good feel but
reliably is paramount. A friend with 300 Merc's spun his Powertech's in
about an hour. I was told that the Turbo Vector three blades, by comparison,
are straighter pitched and the POWERTECHS are more progressive and both have
moderate rake, I was told around 25 degrees. At some point later on, I would
like to test some big dia. progressive pitch three blades that do not spin.
Till then, jury is still out on my four blades as they may not still be
ideal for my boat. If the PowerTech's had the Merc flo-torque hub, then they
may work good for my boat.
The last addition to the boat was a pair of Dana Marine planes, these are
12" wide X 24" long trim tabs similar to K-Planes.
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