high RPM (2200+) brings a slight banging noise to shaft

[bobm]

Im just fishing around here-this is the best board Ive found on the web-
I bought a HR31 with a new westerbeke 30b (35 hours) with a size 16 prop and a 9 pitch...the correct size as stated in the manual is 16 with an 8 pitch...the prop is old and probably out of balance...it is chipped and scarred-the motor can run fine from 1500 to 2000 in fact it purrs at 2000 and the shaft and prop are fine at that RPM. The problem is the cruising speed, as stated in the manual, is an rpm of about 2500...when I put it up that high it starts banging around-the cutlass is tight, but I think I will screw it and the shaft up if I run with all that banging...the banging is near the prop and it sounds bad...shouldnt the motor and the prop run fine at all RPMs?

I hope it is just the fact that the prop is the wrong pitch and is old...Im eventually going to have a mechanic look at it and was wondering if anyone on the board has any ideas I can float to the mechanic...the owner of the little yard I was at previoulsy at said the shaft and motor are aligned...now Im at Yankee POint, outside of Deltaville, Irvington and they seem to be a first class yard and I hope they can set me straight.

Thanks again
Bob
HR 31



merrick@pop.net

[Boyd]

Hi Bob...

Whats a HR31? What is the underwater profile. Full keel or fin keel?
Dont run at that speed until you get it fixed. Sounds like it could damage something.

Could be ....

Something wrapped on the prop.
Prop way out of balance causing the engine to shake.
Prop shaft is bent.
Rudder shaft is lose and the rudder vibrates.
Cutlass bearing is not good
Transmission flange not tight.
Motor mounts not tight.
Motor and shaft not aligned.

Some part of the engine is touching something else and making the banging noise. Such as the muffler. Mine had almost rubbed a hole in the hull made a thumping noise at idle. The clue was the pile of dust under the muffler. PO hadnt noticed at all.

Does the engine vibrate excessively with the transmission in neutral at that rpm? Can you feel the bumping when you put your hand on ...

1. Stuffing box
2. Engine
3. Transmission
4. Hull

Good Luck
Boyd
s/v Tern
Fort Lauderdale, Fla

Im just fishing around here-this is the best board Ive found on the web-
I bought a HR31 with a new westerbeke 30b (35 hours) with a size 16 prop and a 9 pitch...the correct size as stated in the manual is 16 with an 8 pitch...the prop is old and probably out of balance...it is chipped and scarred-the motor can run fine from 1500 to 2000 in fact it purrs at 2000 and the shaft and prop are fine at that RPM. The problem is the cruising speed, as stated in the manual, is an rpm of about 2500...when I put it up that high it starts banging around-the cutlass is tight, but I think I will screw it and the shaft up if I run with all that banging...the banging is near the prop and it sounds bad...shouldnt the motor and the prop run fine at all RPMs?

I hope it is just the fact that the prop is the wrong pitch and is old...Im eventually going to have a mechanic look at it and was wondering if anyone on the board has any ideas I can float to the mechanic...the owner of the little yard I was at previoulsy at said the shaft and motor are aligned...now Im at Yankee POint, outside of Deltaville, Irvington and they seem to be a first class yard and I hope they can set me straight.

Thanks again
Bob
HR 31

boyd @wbta.cc

[Patrick Turner]

If it sounds good at all the lower rpm's and you are able to reach full rpm's as stated by the manual, it might be that you are experiencing cavitation which can sound like glass beads or bb's hitting your hull, but it can also make a banging sound. That sound is really little explosions of pressure against the hull. If the prop is really chipped and old, it might be time for a new one anyway. Get it pitched to the factory specs for you boat/engine and keep the old one as a spare. Talk with a good prop shop and see what they have to say. Also check really stupid things like....is there a seacock handle that is near a bulkhead that at 2500 rpm's starts to shake just right and bangs the bulkhead. I had a loud irregular ratteling going on that sounded like it was coming from the prop. If I stood along side the boat at the dock, I could hear it coming from under the boat. It turned out to be the aforementioned seacock and the sound was just traveling throughout the hull. Took me days to figure out....I even had a diver check out the prop zinc. Silly me.

Pat



patrick.t@attbi.com

[bobm]

Hi Bob...

There isnt anything on the prop-the boat/motor/shaft and prop all run fine, with no banging or anything from 1500 to 2000 rpms-it is smooth as silk and I make pretty good headway-there is no problem at those rpms-its just not the rpms that the motor should run at...

At higher RPMS, right when I get over 2000, a small rapping starts, and it gets louder and occurs more as the rpms are increased-I back it off to 2000 and it will immediately stop...the motor idles fine at 1000.

BTW Halberg Rassy 31-full keel-not a Cape Dory-though Im still looking for a good Cape Dory-older one from the late 70's early 80's in the 33 size

Bob



merrick@pop.net

[Al Smith]

We just went through something like that and with the help of this board, decided that it was the cutlass bearing. Turned out that the bearing was bad, abut also the alignment was off, causing the bearing to go.

Yankee Pt. Marina is a good one, as is Custom Yachts in Irvington. If they cannot help you, Henry Lackey at Deltaville Diesel can.

Al



saylr@adelphia.net