Trolling valves

[Willallison]

Many larger sportsfishing boats are fitted with "Trolling Valves" to allow the boat to travel slowly without understressing the engine(s). I believe they also allow the boat to travel slower at idle than would otherwise be the case.

What are they and how do they work?

[Nomad]

They have them for some outboards(aftermarket) now too. I would never have an inboard without one. It also can be helpful in some docking situations.

It is a add on to your gear when you buy it. Basicly it works as another gear ratio.

[Nomad]

Here is a quote from another site:

My experience with trolling valves is that they enable a high powered diesel sport fishing boat to troll at a slow speed without having to take the transmissions out of gear. For instance, I often run a 47 Post with twin 635HP Cummins and big reduction gears and props. At dead idle, the boat makes 6.5 knots. Trolling valves would allow an amount of transmission fluid to bypass the drive, permitting the vessel to reduce idle speed to aslower speed necessary for certain types of fish.

Running any engine at prolonged slow speeds can have problem with carbon deposits--diesels are not immune. Fishermen use what is called a trolling valve--basically a bypass of fluid--on transmissions with diesel engines when running at slow speeds. In the Pacific North West trolling speeds are often as slow as one knot--impossiable to achieve even at idle with most engines. The carboning problem is especially a problem with turbocharged diesel engines. The other way around this problem in gas engine boats is the kicker" motor--an outboard on a bracket--today preferably a four stoke which is sized to allow slow speed trolling and enough speed as an emergency get home engine.

[Willallison]

Wouldn't you know it - the day after starting this thread, I get my copy of Passagemaker magazine and there's a several page article about gearboxes in general and a side bar about trolling valves.
But here's the rub. In what I will call a hydraulically operated clutch-plate (albeit many plates) gearbox, the valve simply bypasses some of the fluid, reducing the pressure on the plates so that they are able to slip and reduce the rotational thrust to the shaft. Most manufacturers say you must not operate the system at over 1000 rpm or you will damage the plates.
To me this seems kinda dumb. Ok, it allows a vessel with a high idle speed (like 8 knots) to travel slower, but surely prolonged plate slippage will shorten the life of the plates...? And we all know that big diesels don't like to be operated for extended periods at slow revs. Further, the manufacturers don't recommend using the valves when docking as delays in the shifting can change the way a boat responds - sometimes resulting in an expensive brush with the pier.

This (rather long windedly I must admit) brings me to the point. Why don't we see more boats fitted with what I would call a truly hydraulic gearbox: the engine mated to one hydraulic pump and a (probably much shorter) prop shaft mated to its reciprocal pump. That way the amount of rotational thrust can be varied by simply opening or closing a valve between the two pumps, almost regardless of engine revs. You would eliminate any alignment problems, you could greatly reduce shaft lengths and weight, engines could operate at their most efficient revs without fear of damage to any of the propulsion system. Engine(s) could be placed without regard to shaft angles etc etc, thus optimising CG and accomodation space issues.

Must be missing something.....cost ?

[Nomad]

Cost, just like with everything else.

[Willallison]

http://www.twindisc.com/TDFiles/MGX%20Ad.pdf

.....A partial solution to my gripes - but I still see my solution as best. ("My" is a relative term here - no doubt someone will provide a link to someone who's done it before....)

[Jerry l Jones]

what about power loss,converting from one type of power to another. How would this differ from driving a generator and then using an electric motor to drive prop

[Nomad]

Will, sure diesels aren't the best engine to run for a lon time at slow speeds, but it is better than poping the engines in and out of gear for 6 hours while trolling. I personally will take one engine out of gear every now and then and rev it once or twice as suggest to me by a mechanic. They have their place and are not right for all applications

[yipster]

interesting! and once hydrolic it aint only for trolling, the system can do much more. i like will's valve but think its a clutch valve? i've seen hydrolics used on small sloops lately and wonder about cost.

[Willallison]

I personally will take one engine out of gear every now and then and rev it once or twice

As I understand it, this won't really address the problem. It's prolonged use at low load that causes cylinder glazing. Simply giving the engine a rev whilst in neutral may be better than nothing, but it doesn't seem to be the solution. I guess that in a sportsfishing situation you would at least run to and from the fishing grounds with the engines under more substantial load.

As Yipster says, the hydraulics could be used for more than just propulsion (and dare I say it, the possibility of remote location if the engine would be ideal for his SWATH... )

Jerry, you make a valid point about power loss. I'm no engineer so couldn't tell you if this would be a significant factor, but I wouldn't have expected the loss to be any greater than that found in any other type of hydraulically actuated box. In the example you cite, you are actuallu transforming one kind of energy into another, whereas all I'm talking about is a different way of transferring it to the prop. There's some pretty broght guys on this board - perhaps one of them will let us know...

[sailvayu]

I’ve only seen a hydraulic pump used to drive a shaft with remote engine once in a racing sailboat. It really didn’t work very well. The problem (not counting leaks) is that power is a result of energy over time. It’s easy to produce energy from a motor, but to move that energy and create power at the shaft you need to move it fairly fast, this requires large pipes and hoses, and also creates a lot of friction which is dissipated in the form of heat. Hydraulics are getting better all the time but physics keeps getting in the way of using it for anything but slow moving equipment (have you ever seen a fast backhoe) I’m sure someone somewhere will find a way around the problems one day.

[yipster]

I’ve only seen a hydraulic pump used to drive a shaft with remote engine once in a racing sailboat

is that within the rules?

joking, but its the first time i hear a bad word on hydrolics apart from "little more expensive". your physics make sense however.
conservative http://www.vetus.com/frame-cat.htm has hydraulic bow & stern thrusters, hydraulic cylinders, hydraulic pumps, hydraulic steering systems. (guess on one pump) and i've seen hydropower used for more...

when i talk to a hydroman i will ask for that power loss! (iff he knows)

yipster

[yipster]

better yet go to http://www.vetus.nl as it has more info also on Hydraulic marine propulsion (under the H from the sales program tag) y

[Willallison]

Excellent link Yipster!
Like all my great ideas, someone else has come up with it before me !!
The largest model produced by Vetus can absorb about 60hp. I wonder if systems exist for higher hp & speed applications...?

[sailvayu]

Good link, leave it to Vetus to come up with something differant I do question the statement "In addition, should the propeller become fouled or touch the bottom due to running aground, the risk of damage to the propeller shaft assembly, the hydraulic motor or the boat’s engine is almost nil. An integrated pressure relief valve ensures that in the event of overloading, the hydraulic motor is safely bypassed." Seems a bit optimistic to me. Also seems I've heard that mounting an engine transverse is not good due to the rolling of the boat causing stress on the bearings while it's running I know of some gen sets mounted like that though, anyone else hear of this? 60hp is higher than I would have thought posible without too much heat. I'll have to get the calculator out and see what the numbers say one day when I have some free time Anyhow I like the idea and it does open some interesting design posiblities, I would like to learn more perhaps the time has come, as for cost this might be offset by using this power to run winchs and such saving some expense in electric motors.