Help with a pontoon boat prop

[mfrank84]

We bought a Sylvan Mirage 818 pontoon boat last year. We bought the largest engine we could get, a Yamaha T60. The prop that came with it is a 13 1/2 X 9 Talon SDS Aluminum prop. My question: Is this the prop that comes standard on these engines? If so, how would one determine if there is a better prop option for a pontoon boat vs a more traditional hulled boat. I've read the sticky on props and I'm going to try to include as much information as I can following the template that was suggested.

1) Performance Issue you are trying to correct: Trying to get a little more speed given our HP limitations.
2) Current Prop: Yamaha, 6EK-45941-00-00, Aluminum.
3) Diameter and Pitch: 13 1/2 X 9
4) WOT: 6000 RPM, 21 MPH with four adults and 21 gallons of fuel.
5) Engine Make and Model: 2017 Yamaha T60
6) Boat: 2017 Sylvan Mirage 188 (19'), two tubes, Approximately 1690 lbs dry weight (boat and motor)

We have approximately 40 hours on the engine. We've noticed a decrease in speed according to our speedometer of 4 to 5 MPHs. The engine just had it's first factory authorized service. I inspected the prop and can't find any damage that I feel would cause any problems. Would a SS prop be a better choice for what we would like to achieve? Your comments and suggestions would be greatly appreciated.

 

[Scott Danforth]

welcome aboard

your propped correctly. if you want more speed, buy a different kind of boat.

 

[ahicks]

Though it sounds as though you're doing well with it, you might find another mile an hour or 2 messing with it.

My experience with the Merc and Honda 4 stroke engines seems to indicate they may be happier running at rpm's slightly lower than factory suggested max rated - like 5500 or so. They darn sure sound better. If you're up for it, trying a 10" prop may work out well for you.

The other piece is you might play with your engine height. The higher you can run it without getting into trouble in hard turns and so on, the faster you'll go.

With the power and speeds we're talking about here, you can assume stainless props are for (expensive) bling only.

 

[NYBo]

Welcome to iBoats! :welcome:

Do you keep your boat in the water? Crud growing on the 'toons can slow you down.

 

[mfrank84]

welcome aboard

your propped correctly. if you want more speed, buy a different kind of boat.

Thanks for the welcome. I'm not looking to race anyone, but I would like to get the few MPHs back it seems we've lost.

 

[Scott Danforth]

Simply moving the beer cooler can affect a 'toons performance.

 

[mfrank84]

Welcome to iBoats! :welcome:

Do you keep your boat in the water? Crud growing on the 'toons can slow you down.

Thanks NYbo. It does stay in the water. I remember the marina we bought it from mentioned that accumulated growth could slow it down a bit. I checked it this weekend and there was minimal growth on the tubes.​

I went to the Yamaha prop web site and entered my info on their prop selector and it came back with recommendations of a 14" prop, in their Pontoon Performance, and Pontoon1 Series, with a pitch range of 9 through 11. It also listed my current prop as a choice as well. Any idea what the difference could be in these props other than they are stainless steel? ​

 

[mfrank84]

Simply moving the beer cooler can affect a 'toons performance.

Interesting. I've got a lot to learn. In my response back to NYbo I mentioned the Yamaha web site recommended several props with pitches between 9 and 11. Would a 14 X 11 offer any improvement over the 13 1/2 X 9 that came with the engine? would it cause any problems. Thanks.

 

[Scott Danforth]

Your slightly over reving. Going to an 11p woulnt hurt

 

[NYBo]

We've noticed a decrease in speed according to our speedometer of 4 to 5 MPHs.

This is what concerns me. It isn't a prop issue if this is accurate and the prop is still in good condition. Check for a spun prop hub, and verify your speed via GPS. A smartphone app works well for this; pitot speedometers are not particularly accurate. A decrease in speed usually results in a corresponding decrease in WOT RPMs.

 

[mfrank84]

Something was different Sunday when I took my sister and BIL out. Top rpm has always been 6000 at full throttle. Sunday it was 6200 at full throttle. Any significance in this small increase. I wished I understood the dynamics of this better.

Dan,

would the slightly larger pitch allow for the same, or slightly higher speed at a lower RPM. Just thought I read that somewhere. I most certainly could have misunderstood what I was reading though. Another site I visited with a prop selector had 14 X 13 as an option. I'm just getting a little confused. But I'm trying to understand.

 

[WesNewell]

I think the T60 has a 2.33 gear ratio. if that's the case you should probably be running a 11P-13P prop. A 9P sounds about right for 1.85 gr engine

 

[Scott Danforth]

where were they sitting? simply raising your motor to the proper depth will significantly change your RPM

 

[icwingman]

check your toon for water in them it will definately slow u up

 

[mfrank84]

I think the T60 has a 2.33 gear ratio. if that's the case you should probably be running a 11P-13P prop. A 9P sounds about right for 1.85 gr engine

Yes. According to the Yamaha Outboard brochure, it has the 2.33 gear ratio. If I'm understanding correctly, The lower pitch gives me more torque at take-off but slower speeds once on a plane. As I go up in pitch the torque decreases but the speed on a plane increases. Do I have this right? Appreciate the help.

 

[WesNewell]

That's correct as long as you don't go so high in pitch that the rpm falls below recommended wot range. Once you go below that, it lugs the engine putting more stress on it and probably shortens its lifespan.

 

[jimmbo]

Yes. According to the Yamaha Outboard brochure, it has the 2.33 gear ratio. If I'm understanding correctly, The lower pitch gives me more torque at take-off but slower speeds once on a plane. As I go up in pitch the torque decreases but the speed on a plane increases. Do I have this right? Appreciate the help.

As you go up in pitch the load on the engine increases and the result is a lower max rpm. In most cases when propped so the engine is running in the recommended WOT rpm range, changing the pitch within a given lineage of props, but still remaining in the WOT range, results in top speeds not much different from each prop. Changing to a different brand, different model of same brand, or changing to a stainless, makes it to comparing Apples to Oranges