Placement of counter-rotating engine on Tomcat?

M

matt_unique

New member
I'm curious to hear from other Tomcat owners, do you have the counter-rotating engine on the port or starboard side?

My research indicated the Tomcat is best served with the counter-rotating engine on the starboard side. My 08 engines are being installed today at the Suzuki dealership (swapping out 07 140's that originally came with it). The engine dealer was concerned because he had never installed the counter-rotating engine on the starboard side as I had requested and called C-Dory. 48 hours after his first call they returned his call to say this would void my warranty, provides no advantage for the Tomcat, and they would require me to sign a warranty waiver if I wanted the counter-rotating engine installed on the starboard side.

Needless to say I told the dealer to install the engines as instructed by C-Dory to retain my warranty coverage.

Thanks for the replies.
 
Matt, Our Honda's are mounted in the factory approved configuration, CR engine to Port. Someone on the site had theirs opposite of this and reported good results. Hopefully they'll jump in here and enlighten us. Possibly Dr. John on Tomahawk.
 
It is normal on twin installations to put the CR motor on the port side.

The idea is that the 'prop walk' causes the boat to 'walk' to stb when the stb motor is in forward (and the stb prop is turning clockwise, viewed from the stern)and the boat to 'walk' to port when the port motor is in forward (and the port prop is turning counterclockwise viewed from the stern).

'Prop walk' is like a wheel rolling on the ground. A clockwise turning prop(viewed from astern) will 'walk' the stern of the boat to stb.

If one motor is in forward and the other is reverse, the natural 'prop walk' helps rotate the boat.

My opinion follows
Mounting the motors so that the CR is on the stb side would counteract this action and make the boat more difficult to handle.

If any Tom Cat owner has different information, please let us know.
 
The following text concurs with Larry and was taken from another forum. This is also my understanding of the issue from past boats I have owned. The forum went on to say that some Navy vessels apparently do the opposite for reasons better known unto them.
Consideration should also be given to "toe-in" and "toe-out" on any hull with a deep "V" which would not apply to CD's but might be true for the TC.

"In twin screw applications there are two possible configurations


"inboard turning" - the stbd shaft has a LH prop and the port shaft
has a RH prop.
"outboard turning" - the stbd shaft has a RH prop and the port shaft has
a LH prop.

Outboard turning is the most frequently seen application. The reason, is
handling, as, for the most part the same boat with "inboard turning"
will handle totally differently from one with "outboard turning" props.

Outboard turning: The individual props, complement the offset thrust of
props with prop walk, i.e., when going ahead on the stbd shaft alone the
offset thrust tends to turn the boat to port while at the same time,
propwalk will pull the stern to stbd, increasing turning rate. Going
astern, the offset thrust/pull and propwalk work together to pull the
stern to port.
The advantages to this are fairly obvious ..... you can use engines
alone to steer both ahead and astern, and to increase turning rate you
can simply add throttle and basically leave rudders "midship" (<G> not a
practice I agree with in all cases).
Naturally, the degree of ease that a boat with this configuration will
turn or twist, or walk, will depend on other factors as well (prop
spacing, rudder size, hull configuration, etc.).

Inboard turning: Totally different If your one of those
who never learned how and when to use rudders when maneuvering your twin
screw, outboard turning, propped boat, standby, you may be in trouble.
With this configuration, the offset thrust is countered by the propwalk.
What happens when you put the stbd shaft in gear, ahead or astern? You
go straight. Add throttle, what happens? You go straight. Try to twin
screw? You sit there and throw water ahead and astern. Solution? <G>
That's why they put those rudders back there and you best start learning
to use them under maneuvering conditions.


My 2c worth.

Merv
 
Most twin screw Naval Vessels today have screws that both turn same direction. But they have controlable pitch props so they can totally control any prop walk. Nearly all are either diesel or gas turbine and the props never stop turning!

Charlie
 
Just wondering why putting the left hand rotation on the stb side would make any difference in handling in close quarters? The torque effect will still be present, just opposite engine. The boat will still turn with one engine foreward and the other reverse.

