Bravo III rumbling sound

[charlieft]

Hello All,

Tonight when we were coming back from a short cruise I noticed that there was an intermittent rumbling sound coming from the drive train. The motor is very quiet when I rev it in neutral, but when it's in gear between 1500 and 3000 rpm there is a low rumble that was never there before. The rumbling comes in surges with quieter running in between the rumbles. This happened after I was running at around 3800rpms for 15 minutes or so in ~4 foot following seas.

Anyone ever experience this? Could this be related to the prop timing issue in NoWakey's post?

Thanks,
Charlie

 

[Dave S]

It won't have anything to do with prop timing.

Unfortunately there is no easy answer on this one. We could all hypothosize what you are hearing but If it were my boat, I would have the outdrive pulled and have everything checked out. It could be the u-joint or gimball bearing or maybe your coupler is worn or something is wrong in the drive itself. But pulling the drive will allow all that stuff to be checked out. At the same time everything can be serviced as well such as greasing the splines and the u-joint and the gimball bearing and the engine alignment can be checked. If it's been more than a year since you changed your outdrive gear fluid, I would get that done too.

 

[Sea Ray 300]

Hello All,

Tonight when we were coming back from a short cruise I noticed that there was an intermittent rumbling sound coming from the drive train. The motor is very quiet when I rev it in neutral, but when it's in gear between 1500 and 3000 rpm there is a low rumble that was never there before. The rumbling comes in surges with quieter running in between the rumbles. This happened after I was running at around 3800rpms for 15 minutes or so in ~4 foot following seas.

Anyone ever experience this? Could this be related to the prop timing issue in NoWakey's post?

Thanks,
Charlie

Try this first.
Trim the outdrive to the full down position, and see if it goes away.
When I trim mine up, more than a tiny bit, I get a rumble, on the verge of cavitation.
Therefore, I keep them nearly all the way down.

Let us know if it solves the problem.

 

[charlieft]

Thanks,

I will try trimming the drive down. I planned to take the boat out and gather more info before talking to the mechanic.

It sounds like an exhaust sound that's resonating in cycles.

Before our return trip to the marina we were anchored in shallow water and I had the drive trimmed up as far as it would go. I put it back down, but maybe it didn't go down as far as I thought. How accurate are those trim gagues? The smartcraft screen also has a digital readout that changes whenever I tilt the drive...I'm still working on interpreting the numbers.

-C

 

[Sea Ray 300]

Thanks,

I will try trimming the drive down. I planned to take the boat out and gather more info before talking to the mechanic.
It sounds like an exhaust sound that's resonating in cycles.
Before our return trip to the marina we were anchored in shallow water and I had the drive trimmed up as far as it would go. I put it back down, but maybe it didn't go down as far as I thought. How accurate are those trim gagues? The smartcraft screen also has a digital readout that changes whenever I tilt the drive...I'm still working on interpreting the numbers.-C

Charlie,
The trim gauges are not that accurate, and when you said that you were in shallow water, the first thing that came to mind was that you trimmed the drive.

I'd suggest re-trimming, and hopefully that will solve your problem.

 

[bobmcd33]

Check the balance of your props... mine are getting fixed now.... they will cause quite a vibration in the outdrive if they are out of balance (and shake the hell out of your outdrive).