Problem with power on turns II

[SooLineRob]

Hi all,

I didn't want to hijack the other thread, so here's a similar one...

Boat: 2004 FW 18' Freedom F/S bowrider.

Powerplant: Mercruiser 4.3L carb V6, 190 HP, Alpha One stern drive I/O, 14.25" 21" pitch aluminum prop with Flo Torq II hub.

Background: Last weekend while coasting forward at ~5-7 MPH/fast idle RPM's in 4' deep water, I heard a muffled "thump". Shut off engine and inspected stern drive/prop from in the water; no visible damage. Boat ran normally without any sign of trouble such as vibration, etc.. Once boat was drydocked, discovered one of three prop blades WAS bent out of alignment by 1/2". Appears I clipped something wood, like a tree stump or submerged log. Took prop to shop for rebuild/repair/balance, purchased exact new replacement (spare) prop. Installed new prop and hub kit per Mercruiser manual correctly.

Problem: After initial test run with new prop without incident, I throttled out for open water for the day. Hours later, while making hard turns (steering wheel against stops) increasing TO full throttle, the boat lost forward motion and engine RPM's hit the rev limiter. Once boat was drydocked, inspected prop/hub/engine compartment, finding no visible signs of a problem.

Discussion: I was turning the boat after quickly coming off plane, making tight (180, 360, and 540 degree) turns, in 1-1.5 foot swells due to wind and wakes. Speed was about 10 MPH while making the turn. With the steering wheel hard-over either direction, I was quickly increasing throttle to WOT. The engine was up around 3500-4000 RPM's, while still making a turn, when it felt like I slipped into "neutral", causing loss of forward momentum and a spike in the RPM's. I quickly reduced throttle and regained my forward motion around 2500 or so RPM's. I do not recall exactly where I had my trim set. Other than the two times this event occurred, the boat ran/is running fine. A "marine mechanic" I know said it was just normal cavitation by an improperly trimmed stern drive. Before heading out on the lake next time, I wanted to run this by ya'll...

It's quite possible I was turning harder and faster than I have thus far in my rookie boating season. My trim was most likely set too far up/out for my speed and turns. And the water surface was choppier than before due to numerous converging wakes and waves due to 15-20 MPH winds that afternoon. And before anyone thinks I was acting reckless, I wasn't any closer than 1000 yards to the nearest boat/jet ski when making this these turns; I was turning around to follow them and catch up to them as they were heading away from us ... you know, for the sake of my single friends aboard that day (my wife was present and encouraged the idea)! The event kind of bothered me, since it was something unexpected. I've read over the topics concerning props/hubs spinning and slipping, couplers, dogs, and clutches damaged or failing, and other mechanical issues for this type of event. Is this the first time I've experienced "cavitation", or should I be looking for a mechanical problem?

Thanks again for helping out a newbie...

 

[Irv964]

Re: Problem with power on turns II

Sounds like cavitation to me too but with out being in the boat I can't say 100% it is. Is your prop in good shape? What make and how old is it? Props can loose there edge/cupping over the years and this may also be a reason for your cavitation?
Post up a thread in the props section and see what more knowledgable people have to say about it. Good Luck..........Irv964

 

[SooLineRob]

Re: Problem with power on turns II

Hi Irv964,

The prop is a brand new out-of-the-box aluminum Mercury Black Max with a Flo Torq II hub. The symptom of "slipping into neutral while turning at high RPM"s" happened on the first time in the water with the new prop/hub.

I don't think I did any damage to the powerplant after the prop strike last weekend. I was going pretty easy and heard the muffled "thump", and didn't feel the strike in the steering wheel or boat. The damaged prop had a scuff on one single blade, and that blade was only bent (smoothly) 1/2". I tried to take a picture of the damaged prop, but the damage was so slight it wasn't visible in the photo. No other symptoms after the prop strike, and I removed that prop for repair and replaced it with the new one.

Although I'm fairly mechanically inclined (former auto mechanic for 5 years), I'm not familiar with marine systems. With my untrained eye, I don't see any mechanical problems. The coincidence of my "problem" happening immediately after a prop change had me concerned. And having suffered a prop strike, although mild, I felt that should be mentioned in order to look beyond the prop/hub for any problems.

