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Coastal crew
Joined: 26 May 2015 Posts: 14 City/Region: Courtenay
State or Province: BC
C-Dory Year: 2001
C-Dory Model: 24 Tomcat
Vessel Name: Salty Roads
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Posted: Tue May 26, 2015 11:51 am Post subject: Tom Cat 24 resonance at low RPMs |
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Hello all,
I've been looking forward to this day for sometime, becoming a C-Brat that is. Well I'm hoping to. I sea trailed a 24 Tom Cat over the weekend and found that at lower RPMs a loud resonating sound was coming from the transom area. In fact there were two. One sounding like the boat had a diesel motor thumping away and another at higher RPMs that sounded like a high pitched droning sound, like the props of a small plane, for reference. There was definitely a sweet spot at about 4000 RPM and she quotes right down.
Can anyone with a Tom Cat or experience on one comment on this.
Thank you
A soon to be budding brat |
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BrentB
Joined: 15 Jul 2006 Posts: 4419 City/Region: Greenwood
State or Province: IN
Photos: BrentB
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Posted: Tue May 26, 2015 12:03 pm Post subject: |
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Are the motors 2 stroke? _________________ Brent Barrett |
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thataway
Joined: 02 Nov 2003 Posts: 20808 City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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Posted: Tue May 26, 2015 12:24 pm Post subject: |
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I have ridden in several Tom Cat 24's, and didn't remember any sound/vibration as you describe.
Was the cabin door open. We usually ran with the door closed.
I would try running the boat at an idle on one engine, then the other, so see if it is isolated to the engine.
Is there any possibility that there was some hull slap from chip?
I would check the transoms for any deflection when you put your full body weight onto the lower unit, with the motor trimmed all of the way up to the trailering position.
Welcome aboard! _________________ 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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Coastal crew
Joined: 26 May 2015 Posts: 14 City/Region: Courtenay
State or Province: BC
C-Dory Year: 2001
C-Dory Model: 24 Tomcat
Vessel Name: Salty Roads
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Posted: Tue May 26, 2015 12:44 pm Post subject: |
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Hi Bob,
The sounds only occurred while under power and not at idle. Closing the door definitely helped but the cause is my concern. I will be having the hull and motors surveyed next week and will hopefully get some professional options, though the surveyor will likely not have any experience with the a Tom Cat.
Unfortunelty the water was flat calm the day we were out. I had hoped to go out in some chop to see if there was tunnelling or slapping. I have a 18 Nautico and am experienced with hull slapping in rough water.
If I understand your last comment correctly I will have to wait to pull the boat to check for deflection in the transom.
If you have any other tips or comments they would be highly appreciated. |
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BrentB
Joined: 15 Jul 2006 Posts: 4419 City/Region: Greenwood
State or Province: IN
Photos: BrentB
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Posted: Tue May 26, 2015 1:02 pm Post subject: |
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I would check the props (type, size, condition, connections, installation, etc) and check lower unit fluid levels. It is nice to have a second person driving and you can listen then trade positions,
Let us know the outcome |
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rogerbum
Joined: 21 Nov 2004 Posts: 5922 City/Region: Kenmore
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 255 Tomcat
Vessel Name: Meant to be
Photos: SeaDNA
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Posted: Tue May 26, 2015 1:03 pm Post subject: |
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When the RPMs are closely matched on twin engines, one can often hear the "beat frequency" of the two engines. It's usually not that loud but one can hear it. The frequency is equal to the difference in RPM's between the two engines and will vary if you independently adjust the RPM's of one engine. _________________ Roger on Meant to be |
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Coastal crew
Joined: 26 May 2015 Posts: 14 City/Region: Courtenay
State or Province: BC
C-Dory Year: 2001
C-Dory Model: 24 Tomcat
Vessel Name: Salty Roads
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Posted: Tue May 26, 2015 2:04 pm Post subject: |
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Motors are 2000 vintage 90 hp Honda's. One looked to be running a little rougher then the other. The other odd time was that the throttle controls were wrong, the left starboard control controlled the port motor and vise versa. |
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trpsurf
Joined: 12 Oct 2010 Posts: 111 City/Region: Pasadena
State or Province: CA
C-Dory Year: 1997
C-Dory Model: 24 Tomcat
Vessel Name: Oski
Photos: C-Pelican
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Posted: Tue May 26, 2015 10:45 pm Post subject: |
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Glad to hear you are looking at a 24' Tomcat. We love our boat and I would be happy to answer any questions you might have. We purchased ours about 18 months ago and we now have most of the kinks worked out.
We have relatively new (400hrs) Honda 135's. They don't really make any noises at low RPMs. I am guessing that you need a tune up or something.
