Kicker prop, 3 or 4 blade

[roscoe]

I recently upgraded my kicker, wanted a bit more umph, and found a great deal on a Merc 15 with electric start.

Now I'm looking for a new prop for trolling.
Looking to slow the boat down.
Currently running a 3 blade 9p prop. It runs at almost 3 mph at idle.


Options are either a 4 blade 10 x 5p, or a 3 blade 9.75 x 6.5p.



Which do you think would be best? Which will actually troll slower ?

18' aluminum 1800-2000# load.

 

[Bob_VT]

The 4 blade 5p sounds nice and the small effect of fuel use should not bother you. It will be like a small tug boat and push you along in any weather.

 

[steelespike]

Are you using a gps for speed?Are you dealing with any currents or tides?
3 mph calculates to almost 1000 rpm @ idle.The motor should be at about 700-750.
700 calculates at about 2.1 mph. I had to guess at the prop slip.I used 25% at 1000 and 30% at 700.
The rpm is more a concern for premature wear of the clutch dog when shifting at 1000 rpm.
You do need less pitch to push that boat and stay closer to wot rpm if you have to use it as a back up.
A 4 blade should give better control.
Usually prop selection doesn't solve trolling speed though with a kicker motor it may work.

 

[blackhawk180]

I had the same problem with my 9.9 bigfoot on my 18' Alumaweld. I like to troll for sockeye and kokanee and both like around 1.2mph. I went to a 4 blade, lowest pitch I could find and it works perfectly. if I troll kings, I switch back to the stock prop or just rev the kicker a bit. I also added troll master to provide throttle control from the helm. Love it.

 

[roscoe]

Yes speed was gps, but I have only had it out once before winter hit, and there was a breeze.
2.8 was on the gps.
Have not had a chance to go thru the motor yet, but will in the next month.
Figured I would need to turn down idle, did not have the tach with me, as I just wanted to fish "one more time" this fall.

My main concern was if there would really be much difference between these props, as the 4 blade
a) has more diameter,
b) has the extra blade,
c) is a hi-thrust model

But the 3 blade has a much smaller blade surface.



Monday 100% Precip. Snow likely. High 28F. Winds ENE at 10 to 20 mph. Chance of snow 100%. 3 to 5 inches of snow expected.

Monday Night 80% Precip. Cloudy with snow. Low 21F. Winds NNE at 10 to 20 mph. Chance of snow 80%. Snow accumulating 1 to 3 inches.

 

[undone]

All the small Mercs use the same props, I have an 8hp, but its the same prop as the 15 (unless you're talking 4 strokes). I went from the three to a 7"P 4 blade and can troll at less than 1 MPH. Go with the 4 blade whichever pitch you choose.

Slightly smaller aluminum jet boat. Got the prop here on iboats.

 

[roscoe]

ok, 4 blade it is.
I've only got 4 months to find one.

but.... I can probably find 2 used 3 blade props for the same price.

I upgraded from a 1973 9.8 with the phase maker ignition, and that tiny little prop.
Never could get enough umph out of the motor to control it very well, and in reverse, it didn't move.
I certainly didn't need to go up to a 15 (1990 2 stroke ), but if I'm gonna hang 85 pounds on the boat, I might as well have the hp.