catchersrock
Ensign
Posts: 548
Location: Maiden NC
Sea Pro model and year: 2020 Sea Pro 228
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Post by catchersrock on Sept 21, 2018 5:23:35 GMT -6
Good morning everyone,
So, I just repowered my 1900cc with a new Mercury 150 pro xs 2 stroke. My previous engine was a 150 optimax. The only thing I reused from the previous set up was the prop, though I did put a new hub in it. The numbers stamped on the prop are 48 16314 17P. I believe that is a 17 pitch, 14.5 inch prop. The motor is hung in the same holes as the previous set up. I have lost 300 to 400 RPM and 4 to 5 MPH going from the old motor to the new one. Just finished the break in and top numbers are 45 MPH at 5500 RPM. I would like to at least be back where I was, I had hoped for some improvement.
Do I need to give the motor some time to run in? Change Prop for the new motor? I had noticed on the previous set up that the motor seemed to hung low. Pict below. The centerline of the prop shaft is 4 to 5 inches below the drain plug. I know on the speed junky bass boats, that is closer to 0". What would be the effects of raising the motor a bolt hole or two. Any other SV's out there that can let me know how their motor is hung?
Thanks,
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catchersrock
Ensign
Posts: 548
Location: Maiden NC
Sea Pro model and year: 2020 Sea Pro 228
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Post by catchersrock on Sept 21, 2018 5:28:09 GMT -6
Forgot the picture
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Post by Juan on Sept 21, 2018 11:34:32 GMT -6
If I'm not mistaken, the max recommended rpm at WOT is 5750 so you're very close if that's the case. If it were mine and if the cavitation plate is running at or near the top f the water as it should, I'd give it more time to loosen up before I considered moving it around on the transom or changing props. It might be nothing more than poor quality fuel or maybe some extra weight in the boat causing the lower rpms. I agree that something isn't quite right since I would expect a slight improvement in performance with an XS over the Optimax.
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catchersrock
Ensign
Posts: 548
Location: Maiden NC
Sea Pro model and year: 2020 Sea Pro 228
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Post by catchersrock on Sept 21, 2018 11:44:06 GMT -6
If I'm not mistaken, the max recommended rpm at WOT is 5750 so you're very close if that's the case. If it were mine and if the cavitation plate is running at or near the top f the water as it should, I'd give it more time to loosen up before I considered moving it around on the transom or changing props. It might be nothing more than poor quality fuel or maybe some extra weight in the boat causing the lower rpms. I agree that something isn't quite right since I would expect a slight improvement in performance with an XS over the Optimax. Thanks Juan. The catalog number for max rpm is 5750, but, the service manual lists max at 6000 and the guardian system kicks in at 6300. I have done some reading and it looks like it is recommended that the plate is in line with the bottom of the boat, which is pretty much where I'm at.
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Post by gnrphil on Sept 21, 2018 14:46:41 GMT -6
The difference you're seeing may be to do with the different gear ratios, the pro xs has a 2.08 and the old motor a 1.86 or 7 I believe. Using the same prop on both would give different results.
Edit: Just played with the mercury calculator and the difference between the two gear ratios yielded a 5 mph difference, I can't explain the lack of rpm though.
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Post by freezerfiller on Sept 21, 2018 15:14:47 GMT -6
The difference you're seeing may be to do with the different gear ratios, the pro xs has a 2.08 and the old motor a 1.86 or 7 I believe. Using the same prop on both would give different results. Edit: Just played with the mercury calculator and the difference between the two gear ratios yielded a 5 mph difference, I can't explain the lack of rpm though. If that's the case, you would think it would yield higher rpms...
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Post by freezerfiller on Sept 21, 2018 15:15:57 GMT -6
I'd look at the cav plate while on plane and see if you need to go up a hole.
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Post by gnrphil on Sept 21, 2018 15:25:54 GMT -6
The difference you're seeing may be to do with the different gear ratios, the pro xs has a 2.08 and the old motor a 1.86 or 7 I believe. Using the same prop on both would give different results. Edit: Just played with the mercury calculator and the difference between the two gear ratios yielded a 5 mph difference, I can't explain the lack of rpm though. If that's the case, you would think it would yield higher rpms... I don't know to be honest, would it ?.
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Post by gnrphil on Sept 21, 2018 15:30:33 GMT -6
Interesting point also is he's getting -6% slip with those numbers !!!!!
