Thank you all.
As to BruceD and Bruce1946 both are me, I have been trying for years to get this corrected and bring all into one and the same person. I have written the support team many times with no response!

John, et al.,
I found that with three propped model boats the center motor does not need a esc. When accelerating, do as normal with the two outer motors and use a switched channel for the center (on/off, only) to kick in. The third motor kicking in is fairly smooth as the boat should be moving somewhat fast.
This is not only reduces the cost of another ESC, but with most transmitters having only two gimbals which are generally for motor control in the vertical axis you can use one of the auxiliary switches for the center motor.
The center motor is not needed for backing up.
Lew

Hi Bruced, just to clarify, are Bruced and Bruce1946 the same user?

My answer remains the same.
The side propellers should be chosen in counter-rotation to cancel out the lateral effect [so clockwise on the right and counter-clockwise on the left].
The center propeller is irrelevant.
Any remaining lateral effect will be corrected with the rudder, as with real boats.

You can also test with only two side propellers in counter-rotation (the center one temporarily absent) and evaluate the boat's tendency.
If you notice it, choose the center propeller that counteracts it.
For example: with the two side propellers in counter-rotation, I notice (in forward gear) a lateral shift of the stern to the left. So I'll choose a right-handed center propeller.

The simple answer to the original problem, the boat pulling in one direction when accelerating, is to apply some opposite rudder. Full size boats due that, aircraft do that and the issue is solved. if you find that pull is constant then add rudder trim to correct it. KISS

hi there

I believe this question may have been asked on Mayhem Forum and to which I posted several photographs of fast plaining vessels, to show which way the props turn. But, having said that, we will try this way .... normally you would have your 2 outboard props turning inwards; and, depending on the design of the vessel, the centre prop will either rotate port or starboard. However, on lifesized vessels, they have the ability to control the speeds of the props whilst the vessel is turning. Slow the inboard prop down and speed the outside prop up, depending on which way the vessel is turning. Normally whilst performing manouvres like this the centre prop is slowed down, so, it doesnt influence any turning. In model ways, we can assimilate this as there are mixers on the market which we incorporate with our speed controllers which allow us to do this. One of them is from ACTion which has the speed controllers and the mixer combined. This allows you to add a 3rd speed controller for your centre prop. There are obviously other mixers on the market.

As far as prop walk - it would be very negligable on our scale models unless all the props are turning in the same direction when it does have affect.

John

So on the main question Best way of setting up 3 props Selection. I am building a Dumas PT 596 48" Glass planning hull I am building to Scale 1:20 and several people in the past have said they have had issues with this boat tracking right and that rudder control is slow. The rudders are small only 60% of the rudder (just below the Prop Hub) is in the prop stream. and I am going to increase the prop length by a 1/2" hoping to prevent this.
My question is how to set up the 3 props, Left prop CC, Center Prop CC or CW, right prop CW. I will have proportional motor RPM's with all 3 motors.
Looking at photos of freighters and other non-planning hulls is not the same as a PT boat.
thank you

Yes, Chum, a dedicated discussion on this topic would be very interesting.
In the meantime, I've tried to provide helpful information for Bruced; I hope he'll benefit from them.

This could be an interesting discussion. I have only done one 2 prop boat and I used contra rotating props. Interestingly it cancels prop walk but can also lift or drop the stern depending on rotation direction. As for a boat capsizing/rolling over, I have one of my over powered single prop 3D printed hulls which I have never had at full throttle as when it rises up on the plane, the torque generated by the large brushless motor rolls it over. I know this can be compensated for by trim tabs, changing thrust angle and all the other good things, but it was just an experiment in hull design 😁

TD,
As you & Lewz have pointed out we’ve strayed off topic from bruced’s original question. I’ve never built a boat with three screws so if I did I would be asking about how to do it from those who have. Seems to me that bruced’s issue could be a myriad of things; prop walk, shaft alignment with the keel, differences in motor rpm, & possibly other factors. That said, the discussion to date brings up many interesting propulsion questions for me. Among them; why three props, inward v outward rotating dual prop installations, & compensating for prop walk in single screw boats. BTW, single prop aircraft have the same prop walk issues. Unless you apply opposite rudder to the direction of turn it will yaw in the turn.

