95 355 Aft - noise level

[chpsk8]

So I bought this boat a couple years ago now and have been working on getting it back in tip top shape.
One nagging question I’ve been having is this... how loud should it be in the aft stateroom at anything over about 9mph?
I have noticed that it seems unusually loud in our stateroom. It’s worse in the head and seems to get quieter as I move to the port side, but it’s not that big of a space so it could be an illusion.

When I lift the hatches and listen to the gearboxes they don’t make any odd noises. The cutlass bearings are three years old, the shafts are also new and they turn by hand easily. Both have a very slight wobble, but there is no vibration at any speed.

I noticed this spring that the starboard prop had a slightly bent blade and it was clearly repaired at some point. The leading edges were of color and you could see where work was done. I sent that prop out to be scanned and refreshed.

Not sure what else I should be looking at now. Even the yard is a little puzzled. Once the prop comes back this week they are going to stethoscope the gearboxes again to see if they hear anything.

Part of the problem is that it seems loud in there, but is it maybe supposed to be? What I’m hearing could only be explained as a howling. It doesn’t drone, it doesn’t vibrate, it doesn’t pulse, it’s pretty steady and follows the rpms. You sure aren’t taking a nap back there that’s for sure.

Just looking for some thoughts on how loud that room is underway.

FWIW my 95 is hull #1. So most of the drawings don’t align with what my build has. Makes things kinda fun tracing wires and plumbing runs!

[bud37]

I don't know that boat in particular but I can say that lots of times sounds like that can be traced to exhaust systems. Sometimes hangars need to be isolated from vibrating thru their mounts to the floors and bulkheads. Check your mufflers and hose as well.

Hull #1...wow

[Viper]

Source of the post....Both have a very slight wobble,....

They shouldn't be wobbling. In all this, has anybody removed the fasteners from the shaft couplers and checked alignment? Are you noticing the the wobble at the shaft logs? Has anybody checked those?

Almost sounds like you're describing a strut bearing, shaft log, or tranny haul. They will all amplify in the aft cabin.

Curious to see what they find with the prop and whether that makes a difference.

Is she blocked on land right now or is she in the water?

[chpsk8]

She’s on blocks right now. Where I can see a slight wobble, and I’m talking slight, is at the coupler to the trans. There’s no noticeable movement as the shaft leaves the hull.

When you rotate the shaft by hand it is very smooth and easy to move. The yard is going to take the coupler bolts out and align everything as part of the troubleshooting. They are also going to run through the rpms with the prop off and see if they can hear anything.

So I’m guessing you guys are confirming it shouldn’t be too loud in that aft cabin? So I’m not chasing a ghost at least!
Keep the ideas coming, I’ll post progress as they diagnose it. They are really good and don’t want to just throw parts at it, but sound is pretty subjective also. Makes it a little tough to trace.

[tomschauer]

I have a 1998 355, keep in mind you have two big block chevy engines just forward of your aft cabin with about 3/8" of plywood for a noise buffer. Also, the props are directly below the aft cabin, so yes, it is noisy back there. You should hear the engines, tranny hum and some noise from the props, but it should all be steady an consistent, no thumps or vibrations.

[bud37]

Source of the post When you rotate the shaft by hand it is very smooth and easy to move. The yard is going to take the coupler bolts out and align everything as part of the troubleshooting. They are also going to run through the rpms with the prop off and see if they can hear anything.

Be aware that any proper FINAL shaft/engine alignment should be done with the boat in the water, relaxed for at least 24 hours for best results.

[chpsk8]

Source of the post I have a 1998 355, keep in mind you have two big block chevy engines just forward of your aft cabin with about 3/8" of plywood for a noise buffer. Also, the props are directly below the aft cabin, so yes, it is noisy back there. You should hear the engines, tranny hum and some noise from the props, but it should all be steady an consistent, no thumps or vibrations.

Have you ever noticed it's louder on one side than the other? Ours is loud on the starboard side but that's also the side that doesn't have a bed to muffle anything. Loud like you would need to elevate your voice to be heard. Not shouty loud though.

Bud - we'll be sure to do the final check in the water so everything is soaked through for sure.

[chpsk8]

Quick update on the diagnosis.
Prop came back super nice looking and back in spec.
Put a dial indicator on the shaft and it's out around 7 thousandths on both ends, so that's been yanked and sent off to get straightened.
Next was to look at the trans. Ran in forward and reverse and definitely hearing the wrong noises in there. Tech called his expert and they said to pull it and get it rebuilt. I'll get the details on why later. Sometime before me buying the boat the PO ran over a channel marker and wrapped the chain around the running gear completely stopping the starboard motor. It's very likely that when they did the repair from that damage they either didn't look at the trans, or this problem accumulated with time after that incident and I get the fun of fixing it. The trans guy said a hard stop will cause some gears to twist and shear, so he's got a full on rebuild spec'd into the cost.

So off to Michigan the trans goes, should take a week to rebuild, then back here to MN to get reinstalled. Hopefully in a couple weeks we'll be back in the water with a little lighter wallet, but a much quieter boat. I'll post more as things progress.

[Viper]

Glad you figured it out. Hopefully that will be the end of it. Thanks for following up and keeping us in the loop.

[tomschauer]

Glad you found these problems before they left you dead in the water. Sorry you found expensive problems.
I don't mean to pee in your corn flakes, but even after this is all done, you wont be able to "nap" in the aft cabin while under way on plane unless you are passed out drunk or deaf. It is noisy by design.