Mercury 115 vibration - help please

[Deleted]

2006 Sea Pro 186cc with 115 Mercury 4 stroke (not Verado). When easing on to plane with partial throttle the motor vibrates the hull and console pretty bad. I also hear a bit of what I think is prop chatter, but can't say for sure. Once on plane the sound and vibration goes away, and the motor is smooth as butter topping out around ~5900 rpm and ~36 mph, so I don't think this is a motor issue. More likely it's a prop issue or operator trim issue ...

The boat is new to me, so I may not be trimming the motor correctly. I was trimmed down on the first water test, and didn't think to try getting on plane trimmed up.

The prop is a stainless steel vengeance that apparently came with the boat new. I'm pretty sure it's a 14 diameter, but will have to check the pitch (in storage right now). Anyway, it has this hub assembly I have never seen before. I am used to a cotter pin setup. This looks like a circle with teeth on it. I am guessing it's a Torque I,II,III or the like. Googling suggests this particular motor is known to vibrate with SS props due to their weight, and suggests the hub needs attention/tightening.

[Juan]

Sounds to me like you've already pegged the possible problem... sure sounds like a prop issue to me. I doubt trimming the motor one way or the other would make any difference but I also wouldn't think that the added weight of a SS prop would cause a vibration unless maybe one or more of the blades were damaged or dented.. a vibration could possibly cause a problem with the prop shaft seal so I'd try another prop to see if that eliminated the vibration.

[Deleted]

Spoke with the prior owner, and they keyed in on the fact that I was trying to plane with partial throttle. They recommended I peg the throttle to get on plane, that should eliminate the vibration, and most motors will have a difficult time with that much load and partial throttle. My prior boat didn't but in theory it makes some sense, guess I'll find out this weekend.

If it doesn't resolve itself, I agree with you Juan it may be time to try a new prop. The prior owner was extremely meticulous (EXTREMELY), and the SS prop on the boat appears to be in perfect condition ... except that the edges are sharpened. This could be the issue, perhaps the prop is out of balance. I doubt it is knowing how the prior owner treats his stuff, but it is a possibility. I confirmed it is a 14 pitch (not diameter) and a 13.375 diameter. I am also wondering if the hub might be bad ...

[T-Topless]

The prop could be loose. Check it by hand and tighten it if necessary.

The Sea Pro 186CC test in 2007 by Mercury with the Merc 115HOP motor like yours was done with a Vengenance 14dx10p prop (yes - only 10 Pitch). rnr-marine.com/SeaPro.shtml#seapro186cc

They saw 38mph and 4.4mpg and 0-20MPH took 8.75secs, which is relatively slow. Its hard to imagine this speed with the 2.33:1 gears and just 10" of pitch.

[CaptWoody]

"They saw 38mph and 4.4mpg and 0-20MPH took 8.75secs, which is relatively slow. Its hard to imagine this speed with the 2.33:1 gears and just 10" of pitch."

I agree it is hard to imagine that speed. That is around the specs I get on my 90 HP and it has a 21 inch pitch. I am overpitched, should most likely be 19 or 17, but I can't imagine a 10 inch pitch.

[Deleted]

10 pitch threw me for a loop too. I was using the performance report as a benchmark for what I should expect, but clearly I'm not comparing apples to apples. I checked Mercury for prop recommendations. 14 to 16 pitch is recommended, yet they tested the boat with 10 pitch Another possible difference with the performance report is the 20 inch motor shaft. I thought mine was a 25 inch shaft, I'll check.

Prior owner claimed over 40 mph top speed on a perfectly flat bay, and I had my doubts due to the performance report with top speed ~38, but now it makes sense with the higher 14 pitch prop.

When I removed the prop the bolt was very tight, but at the time I didn't think to wiggle the prop and see if it moved any. Next time I will and report back. Thanks for the tips, it's best to know as much as possible so nothing get missed.

[Deleted]

Reinstalled prop nice and tight + full throttle getting on to plane = no issues.

[T-Topless]

Still vibrates if you don't use full throttle?

[Deleted]

Not sure. Once it was working right, I went fishing and didn't mess with it anymore. We did run in the 5-8 mph range for a bit, and I don't recall any vibration. I'll check specifically next time. Weather has been bad, so it might be awhile.

One difference I do recall is that the prop chatter is gone, which leads me to think it was a loose prop.

[Deleted]

Update. Now that I have had some time operating the boat, I'd say there are no issues with abnormal vibration at any speed. I was still getting a little noise after tightening up the prop, but found the latch to the livewell was resonating while getting on plane. The roundish metal handle sits in a metal housing, and they rub together causing the noise. Put your finger on the latch while going on to plane, and the noise is gone.

This motor is too quiet, it's got me thinking every little noise is cause for concern.

[Simple Man]

I'm glad your prop wasn't out of balance. You would be replacing a lower unit by now if it were and you kept running it.

[brian186dc]

I have a 07 SeaPro 186dc, with the Merc 4 stroke 115. Basically the same just different layout. The Vengeance prop came standard with the boat , hated it . I went with a Powertech SCD4 4 blade 17p, night and day on the hole shot and midrange acceleration .Boat also had a jackplate 5.5 set back; Top speed was 41.2 (GPS), 2 people, gear ice and 40 gallons of fuel. To make the hatches stoff rattling I just put a dot of marine silicone, so the handle latch sits on that rather than on the metal.