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Need help with power issue.

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brian petrocelli

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I have an older 2012 Bennington GCW2275. Great boat - very low hours and in pristine condition. However, I have it up at a small mountain lake in CA - at 5,500 foot elevation. I'm struggling with the power. I have a Yamaha 150hp. Other owners of this same boat / engine combo reporting somewhere in 28-35mph top end. (with 1-2 passengers). I'm struggling to get over 20mph... even when solo! Is there anything I can do to the engine and/or swapping props for more performance and top end speed ? Thanks.
 
I previously had a 23 ft RCW SA with a 150 ,I was able to hit 38 with clean toons, full tank ,2 adults . What size is your prop? 22 ft with a 150 should be around 15 x15. I have a prop chart, but I don't have access to it right now . I'll post the suggested size in the morning.
 
I have a 2012 RCW2275 with a Yamaha 150 with ESP running a Mercury Eneria 15x15 prop. Top speed is 35 with 2 adults and a large dog. Is it a tri-toon? Does it stay in the water all the time?
 
Welcome to the forum Brian! I think what GMM was trying to say is do you keep your boat in the water and are the pontoons so dirty you can't get your boat over 20mph! I was thinking the same thing...... Really dirty pontoons? Or is there possibly water in your pontoons that is weighing your boat down ? Your 150 should easily get you in the upper 30's/40!
 
What RPM‘s are you running? I’m not a big prop knowledge guy but first and foremost we need to verify your engines even reaching correct RPM’s then prop from there. Also as BK mentions, verify your toons are clean, then if need be, check for water. You’ll usually notice listing from side to side or boat sits front/rear extremely low in the water.
 
I think answers to each question above will be essential to getting proper feedback and suggestions. Not enough info currently to help. However, everyone is correct that you should normally have that boat into at least the mid-30’s. Questions to answer from above, with a couple additions in my mind to get suggestions.
Tier 1 Questions:
- Conditions/cleanliness of pontoons?
- Evidence of listing in any direction/ water in pontoons?
- RPM’s at WOT?
- what prop do you have (brand, diameter, pitch)?
- which hull do you have? 2, Elips, EPP, SPS or ESP?

Tier 2 Questions:
- Water conditions and load at WOT?
- Motor mount height?
- Has it always preformed this poorly (11 year old boat), or something new?
 
Good advice above although no one responded to your input with regard to altitude. As you are well aware, at your elevation your engine power will be down approximately 15%. That alone does not explain the large discrepancy in speed but it will be a contributing factor. When you get everything sorted out you may discover that to achieve max power engine speed you will need less pitch than what others have reported.
 
First question (that's already been asked, but not yet answered) -- pontoon or tritoon? I had a 2011 2275 GCW pontoon (two tubes) with a Yamaha 115. Top speed in ideal conditions with clean toons was 26 MPH. Growth on the toons can rob a shocking amount of speed. Easily 5 MPH.
 
Drag and weight plays a big role. My new Bennington with standard 2 tubes and 115 hp motor - 26 mph. After tube replacement with the same single motor - 38 mph. The tear off tubes went on a lightweight pontoon up north having identical motor - 30 mph.
 
5500' MSL is definitely high enough to make for a new ball game! Check the general rule-of-thumb below:

  • Reduced oxygen in high altitudes can lead to inefficient, sluggish engine performance because there is less air to feed the internal combustion engine. Generally speaking, an engine loses three percent of its rated power for every 1,000 feet of altitude gained.
I would expect the WOT RPM is way down compared to near sea level. Going from near sea level to 5500' requires a pitch reduction of some 3-4". See the link:

acepropeller.com

How High Altitude Will Affect Propeller Performance - Ace Propeller

If you boat at higher elevations, one of the first things you notice is decreased power. This is because air has less oxygen at higher elevations resulting in reduced performance. One way to compensate is by using a prop with a reduced pitch. This makes it easier for your engine to reach the...
acepropeller.com acepropeller.com


Also at that altitude, a nominal 150 HP motor is roughly equivalent to 125 HP. Forget about what the motor should do at sea level.
 
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So elevation has been pointed to a few times. Yes that will have a decent impact on performance… But the performance being reported is far lower than what I believe the elevation issue would create.

At least for me, the elevation doesn’t explain the performance numbers being reported. Something else is going on. His top end will be lower than normal, but should still be decently above what they are reporting. That circles me back to the questions being asked above, to which, we’ve received no answers…
 
To be sure, there may be more than one issue. More info would definitely be useful.

However, IF the motor has a prop appropriate for sea level ops, it can't get to the normal power band/RPM. Performance will be far worse than expected and below the 125 HP equivalent in the above post. That estimate assumes a prop that lets the motor get to it's rated RPM (meaning 3-4 inches less than normal pitch...likely more like 4).

I'd expect the reason the overloaded motor has any usefulness is that the computerized EFI is attempting to provide the correct mixture for the significantly reduced air mass flow. In other words, fuel flow is way down and so is power.
 
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Interesting. But barely cracking 20mph solo? That’s gotta be a nearly 42-48% performance drop from what is possible at sea level with that boat and motor. :oops:

Elevation impacts on motors are certainly not my area of expertise at all coming from Michigan. Their performance hit just seems so over the top in my mind. I guess I’d expect 10-15%, maybe 20%. But not 40+%.

Darn you! Now I have to avoid this becoming another boat info rabbit hole I jump into on the internet. :p
 
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