Cavitation or slipping transmission?

[2500HD]

2000 supra santera with a hurth hsw 450d transmission.
Boat has been great but as of late i have been adding more and more weight for surfing. In doing so i have noticed the rpm's starting to fluctuate. This is also accompanied by an occasional shudder when the rpm's come back down. The boat doesn't seem to have any fluctuation out of the hole when pulling a skier and getting on plane, just when slammed and surfing. My question is would the transmission slip all the time or only under a heavy load like surfing? I would love some input before pulling the tranny and doing what might be an unnecessary rebuild. Thanks!

[Cusefan78]

If it's slipping the Rpms would fly up then when it catches they will drop to normal. Be careful with the weight. If you keep slipping the tranny you will glaze the discs and fry them. I would back off the weight

[Kma4444]

Sounds like cavitation to me for sure. The trans wouldn't do that too many times until it was done for. Smell the transmission fluid, your nose will know for sure if it has been slipping. I would be willing to bet it's your prop. Get an ACME and be amazed.

[2500HD]

Got an oj prop on it already, but it isn't the exact one i want. It's a 13.5x14.5 what nettles had recommended was a 14.5x13.75 acme 916. I just happened to find this one for half the price.
I did inspect the tranny fluid and it's a nice red color with no burnt smell. All things point to cavitation but i wanted second opinions before screwing something up.
I just put my wakeshaper back on the boat so i won't have to slam it, hopefully this take care of the cavitation issue.

[chris young]

There is a third, much less likely option, but it did happen to me. The PO never put the cotter pin in when he had the prop off (I'm assuming, as I have a photo of the boat from underneath before I bought it and no cotter pin.) I'm to blame, I never bothered to check.

Anyhow, over the summer the nuts came loose and the prop shortly thereafter. Somewhere along the line the key made it's way out. Following that the shaft would slip in the prop then the force would push the prop back on and the slip would disappear. Probably not the case for you, but it's worth taking a look.

[2500HD]

Chris, that is one of the first things i checked after i remembered your post about losing the key and your driveshaft. All is nice and tight under there.

[svahle]

Have you checked the fluid level? I don't know about your specific tranny, but the velvet drive in my '86 Sunsport is finicky about the fluid level. This might be a foolish suggestion, but if the fluid level is a little low, the boat weighted more heavily in the rear, plus the attitude of the boat while surfing could it cause the fluid to run toward the stern starving the pump of fluid and causing slipping. My fluid level was a little low two summers ago and I experienced slipping only when accelerating from a standstill or very slow speed and turning. Just a thought.

[CornRickey]

I dinged up one of the flutes on my prop this summer. I never had a issue with it until had three tubes with 9 kids behind the boat. No problems out of the hole going straight but when I turned to the right and straightened it would rumble and rpms would wise then drop. It was cavitating and went away when I changed out the prop.

[2500HD]

Tranny fluid is good and prop is good. It only happens when it is choppy so cavitation is the likely suspect.