Help! Speed and RPM seem way off!

BobbyZ

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I have a 2018 23SSBXP with SPS and a Yamaha 175 SHO. The prop is a Reliance 14.5 x 15 SS. With myself and my wife 2 small children nothing else on the boat I was only able to get 5600 RPM and 38 MPH max after playing with the trim quite a bit. I was expecting top speed to be higher and rpm to be a little higher. I am mounted in the highest hole #1 so motor is at lowest position in water. Seems I'm lacking some performance. Can anyone help me out here. Live the boat but I was hoping for a 44mph top speed and around 40 with 4 ppl on it. I test drove exact same boat brand new 2 years ago and hit 42 with 2 adults not even trying or playing much with trim. Thx in advance. Rob
 

mtudb24

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Hmmm. Interesting. Max RPM for the sho I believe is 5000-6000 with 175hp being made at the middle at 5500. So RPM's are about right.
What is your toon config? 2 log or 3 (SPS, ESP, etc)? Lifting strakes / under skinning? Are they clean? Is the boat new to you or did you have better performance last year?
Its a big boat at 24'9 LOA and about 2400lbs dry weight. How much fuel you have?

If you had better performance last season, maybe some water in the logs? Is the waterline on the toons the same as last season? How many hours on the motor? If it has a lot of hours, have you put new spark plugs in it? I know my Mercury Pro XS likes new plugs about every 2-3 years for some reason.
Todd
 

Lay Lake

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I'm thinking your speed and rpm's are about right. I have the same boat with the f150 and am about 36 with 2 adults and 2 kids aboard. Also, water conditions can change your speed several mph if it's choppy and/or windy.
 

BobbyZ

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Complete underskinning pontoons are spotless, I don't keep in water
 

BobbyZ

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What holes are ur motors mounted on as far as height. Top hole or 1 or 2 down?
 

mtudb24

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What holes are ur motors mounted on as far as height. Top hole or 1 or 2 down?
My 2275 RCW with 150hp Merc Pro XS is mounted in the 2nd hole. Came from factory at the top hole (as yours, lowest mounted) and I moved it up after the 1st season. Got some minimal gains.
Did you have better performance in previous seasons, or are your calculation's based on the test drive you did on a different boat (but same model as you bought?)
 

BobbyZ

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This is first year for me. Just picked it up used from original owner. I drove a 22 footer with same motor and prop. Im getting speed from my Garmin GPS trimmed at 3/4. What prop are u running? Im gonna prob be switching to an aluminum just because of the rocks. Did u see any rpm increase or speed increase at all raising the motor a hole? I was told expect 100-150 rpm increase per hole and 1-2 mph.
 

mtudb24

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i was running 15x15 Mercury enertia (one of the best pontoon SS boat props on the market) that came from the factory. Ended up moving up 1 hole and changing to a 15 1/8x14 enertia to get the unloaded weight back up to 5750 rpm upper range lightly loaded. Very happy with this set up as I gained some top end and low end quick rpm swing up to pull tubes. My boat is smaller then yours but i have the twin 32" tubes which is very fast (for a twin tube boat) but still have the "slide" into turns where a 3 toon boat will run circles around me. But straight line speed is good at over 40. And rough water handling is very good with the extra 1000lb buoyancy per tube over standard 25" toons.
 

Mozekian

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I have a 22’ with the same engine and prop, I’ll hit very low 40s without perfect conditions, so I don’t think your performance is anything out of the ordinary based on it being a foot longer than my boat.
 

David G

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I had a 22ssx w/ 175 Yamaha and could go 40-41, sps logs
 

Potomacbassin’

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Something is off here. I also have a 23ssbxp with a 250 and hit 50. I have a hard time believing 75 hp is worth 12 mph.

One thing to check is that you're running 89 octane. Those SHO's advance timing and need the 89 to get the full potential out of it.
 

BobbyZ

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Something is off here. I also have a 23ssbxp with a 250 and hit 50. I have a hard time believing 75 hp is worth 12 mph.

One thing to check is that you're running 89 octane. Those SHO's advance timing and need the 89 to get the full potential out of it.
I'm running non ethanol 91. Taking it out again today so we will have to see.
 

Potomacbassin’

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I'm two holes up as well - provided 2mph more top speed but even better fuel efficiency across the RPM was significantly improved. You lose some turning as the prop can vent a little so there are tradeoffs.
 

Vikingstaff

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I think 44 mph is more in line with a 200 VMAX or Mercury Verado…not a 175. I think you are in the ballpark already, but might squeeze a tiny amount more out of it. The fact that your boat is a couple feet longer than what you test drove a couple years ago probably accounts fro some of the difference right there.

AND if you switch to an aluminum prop as you mentioned above because of concerns with contact with rocks, you are going to lose a fair amount of performance…not gain any regardless of prop size.

That said, I think you could raise your motor one spot. Having it mounted at lowest setting on a SPS likely means it is sitting just slightly too low in the water and has some unnecessary drag. I think you can raise it up one spot and still not have any cavitation in turns, but you wont know for sure until you give it a try.

Again, I think your boat is about spot on. Maybe go up one pitch on the right SS prop if focused on getting it totally dialed in.

Would I expect you at 40-41 with a light load in perfect conditions…sure. But you are not far off now, and if switching to an aluminum prop, I don’t believe you’ll be there at all. That 175 Vmax will flex an aluminum prop and thus not hit its performance potential. Maybe not even get close to it.
 

BobbyZ

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I think 44 mph is more in line with a 200 VMAX or Mercury Verado…not a 175. I think you are in the ballpark already, but might squeeze a tiny amount more out of it. The fact that your boat is a couple feet longer than what you test drove a couple years ago probably accounts fro some of the difference right there.

AND if you switch to an aluminum prop as you mentioned above because of concerns with contact with rocks, you are going to lose a fair amount of performance…not gain any regardless of prop size.

That said, I think you could raise your motor one spot. Having it mounted at lowest setting on a SPS likely means it is sitting just slightly too low in the water and has some unnecessary drag. I think you can raise it up one spot and still not have any cavitation in turns, but you wont know for sure until you give it a try.

Again, I think your boat is about spot on. Maybe go up one pitch on the right SS prop if focused on getting it totally dialed in.

Would I expect you at 40-41 with a light load in perfect conditions…sure. But you are not far off now, and if switching to an aluminum prop, I don’t believe you’ll be there at all. That 175 Vmax will flex an aluminum prop and thus not hit its performance potential. Maybe not even get close to it.
Thanks for the info. Def gonna try next hole. I was looking at it today and motor shoots a little roost even when trimmed. I think one hole will get me best set up. I'll try that then dial in the prop later.
 
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