Funny noise

[wumhenry]

Originally Posted by timebandit

I will put my $20 on the rudder pivot points.

The funny noise isn't affected by movement of the steering wheel. I'm pretty sure it's in the drivetrain.

[wumhenry]

Originally Posted by Gene T

You still have a cutlass bearing, but a bad one probably wouldn't sound like a chatter. Your rudder might be making the noise, being buffeted by the prop.

Heavy powering in waves would cause the stern to squat, or sink lower than normal. This could change several things, one is the exhaust. If the exhaust is now submerged that could cause interesting noises. Does the sound change if you change the engine RPM?

I doubt we can diagnose it for you, I would try to repeat it with someone else driving the boat so I could crawl around below deck and listen. Sound travels so you might need to use a listening stick.

Why would the rudder be buffeted by the prop in a heavy chop but not in flat water?

[Gene T]

Originally Posted by wumhenry

Why would the rudder be buffeted by the prop in a heavy chop but not in flat water?

Lets look at what's different. In a heavy chop the boat will be going slower through the water with the same RPM of the prop, so the effect of the prop wash will be greater.

[trantor12020]

wumhenry, can you dive in and check the free play of your cutlass ? Take alook at the prop nut too, make sure it isn't loosen. Mine was loosen and ocassional the prop moved some, making crocking noise. Then is reseated as the nut tighten itself through spinning action. Funny things happen.

[wumhenry]

Originally Posted by trantor12020

wumhenry, can you dive in and check the free play of your cutlass ? Take alook at the prop nut too, make sure it isn't loosen. Mine was loosen and ocassional the prop moved some, making crocking noise. Then is reseated as the nut tighten itself through spinning action. Funny things happen.

I can easily turn the prop shaft by hand (inside the boat) with the tranny in neutral. Does that tell you anything about the condition of the cutlass bearing? (Not trying to be smart-alecky; I'm not sure whether it does or doesn't mean that the cutlass is OK.)

Re the loose-prop-nut theory: I'll check the nut, but I don't have much hope that'll solve the problem because the noise is constant when I'm motoring in a chop, not occasional.

[wumhenry]

Originally Posted by Gene T

Lets look at what's different. In a heavy chop the boat will be going slower through the water with the same RPM of the prop, so the effect of the prop wash will be greater.

What happens when the rudder is buffeted by prop wash? I mean, what is the process that produces a funny noise? Can it result in damage?

[sailaway21]

wumhenry,
While it does not sound correct to you on first glance, your engine is not nearly as "loaded" in calm waters as it is in a seaway. You can be at high rpm and still have a relatively unloaded engine. In a seaway the prop is going to come under heavier load due to vessel motion as well as rudder effects. I'd pursue as suggested by Rick above, it does not sound like a sound with a happy ending left unresolved.

[Gene T]

Originally Posted by wumhenry

What happens when the rudder is buffeted by prop wash? I mean, what is the process that produces a funny noise? Can it result in damage?

Any funny noise can cause damage, so you need to figure out what it is. It sounds like you have a full keel boat, with the rudder attached to the keel and a cutout for the prop. If not it is probably attached to a skeg, in either case there are pin type hinges to support the rudder. If these have play in them the rudder can vibrate, or rattle as the blade of the prop pushes a pulse of watter past one side of it. If the rudder is well balanced it won't vibrate while sailing because the water passing by can stabilize it. If you keep your boat in a slip and can tie it securely to some stout dock cleats you can power the boat up in forward and see if you can duplicate the noise. It actually doesn't put much strain on the dock or cleats, it's a small motor after all.

Note: this may not even be the noise you are hearing. It could be something completely different

[trantor12020]

Originally Posted by wumhenry

I can easily turn the prop shaft by hand (inside the boat) with the tranny in neutral. Does that tell you anything about the condition of the cutlass bearing? (Not trying to be smart-alecky; I'm not sure whether it does or doesn't mean that the cutlass is OK.)

Re the loose-prop-nut theory: I'll check the nut, but I don't have much hope that'll solve the problem because the noise is constant when I'm motoring in a chop, not occasional.

Nope not same. You'll have to grap the prop and lift it up and down. If the cutlass has 1-3 mm play in it, you'll know straight away. You have to get wet unless you intend on hauling it out of water.

[wumhenry]

Originally Posted by Gene T

Any funny noise can cause damage, so you need to figure out what it is. It sounds like you have a full keel boat, with the rudder attached to the keel and a cutout for the prop. If not it is probably attached to a skeg, in either case there are pin type hinges to support the rudder. If these have play in them the rudder can vibrate, or rattle as the blade of the prop pushes a pulse of watter past one side of it.

So if the rudder is being buffeted, I'd feel vibration through the steering gear, no? I haven't felt any unusual vibration in the steering wheel when the funny noise crops up.

Originally Posted by Gene T

If the rudder is well balanced it won't vibrate while sailing because the water passing by can stabilize it. If you keep your boat in a slip and can tie it securely to some stout dock cleats you can power the boat up in forward and see if you can duplicate the noise.

I only get the noise when powering in a chop, so I don't think I could reproduce it while the boat is immobile in a slip.