Porpoising

Superphil69

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Just bought a G23 with a Mercury 250XL

Owner before me says that he experienced porpoising at WOT. He was correct..
Trim is at 2 when occurs. Motor is mounted on lowest position, highest hole.(meaning it has a lot of room to come higher out of water)
My belief, and all that I read is that this is caused by the motor being mounted too low in the water.. Drag is causing boat to push down at higher speeds, creating issue.

Be curious to hear what the group has to say. I am getting 48 mph, but I think that over 50 is where I should be and that I shouldn't have to run at such a flat trim. i.e. I should be able to get that bow out of the water more, way more, and help gas guzzling a little too...
 

BigKahuna

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Hey Superphil. Couple things. Check to see if the ventilation plate on your outboard is even with or just skimming the top of the water when you are at speed. If it is it's most likely mounted correctly. If you can't see it it's probably too low in the water. Another factor could be weight distribution in your boat. Too many people/weight up front or in the rear can play a part. You can get rid of the porpoising by playing with your trim angle. Start out in neutral trim and as you accelerate trim up to bring the front out of the water. The more your boat comes out of the water the faster you will go. If your prop begins to ventilate or lose grip back the trim down. If your boat begins to porpoise back down on the trim also. You're trying to find that sweet spot where your boat is running at speed with no porpoising or ventilation and optimum fuel economy.....
 

lakeliving

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I raised my motor up one hole. It helped with top speed but hindered the ability to make sharp turns while under speed. There is always a give and take!
 

Superphil69

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Hey Superphil. Couple things. Check to see if the ventilation plate on your outboard is even with or just skimming the top of the water when you are at speed. If it is it's most likely mounted correctly. If you can't see it it's probably too low in the water. Another factor could be weight distribution in your boat. Too many people/weight up front or in the rear can play a part. You can get rid of the porpoising by playing with your trim angle. Start out in neutral trim and as you accelerate trim up to bring the front out of the water. The more your boat comes out of the water the faster you will go. If your prop begins to ventilate or lose grip back the trim down. If your boat begins to porpoise back down on the trim also. You're trying to find that sweet spot where your boat is running at speed with no porpoising or ventilation and optimum fuel economy.....
It was porpoising with just me on boat and a full tank. IMHO the plate did look low in the water
 

Superphil69

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Its going to a dealer this Sunday to get raised, at least I hope so.. I will re-post once complete, and results..
 

Jb75

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Its going to a dealer this Sunday to get raised, at least I hope so.. I will re-post once complete, and results..
In my experience raising my motor allowed me to run more trim angle with less porpoising. But I’ve since moved it back down to the lowest setting as we do more water sports than anything and didn’t like the grip I lost in turns. Good luck. Keep us posted. My boat runs 45-47 most days as mounted. 46-49 when raised a hole.
 

Vikingstaff

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That’s always the trade off, raising it for those benefits, but losing grip in turns, or having it a bit lower, but full grip and maneuverability. Minimally it seems like you could just trim the motor while at WOT to get rid of the porpoising. Does trimming it not help?
 

Superphil69

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That’s always the trade off, raising it for those benefits, but losing grip in turns, or having it a bit lower, but full grip and maneuverability. Minimally it seems like you could just trim the motor while at WOT to get rid of the porpoising. Does trimming it not help?
It does to a degree but I feel like I am almost plowing
I have never had a boat that is at zero trim at WOT.. Just seems odd..
 

Vikingstaff

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It does to a degree but I feel like I am almost plowing
I have never had a boat that is at zero trim at WOT.. Just seems odd..
That does seem odd. Just thought I’d ask. Hopefully it can get resolved asap with remounting the motor.
 

SEMPERFI8387

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Sandbags in bow seats should help ..... sorry couldn’t resist. :p
 

Superphil69

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Well, news was not as expected. It appears as if the motor being in the lowest position is the best it can be. Tech said it actually should go lower. I just got the call. I am so confused.
Said it was a pre-rigging issue from Bennington.
I have no idea what to do now..
 

Vikingstaff

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Well, news was not as expected. It appears as if the motor being in the lowest position is the best it can be. Tech said it actually should go lower. I just got the call. I am so confused.
Said it was a pre-rigging issue from Bennington.
I have no idea what to do now..
Wait, what?

Pre-rigging should not impact what hole the motor can be mounted in. It should be set up in a way that allows it to be moved to any hole mount. I’d have them walk me through it and point that out - In Person…partially since the dealership does the final rigging and mounting of the motor.

I question if it is connected to pre-rigging on Bennington‘s end (or if that is the dealerships excuse) vs. actual dealership rigging on their part (and thus their responsibility). By having them walk you through it in person, you can really see which party is at fault here because it should be moveable.

However, saying it cannot be moved, when it is made to allow that flexibility, would not be an acceptable answer for me.

For perspective too, my dealer origianlly did a POOR job on placement and rigging of my fuel-water separator. In year two this poor rigging led to the wires for the sensor being pulled out if it and my motor defaulting to safety mode because it couldn’t read moisture levels in the fuel line. The dealerships took responbility for poor rigging placement and corrected it.

If your dealership botched some aspect of rigging, they need to take responsibility and rectify it. However, if it is actually on Bennington’s end (seems unlikely, but maybe something went astray in assembly), seems like Bennington would remedy that under their warranty.

Follow back up on this one. Something doesn’t sound right to me…one way or another.
 

Superphil69

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To be clear the motor can be moved, but only up. Its on the top hole.
I will take pictures before I put it in and move it back to its dock
 

SEMPERFI8387

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Bennington does not “rig” motors, just the throttle/cables. Sounds like dealers trying to blow smoke ...
 

SEMPERFI8387

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I know this sounds dumb but does your boat sit “lower” in water than normal, or do you have a local scale to weigh it? I’d it possible it may have water in a chamber on each side causing weight balance issues and porpoising? I know that sounds dumb and far fetched but crazier things have happened.
 

Remediation

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On Semper's thought, if on a trailer stand beside it and have the truck jerk the trailer. If there is water in the toons you will hear the sloshing. Ask how I know!
 

Superphil69

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Photos as promised.
 

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