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Sea Wolf



Joined: 01 Nov 2003
Posts: 8650
City/Region: Redding
State or Province: CA
C-Dory Year: 1987
C-Dory Model: 22 Cruiser
Vessel Name: Sea Wolf
Photos: Sea Wolf
PostPosted: Wed Nov 14, 2012 7:23 am    Post subject: Re: cavitation Reply with quote

adoryable wrote:
Does anyone else have this problem? I am experiencing engine revving on my 16 foot Angler (1989) with a new 50 HP Honda. The engine and prop were professionally installed by a dealer in Portland OR (who sells C-Dorys) and the plate is at the correct level in relation to the bottom of the boat. The prop has been checked and is not slipping. The motor is mounted at the lowest point.

The motor revs when running at 4500 RPMS or above (17 knots or more) when moving with following seas, and occasionally when going into modest swells. The revving is worse when I have a second or third passenger onboard. I have tried adding a after market plate which helped somewhat.

I also sucked air (and revved up) when making turns, but the add on plate helped that situation considerably. Could this just be a fact of life for this flat hull design?


adoryable-

I think this is just as you say in the last sentence: "a fact of life for this flat hull design", though also for the short length of the hull (compared to the wave size).

The buoyancy of the flat aft hull and the short length of the boat just lifts (pitches) the motor skeg up a lot in short, steep seas, causing ventilation.

Good that you added the plate (Permatrim would be longest and best.)

Joe. Teeth Thumbs Up

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adoryable



Joined: 14 Nov 2012
Posts: 2
City/Region: San Francisco
State or Province: CA
C-Dory Year: 1989
C-Dory Model: 16 Angler
Vessel Name: none
PostPosted: Wed Nov 14, 2012 11:42 am    Post subject: cavitation in 16 ft Angler Reply with quote

thanks for your response.... I think the problem I have with my little C-Dory is that it is so solid, stable, and comfortable that I forget that it is a 16ft skiffI and I expect it to perform like a much bigger, heavier boat !

The after-market plate I put on the motor is small ("SE Sport 200) so I may look into your recommendation.
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Marty



Joined: 05 Sep 2011
Posts: 8
City/Region: Tacoma
State or Province: WA
C-Dory Year: 1988
C-Dory Model: 22 Cruiser
Vessel Name: Nakiska
PostPosted: Wed Nov 14, 2012 11:06 pm    Post subject: Reply with quote

You are not alone. Our story is almost identical. We have the same boat and same motor. We bought ours in June from the original owners. Ours does the same exact thing you described. Our mechanic is stumped. We just had the lower unit replaced and it didn't make a difference. If you figure it out we would sure like to hear from you. Thanks Marty
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curioustraveler



Joined: 26 Apr 2019
Posts: 211
City/Region: Annapolis
State or Province: MD
Photos: Curioustraveler
PostPosted: Tue Sep 01, 2020 8:41 am    Post subject: Reply with quote

Hello C-Brats,

I'm resurrecting this old thread to see if what I experienced this weekend is normal.

We had pretty heavy following seas for two days straight and I kept hearing what sounded like my motor trying to cavitate. It was only for a split second each time but was pretty constant. Following seas are tough because they make the motor work so much harder and it sounds different from one moment to the next but it definitely sounded like it was borderline cavitating. I didn't notice any obvious slipping but again, it was tough to tell in these seas because everything is constantly changing anyways. I didn't see any sudden increases in the RPM's.

This was our first time in following seas this large, the boat had much more weight in the bow then normal, and the tabs were trimmed all the way up to try to keep the bow up. I had the motor trimmed all the way down though because of what I thought was cavitation.

This is the first time I've had this issue and I'm hoping it's related to the seas or extra weight. If I get a calm day this week to take her out and see if I notice anything.

Is this normal based on the different conditions of the boat and seas? Or is it something to be concerned about? We have another trip planned this weekend so I want to make sure we're good to go. Anything I can check for myself (she's in a slip, not on a trailer.)

Thanks
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thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Tue Sep 01, 2020 10:39 am    Post subject: Reply with quote

Above Joe mentions "Ventilation", instead of Cavitation. This is important, because the "cure" is radically different. Note that the video also explains why the boat "blows out" or ventilates in hard turns.

Quote:
PROPELLER CAVITATION


Cavitation if the formation of air bubbles on the propeller. Cavitaion usually occurs as a result of damage and you'll feel it in the form of vibrations.

Cavitation is bad for three reasons. First it can physically damage the propeller. Secondly, it causes those vibrations which makes your ride less comfortable. Thirdly it reduces bite, which reduces efficiency.


PROPELLER VENTILATION


Ventilation, on the other hand, is the propeller sucking in air. This may happen because you have the engine trimmed up too high. It can occur because you're jumping waves and the back of the boat is actually coming up near the surface of the water, or perhaps you have a really sharp turn and as the boat leans your propeller is too close to the surface.

Ventilation is also bad mostly because it can cause a radical reduction in thrust and also it can cause your engine to over-rev.


CAVITATION AND VENTILATION HOW CAN YOU TELL THE DIFFERENCE?


