Low-RPM toggle switch

[Fire99]

Evening gang,

Probably a simple one to answer for many but I have twin 3126B Caterpillar engines on my Trader and a Low Rpm toggle for each engine. When I select it, it drops the idle rpm from 680ish to 540 ish... I'm guessing this toggle has something to do with low speed handling in marinas etc but can anyone shine a definitive light on what the point of the toggles is?

Thanks all,

Nick

 

[Portofino]

Or fishing trolling .More State side enabled .
I was told here in the Med the three 6 s for Tuna .6 miles out , 6 hrs and 6 knots .

 

[Fire99]

Or fishing trolling .More State side enabled .
I was told here in the Med the three 6 s for Tuna .6 miles out , 6 hrs and 6 knots .

So what does it do? Does it make the throttles less responsive so for argument sake a couple of inches of throttle action will have less rpm increase?

 

[Portofino]

Two speeds at first click a lower one or higher .Might be useful with tolling for fish for hrs on end .

Marina manoeuvres needs zero throttle just click up or back responsiveness is NA .

A lower rpm your 540 might mean 3 sec a in a click as opposed to 1 .

Mines ( MAN s ) twixt the two at 600 tick over fwiw .Which equates to something stupid ( big pitch props WOT 2100 ) like 8.5 knots at tick over .
I haven’t attempted to fish for tuna btw in this boat , but the previous S Squeaker would do 6 knots .

 

[Fire99]

Two speeds at first click a lower one or higher .Might be useful with tolling for fish for hrs on end .

Marina manoeuvres needs zero throttle just click up or back responsiveness is NA .

A lower rpm your 540 might mean 3 sec a in a click as opposed to 1 .

Mines ( MAN s ) twixt the two at 600 tick over fwiw .Which equates to something stupid ( big pitch props WOT 2100 ) like 8.5 knots at tick over .
I haven’t attempted to fish for tuna btw in this boat , but the previous S Squeaker would do 6 knots .

Gotcha.. Thanks for that.. I've got Titanic sized (well almost) props on mine and on the higher setting the boat is doing about 5 knots+ on tick-over. I've never tried the lower one to be honest. Well not yet anyway..

 

[Nito]

Try Google or searching ‘trolling valve’. I suspect this is what you have. It affects the transmission, allowing clutch slip I believe to reduce output to prop. I remember reading about a reference to trolling valves in a couple of manuals on our 3126 equipped with the ZF trans, though ours isn’t fitted with trolling valves.

 

[Fire99]

Try Google or searching ‘trolling valve’. I suspect this is what you have. It affects the transmission, allowing clutch slip I believe to reduce output to prop. I remember reading about a reference to trolling valves in a couple of manuals on our 3126 equipped with the ZF trans, though ours isn’t fitted with trolling valves.

Thanks mate.. That's interesting.. I'll have a bit of a google trawl.. I've had these two switches on the dash that so far I've not had a clue what they do and the boat manual seems to leave it up to you to work it out.

 

[Fire99]

Try Google or searching ‘trolling valve’. I suspect this is what you have. It affects the transmission, allowing clutch slip I believe to reduce output to prop. I remember reading about a reference to trolling valves in a couple of manuals on our 3126 equipped with the ZF trans, though ours isn’t fitted with trolling valves.

I did a quick google and it looks like the low-rpm switch brings in a low idle and drops a cylinder (apparently) to bring speeds down a bit.. Allegedly.

 

[IDAMAY]

Despite what Porto says, the switches are designed to lower tickover speeds in the marina. I always switch down before entering any berthing or mooring area to avoid sudden movements. You should find a max of 3 to 4 kts at the lower speed and it means you don`t have to adjust the revs, just play with the gearboxes and thrusters.

Hope you are enjoying the Trader, if not the weather. It`s pants up here in Oban.

 

[Fire99]

Despite what Porto says, the switches are designed to lower tickover speeds in the marina. I always switch down before entering any berthing or mooring area to avoid sudden movements. You should find a max of 3 to 4 kts at the lower speed and it means you don`t have to adjust the revs, just play with the gearboxes and thrusters.

Hope you are enjoying the Trader, if not the weather. It`s pants up here in Oban.

Ah haaaa. I see. My controls are combined gears and throttles unlike my neighbour's 54 who has separate gears / throttles but I'm sure the concept works ok with both. This will certainly help when departing the berth and the boat goes from 0-5kts in about 0.1 seconds the second I gain drive. haha

The Trader is great though keeping me busy. A few years of little use has meant a fair list of 'recommissioning jobs' but I get to know the boat very well and it's satisfying getting issues fixed. Weather here is blowwwwwwyyyy today. I won't be as far up as you but hoping to be over around Aran next month..

