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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Fri Oct 05, 2012 10:46 pm    Post subject: Cavitation Reply with quote

I am having trouble with cavitation on my 1982 22ft cdory cruiser. It has a 70hp Johnson long shaft. It wants to cavitate and rev up when turning even at moderate speeds. It is worse in any amount of seas. Any suggestions?
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Jack in Alaska



Joined: 17 Aug 2004
Posts: 1190
City/Region: Anchorage/Ninilchik
State or Province: AK
C-Dory Year: 2005
C-Dory Model: 26 Pro Angler
Vessel Name: HIGH TIDE II
Photos: HIGH TIDE II
PostPosted: Fri Oct 05, 2012 11:06 pm    Post subject: Reply with quote

C-Dory did not make a cruiser model in 1982. Angler only.
I had a 1983 C-Dory angler for 26 yrs. The only time I had cavitation problems was in a big following sea.

Is your motor tilted so it is vertical in the water, cavitation plate ok???, prop blades ok??. Could it possibly be the prop clutch rubber slipping.

That 70 hp was probably the original engine as that is what was installed on them at the factory. 3 cyl. 70 hp Johnson.

_________________
On the HIGH TIDE-II, wife Carolyn and I.....Another summer fishing on the HIGH TIDE II in the Cook Inlet at Cape Ninilchik, Alaska.

HIGH TIDE-II; 2005 26' ProAngler; 2003 200 Honda / 2009 9.9 Honda high thrust
No. CD026021I405; AK-5008-AK
MSSI No. 338143486(cancelled)

HIGH TIDE; 1983 Angler Classic 22'; 90 Honda/ 9.9 Tohatsu-sold 2009 to son Dan (flatfishfool)
Stolen & stripped in Aug. 18
Bare hull & trailer sold in Nov.
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Fri Oct 05, 2012 11:40 pm    Post subject: Reply with quote

Typo, it's a 1988, I do not have a cavitation plate, the wheel is like brand new, and i run the motor at the recommended spot on the trim gauge indicator. It powers up nicely and runs fine even with a full load; no slipping. But as soon as I give any rudder that is more than a mild turn, she cavitates and revs up. Any way of checking the slip clutch on the wheel?
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Fri Oct 05, 2012 11:53 pm    Post subject: Reply with quote

Typo, it's a 1988, I do not have a cavitation plate, the wheel is like brand new, and i run the motor at the recommended spot on the trim gauge indicator. It powers up nicely and runs fine even with a full load; no slipping. But as soon as I give any rudder that is more than a mild turn, she cavitates and revs up. Any way of checking the slip clutch on the wheel?
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Jack in Alaska



Joined: 17 Aug 2004
Posts: 1190
City/Region: Anchorage/Ninilchik
State or Province: AK
C-Dory Year: 2005
C-Dory Model: 26 Pro Angler
Vessel Name: HIGH TIDE II
Photos: HIGH TIDE II
PostPosted: Sat Oct 06, 2012 12:01 am    Post subject: Reply with quote

A 1988 has a completely different bottom design from the pre 1985 models so I do not have any knowledge of those.
A good prop shop could check your prop slip clutch rubber.
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Sat Oct 06, 2012 12:09 am    Post subject: Reply with quote

Good idea! Thanks. Any other suggestions would be much appreciated!. I've seen some mixed reviews on cavitation plates; anyone had any luck with one.
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starcrafttom



Joined: 07 Nov 2003
Posts: 7878
City/Region: marysville
State or Province: WA
C-Dory Year: 1984
C-Dory Model: 27 Cruiser
Vessel Name: to be decided later
Photos: Susan E
PostPosted: Sat Oct 06, 2012 3:14 am    Post subject: Reply with quote

You do have a cavitation plate, All motors do. you may not have a aftermarket wing that attaches to your cavitation plate. I would see if the motor is set on the highest set of holes in the bracket. if you look where you motor mounts to the transom you will see two rows of holes with at least 4 (two to a side) bolts in them. You should have your motor set as far down on the transom as possiable. what you are trying to achive is to have your cavitaion plate level with the bottom of your hull when the motor is trimmed all the way down.

You also said the the motor was trimmed up to the recommended spot? recommended by who?? the marks on the gage mean nothing. there just there to give you a guide. Trim is set by the driver for the conditions, which are always changing just at the trim should be.