On most inboard engines, the right hand prop is on the right side, the left hand prop on the port side. On many outboard cats this is the opposite, to give more stern lift. What the factory configuration is--may be subject to debate, since my counter rotating is on the stb side (left hand prop) and the engine was set up at the factory--and I believe that Matt confirmed that.
 
Well it's my nature never to trust this kind of information until I double and triple check....shortly after the call from my engine dealer I called C-Dory and actually reached someone immediately. I spoke to Frank in the warranty department. He spoke to Tom Cole (sp?) who does the engine rigging at C-Dory. He confirmed that the counter-rotating engine can indeed be installed on the starboard side and would not affect my warranty. If my dealer was told otherwise by another person at C-Dory that information was incorrect.

I immediately called my dealer who said he just got off the phone with C-Dory and they corrected the previous information. The CR engine will be installed on the starboard side as I had originally requested.

Talk about a hair raising evening....

Thanks for the responses.
 
matt_unique":3v0766i2 said:
My research indicated the Tomcat is best served with the counter-rotating engine on the starboard side.
Click to expand...

What did you find in your research (i.e., why is one better than the other)?

Warren
 
My conter-rotating prop is on the starboard side (set up by Wefing's marine). The prop walk effect is clearly minor; the stern moves in the expected direction in forward and reverse with one engine in gear even at low speeds.
 
Doryman":22kxr1u7 said:
matt_unique":22kxr1u7 said:
My research indicated the Tomcat is best served with the counter-rotating engine on the starboard side.
Click to expand...

What did you find in your research (i.e., why is one better than the other)?

Warren
Click to expand...

The consensus was that the advantages are subtle, but that the CR on the starboard would raise the stern a bit. I also wanted this configuration to take advantage of prop walk when docking. The prop walk on outboards is usually negligible but I will be running the 16 x 21.5 props and the theory made sense.
 
Matt- a minor point:

In my single engine trawler with a large fixed prop and no rudder effect while in reverse in low speed, prop walk was a significant and useful tool while docking.

With outboards, I have the ability to swivel the motors, so I don't need to even think about prop walk to make the stern go in to the dock. Also, with twin counter-rotating engines, if I really wanted to use the prop walk to move the stern in either direction, I could just put the appropriate motor in gear. It should not matter which motor is on which side.

What do you think?
 
As Alok posts, I usually back, using the wheel to turn the engines--I do use the props to spin the boat in place. But, the slab sides of the Tom Cat tend to act as keels, so as Matt says prop walk is minimalized.

I have been able to walk the boat sideways, as in twin scew inboards, but only in very calm water--probably not practical.

I find that the Tom Cat is a delightful boat to handle--but I feel all outboards are easy in comparison to some big sailboats, with small props.
 
I have no experience with "real" prop walking boats (the inboards, etc. that Bob mentions.) All I can say is that I find maneuvering the TC in close quarters using only the throttles is much easier than using the helm on my previous single-OB Hewescraft. I'm spoiled!

Warren
 
Matt

Our TomCat 255 was rigged at the C-Dory factory, and has the counter rotating motor on the starboard side. Who at the factory told you it would void the warranty?
 
Alok":16jnqb4e said:
Matt- a minor point:

In my single engine trawler with a large fixed prop and no rudder effect while in reverse in low speed, prop walk was a significant and useful tool while docking.

With outboards, I have the ability to swivel the motors, so I don't need to even think about prop walk to make the stern go in to the dock. Also, with twin counter-rotating engines, if I really wanted to use the prop walk to move the stern in either direction, I could just put the appropriate motor in gear. It should not matter which motor is on which side.

What do you think?
Click to expand...

I agree. On the single inboards the prop walk is unreal...without touching the wheel I can move the stern perpendicular about 18". On the twin outboards (non-counter rotating) the prop walk is negligible, I too turn into the dock as I'm reversing engines to walk the stern then hard over in the opposite direction to null this movement before shifting to neutral. The twin outboard vessels I'm referring to run Merc 90's. My 150's will be running much larger props and if there was to be any prop walk at all I wanted it heading toward the dock. I learned after that the CR engine placed to starboard would also provide some stern lift. So from my research the real benefit was in the stern lift.
 
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