transmissions in trolling mode

I troll with trolling valves engaged for hours at a time. I have to go about 2 knots when fishing for salmon. Doesn’t hurt anything as long as you stay below 1000 rpm. My controls won’t let you go above 1000 anyway.

However, I do not use my trolling valves for docking. I don’t like the slow reaction. I just clutch in/out with my engines at slow idle which is 500 rpm.

We had manually-controlled trolling valves on our previous boat with ZF gears. We trolled a lot at idle RPM and between 2.5-3 kts, no issues over several years. We could change RPM a little, yes always less than 1000, but generally that was only useful for some temporary steerage correction. No need for increased oil change frequency... We never used our trolling valves for docking, but I've recently heard some might do that...

Our current ride -- MANs with Twin Disc gears -- has electronically-controlled trolling valves, that are unfortunately not yet working. Troubleshooting in progress, but we're guessing it's at least partly because they were never used over the ~17 years.

So far, we think: Our MAN (Rexroth) control system doesn't really vary RPM when in trolling mode. Instead, the controls vary the degree of slippage.

That's from reading the manual. Your MAN guy, or your gear guy, can advise too.

(Conceptually, I suspect it might be possible to set the RPM higher than idle BEFORE putting the control in Troll mode. Haven't experimented with that.)

-Chris

Same on mine (MAN V10 with ZF gearbox and controls) - only controlls gearbox pressure, no increase in rpm. When a higher rpm is selected (throttle movement higher than 30 degrees) trolling mode is deactivated automatically. Spoke in length to ZF about it, trolling has absolutely NO influence on wear and tear.

Trolling in high idle setting doeas not work on my boat. Only use trolling when approacing the berth, not for docking as too little control/repsonse.

I too have ZF gears and controls but with CAT power. My 2020 era controls can be programmed for trolling rpm but not something you can do on the fly. I left mine at factory setting which is idle rpm of 600. I almost always troll at 500 rpm with slow idle engaged and only running one engine. But that’s because I’m looking for a really slow speed. Regardless of my trolling speed, I never understood why you want to be in troll mode above idle speed? If one wanted to be in troll mode at say 800 rpm, why wouldn’t you simply not use troll mode and run fully clutched in at idle speed or above?

I really like the ZF controls and troll mode. I get a read out of % of throttle or when in troll mode, % of slippage if you want to think of it that way. I also see shaft rpm and clutch pressure. I can increase clutch pressure in troll mode up to 70% of throttle range, anything above that and it fully engages the clutch.

No such thing as a 1500hp MAN engine - I suppose you are referring to the 1550hp (aka D2842LE433), right?
Anyway, when talking of trolling valve you should rather specify the gearbox model, which is more relevant.
Unless you're actually referring to low idle mode, which is a way to electronically reduce idle speed that someone call trolling mode.
But that doesn't affect the gearbox slip.

+1, that doesn't make any sense to me.

Yep, you could say I'm more familiar with Med docking than with car parking...
And FWIW, I agree with Dockmaster in preferring a swift boat reaction upon throttle engagement, while docking.

Actually, my boat neither has a slow idle function nor a trolling valves, so I don't have a choice, really.
But while I hate the fast docking style of some Sunday boaters - and in fact a lot of my docking time is spent out of gear, with the boat slowly moving just by inertia - I like to know that right upon gear engagement the boat reacts promptly.
So, I even if I would have electronic throttles and engines capable of slowing down the normal idle speed, I don't think I'd bother using it.

With MAN common rail engines like yours, the typical throttles pairing is with the so-called Mini Marex levers, the black ones with the command button on the left and the synchro/throlling button on the right.
If that's what you've got, here's a couple of comments.

First, if that trolling function is what you were referring to in your OP, it's actually a bit misleading terminology, because what that button does is electronically reduce the engines idle speed, regardless of whether your gearboxes are actually equipped with trolling valves or not (my guess is they are not, BTW).

Second, the delay quite likely doesn't depend on whatever gearboxes you've got, but rather on the electronic controls, and if so it should be adjustable.
Also because in some conditions, even 2 seconds wouldn't be enough to avoid destroying the gearboxes: just think of the crash/panic test (which should be part of the initial engines commissioning), where you move the levers as fast as you can from WOT forward to WOT reverse, in one hit.
If forward would be disengaged with "only" a 2 seconds delay, the engine would still be well above idle, and also the following 2 secs before engaging reverse wouldn't be enough to avoid damages.
But the controls should take care of all that, allowing engage/disengage not only depending on a fixed delay but also on the actual engine RPM.
Anyway, a 2 seconds delay upon any engage/disengage with engine already at idle is something I've seen on several boats, and while I appreciate it can be a bit annoying, it could well be the original setting the boat came with.
But as I said, your MAN engineer should be able to reduce it for you, if you wish.
He will probably advise against it, and possibly ask you to sign a waiver of some kind, but...
...You pays your money and takes your choice!

FWIW... with practice, I've eventually gotten to the point where I can anticipate gear engagement, and I can (usually) even move the control out of gear just as a prop begins turning. Almost before a prop starts turning.

This is with the standard timing delay. No use of trolling valves really required.

That was not without a learning curve, but OTOH I was already so used to gear-in/gear-out movements, with no additional throttle usually required -- that adding any additional mandatory futzing with the levers (as being in trolling mode might necessary) would be a significant distraction.

YMMV, of course, but you might give it some getting used to before jumping to a trolling valve solution.

-Chris

With trolling mode used in docking you presumably loose the port/starboard kick you get from gear engagement and then have to rely on the use of a stern thruster to kick the back end into position. This might be advantageous when docking as each item engine or thruster would only provide one prescribed direction of movement but it would rely on having a stern thruster. In the boat I am getting trolling mode has been described as proportional thrust up to 100% of thrust at idle speed. Anyone use trolling mode for docking with a stern thruster?

I would not reccomend docking in trolling mode at all... As you have reduced gearbox pressure a change of direction (e.g. stopping) will be very sluggish and unpredictable - for example if you are moving ahead and select reverse in order to stop, the clutch may slip and not be able to turn the prop in the opposite direction. I guess with a lot of practice it would be possible to do safely but personally think the disadvantages outway the advantages....

Many thanks for that input I can imagine the problem coming when you are not expecting.
Had few issues in normal drive mode using the sideways kick from gear engagement but certainly having had the odd time a stern thruster would have been beneficial pleased to have one on the new boat

We don't have a stern thruster, but...

Gear response when we're our trolling valves are enabled is slooooooooooooooooowwww... to the point where it wouldn't be helpful while docking.

Our brief shots of IN (and back OUT) of a given forward or reverse gear -- like about 1 second each -- are what we find most effective.

-Chris