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Post by Juan on Sept 21, 2018 16:03:34 GMT -6
If that's the case, you would think it would yield higher rpms... I don't know to be honest, would it ?. I'm guessing the difference in gearing may be the answer. I thought about it but was too lazy to check to see if there was a difference in the two. I'd guess the larger gear case in the XS would result in fewer revolutions at the prop than the smaller gear case in the Optimax was turning... and if that's the case, you would think you could decrease prop pitch a number or two to increase the rpms to get it in the recommended WOT range.
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catchersrock
Ensign
Posts: 548
Location: Maiden NC
Sea Pro model and year: 2020 Sea Pro 228
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Post by catchersrock on Sept 21, 2018 17:58:37 GMT -6
Thank you so much guys. I had no idea the gear ratio was different. I will do the research and math to track that down.
Thanks again,
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Post by freezerfiller on Sept 22, 2018 15:10:58 GMT -6
But if the new motor turns 10% more rpms, for the same prop revolutions, assuming hp is true, he should be getting 10% more rpms than he was, not less.
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Post by Juan on Sept 22, 2018 17:02:21 GMT -6
But if the new motor turns 10% more rpms, for the same prop revolutions, assuming hp is true, he should be getting 10% more rpms than he was, not less. This is starting to get confusing and maybe I'm missing something here and I see your point but have to disagree. If there's a difference in rpms by 10%, the difference in rpms at the prop wouldn't be 10% more rpms than he was getting because of the difference in gear size in the two motors. I think there would be a difference but not 10%
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Post by freezerfiller on Sept 24, 2018 10:10:30 GMT -6
But if the new motor turns 10% more rpms, for the same prop revolutions, assuming hp is true, he should be getting 10% more rpms than he was, not less. This is starting to get confusing and maybe I'm missing something here and I see your point but have to disagree. If there's a difference in rpms by 10%, the difference in rpms at the prop wouldn't be 10% more rpms than he was getting because of the difference in gear size in the two motors. I think there would be a difference but not 10% You are correct it is more like 6%. My point is if the new motor is geared lower, it should spin more rpms for the same prop speed.
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Post by Juan on Sept 24, 2018 14:21:34 GMT -6
This is starting to get confusing and maybe I'm missing something here and I see your point but have to disagree. If there's a difference in rpms by 10%, the difference in rpms at the prop wouldn't be 10% more rpms than he was getting because of the difference in gear size in the two motors. I think there would be a difference but not 10% You are correct it is more like 6%. My point is if the new motor is geared lower, it should spin more rpms for the same prop speed. I "think" I'm finally seeing what you're saying. I'm thinking that his new motor is like our Suzukis.. it has a lower gear ratio (2.08 to 1) than his Optimax had (1.86 to 1)..which should allow him to use a slightly larger prop without reducing rpms and I would think using his old prop on the new motor would cause the rpms to be a little higher but they aren't. I give up... trying to figure this one out is giving me a headache.
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Post by AHHHH-Spray on Sept 26, 2018 11:52:11 GMT -6
Where's the guy that did all the maths for fuel tank capacity? Maybe he can explain this one too.
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catchersrock
Ensign
Posts: 548
Location: Maiden NC
Sea Pro model and year: 2020 Sea Pro 228
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Post by catchersrock on Mar 8, 2019 10:19:33 GMT -6
Guys
After trying to read all I could and talking to a few local shops, I bought a 16" Pitch Mercury Enertia I found on line and got a good deal. So, I dropped from the 17" Vengance to the 16" Enertia. RPM's up to 5800, Top Speed unchanged. Big change in handling. Boat seems to me to be riding much higher in the water and trims out like a bass boat, even gets a little squirly at the top, trimmed to the max. The ride is very different. Bow seems to be higher. When I ran down the trim tabs to drop the bow, the boat got pretty loose in the rear end and lost most steering response. The ride and handling on the Vengance is much better. The boat does jump out of the hole on the Enertia and planes at lower speed. Also, the blow out on sharp turns I would see on the Vengance is gone on the Enertia.
Im confused!
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Post by Juan on Mar 8, 2019 13:12:12 GMT -6
Since you gained 300 rpms with the Enertia you're now closer to factory recommended rpm at WOT and I'd guess it's running more efficiently than it was. They say EVERY prop manufacturer (even the exact same specs) performs differently so an 16" Enertia could act differently than a 16" Votex or Solas, etc. There's a LOT of trial and error involved in finding the perfect prop. I've been happy when I find one that gets close. I'd run the Enertia and get used to the changes if it were me.
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