Throttle lever reaction delay

[Eren]

My boat has MAN engines with Bosch Rexroth control levers. There is a time lag of 1 to 1.5 seconds from the time that I push the lever to gear until the prop begins to revolve. I got used to it now but it can be a bit nasty while mooring under heavy wind or other not ideal conditions. I asked about this to the MAN service engineer but he wasn't able to give me satisfactory answers. Does anyone here have any ideas how to fix this?

 

[jrudge]

A few questions to get this going! How old is the boat, and has it always been like this, have you owned if from new. do both engines exhibit the same lag?

There is always some lag as the electronics just tell a servo what to do - so the final link is mechanical as opposed to any clever electronic tricks. I have never tried to time it but lets say half a second is the norm.

 

[Deleted User YDKXO]

My boat has MAN engines albeit with ZF electronic controls and whilst there is a bit of a delay in responding its certainly nowhere near 1 - 1.5s

 

[BartW]

I'm not familiar with this type of controlls,
but in adition to the questions / remarks from Jrudge,
my first approach would be; try to find out of the delay is in the electronics,
or more likely in the hydraulic(?) activators

when the latter, is there enough pressure / too much resistance / warn out activators, ...

 

[jfm]

I have had 2x boats with ZF and before that 2x boats with Volvo EDC/EVC. And I have driven several others including the Rexroth version (eg a Manhattan 70 with MAN1360). In all cases the delay is more like 0.5seconds. 1.5s is much too long, if you're in a tricky situation (like mooring in a strong wind)

 

[asteven221]

Agree with JFM. 1-1.5 secs is an eternity in a difficult situation. My Morse electronic controls have a built in delay too, which is I estimate about 0.5 sec maybe slightly more. It's designed that way to stop you changing from fwd to astern so suddenly you end up trashing the gearbox. The Morse controls have dip switches in the controller that allows the delay to be changed, so maybe your's have the same or similar.

 

[Eren]

Thanks for all your valuable inputs.

Here are replies to all questions:

- The boat is 7 years old and I own it in the last 6 months.
- The lag is the same for both engines.

Having the same lag at the both engines tells me that this is some kind of "setting" issue, rather than an error. Unfortunately manuals for the control lever are not available. Therefore I wanted to ask if anyone has dealt with a similar problem before.

 

[Deleted User YDKXO]

I suggest that you find the installation manual for the Rexroth controls because I would guess that whoever installed them would have had to set the throttle response delay (along with a load of other parameters). You might be lucky and find you can do this through the control heads themselves or more likely you will have to get a Rexroth technician to plug into the control boxes

 

[BartW]

....have had to set the throttle response delay (along with a load of other parameters).

why would one want delay in there ?
should'nt this function react alway's as fast as possible ?
just wondering

 

[Deleted User YDKXO]

why would one want delay in there ?
should'nt this function react alway's as fast as possible ?
just wondering

I would guess to protect the gearbox and drive when going from forward into reverse or vice versa. I presume that a fraction of a second is required for the inertia of rotating in one direction to subside before power can be applied in the opposite direction

 

[MapisM]

I asked about this to the MAN service engineer but he wasn't able to give me satisfactory answers.

First things first: change your MAN service engineer.

That said, which engines and gearboxes do you have, exactly?
I am asking because what jrudge said (the electronics just tell a servo what to do - so the final link is mechanical) is not always true.
The latest generation of electronically controlled engines and gearboxes don't need any actuators, because there's no mechanical link at all, just wires connected to an ECU which decides if what you are asking it to do is acceptable or not, so to speak.

