Yamaha VMAX 90 on a 20ft pontoon

Messages
12
Reaction score
3
Please forgive me for my ignorance, but how does going to a lower pitch prop, slow the engine RPM's down?
 

Darringlock

New Member
Messages
2
Reaction score
0
Can someone please answer this question? I have the exact same set up and I need to know which prop will get me the fastest speed?
 
Messages
12
Reaction score
3
I spoke with 2 prop shops yesterday and one of the guys is sending me a new prop, same pitch and diameter, just better quality. I will update once I try it out.
 

PartyBarge

Well-Known Member
Messages
71
Reaction score
47
Please forgive me for my ignorance, but how does going to a lower pitch prop, slow the engine RPM's down?
Ahhh...the answer to that one is easy. In this thread/situation the lower pitch prop is of a significantly different design intended for high load/moderate speed applications. The result is way less slippage and better manners (no or little cavitation).

You might think of the Quicksilver Nemesis Pontoon as a purpose-built versus the Yamaha K-series as a generic compromise. Sort of like the difference between 'all weather" tires and no-kidding snow tires.
 
Last edited:
Messages
12
Reaction score
3
Here's an update to my prop issue. I went with the recommendation of the guys from The Prop Shop in Soddy Daisy, TN. They sent me a Solas Amita 3, 13.5X15 prop. Put it on Saturday and run it. Keep in mind, it was just my wife and I, plus the big parachute up. WOT 5800rpm, top speed, 25mph. Smooth water and a bit windy. So, in a nutshell, no more overspeed on the motor or ventilating. I'm happy with the results. Thanks for everyone's input. Side note, if this didn't work, I was going to go with the Nemisis prop. I would have never thought there would be that much difference with a better quality prop.
 

Darringlock

New Member
Messages
2
Reaction score
0
I am happy that you figured out your prop issues, it was driving me crazy!! I found a used prop on Ebay. It is a Yamaha Pontoon Special part #MAR-PNTN3-V4-13 and with my wife and I with top up and a full Yetti = 750 LBS. At WOT 6000 RPM, top speed was 28.2!!! Much better than 5000 RPM and 19.2MPH!!!! Now if anyone can help me find Bennington docking lights it would be greatly appreciated!!
 

PartyBarge

Well-Known Member
Messages
71
Reaction score
47
All good to read. It is not well enough known that most manufactures have props intended for high load/low speed applications. Some specifically use the word "pontoon", others use various cryptic terminology like "high thrust".

Lalexander, your calculated slippage is still ~29%. Yes, good enough is good enough. Consider the slippage for Darringlock should be around half that...maybe less. However, the Yamaha Pontoon costs some multiple of the Amita!

Here is an example of another aluminum 4-blade. Of course there is a 15p version, but caution would be advised with that one for you. Note we used to run a 15p K-series before discovering the Nemesis pontoon.

 
Last edited:
Messages
12
Reaction score
3
Party barge, I appreciate all your help and advice on this issue. Prop pitch is all greek to me, but I'm learning fast. My first concern was getting the motor slowed down, which we accomplished. Next hurdle is maybe a little more top end speed, so maybe next season I'll give the Nemesis pontoon a shot, but, do I stick with the 15P or drop down to a 13P?
 

PartyBarge

Well-Known Member
Messages
71
Reaction score
47
That is exactly the question I struggled to answer after figuring out the Yamaha K-series props were not getting the job done. I think your motor has a 2.33 gear ratio (about the same as ours). Confirm that. Otherwise , you motor is ~20 pounds lighter and has 0.2L more displacement compared to our 2004 90. Next, do your own slip calculation here:


IF you get about the same 29% I did, there is a better solution as a Nemesis (or similar) will cut slip in half (or better). Normally Merc recommends the same pitch for the Spitfire/Nemesis/High5 lines IF WOT RPMs are nominal. However, that does not consider a situation with excessive induced slippage. For our modestly powered boats, reducing slippage is going to drop RPM all by itself. I sprung for the 13p and it worked out to be a perfect choice for our pontoon. Nominal WOT is ~5600 and max load, hard turn, RPM drops to no less than 4900. The 15p Nemesis on our boat would not be a good choice. Interesting aside, the idle/low RPM speed for the 13p Nemesis is about the same (maybe better) than the 15p Yamaha.

IF you have 25" tubes (we have 23" tubes) and don't load up too heavily, 15p would likely work OK. Without either one of those, I'd go for the 13p. Note that the 15p Nemesis is not part of the pontoon series (that is the 10-13p range). Don't know if that really makes any difference....
 
Messages
12
Reaction score
3
Hey party barge, so you guys talked me into the Nemisis prop, please give me your thoughts, 13.5 x 13. Where is the best place to get one with the hub?
 

DejaWiz

Well-Known Member
Messages
279
Reaction score
209
Location
Nebraska
Looking at Yamaha performance test results, perhaps a 13.125x14 or 13.25x14 might be good candidates.



Keep in mind that these are 22S series (21' pontoon length) with the straked twin ellipticals, so they will ride higher out of the water and have the capability to get on plane.

If you don't want to go with a prop in one of those sizes/pitch, then 13.5x14, 13.5x13, 13.625x13, or 13.75x13 may be ideal...and probably lean towards the slightly bigger diameter with the slightly less 13 pitch.
 
Top