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nvhguy52

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What is the recommendation for best speed on a 2075 w/ 90hp Yamaha? The Marina provided a prop that acheives 22mph at 6000 rpm. I would like to bring down the revs and hopefully increase speed. Ultimately get the engine in the 5500-5600 range.
 
What pitch and diameter r u currently using?

Todd
 
nvhguy52 said:
What is the recommendation for best speed on a 2075 w/ 90hp Yamaha? The Marina provided a prop that acheives 22mph at 6000 rpm. I would like to bring down the revs and hopefully increase speed. Ultimately get the engine in the 5500-5600 range.
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Go down 1 number in pitch.
 
If you want to decrease wot rpms you will need to increase pitch. Example: if your running a 15 pitch, going to a 17 pitch of the same brand/model of prop will normally decrease your WOT 400rpm.
 
Fyrfightr said:
If you want to decrease wot rpms you will need to increase pitch. Example: if your running a 15 pitch, going to a 17 pitch of the same brand/model of prop will normally decrease your WOT 400rpm.
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You know, upon re-reading, I realized I goofed up.

I thought you were IN the 55-5600 rpm range and wanted to get the right prop for max speed, which would be one that would bring you to your (presumed) 6,000rpm top engine speed.

Fyrfighter is correct, but now that I have re-read it, your post begs the question; why do you want to decrease engine speed?
 
I want to decrease engine speed to get it more into the operating range 5000-6000 rpm per Yamaha. Also, speed was not what I expected when moving up from a 40hp Mariner. Old boat (same size as new boat) was 18 mph w/ 40 hp @ 4900 rpm. New boat is 90hp 22 mph @ 6000 rpm. Great hole shot. Was up to 6000 rpm in a heartbeat.

Put new prop on today. Now 5600 rpm & 24 mph w/ full fuel and 5 adults on board. Better but I think I can try going up one more pitch. Currently at 13.5 dia X 15 pitch. Maybe next week.

The guys at the Marina (Secord Marina) are great to work with. Thanks, loads, to them and all who replied to the post.

ericscher said:
You know, upon re-reading, I realized I goofed up.

I thought you were IN the 55-5600 rpm range and wanted to get the right prop for max speed, which would be one that would bring you to your (presumed) 6,000rpm top engine speed.

Fyrfighter is correct, but now that I have re-read it, your post begs the question; why do you want to decrease engine speed?
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I have a 2274 GLI with a 115 Merc four stroke. It has a 15 pitch prop on it. I can get 23 mph out of it with 2 adults and 1 child. Does this sound right? The motor is mounted in the 2nd hole from the top and the wot is 6400 rpm's. Thank's for any input.
 
You're in the ballpark.

I had a slipmate with a boat identical to mine, except he had a 90 Yam and I had a 50 Yam.

We tested both boats on the same day, with the same GPS and did it at the beginning of the season (2008).

I hit 18, he hit 23.

Your boat has 25 more horse, and extra foot in length and was carrying more weight. Hitting the same 23 means you're in the ballpark.
 
ericscher said:
You're in the ballpark.

I had a slipmate with a boat identical to mine, except he had a 90 Yam and I had a 50 Yam.

We tested both boats on the same day, with the same GPS and did it at the beginning of the season (2008).

I hit 18, he hit 23.

Your boat has 25 more horse, and extra foot in length and was carrying more weight. Hitting the same 23 means you're in the ballpark.
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I was wondering if I switced to a higher pitched prop to drop the RPM's down would that help my top speed. When I am running wot it seems like I have some cavitation. I checked the mounting and the motor is in the second hole from top. Thank's for any thoughts and input.
 
What you are having is ventilation ( cavitation is rare in pontoons ). Moving your motor down should take care of it, getting you more bite in clean water.
 
Boomers dad said:
What you are having is ventilation ( cavitation is rare in pontoons ). Moving your motor down should take care of it, getting you more bite in clean water.
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Thank's for your help. Does moving the motor that little bit make that big of difference? Does running the motor at the high end of RPM range hurt it? Changing the prop would not substitute for dropping the motor? Once again thank's.
 
You want the boat to run in the upper range of the rpms with a typical load at WOT. You don't want to be under your low limit that will mean your are lugging your engine with is very hard on it. Ventilation is caused when air is drawn into the prop. Lowering your engine will get your prop into clean water. Once you get your engine lowered then you can change props if needed. Why spend hundreds of dollars on props when moving the engine will take care of it?

Good Luck
 
Easy guys...

Let's not get a ruckus up just because it's Saturday night.
 
I've got a 2050FSI with a 90 Yamaha. At WOT I'm only turning 5100 RPM. Am I lugging the motor? I average about 2.3 gph when pulling a tube so I'm kind of reluctant to change anything. I get the 5100 whether I'm by myself or I've got my wife in the boat and 2 teens on the tube. Yamaha says I should be in the 4-5 gph at those reps. I lose about 300 rpm when I get more people on and try to pull. Do I really need to get closer to the 5500-5600 range to be easier on the motor or am I OK where I'm at? I'll check size/pitch later. I looked but forgot to right it down the other day.
 
seven twenty said:
I've got a 2050FSI with a 90 Yamaha. At WOT I'm only turning 5100 RPM. Am I lugging the motor? I average about 2.3 gph when pulling a tube so I'm kind of reluctant to change anything. I get the 5100 whether I'm by myself or I've got my wife in the boat and 2 teens on the tube. Yamaha says I should be in the 4-5 gph at those reps. I lose about 300 rpm when I get more people on and try to pull. Do I really need to get closer to the 5500-5600 range to be easier on the motor or am I OK where I'm at? I'll check size/pitch later. I looked but forgot to right it down the other day.
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Well, you're not lugging it, but you're leaving almost 1,000rpm on the table.

Ideally, you want the full forward position of the throttle to correspond with the maximum RPM.
 
ericscher said:
Well, you're not lugging it, but you're leaving almost 1,000rpm on the table.

Ideally, you want the full forward position of the throttle to correspond with the maximum RPM.
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I realize that, but what am i going to use fuel wise with another 500rpm? Yamaha says I should use 5-6gph at 5500. I'd love the extra speed and power but at $4+/gal I'm kind of afraid to spend the money on a new prop. If I knew that my fuel rates would stay within a gal/hr of what I was getting now I'd switch in a heartbeat.

Anybody else with a 90 yamaha got some real #'s to compare to?
 
seven twenty said:
I realize that, but what am i going to use fuel wise with another 500rpm?
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You can still set the throttle where you want it. The reason you're 900rpm down is because you've got too much prop. It's like being in shape to bench press 200lbs and someone slips on a couple of extra plates.

Don't get me wrong...

It's absolutely your decision. We're just talking.
 
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