If you can feel vibration and your propeller has visible pitting, you have cavitation and you probably need professional help. If, however, your engine is over-revving you have a ventilation issue and this is usually something you can fix yourself.


Here is a link to the video which explains it very well

In Colby's case there may be ventilation, if the prop is nearing the surface of the water. Trimming the motor all of the way down may push the bow down, and actually make the ventilation worse. You want the speed in heavy seas from aft to just keep you on the back of a wave. If you want to go faster, then it is time for "Throttle man".....in offshore racing boats there is one "driver" who tends to the throttles. I drive with on hand on the throttle and the other on the wheel in heavy seas. As you come off the top of a wave, you pull the throttle back, and then apply as you start to go up the next wave.

I don't remember if you 25 has a Permatrim? It should be running just on the surface of the water under normal calm conditions. Same for "cavitation" or ventilation plate.

How high are the RPM going when you are experiencing what may be ventilation?

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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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curioustraveler



Joined: 26 Apr 2019
Posts: 211
City/Region: Annapolis
State or Province: MD
Photos: Curioustraveler
PostPosted: Tue Sep 01, 2020 3:01 pm    Post subject: Reply with quote

I believe you're correct, it sounds more like ventilation not cavitation.

We have a 22 with a 90 Honda. No permatrim. We've only had her about 5 months but we've used her a ton and haven't had any problems. No issues with sharp turns either.

This weekend was the first I noticed it, and it wasn't bad, it just wasn't a sound I'm used to hearing. I figured it was due to more weight in the bow, the way she was trimmed, and the heavy following seas.

Your suggestion on motor trim makes sense. I trimmed it all the way down thinking I was keeping the prop in the water but maybe I was actually lifting the stern out?

We were cruising around 4000 RPMs. About 16 knots with the seas pushing us, Fast enough to push up and over the waves and surf down.
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clayhubler



Joined: 03 Aug 2019
Posts: 280
City/Region: La Center
State or Province: WA
C-Dory Year: 2003
C-Dory Model: 22 Cruiser
Vessel Name: Hammerhead
Photos: Hammerhead
PostPosted: Wed Sep 02, 2020 10:41 am    Post subject: Reply with quote

I also have some kind of ventilation issue. I thought it would go away after I installed the permatrims, but it has not. On my boat, with twin 40's, I have to throttle up gradually. With my past boats I always go full throttle to get up on plane and then back down. But with our 22 both engines rev and I am forced to reduce power to get the props to bite. This only happens on acceleration. I don't notice this when turning, but I also don't make sharp turns. When my trim indicators at the helm are 'level' the cav plate is even with the bottom of the boat. I don't think the props are slipping because both lower units on my boat were brand new when I bought it. Should I lower the engines?
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thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Wed Sep 02, 2020 11:05 am    Post subject: Reply with quote

Where are the permatrims when the boat is at planing speed? Something in the dynamics of the motors and hull is causing the ventilation when accelerating. I generally bring the throttle up slowly--but you are correct that most boats do well with full throttle.

I would expect ventilation when on plane if it was the height of the motors. I would put the trim tabs all of the way down. What position are the engines in when you apply full throttle? Too far up or too far down may cause interaction between the prop wash from the twins.
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Foggy



Joined: 01 Aug 2013
Posts: 1518
City/Region: Traverse City; Northern Lake Michigan
State or Province: MI
C-Dory Year: 2014
C-Dory Model: 26 Venture
Vessel Name: Boatless in Boating Paradise
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PostPosted: Wed Sep 02, 2020 7:08 pm    Post subject: Reply with quote

Well, about skiing, I learned behind a 16' Peterborough wood hull with a 10 hp
Johnson when I was about 8 Y/O (? lbs) circa 1950. Last slalom, w/o spills, was
a few years ago about age 74. Now, ben-thee-don-dat. On to new stuff.

On chronic cavitation, always check the "X" dimension - an important motor
mount/lower unit mounting height on the transom for O/Bs and I/Os. Props
love sucking in air if too high.

Aye.

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curioustraveler



Joined: 26 Apr 2019
Posts: 211
City/Region: Annapolis
State or Province: MD
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PostPosted: Sat Sep 05, 2020 9:55 pm    Post subject: Reply with quote

Did 27 miles today in mixed seas without any of the ventilation issues I had last weekend. So it appears it was a combination of the large following seas and how I had her trimmed.
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thataway



Joined: 02 Nov 2003
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City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Sat Sep 05, 2020 10:14 pm    Post subject: Reply with quote

Good to hear that there is really "no problem" with the boat. We all have learning curves, and each of us learns from this site daily.

Thank you for posting your experience...and I will wish you fair winds, but not always fallowing seas that are steep!

Have fun.
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hardee



Joined: 30 Oct 2006
Posts: 12632
City/Region: Sequim
State or Province: WA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Sleepy-C
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PostPosted: Sun Sep 06, 2020 7:18 pm    Post subject: Reply with quote

YUP, great to hear you had a good ride.

As Bob said, Fair winds and Following Seas --IF they are big, round roller types. It that short, steep, white stuff on the top that take all the fun out if it.

Harvey
SleepyC Moon


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