2009 merc 50 hp question

[Branp]

I just tried my (new to me) merc out today. Everything ran real nice except a little sound I noticed. I only ran WOT for short bursts due to lots of crap floating in the river, but when I decelerate, quickly, i would hear some kind of "rattleing" sound. I really didnt try backing off slowly cause normally I was slowing down to avoid debris. I searched google and got a range of answers. Any thoughts? Thanks

 

[richg99]

Rattling....MIGHT describe cavitating. The prop is sucking air in and making that strange sound due to water bubbles (instead of all real water) contacting the prop blades.

It can happen if your motor is too high; if you are hitting waves; wrong prop; going too fast for the prop/motor/height setup. If you slow down, does it go away? If you can adjust the tilt/trim, it would go away if you adjust the motor trim IN, towards the boat.

Or...it could be the motor knocking....but I doubt it. Rich

 

[wasilvers]

Moter might be high where the exhaust is heard more (especially at wot). Motors do sound diff on fast deceleration than acceleration. But if it got your attention, maybe there is something to check out. Basically, my post is useless, lol.

 

[Branp]

Thank you both for the replies. I think I need to get out and do some more testing on it. I need to try different trim/tilt settings and also an answer I seem to hear a lot is decelerate slowly. Ive read some describe it as a racheting sound which is probably more accurate than rattleing. Thanks again. Oh, one more thing, its been awhile since i had a boat with power trim and tilt but if memory serves, dont you start trimmed dow for a good hole shot and than trim up when on plane? What about when slowing down?? Thanks

 

[richg99]

You've got it right. IN (prop towards the boat) for blasting off and getting up on plane...UP or OUT...prop moves somewhat away from the boat for faster speed, after you are up on plane. If you go too far...bow will rise up. Don't do that!

Never thought about it when decelerating. I guess I automatically return it to dead neutral to assist in putt-putting to my next location..
regards, Rich