Good Luck! _________________ Tim
Growing Up Salty YouTube Channel:
https://www.youtube.com/channel/UCMC83MyFWgfzKgGB4MF1RXA
24' Tomcat- Oski
22' Cruiser- C-Pelican |
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SounderSolutions
Joined: 02 Mar 2014 Posts: 74 City/Region: Whidbey Island
State or Province: WA
C-Dory Year: 2009
C-Dory Model: 255 Tomcat
Vessel Name: Frequent-C
Photos: FREQUENT-C
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Posted: Thu May 28, 2015 8:54 pm Post subject: |
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I have Suzuki 140's on my TC. The only time I get those kind of sounds is when the RPMs are out of sync.
There is a difference between a marine surveyor and marine mechanic unless you are getting one that takes on both resposibilities. If there is a question about the engines, get a marine mechanic to run through it. Will be money well spent if even just for the piece of mind.
Feel free to ask any questions you may have. _________________ Steve and Launa
Frequent-C (2009 Tomcat 255)
2009 Trophy Pro 2359
Frequent-C (2006 Tomcat 24)
Tired Again (2011 Thundjet Luxor) |
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Coastal crew
Joined: 26 May 2015 Posts: 14 City/Region: Courtenay
State or Province: BC
C-Dory Year: 2001
C-Dory Model: 24 Tomcat
Vessel Name: Salty Roads
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Posted: Thu Jun 04, 2015 11:41 pm Post subject: |
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A marine mechanic from Honda checked the motors out and gave them a decent bill of health. Aka there is nothing mechanically wrong with the motors that would cause the vibrations and resonance. He did suggest that it could be a result of not having counter rotating motors.
Should these be counter rotating?
If I cannot figure this out I will likely walk away from this boat. Thanks for all your help. |
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Molly Brown
Joined: 02 Nov 2003 Posts: 405 City/Region: Punta Gorda
State or Province: FL
C-Dory Year: 2003
C-Dory Model: 24 Tomcat
Vessel Name: MOLLY BROWN
Photos: Molly Brown
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Posted: Fri Jun 05, 2015 7:09 am Post subject: |
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We have a 2003 with the Honda 90's and our engines are NOT counter rotating. _________________ James, Betty, Luna cat and Moki dog on the TomCat Molly Brown
Started the Great American Loop 03/2024 |
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Sunbeam
Joined: 23 Feb 2012 Posts: 3990 City/Region: Out 'n' About
State or Province: Other
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Photos: Sunbeam
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Posted: Fri Jun 05, 2015 12:33 pm Post subject: |
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I'm not as familiar with this engine size range as many others here, but I'm not sure there are any "smaller" engines that are available with counter-rotating props. I thought that started around 150hp or so? I imagine there may be some Tomcats with the larger/counter-rotating engines, but this would mean that all 22's (for example) with twins do not have counter-rotating props. So it must be possible to have them and not experience issues.
I have been out on a 22 with twins a few times, and I "have" to get the engines synchronized or it bugs me; I would describe that as an RPM hunting type sound (when they are not quite synchronized). I also find that the prop on my (single main engine) 22 will "sing" a little at certain low RPM levels. That sound changes with different props. |
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trpsurf
Joined: 12 Oct 2010 Posts: 111 City/Region: Pasadena
State or Province: CA
C-Dory Year: 1997
C-Dory Model: 24 Tomcat
Vessel Name: Oski
Photos: C-Pelican
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Posted: Fri Jun 05, 2015 1:57 pm Post subject: |
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I have 135's that ARE counter rotating?
Do you have an audio recording you can share? If so, you can PM me and email me.
While I am sure that my engines to make a "bad" sound, they do make a different noise when you put them into gear at low RPM, than they do at a higher RPM.
If you have something I can listen to, I can tell you if it is similar or not to my boat. |
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Sunbeam
Joined: 23 Feb 2012 Posts: 3990 City/Region: Out 'n' About
State or Province: Other
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Photos: Sunbeam
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Posted: Fri Jun 05, 2015 2:57 pm Post subject: |
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Aha, so it goes down to at least 135hp.
Still probably no 22's with twins have counter-rotating props, so it must be possible to have a properly functioning twin setup without them. 'course the TomCat ones would be further apart. |
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Coastal crew
Joined: 26 May 2015 Posts: 14 City/Region: Courtenay
State or Province: BC
C-Dory Year: 2001
C-Dory Model: 24 Tomcat
Vessel Name: Salty Roads
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Posted: Fri Jun 05, 2015 9:07 pm Post subject: |
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Well it looks like I'm going for it!!! Buying the boat that is. I spoke with a very knowledgeable person (my apologies I have forgotten his name) at E.Q. Harbor Services. He provided much information on the boat and based on the information I provided him he figures it's likely a prop issue. There are new SS props and the old aluminum props which I'm going try. Figures crossed! The motors are over due for a tune up which will be completed in the near future. Hopefully this helps as well.
Looking forward to my future cruising of the PNW. |
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