Catalina 350 International Association

I'm not sure if this is an engine/transmission problem or a prop problem, so I'm hoping to get some insight and advice. I have hull #5, so the boat is 12 years old. While driving under power into heavy seas on several occasions, we've lost propulsion. If we turn around and go with the seas, or tack through the seas on an angle at a slower speed, we're o.k. When the propulsion is lost, it seems that there's a bit of noise and vibration underfoot (by the prop?), and I watch the speed drop. Once I put the engine in neutral and then into forward, it will bite again, but would sometimes lose propulsion again. It seems to be in heavy seas and going directly into the waves. It happened at 1800 to 2200 RPMs, but also at a slow speed going up to a mooring.

I have Autoprop and thought it was a problem with the prop or prop alignment. Then someone said maybe the transmission is going. But, I've had many successful hours of running in normal conditions without the problem. I have a new shaft (5 years old) and the cutlass bearing was fine in the spring. There doesn't seem to be any vibration or misalignment in the shaft when the boat is in gear.

Thoughts?? I heard people complain about Autoprop and cavitation, so I almost bought a Flexofold prop at the boat show, thinking that might be the problem. Then, I was advised to make sure that I've identified the problem properly. I'd love to get your advice on this.

Jan
Seaquel
Hull #5

Might be worth looking at your damper plate. Do you have a lot of "chatter" when going forward at idle? Does it get quieter when you give it more throttle instead of idling? If so you may have a damper plate issue. Either way if you are having your transmission serviced or looked at, you will be able to check on the damper plate once the transmission has been removed.

PS are you a Schroeder as well?

I can think of two issues that would give rise to your complaints.
1) Simple cavitation is a really good ( and inexpensive ) answer. Coming down the Malaspina in 20+ knots of winds on the nose, with three foot seas, we had to throttle way back as every time Halona came up on a wave and slammed down, she'd trap a bunch of air beneath the bow and then by moving forward, that froth pocket would hit the prop and nothing to push against. Not true cavitation in the sense that the prop is generating so much negative pressure on the back of the blade that the water is boiling but the effect is the same. HOWEVER.... since you describe the loss of power moving up to a mooring...
2) Transmission (gear) is going bad. Read the posts in Engine : Transmission for a lot more detail. Bottom line: the ZF Hurth gear box is designed to NOT have a thrust bearing, but has a thrust washer. That washer wears and when it does, the clutch plate inside begins to fail to engage, leading to slippage, leading to loss of power.
al

I know you have checked the prop for barnacle buildup. I was moving my boat over to get hauled and noticed I didn't have thrust as normal. When hauled, there were several (not a lot!) of things attached to the folding prop. It doesn't take much to interrupt the laminar flow and create turbulent conditions which reduces lift and then can induce cavitation much easier.

dave