View Full Version : Reverse Vibration
When I select reverse I experience excessive vibration throughout the cockpit. Is this normal? The boat was recently refitted with a completely new driveline including a 3 blade prop. Forward has no problems, infact is a little fast. At 750 rpm I can maintain 3.5 knots, at 1000 rpm 4.5 knots. Rick.
Dakota Jim Russell
08-13-1999, 06:29 am
Did you get a feathering prop? If so, it may be that it is not completely reversing itself. Maxiprops need to be worn in slightly sometimes to eliminate any rough spots. For example, I put mine together, added grease, and reversed it multiple times before I installed it. If that wasnt't done to yours it may be hanging up on a small burr or piece of grit on the gears.
The prop is fixed 3 blade.
I also fitted a R&D Flex coupling (PYI) when the new drive line was installed.
I HAVE A 35.5 AND THE LAST THING I THOUGHT OF WAS THE ENGINE MOUNTS. A 5YEAR OLD BOAT SHOULDN'T NEED IT BUT IT DID. JUST A SUGGESTION
Jim Flowers
08-16-1999, 01:18 pm
That doesn't sound right, like bad pitch and/or diameter selection. If your 37C has a Yanmar 3QM30F with 2.1 to 1 reduction
Jim Flowers
08-16-1999, 01:38 pm
Sounds like it might be a problem with the prop selection. If you have a Yanmar 3QM30F it has a max bhp of 33 @ 2800 rpm and a continuous rating of 30 hp @ 2600 rpm. With a 2.1:1 gear reduction. MaxProp recommended a 16x14 folding 3 blade. If you're getting 53% of hull speed at 38% continuous rated rpm it sounds like your pitch or diameter might be too great. You want to have clearance between the prop tip and the hull of 15% of the prop diameter or more if you can get it. What speeds do you get on level water at 2600 and 2800 rpm and is there any black smoke? Your milage may (and probably will) vary.
The engine mounts were replaced when new engine was installed. The Yanmar was replaced with a 35hp Perkins with a new Hurth gearbox. The prop shaft was new and the shaft bearing was replaced. The shaft appears to run true and the engine was aligned after launching. I do not have the prop specs, but it was matched with the driveline to the boat. The company I purchased the driveline has offered help, ( if i can take it from Ma to Fl ). I have not run the engine higher than 1500 rpm as the engine is new and I would like to run it in gently. But at 1500 rpm I was able to achieve 6.5 knts. Rick.