Can seaweed cause cavitation?

[BigFootTwo]

I have a 2005 Caravelle 23' walkaround with Mercrusier 5.0L Alpha Sterndrive 220 hp.<br />Purchased April 2005.<br />I have 125 hours on it.. twice this season, something strange happened:<br /><br /> Back in July, I was cruising along at 4,000 rpm. All of a sudden there is a sharp decrease in speed and the engine revs up (I didn't notice the tach - I immediately put it into neutral). Tried low speed- was fine. High speed was fine for a few minutes, then it happened again. I took it back to the dealer, and he said the engine and prop were fine, just too much growth on the bottom of the boat and the outdrive. He scraped the bottom, repainted it and it worked great for a few months. (And he didn't charge for it<br /> Last night it happened again. I checked the prop, and there was slime all over it. <br /> Has this happened to anyone else?

 

[walleyehed]

Re: Can seaweed cause cavitation?

You've lost a huge share of the efficiency of your rig...It's got to be very clean and smooth to work like it should.<br />I seen alot of this problem on Texoma.

 

[TilliamWe]

Re: Can seaweed cause cavitation?

bigfoot, if the bottom is that dirty, the boat usualy does some other things weird first, before the prop would slip like that. For example, when my 21ft Chap has much bottom growth, it takes noticeably more power to bring it on plne. It won't turn above 4000rpm hardly (WOT is 4900), and actually tries to backfire. Never had the props slip. But mine is a Bravo 3, maybe that keeps that from happening?<br />In any case keep your bottom clean, it can't hurt!

 

[ufm82]

Re: Can seaweed cause cavitation?

A prop is basically an airfoil, a wing moving through a medium. When the airflow, or in this case the waterflow, is altered, lift is lost. Keeping the bottom clean and keeping your prop clean is critical. I have read that algae growth of just a slime will eat 10% of your horsepower. <br /><br />Do you moor your boat? It seems that if you are getting bottom growth that quickly you need a true bottom paint job. <br /><br />UFM82

 

[crazy charlie]

Re: Can seaweed cause cavitation?

To answer your question,YES !! seaweed on the drive will make you cavitate AND possibly overheat by covering the water intake screen on the drive.If cavitation is caused by seaweed,go from fwd to neutral and then to reverse and give it a slight rev in reverse.You may also cavitate if you trim your drive too far up while under way.Another cause is if the prop needs to be rehubbed.It will work fine at idle and may even get you on plane,but put a little stress as in weight or drag on the rig and the hub can spin but the prop dont.Charlie

 

[trebor0301]

Re: Can seaweed cause cavitation?

Hey big you might want to put it in reverse and give it a quick REV to throw the seaweed off.SOUNDS LIKE YOU HAVE SPUN YOUR PROP.As for the bottom growth problem,have you ever givin any thought on a boat lift.Check out prices on used ones.I would bet they have many boats on lifts at your lake.Look for end of season pricing

 

[BigFootTwo]

Re: Can seaweed cause cavitation?

It just started overheating also. I scrubbed the lower unit, but the overheat alarm won't shut off. When I start the engine cold, the alarm doesn't turn off - so it can't really be overheated yet.... the water temp and oil pressure gauge are all normal.. all fluid levels are good. any ideas on the overheat alarm? It is fresh water cooled. Is the temp gauge for the fresh water system or the salt water part?<br /><br /> I had the boat painted in April, then it had to be scraped and painted again in July. Looks like it needs it again. A lift isn't practical.. it wouldn't fit in my slip. I keep it on the south shore of Long Island.

 

[angus63]

Re: Can seaweed cause cavitation?

I used to loose about 200 rpm over the course of a season due to the bottom growing a brown "great South Bay" beard. Switched to a higher cuprous content bottom paint (ablative) and problem disappeared. Also midseason I pull the boat and use a power washer to remove the brown ring that develops at the waterline. Clean bottom = Happy motor.<br />Good luck

 

[BigFootTwo]

Re: Can seaweed cause cavitation?

Too bad there aren't any "drive through" boat washes like there are for cars... they would make a fortune!<br /> How do you wash off the bottom? I have no trailer.

 

[moderator1]

Re: Can seaweed cause cavitation?

Marina with a lift dock...they lift the boat from a special slip by mobile sling (travel lift) then set the boat on pedestals, power wash or sand and re-paint.

 

[Perfidiajoe]

Re: Can seaweed cause cavitation?

BigFoot you are picking up grass as stated before, it happens to all of us on Long Island. The reverse procedure as described above works to throw the grass off the prop. The overheating may also come from the grass, as it blocks the water intake, or worse, packs up in your heat exchanger, or pump, even may get to the risers. I've see people blow engines in the canal from the grass, don't ignore this. Cleaning the bottom is nice, but take care of the water intake & running gear first! Good Luck, Joe

 

[KIGuy52]

Re: Can seaweed cause cavitation?

Here at Knotts Island Bay we have lots of millfoil and duckgrass. Lots of guys sharpen their SST's to chop it up, but we still have to throw it in reverse occasionally to clear the water intake.