I was unsure about which forum to post this topic, since it could involve the prop or the powerplant. Or maybe there's nothing wrong, and I experienced cavitation for the first time and it caught me off guard. This is my first boat, and my first season. I realize my description of the event may be hard to diagnose without actually being in the boat, so I appreciate any attempt to do so. So I posted this "generic" problem here. If the Moderators feel this is a prop or powerplant issue, please feel free to move this topic to the appropriate forum, and thank you in advance.

 

[Bondo]

Re: Problem with power on turns II

Or maybe there's nothing wrong, and I experienced cavitation for the first time and it caught me off guard. This is my first boat, and my first season.

Ayuh,....

It sounds quite Normal to Me......

 

[Irv964]

Re: Problem with power on turns II

Hi Irv964,

The prop is a brand new out-of-the-box aluminum Mercury Black Max with a Flo Torq II hub. The symptom of "slipping into neutral while turning at high RPM"s" happened on the first time in the water with the new prop/hub.

I don't think I did any damage to the powerplant after the prop strike last weekend. I was going pretty easy and heard the muffled "thump", and didn't feel the strike in the steering wheel or boat. The damaged prop had a scuff on one single blade, and that blade was only bent (smoothly) 1/2". I tried to take a picture of the damaged prop, but the damage was so slight it wasn't visible in the photo. No other symptoms after the prop strike, and I removed that prop for repair and replaced it with the new one.

Although I'm fairly mechanically inclined (former auto mechanic for 5 years), I'm not familiar with marine systems. With my untrained eye, I don't see any mechanical problems. The coincidence of my "problem" happening immediately after a prop change had me concerned. And having suffered a prop strike, although mild, I felt that should be mentioned in order to look beyond the prop/hub for any problems.

I was unsure about which forum to post this topic, since it could involve the prop or the powerplant. Or maybe there's nothing wrong, and I experienced cavitation for the first time and it caught me off guard. This is my first boat, and my first season. I realize my description of the event may be hard to diagnose without actually being in the boat, so I appreciate any attempt to do so. So I posted this "generic" problem here. If the Moderators feel this is a prop or powerplant issue, please feel free to move this topic to the appropriate forum, and thank you in advance.

What make was the original prop? And you only noticed the cavitation/ventilation after putting on the Black Max?? Did I read that right?
I too had a Black Max on my boat and it ventilated terribly in the turns, I practically had to trim all the way down in order to stop it, even going slow pulling a tube. I since changed it out for a Turning Point prop and it is a night and day difference, I still get some on real sharp tight turns but no where near what the Black Max did. I wrote this review in the props section which you may want to read, it covers a lot about the prop, engine height etc.(link below) I am by no means suggesting you purchase one and all your problems will disappear but mearly providing you with some info so you can take an educated guess on what your boat needs or may need? There are a lot of choices out there as far as props go so take your time and educate yourself by reading lots of prop posts and asking questions. Good Luck........Irv964
http://forums.iboats.com/showthread.php?t=269778

 

[tashasdaddy]

Re: Problem with power on turns II

in a turn the when you increase throttle the motor is pushing the stern side ways, it does not move fast enough to recover the water it is pushing, so it starts to grab air, thus increase revolutions, and loss of forward motion. sounds 100% normal. you have to learn what your boat will and will not do.

 

[mvn]

Re: Problem with power on turns II

Ventilation in tight corners was a HUGE problem for my setup until I switched to a cupped stainless prop. As long as I'm trimmed down, she'll turn on a dime and not ventilate at all.

 

[SooLineRob]

Re: Problem with power on turns II

Irv964,

Thanks for the link to your review. It opened my eyes to subtle differences in prop designs/characteristics that I hadn't considered. I'll be reading more about props now. I don't recall the make of my original (now rebuilt/repaired) prop. I just replaced it with a Black Max of the exact same specifications, which was in stock at my (Mercury) parts dealer. And you did read my post correctly; the cavitation/ventilation has only occurred AFTER installing the Black Max prop. The old prop also used a Flo Torq II hub kit, and I replaced the old hub parts with brand new ones during the Black Max install. Since the cav/vent occured after the install, I was surprised/concerned that something mechanical may be wrong. I'm still a newbie, and wasn't familiar with the byproducts of power turns...

Bond-O, TD, and mvn,

Thanks for your replies. I haven't pushed the limits of my boat's performance nor my own capabilities yet. Still learning what my boat can or won't do. And I take it pretty easy on the water. I don't want to go beyond the limits of my experience and spook myself or my passengers! No "submarines" or bow-turns for me; I don't want to end up on youtube.

Thanks gang, and I'll "experiment" some more next week...