Hi Kevin,and all other contributors!
Overwhelmed by all the useful information!
This demonstrates the fantastic value of this forum.
Thanks to all.

John

Hi

I guess you would have had to try the boat with one of the props contra rotating, you may well have seen an increase in speed and thrust. Also the more course the prop, the more critical the effect of loss of water pressure caused by the other and the greater effect of cavitation .

Regards

Kevin

Years ago my brother in law worked for Natal Parks Board on Spioenkop Reserve, which has a huge dam. They had an 18' ski boat fitted with two large outboards (80 hp?) . They both had the same clockwise rotation - yet there was no effect on the boat in terms of yaw or tilt - not sure if there was any effect on speed.
Had a look at the Shark Cage Diving boats here mostly Semi Rigid inflatables or Catamaran hulls up to about 60'. Some of them have 4 x 300hp outboards - minimum is 2 x 250 hp. Same story - all have props turning the same way ............
Not sure what you make of that - but I always try to use counter rotating props on my models anyway - but having seen those not sure I would bother on a full size boat equipped with outboards.
My two pairs of model outboards are counter rotating funnily enough....

Hi Doug

Yes I get the point you make re torque cancellation. The other reason for contra rotation in twin props is the prevention of cavitation of the props. This would occur when one of the props suckswater away from the other. This creates a reduction in pressure around the starved prop resulting in water boiling around the prop blades due to pressure reduction and causing damage and pitting to the prop.

Regards

Kevin

Hi Kevin,
"The purpose of having left hand and right hand props installed on a twin screw vessel is in order to stop one propellor sucking water away from the other, therefore making one of the props inefficient by starving it of water that it needs to develop thrust. "
Well, they say you learn something new every day.
But I'm not sure that the above is a learning experience!
I've never seen that postulated in any analysis of single versus twin screw performance for high speed naval craft. Including those done by the USN Design Bureau. Which prop would under which circumstances 'suck' water away from the other?
The main reason for using opposite prop rotation on a twin screw setup is to cancel out the torque reaction of each screw on the hull (regardless of inboard or outboard rotation for ahead). This effect is even more noticeable on models as they don't have the mass inertia of their big bruvvers😉
I do agree with you though that inboard rotation should be used especially if you have twin screws with a single rudder. Like most WW2 destroyers for instance.
USN calculations and practical trials showed that for twin screw small ships; such as Fast Attack Craft, FPBs, Corvettes etc, with twin rudders that outboard turning screws gave a minimal advantage in manoeuvrability when the rudders were set slightly inboard of the shafts.
Since USS Crocket was a Gunboat (which would now be called an FAC) capable of 50 knots and seems to have two rudders it would seem logical to make the screws outward turning on drspock's model.
Cheers, Doug 😎

"You can use tank steering as the device has two speed controllers in built, but you need to have two channels for this i.e. One channel for each motor."
True - Mode 1. But why waste an RX channel when the built in rudder mixer gives you excellent manoeuvrability anyway
You do normally connect two channels from the RX to the P94 board (Modes 2-4) BUT; one for the rudder and one for the two ESCs.

To avoid any further confusion regarding the P94 board attached is the 'official' data sheet describing the various operating modes available; including reversing the inner motor on hard rudder commands. So spinning on your axis should be possible, depending somewhat on the length to beam ratio of the boat.
But then destroyers aren't built to do that anyway 😁
Mind you, I'm gonna try it with my 1.35m 1/72 H class destroyer; 135x12cm 😉
An' I'll be using the P94 to do it.
I agree with Pete (our 'Rooky😮' Lieutenant) the P94 is the simplest way to get the best of both worlds - if not the cheapest!
But add up the price of two ESC's and a Mixer Board and you won't be far off the P94 price anyway. Maybe above it🤔
Cheers, Doug 😎

Hi John.
Just ad the spec on the component shop p94. You can use tank steering as the device has two speed controllers in built, but you need to have two channels for this i.e. One channel for each motor.

Regards

Kevin

Hi John

The purpose of having left hand and right hand props installed on a twin screw vessel is in order to stop one propellor sucking water away from the other, therefore making one of the props inefficient by starving it of water that it needs to develop thrust. The set up should ensure that each rotates throwing water inwards towards the keel. Even though the props are handed differently and rotate in opposite directions they should both be pushing the vessel ahead or astern together. The motors can be controlled by one speed controller, ahead or astern but with one esc both motors will move ahead or astern together and at the same speed as they both receive the same command from the esc and you only need one channel to achieve this. Alternatively you can use two esc's one for each motor and control them independently and create ' tank steering' two channelsare required for this set up, one for each esc. The component shop device uses one channel to control both motors, along with a feed from the rudder channel. When rudder is applied then the mixing part of the unit slows one of the motors to allow the vessel to turn. The disadvantage is that you reduce the speed of one of the motors on the inside of the turn and therefore the vessel will lose speed. Using this controller does create a type of tank steering but I don't think you can turn on the spot i.e. One motor virtually full ahead and the other full astern.

Hope this helps.

Regards

Kevin

Hi Pete,
Will check that one,cheers!

John

Hi Peter,Thanks for your reply,will look into that.

Martin,
Thanks very much for that.Simple when you know how!

If cost is not an option, then there is nothing better
than a P94 from action electronics, just check out the link below, you will never use anything else again for twin prop boats.👍
Cheers, Pete

https://www.componentshop.co.uk/p94-dual-esc-and-mixer-2-x-20-amps.html

Hi drspock,

1 channel + 1 ESC + 2 motors.

On ONE of the motors you will need to reverse the Positive and Negative wires. ( the motors cannot be operated independently )


2 channels + 2 ESC’s + 2 motors.

On ONE of the motors you will need to reverse the Positive and Negative wires. ( the motors CAN be operated independently or together) ("I think it is called tank steering" )

If using two ESC's with BEC then you must disconnect
one of the BEC's.

Depending on your radio equipment it is possible to be able to operate the motors independently or individually at the flick of a switch.

I think i got this right!!

Hope this helps.

Martin555.

Hi drspock.
I have done a couple of these setups recently and on both occasions I used a Hobbyking Quickrun 860 dual output ESC. You only need one channel and can easily set up the differing rotations. These are for brushed motors. The two outputs cannot be used independently so far as I know but open to correction.
Peter