I hope I was clear and helpfull

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Thomas J Elliott
http://tomsfishinggear.blogspot.com/
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Sat Oct 06, 2012 3:23 am    Post subject: Reply with quote

Correct, I do not have an aftermarket plate, the motor sits on the transom, as low as possible, and I use the trim guide indicator, for what it is; a guide. I use the tach and my ears for everything else to get a nice ride depending on conditions. I have owned and run boats all my life and have not experienced this before. I am curious if a aftermarket cavitation plate might help.
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starcrafttom



Joined: 07 Nov 2003
Posts: 7878
City/Region: marysville
State or Province: WA
C-Dory Year: 1984
C-Dory Model: 27 Cruiser
Vessel Name: to be decided later
Photos: Susan E
PostPosted: Sat Oct 06, 2012 11:52 am    Post subject: Reply with quote

It might help but the lack of one in not the problem. Not sure why this is happening, would have to drive it. Might be the prop as others have said. Not the right size, which is different then not the right pitch. How much space between the top of the prop blade and the motor above it? Any time my 27 start to rev up on a turn I just lower the trim a little and know that that is my max amount of trim.

on edit: how does your cal. plate line up with the bottom of your hull?
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Sat Oct 06, 2012 12:56 pm    Post subject: Reply with quote

I bought the boat back in May; it was in mint condition and I'm the second owner. I put it in the water and haven't pulled it out since. I'll pull it and investigate some of those things. It was dealer installed and the older gal I bought it from doesn't recall any issue like I'm having. Also, if I'm stopped, turn hard over and throttle up it does the same thing, acts like its cavitating and revs up; back the throttle down, steer straight and it bites just fine. I can run around 5400 turns which tells me prop size is correct. I'll usually back it down to 5 or 52 when cruising. Again no issues until I give a little more than easy rudder. Thanks for your feedback.
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Sat Oct 06, 2012 1:51 pm    Post subject: Reply with quote

I bought the boat back in May; it was in mint condition and I'm the second owner. I put it in the water and haven't pulled it out since. I'll pull it and investigate some of those things. It was dealer installed and the older gal I bought it from doesn't recall any issue like I'm having. Also, if I'm stopped, turn hard over and throttle up it does the same thing, acts like its cavitating and revs up; back the throttle down, steer straight and it bites just fine. I can run around 5400 turns which tells me prop size is correct. I'll usually back it down to 5 or 52 when cruising. Again no issues until I give a little more than easy rudder. Thanks for your feedback.
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thataway



Joined: 02 Nov 2003
Posts: 20778
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Sat Oct 06, 2012 9:47 pm    Post subject: Reply with quote

It would be very unusual to put the engine hard over to one side and then give full throttle. Also since these boats are almost flat bottom, (the 1988 boat hulls are the same as current models), they will slip side ways far easier than a conventional V hull or a boat with a keel. Perhaps you are pushing the limit of the turn?

If not then as Tom suggests blade tip clearance, too much cup or rake in the prop, or a slipping hub could be the issue.

If you topping out at 5400 then I would run the boat in the mid to high 4,000 RPM range--not over 5,000 all of the time. What speeds are you seeing--and what is the diameter and pitch of the prop? Aluminum, composite or SS material?

_________________
Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Sat Oct 06, 2012 10:06 pm    Post subject: Reply with quote

I'm on a tugboat right now but will see if my wife can get me my prop specs. I normally don't have reason to go hard over and throttle up; was doing some fiddling trying to figure out when and why it does this, last time home. I guess I haven' owned the boat long enough to know it's true limits. Finding out would seem like a good thing. Just towing my young kids on the tube, going quite slow and moderate turns and it would respond as decribed earlier. Bummed us out!. It will not tow my barely over 100 lb wife on a single ski. It'll cruise comfortably at around 28, the fastest I've seen was around 32. I'll get that info! Very much appreciate the help. Marc
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theleverbeef



Joined: 07 May 2012
Posts: 34
City/Region: Mayger, OR
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
PostPosted: Sat Oct 06, 2012 10:27 pm    Post subject: Reply with quote

The prop is a 14x17. It's what came with the boat. Thanks again!
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journey on



Joined: 03 Mar 2005
Posts: 3593
City/Region: Valley Centre
State or Province: CA
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: journey on
Photos: Journey On
PostPosted: Sat Oct 06, 2012 11:31 pm    Post subject: Reply with quote

I've lost a rubber propeller insert on a Johnson before, and indeed one on a Honda 150. The engine winds up and the boat doesn't go. The insert can be replaced by a propeller shop at a nominal cost..

Cavitation is where, for various reasons, the water pressure around the prop drops below the water vapor pressure and air bubbles form. To cause this on your boat after lo these many years, something must have changed and I don't hear that from you. I would assume from what you're saying, that what's actually happening is that the drive shaft is slipping inside the rubber insert.

It's a reasonable place to start, and cheap as things go.

Boris
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