Anyway, regardless of whether the fly by wire is managed by the Rexroth control unit or directly by the ECU, I believe that the delay you are experiencing is adjustable in both cases - though I'm not 100% positive about MAN electronic engines.
And the adjustability is within limits, anyway: the real time response of fully mechanical levers/engines/gearboxes belongs to a bygone era, I'm afraid... :ambivalence:

 

[MapisM]

I would guess to protect the gearbox and drive when going from forward into reverse or vice versa. I presume that a fraction of a second is required for the inertia of rotating in one direction to subside before power can be applied in the opposite direction

Correct, but in my understanding, the electronic control can actually be much more sophisticated.
I believe (though as I said I'm not 100% positive) that in MAN CRM engines like yours it's the engines ECU that controls everything.
In other words, the throttles delay is not a constant time set in the throttles control unit, but it's processed more cleverly, according to the specific situation.

To make an extreme example, if you are cruising at WOT (i.e. 34 kts in your boat, IIRC?) and you hammer the throttles in full reverse for an emergency crash stop, the engines ECUs wait till the engines rpm goes down to idle, before even disengaging the FWD gear, and then engaging the REV gear, and eventually accelerating again.
In such situation, it obviously takes even more than 1.5 seconds, before anything happens.
Otoh, while maneuvering at idle, there's no need to introduce a lot of delay (if any at all), and the response is much more prompt.

Now, 'fiuaskme, I don't like the idea that the engine builder decided in advance what is best to avoid any g/box damage, no matter what is the highest priority for the helmsman at any given moment.
But from an engineering perspective, it's hard to deny that the above logic makes sense, in principle.

 

[QBhoy]

Have you tried shifting into gear with the floor up and physically watching the shaft starting to move ?
Do you mean it's 1.5 secs before the boat starts to move or until the shafts (or actuator) starts to move/engage ?

 

[Eren]

Have you tried shifting into gear with the floor up and physically watching the shaft starting to move ?
Do you mean it's 1.5 secs before the boat starts to move or until the shafts (or actuator) starts to move/engage ?

It is 1.5 secs before the propellers start to revolve.

In the meantime I have talked with Rexroth service. They told me that the controls do not have delay from N to gear. It has delat of minimum 3 seconds when engaged from forward to reverve or vice versa, which is OK. Eventually they wanted me to check with settings of the transmission. I am not very positive with playing with the transmission settings. I have friendly recommendations about not touching the transmission settings too much. I will once again check for the delay time and will decide what to do.

Thank you very much for all your valuable and friendly help!

 

[jfm]

To make an extreme example, if you are cruising at WOT (i.e. 34 kts in your boat, IIRC?) and you hammer the throttles in full reverse for an emergency crash stop, the engines ECUs wait till the engines rpm goes down to idle, before even disengaging the FWD gear, and then engaging the REV gear, and eventually accelerating again.

Yup, I have seen this done to my boat on sea trials off Ipswich. I didn't enjoy it!

Now, 'fiuaskme, I don't like the idea that the engine builder decided in advance what is best to avoid any g/box damage, no matter what is the highest priority for the helmsman at any given moment.

Yup, agreed, same as "limp home mode" which you might not like if you're on a lee shore in 60 knots of wind, but as you know it is how the world of electronically controlled gear works these days...

 

[Eren]

Yup, I have seen this done to my boat on sea trials off Ipswich. I didn't enjoy it!

Yup, agreed, same as "limp home mode" which you might not like if you're on a lee shore in 60 knots of wind, but as you know it is how the world of electronically controlled gear works these days...

+1

The manufacturers want to be at safe end as much as possible. And it puts the users in difficult situations. For example I don't feel good now to play with the default setup. There should be a better consensus in between somewhere.

 

[MapisM]

The manufacturers want to be at safe end as much as possible.

It's even worse than that, actually.
Manufacturers nowadays pretend to know better - and in advance! - than whoever is in command, regardless of the contingent situation he/she is facing.
As a result, a brand new A320 crashed at an air show because the flight computers, due to a "clever" protection of some sort, delayed the response to the TOGA command from the folk in the cockpit...
...though actually, in that case, also the pilots were to blame, but that's just one example which popped to my mind. :ambivalence: