cavitation problem on 25' pontoonRan

douglaso54

Recruit
Joined
Jul 27, 2015
Messages
1
Hello. In fall of 2013 we purchased a used 2005 Crestliner Angler Edition pontoon with Mercury 115 Four stroke EFI. The motor had a 14" x 13 pitch 3 blade prop. We were using it to troll for fishing and started getting a lot of blue smoke. Mechanic at local marina said the motor was not designed for trolling and that we needed to get it up to 5000 rpm to keep it running good. During winter season purchased and electric trolling motor that mounts to the cavitation plate and a 14" x 11 pitch 4 blade prop and installed all that. Ran entire summer season of 2014 with no problems. We usually run with just the wife and I but have had as many as 12 people on board and no problems. Have had it out half a dozen times this season and about a month ago with just the wife and I on the boat we left "no Wake" zone after putting in and started cavitating when I got above 4000 rpm. Talked to local marina mechanic again and he suggested changing prop. Purchased 14" x 11 pitch 3 blade and put it on. Started cavitating at 3500 rpms. Took the two previous props down to a prop shop in Salt Lake City and had them balanced. Put the original 14" x 13 pitch 3 blade on and it starrts cavitating at 3000 rpm. Havwe talked to numerous boat owners and different mechanics and all say its not an engine problem. Nothing in the engine that can slip which is what it feels like when it happens. Have tried moving weight in boat around, changing trim of motor and nothing seems to make any difference. Can't get above 3000 rpm without cavitating. It has two pontoons, don't know if engine is long or short shaft. Any suggestions? Thank you.
 

1983 ercoa 21'

Chief Petty Officer
Joined
Jan 12, 2014
Messages
632
Something has changed. I would be looking at the trim pin to see if someone moved it . With power trim the pin should be in the hole closest to the transom. Check and make sure nothing else is blocking the way of the motor trimming all the way down. If all that is good unbolt the trolling motor and try it without it.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Something changed certainly not likely the prop.Worked last year,worked this year.
Is this in the water all the time? It will likely need a good scrub down. I would give the trolling motor and mount a close look over.
Check wires, mount bolts. Check the motor mount pod,motor mount.Motor controls look for loose wires perhaps even a defective part of the boat.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
To cause cavitation, either something in front of the prop is screwing up the flow of the water getting to the prop, OR, the prop is somehow able to pull surface air down into it - past the cavitation plate (that's what the cavitation plate's purpose is). This would normally be caused by an engine that's been mounted too high on the transom. In the case of this trolling motor that's been mounted to the cavitation plate - could something in that install be causing it to suck air or screw with the flow of water that the prop is getting?
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,598
Are you sure it's cavitation? Might be a spun prop, or possibly a shifting or gearcase issue(?) Guess you are getting advice (prop change) -- marina mechanic sure it's cavitation?
 

lncoop

Vice Admiral
Joined
Apr 18, 2010
Messages
5,147
Spun prop hub seems unlikely given three different props all result in ventilation. I agree the most likely culprit is something different in the trolling motor mounted on the antiventilation plate. If something has shifted out of position it could be causing an air pocket to develop around the prop. Have you gone over it with a fine tooth comb?
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,598
good point re poss spun prop, but in same light -- cavitation or ventilation on three diff. props? no experience with vent plate mounted trolling motors, but could see where that could affect performance. (Never bought one, but have sure seemed like a good idea for ease of use.)
 

lncoop

Vice Admiral
Joined
Apr 18, 2010
Messages
5,147
good point re poss spun prop, but in same light -- cavitation or ventilation on three diff. props? no experience with vent plate mounted trolling motors, but could see where that could affect performance. (Never bought one, but have sure seemed like a good idea for ease of use.)


Sure. If the issue is being caused by a disruption of water flow around the LU any prop will ventilate.
 
Top