Hope your '54 is treating you well.

 

[Portofino]

Despite what Porto says, the switches are designed to lower tickover speeds in the marina. I always switch down before entering any berthing or mooring area to avoid sudden movements. You should find a max of 3 to 4 kts at the lower speed and it means you don`t have to adjust the revs, just play with the gearboxes and thrusters.

Hope you are enjoying the Trader, if not the weather. It`s pants up here in Oban.

Did you miss what I said in post #4 @ second line down ?

“Marina manoeuvres needs zero throttle just click up or back responsiveness is NA .
A lower rpm your 540 might mean 3 sec a in a click as opposed to 1 .”


The hint / big clue is in the nomenclature “ Trolling valves “ Why are they called such a term ?
Yes they do indeed simplify marina manoeuvres nobody’s denying that .

 

[IDAMAY]

Did you miss what I said in post #4 @ second line down ?

“Marina manoeuvres needs zero throttle just click up or back responsiveness is NA .
A lower rpm your 540 might mean 3 sec a in a click as opposed to 1 .”


The hint / big clue is in the nomenclature “ Trolling valves “ Why are they called such a term ?
Yes they do indeed simplify marina manoeuvres nobody’s denying that .

I read your post quite carefully and, with respect, totally disagree. I would not contemplate the higher revs in a marina even for the click in and out of gear you suggest. Generally the less throttle input at close quarters the better.

 

[Portofino]

I read your post quite carefully and, with respect, totally disagree. I would not contemplate the higher revs in a marina even for the click in and out of gear you suggest. Generally the less throttle input at close quarters the better.

I,am agreeing with you .
To be clear “ Trolling “ is a fishing term .

Parking and indeed a twin shaft is easily done with rudders set a mid ship and simply clicking F-N-R .To turn it one F , t other R and it’s spins on its own axis .No wheel movement .

The tick over dictate the time in F or N .

 

[Nito]

I did a quick google and it looks like the low-rpm switch brings in a low idle and drops a cylinder (apparently) to bring speeds down a bit.. Allegedly.

Ah, apologies then. In the schematics for our ZF boxes (on 3126TA engines) ours are on V-drive so possibly different from your set up, I saw trolling valves as part of the gearbox hardware rather than being an engine thing.

Good luck with it all and enjoy!

 

[Fire99]

Ah, apologies then. In the schematics for our ZF boxes (on 3126TA engines) ours are on V-drive so possibly different from your set up, I saw trolling valves as part of the gearbox hardware rather than being an engine thing.

Good luck with it all and enjoy!

Ahh not to worry, thanks. It took a lot of google hunting to find someone explaining these switches.. Thanks for your help anyway..

 

[Nito]

I suspect with the 3126TA being mechanical injector, you can't shut one piston off easily, hence the difference. I believe the 3126B engines are electronically injected which opens up that option and a better method than allowing clutch slip to allow slow speed running! Ours runs at 6 knots in gear no throttle.

 

[vas]

possibly mixing terminology, but trolling valve is indeed a gbox device to reduce pressure on the disk plates letting them slip and in effect lower prop speed (and boat speed)
idle speed switch is an engine addon dropping the rpm of the engine (creating the same effect but differently and with less wear in the gbox plates)

 

[Fire99]

possibly mixing terminology, but trolling valve is indeed a gbox device to reduce pressure on the disk plates letting them slip and in effect lower prop speed (and boat speed)
idle speed switch is an engine addon dropping the rpm of the engine (creating the same effect but differently and with less wear in the gbox plates)

Thanks Vas.. It's certainly effective at dropping the rpm but I've not tried it in anger yet. One thing with these Traders with their big props is merely engaging drive seems to generate about 5knots..

 

[vas]

it seems that any planning mobo over 45ft has an engage speed of 4.5-5kn.
If I want to do some 3-3.5kn fishing I just switch off one of the engines. OK, the A/P does a bit more work but I don't mind
in port it's in/out of gear job, your life will be slightly easier with this switch!

 

[Fire99]

I suspect with the 3126TA being mechanical injector, you can't shut one piston off easily, hence the difference. I believe the 3126B engines are electronically injected which opens up that option and a better method than allowing clutch slip to allow slow speed running! Ours runs at 6 knots in gear no throttle.

Yeah mine run the HEUI oil pressure controlled injectors and the ECU's that like to give me lots of information on digital displays.. And the odd spurious error message.. They're about as electronic as I'd like to go.. Boat sensors have a habit of getting temperamental. I was chatting to a visitor running Cats and one of his engines shut down mysteriously... Yep, a moody sensor was enough to bring it all to a stop..