Pontoon Prop Sizing

[Vivii]

I have been rebuilding a pontoon and finally got it all ready. We have been out in it the last couple weekends but the tach hasn't been working. I replaced the rectifier this week and it worked great today!

Unfortunately it is showing me what I have been fearing, at WOT my RPM's are low. Like real low, 2400 or so with approx 900-1000 lbs of people and gear today. It has a 73 Evinrude 65 on it that I believe currently has a Michigan Wheel PJ-90C, which I think is a 13 1/4" diameter 17 pitch cupped aluminum prop. The pontoon is a 73 crest 18' pontoon.

From what I'm seeing online in my research I should be looking more at a 13 3/4 diameter 13 pitch or a 14 diameter 11 pitch and I have seen both 3 and 4 blade recommendations. But I'm not seeing anything about cupped or not. What would be the best way to get my RPM's closer to the optimal 4500-5500?

Thanks for your help!

 

[Vivii]

[No message]

 

[WesNewell]

Since I don't know what your pontoon weighs or the gr of that engine I just took 2000# for it and with a 60 hp 2.33 gr engine it calls for an 11P prop. That may or may not help, but I'm pretty sure that a 17P is way too much.

 

[Vivii]

Sorry for my lack of knowledge, what is gr?
Should I keep it as cupped or go back to a traditional? Thanks for your help, I was leaning towards a 14x11

 

[Sea Rider]

Whichever prop style and pitch you intend to buy will need to be water tested at wot on a flat calm water cond. Before that, make sure the motor is 100% running strong even to its full throttle capacity.

Happy Boating

 

[WesNewell]

GR is gear ratio. The chart I use doesn't go back that far, but I'm guessing yours is 2.42. It will be in the owners manual, maybe expressed as the actual gear count, like 12/22 for a 1.83gr. If so divide the lower number into the higher for the GR.
http://www.kirschbaum.at/ki_prop/pdf/2015/RPM Chart.pdf

 

[Vivii]

I ordered a new prop, 14x11. It helped, but not enoug . Went from 2300rpm to 3100rpm. I need to make up another 1400rpm or so. It'll I drop again to a 14x9 that won't make up that difference. What else can I do?

 

[WesNewell]

Or you certain your tach is set properly for your engine? Settings usually on back of tach. What's the dry weight of the toon? What speed or you getting at wot with the 11P prop. Something isn't adding up right. Are you sure the toons are clean and there isn't any water in them. You shouldn't need less than an 11P prop unless your weight is high or there's some other problem.

 

[Vivii]

The toons are clean, the top of them were polished last year the the bottoms we did toon bright only and scrubbed them. I dont believe there is any water in the toons, though with no drain plug in the back it is hard to tell. It doesnt seem to sit low in the water and cant feel it slosh at all.

As far the the tach, from what I see it should be set at 6, but when you turn the dial on the back there is some play so it is hard to tell if it is set right. It is a brand new faria come with my pontoonstuff console.

Is there a way to see if it is set correctly?

 

[WesNewell]

This doesn't cover your year model, but I'd think your engine is a 12 pole model.
https://fariabeede.com/site_manuals/IS0086_V.pdf
Still, you may want to contact them to be sure you have the right setting for your model tach.
https://fariabeede.com/forms/?form=contact

 

[Vivii]

I will send them an email to double check, thank you!

 

[Scott Danforth]

what is the compression on all cylinders?

is it running on all cylinders?

are you getting full throttle?

agreed that the 11p is probably correct and the 17p was way over-propped, however you probably some other issue. running over-propped for a while will lug the motor......lugging will kill a motor

on a 'toon, motor height is critical.

make sure your motor is high enough its not plowing and low enough that it doesnt ventilate when someone walks forward.