U Boat differential steering

As part of my Darnell U Boat rebuild I’m wondering how efficiently differential (thrust) steering of the motors would work. The hull is of course very long and narrow with resultant minimal distance between the props. So questions:
1. Who has employed this configuration and how well does it work
2. Do you merely stop or reverse the inner motor

Thanks

It will help a lot, especially at low speeds where its needed. just stopping one wont yaw it very much due to the legnth of the sub and its vertical stabilisers but when you run them in opposite directions it should turn much tighter, even on the spot when stationary.

geofrancis wrote:It will help a lot, especially at low speeds where its needed. just stopping one wont yaw it very much due to the legnth of the sub and its vertical stabilisers but when you run them in opposite directions it should turn much tighter, even on the spot when stationary.

Thanks, that’s helpful

Sorry to disagree Geofrancis but I have tried it a couple of times on my subs with poor results. (One ESC per channel - so called tank control)
Admittedly my main requirement was turning the sub while more or less stationary not differential steering but this effect seemed disappointing also and not worth the extra channels and complexity. ( I tend to control twins with 2 ESCs fed by a "Y" lead.)
As you say NYK, the problem is with most subs, they are so long and thin with very little distance between the props.
The result is lots of amps and prop wash but not much movement!
If you need a small turning circle (small pool etc) you may be better off looking at some form of bow thruster or adding extra rudder area. (clear plastic clip-on can work)
I have also used a clip on bow thruster (a prop in a tube ) successfully on near "paddling pools " at Exhibitions etc.
Turning circle on subs is a perennial problem.
David

david f wrote:Sorry to disagree Geofrancis but I have tried it a couple of times on my subs with poor results. (One ESC per channel - so called tank control)
Admittedly my main requirement was turning the sub while more or less stationary not differential steering but this effect seemed disappointing also and not worth the extra channels and complexity. ( I tend to control twins with 2 ESCs fed by a "Y" lead.)
As you say NYK, the problem is with most subs, they are so long and thin with very little distance between the props.
The result is lots of amps and prop wash but not much movement!
If you need a small turning circle (small pool etc) you may be better off looking at some form of bow thruster or adding extra rudder area. (clear plastic clip-on can work)
I have also used a clip on bow thruster (a prop in a tube ) successfully on near "paddling pools " at Exhibitions etc.
Turning circle  on subs is a perennial problem.
David

true when you are on the surface you are going to have cavitation problems when running the propeller in reverse. I just read the post title again and its a Uboat so it has rudders behind the propellers so it will be quite manouverable as subs go compared to something with the rudders ahead of the propellers that dont turn at all so runing the propellers opposite wont help as much.




I have done a lot of testing using water pumps for manouvering thrusters. di directional car washer pumps work really well they are fully sealed and you just need a 8mm outlet for the thruster so its easy to hide. you can also use a geared water pump mounted inside the WTC with hoses going through the bulkhead.

https://www.theassociationofmodelsubmariners.com/t1979-water-jet-manouvering-thusters

david f wrote:Sorry to disagree Geofrancis but I have tried it a couple of times on my subs with poor results. (One ESC per channel - so called tank control)
Admittedly my main requirement was turning the sub while more or less stationary not differential steering but this effect seemed disappointing also and not worth the extra channels and complexity. ( I tend to control twins with 2 ESCs fed by a "Y" lead.)
As you say NYK, the problem is with most subs, they are so long and thin with very little distance between the props.
The result is lots of amps and prop wash but not much movement!
If you need a small turning circle (small pool etc) you may be better off looking at some form of bow thruster or adding extra rudder area. (clear plastic clip-on can work)
I have also used a clip on bow thruster (a prop in a tube ) successfully on near "paddling pools " at Exhibitions etc.


Turning circle  on subs is a perennial problem.
David

Your answer pretty much confirms what I thought. Odd though as I was at a show the other week where a chap had a couple of nicely built subs one of them being a U Boat. I posed the same question to him and he said that differential steering worked well.
In terms of my options I was considering replacing my single esc with a P94L Dual Esc and rudder Mixer which is a simple swap out job. I’d considered a bow thruster but this becomes far more involved. I have absolutely zero space available in the WTC so it would need to be a totally external installation. A quick google would suggest that the bow thrusters on sale assume that the motor is contained with the (dry) hull. As this is not an option I would need to fabricate a watertight container for the motor whilst ensuring none of this interferes with the front planes and linkage, nothing is impossible but it does get complicated.

I guess if a fully waterproof thruster/motor assembly was available this would eliminate one problem, does anyone know of such a unit?

the car washer pumps are sealed, im going to mount one outside the WTC for my sub and just run the wire through.

geofrancis wrote:the car washer pumps are sealed, im going to mount one outside the WTC for my sub and just run the wire through.

Are they truly hermetically sealed? I’m not convinced that there is sufficient power in the water jet to turn a Darnell sub, it’s nearly 6ft long and is pretty heavy.

it would work for low speed manouvering, they become less effective the faster you go. the washer pumps are sealed since they are designed to hold water for years and operate in an engine bay but I have no idea to what depths the seals would work to. i wasnt planning on going more than 1m so its not something i tested.

I tried differential steering on a 1/32 scale type II u-boat, and it was useless.

I plan on putting the reversible "bmw" style pumps in both the bow and stern of the giant 8' type XXI that i tested over the weekend.