Should torque steer trim tabs be set on new TomCats?

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drjohn71a

New member
Hey there...

I noticed very strong torque steering when using only the port or starboard engine on my new TomCat up in Seattle. I do not have access to the boat, and it was a rainy mess most of the time I was up there, so I am just guessing that the trim tabs on the engine legs were left straight and not set to eliminate torquing pressure from the props.

I also noticed that Brent and Dixie cruised for periods on a single engine and wonder if you'd have to correct for torque steering in order to do that. I wondered if the engines were more efficient as a set, each torque offsetting the other, if they were not corrected for torque steering.

Any info would be appreciated.

John
 
John,

Are you sure it is torque steer or just the one engine being so far from the center line. I forget which way the torque is going to push you (probably to port on a clockwise rotation), meaning if you are running the starboard engine, the boat would definitely pull to port. If you were on the port engine only, the position of the engine would tend to counteract the torque. I may have the directions confused but the problem sounds more like a thrust vector than a torque issue.
 
Well, Tom, maybe it is just "prop walk", but it is stronger than I have felt in dual inboard installations. Maybe you are right in thinking that the wide spread between the outboards is exhagerating the turning effect.

I am thinking of trolling with one engine, maybe even slow cruising that way some, and wondered if you'd just have to correct for the strong turning effect by steering the other direction.

The effect is so strong that you can actually drive the boat, with engines steered straight and at idle, by alternatively engaging one or the other in the minimum forward position.

Last nite I was awake thinking just what you are now saying.... oh well.

btw, engaging only the port engine moves the stern to port and engaging only the starboard engine moves the stern to starboard.

Thanks , John
 
drjohn71a":1aza8wj6 said:
btw, engaging only the port engine moves the stern to port and engaging only the starboard engine moves the stern to starboard.

Thanks , John
Click to expand...

That's a dead give away unless your engines are counter rotating which I doubt very much. It's gotta be the engine spacing. If it was prop walk with engines rotating the same direction, they'd each go the same way. Prop Walk is most/only noticible at very low speeds, otherwise thrust direction takes over...

Charlie
 
Captains Choice":2rtdupaf said:
That's a dead give away unless your engines are counter rotating which I doubt very much. It's gotta be the engine spacing. If it was prop walk with engines rotating the same direction, they'd each go the same way. Prop Walk is most/only noticible at very low speeds, otherwise thrust direction takes over...

Charlie
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Why do you doubt that the engines are counter-rotating? Mine are, and I don't think that my boat is that unusual. Les told me that one of the reasons he stopped selling Tom Cats is because of the expense of carrying an inventory of counter-rotating engines.

There is a Tom Cat on the board who has posted about cruising economically on one engine. Hopefully he will comment here.

Warren
 
Yes, the TomCats are definitely counter-rotating. Les told me the same thing... too expensive to carry dual rotating engine sets of three different manufacturers.

Seeing what you are saying makes me think it is mainly prop-walk. Maybe it is because the TomCat is relatively lighter than the dual prop boats I've been on before. I just thought the small diameter Honda props would walk less than the big bronze props on inboards.

Thanks for all your input, John
 
Lori Ann":1jogo3p3 said:
Captains Choice":1jogo3p3 said:
That's a dead give away unless your engines are counter rotating which I doubt very much. It's gotta be the engine spacing. If it was prop walk with engines rotating the same direction, they'd each go the same way. Prop Walk is most/only noticible at very low speeds, otherwise thrust direction takes over...

Charlie
Click to expand...

Why do you doubt that the engines are counter-rotating? Mine are, and I don't think that my boat is that unusual. Les told me that one of the reasons he stopped selling Tom Cats is because of the expense of carrying an inventory of counter-rotating engines.

There is a Tom Cat on the board who has posted about cruising economically on one engine. Hopefully he will comment here.

Warren
Click to expand...

Warren, I doubt it because it's extremely rare and I'd bet a :cocktail and a couple of :beer :beer 's too that yours aren't. Where did you buy yours? I've been wrong before though, as my bride tells me often! :cry

Charlie
 
We wouldnt consider selling a Tomcat without counterrotating motors, and we mount them backwards! [ Port on Stbd side and vice versa] We learned this trick from other catamarans we sell . The just are more efficient that way . We even trained the factory to mount them that way for us when they rig one for us and I think they do it on all the boats now. It does not work on a monohull.
The torque tabs on the lower units of the motors will not affect your issue .Keep them close to straight and symmetrical as they just create drag that the engine "feels" . They are not real noticable with the hydraulic steering and they will not steer your boat.
First of all you need to trim the unused motor out of the water cause it creates a huge drag .
The boat itself being pushed from only one side creates a good bit of drag itself .Kinda like side tying to another boat ,and running , if you have ever done that . Thats what you are feeling . At low speed its not too bad and gets worse the faster you go . I hope this helps .
Marc
 
I may stand corrected.... :oops: If they really are on that boat.

I thought they were very rare.... But then I thougt virgins were too.... :shock: :gift :hug

Hard for a Naval Officer (even a former one) to admit too!! :!:

Charlie
 
I would guess that prop walk is part of what you are experiencing. I would also guess that the wide engine spacing is the greater part of the equation.

On one engine, as stated above, you will see improvement by lifting one engine out of the water to reduce drag. Ultimately, to go straight on one engine (in the case of trolling for example) you can compensate by making a slight opposite adjustment with the steering wheel.
 
Thanks Marc and all for the great feedback. I don't know why it did not occur to me that having one engine down and dead would act like dragging a paddle on a canoe! I was kind of thinking that activating those torque trim tabs might just create drag for no reason and your feedback seems to reinforce that.

Thanks, John
 
Marc,

Does "backwards" mounting of counter-rotating propellers mean that the clockwise rotating prop is on the port side and the counter-clockwise rotating prop is on the starboard side (rotation viewed from the rear)? On what basis is it felt that they are more efficient in being mounted backwards.

Thanks for posting.
 
If propwalk is a significant factor in the slow speed turning on one engine, then it seems to my senses, while on the boat, that the counter clockwise outboard is on the port on my TomCat. Is this the backwards? It kind of makes sense to me to put the counter rotating on the port, but I have not had time nor weather to correctly analyse this.

Now, if I'm supposed to truly mount them backwards, then C-Dory is gonna have to revise those Armstrong brackets and the steering and even the windshield wipers, unless I'm sposed to be running in reverse all the time... Although, come to think about it, that'd make it easier to troll whilst resting on the porcelain throne!

John
 
Unfortunately Brent and Dixie left our home before I had checked on the list--so I cannot ask them--but my experience is that there is definate pull from the engine--more than in inboard twin screw boats. As Marc says, the faster you run the boat on a single, the more the boat pulls to the side.

However I had the impression that the boats with the liquid tie bar were not susposed to be run with the engine all of the way up????

Yes, my boat has counter rotating engines--they are "backward" as Marc notes. The pull is not prop walk, but due to the asymetry of propulsion force and the hull configuration. There is some prop walk , but most noticable in reverse--as in most boats.
 
Thanks Bob.... But, exactly what is "backward"? Which prop is where? Why is one way considered "backward"?
What is a "liquid tie bar"? Hydraulic steering?
John
 
I just got caught up with the site , Wow , lots of stuff going on ! As for the motor mounting , the left hand rotation motor is mounted on the right side as you look at the stern towards the bow [ or , standing behind the boat looking forward] the right hander is mounted on the left .

Hoop, we are a long time Twin Vee Catamaran dealer and they did some testing a number of years ago and found that they consistently picked up a knot or two with this 'Backwards" setup . They are also a planing design like the Tomcat . If it were a displacement cat like a Glacier Bay , I dont know if it would have the same effect .
We also got our first Tomcat with 2 righthanded motors and it was night and day when we switched to a counter rotator on the right side .

John , The liquid tie bar system is a proportionong valve to keep the alignment of the motors consistent hydraulically or with set amounts of fluid going to each cylinder as opposed to one cylinder controlling both motors with a mechanical Tie Bar between the motors. They do it to clear the transom for boarding and to keep from having an extremely long tie bar which is not as strong as a short one . Bob is right that the systems dont like one engine " up " all the way as it harder to turn while tilted. Lots of geometry going on .Again the faster you go the more the steering system has to work , and they can only do so much before it spits fluid from somewhere [there is a relief valve in the reservoir cap and on the helm pump itself ]. So slow speed is ok for one engine up and only lift it to just clear of the water or a little less than that . Again , I hope this clarifies a little .

BTW, its always a good idea to carry a quart of steering fluid [seastar oil] on board .

Marc
 
Marc, Thank you so much for all that info. You know these boats don't seem to come with a concise instruction manual. My manuals, stacked up, are almost 8 inches tall!

So good to hear what we need to be careful of, and about the extra steering fluid.

Thanks again! John
 
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