Need help selecting best prop

[glrichards]

2 weeks ago got new pontoon home. Put it on the water only turn 3200 rpms. Prop was 13.5X15 Called dealer he sent a new prop 14X13 Black Max put it on went back to river. This time turned 4200 RPMS 18.75 MPH on GPS.Do I need to drop to 11 pitch or go 10 pitch or drop to a 9 pitch.
The pontoon is a 24 ft Tahoe cascade 2175 lbs.
The motor is a 2008 Mercury 115 EFI 4 stroke 401 lbs.
Usually have 6 average sized people on board 6X175= 1050 lbs.
And about 400 lbs of gear.
I need all the help I can get this is driving me nuts(short drive). I understand the need to get the rpms up don't want to hurt the engine by lugging it.
Any and all help will greatly help the sanity of an old man.


Thanks

 

[steelespike]

Re: Need help selecting best prop

I'm surprised you got 1,000 rpm with a 2 inch pitch change.Typically 200 rpm for each inch change.Is your testing with a full load?If not I think someting is screwy with your setup.
I have a report somewhewre of a 50 pushing a 24 ft at 18-20 mph.
with the 15 you are 2,300 rpm below what typically is 4 stroke rpm range.
Full load or not That adds up to a drop in pitch of 11" that leaves you with a 4" inch pitch.
obviously "something ain't right"I would start with a tach check.Maybe set wrong.Careful weight distribution,motor too low,throttle not open all the way.
New or not maybe the motor is a cylinder short.

 

[glrichards]

Re: Need help selecting best prop

The testing was done with 24 gallons of fuel an 6 people on board. that is pretty much a full load.

 

[steelespike]

Re: Need help selecting best prop

I think we can tell better where your propped at with a light load test.
one or 2 people.Its pretty obvious your not going to make rpm with a full load.
And you wouldn't be expected to.

 

[glrichards]

Re: Need help selecting best prop

Well Steelspike you were right the motor was a cylinder short. After your reply I went and checked everything again throttle settings,motor height, and every thing I could think of.When I put the hood back on the top pencil coil didn't look right when I squezed the connection it moved in about 1/16 and snapped. Checked the engine on muffs and it sounded better. Took it out on the river and it turned 5600 rpms forgot the gps but will check it all again this weekend.

Thanks for all your help.

 

[glrichards]

Re: Need help selecting best prop

After getting a lot of help from the experts on this site I now have got it going in the right direction.

Took the toon out today with the 14X11 prop the engine turns 6375 rpms and top speed is 27.7 mph on gps. not bad for a 24 ft. toon that weighs 2174 with a 115 4 stroke that weighs 401 lbs with 2 people that weigh 500 lbs(both together not each) 10 gallons of gas and 300 lbs of gear. WOT is 5800 to 6400 on this engine.

Thanks for all the help.

 

[steelespike]

Re: Need help selecting best prop

Well Steelspike you were right the motor was a cylinder short. After your reply I went and checked everything again throttle settings,motor height, and every thing I could think of.When I put the hood back on the top pencil coil didn't look right when I squezed the connection it moved in about 1/16 and snapped. Checked the engine on muffs and it sounded better. Took it out on the river and it turned 5600 rpms forgot the gps but will check it all again this weekend.

Thanks for all your help.

If I answer enough Qs I'm bound to get it right sometimes.Looks like your cooking now.Did the dealer not do a test run?

 

[Randybeall]

Re: Need help selecting best prop

Don't get rid of that 13 pitch prop. When you get that thing properly broken in it might be the right prop. Steel asked if the dealer did a test run, LOL! I don't know when I have heare a better, clean joke...... Glad it got worked out for you. Happy Boating.