Later this afternoon I will try to start a new thread that delves into what I think are interesting questions that may result in diverse viewpoints.

Hi Chum, sorry for any possible misunderstandings in the translation.
In Italian, "effetto evolutivo" of the propeller could be translated as "evolutionary effect" of the propeller.
I don't know why I translated it as "lateral displacement." I'll re-edit the message.
Thank you so much for pointing that out.
To avoid any misunderstanding, I mean the lateral displacement of the propeller. A secondary and unwanted effect compared to the traction or thrust effect (forward or backward).
I believe and hope that people of good will like you have already understood this, hahahaha.
This effect, as I've already said, is felt in real boats when they move from a standstill.
In real boats, this effect is exploited when docking.
When underway, it's almost irrelevant. But now I learn from you that at very high speeds they even capsize. I honestly didn't know that and would never have imagined it.
As for the model, I think at least the side propellers should be set in counter-rotation (right-handed propeller to the right and left-hand propeller to the left). The center propeller should be either left or right.
How would you do it, Chum?

US built PT boats during WWII were built with all three propellers turning in the same direction. Right handed, or clockwise when viewed from the stern looking forward.

Contrary to some comments here, there is a "prop walking effect" when going forward. So, the original question was about a model PT boat and that is what I will try to answer here rather than something non-applicable.

There were some complaints way back when about this affect and the helmsman had to correct and compensate for it, mainly at lower speed. At higher speeds, the hull acts more like a rudder helping keep it on course. I read a lot of books and articles on PT boats.

As for a model PT boat, my 1/20 scale Elco "77" does not have much of a walk, but I must admit my center prop has a left hand pitch to it. This counteracts the two outer right had pitched props.

When determining if a model has any walk one would need to zero the rudder then run the boat like that to see if it deviates off a straight course. Model characteristics are different from a real ship, one being that a model's props might turn at 8,000 RPM vs 2,300 for the real boat. Also, how can you notice if the boat is walking off course unless you have zeroed the rudders. Most of us would probably adjust the transmitter's rudder trim to straighten out the course.

Lew

Chumm,
We have to put this in perspective. The last US ships built with three props were early(very) destroyers. After the steam plants developed and the turbines to match, two props became the rule.
However, foreign navies built three shafted ships right up to WW 2. See the German capital ships for example.
As to which combination proved most effective, that question needs to go to the engineers.
It certainly did not do Bismark any good...

No worries Alessandro. I’ve never built a three screw version so often wondered what direction of rotation of the center prop produced the best performance. In the U.S. it seems like three outboard engines are standard today.

Prop walk, which I believe you call lateral displacement, is a problem at high speed. One of my single screw lobster boats, originally set up for racing, could easily roll over at wide open throttle (WOT).

Bruce and Chum sorry, I meant to write hi Bruce, it was a reply to your message, now I corrected it by re-editing the message.

Essatto!

Hi Bruce.


Perhaps I wasn't able to translate and understand well, so I'll speak in general terms. I hope it helps.

Whether a propeller is right-handed or left-handed is a characteristic known to the manufacturer and the seller. When purchasing, you choose the one you want. You can also find out or verify it later with a simple test in the water.

A right-handed propeller in forward gear moves the stern to the right and, consequently, the bow to the left.
A right-handed propeller (seen from behind) in forward gear rotates clockwise.

A left-handed propeller in forward gear moves the stern to the left and, consequently, the bow to the right.
A left-handed propeller (seen from behind) in forward gear rotates counterclockwise.

The exact opposite occurs in reverse.

The lateral effect (evolutionary effect) of the propellers is noticeable when the boat is stationary. It is noticeable when starting, then fades.
When the boat is moving forward, the lateral effect is almost no longer noticeable.

In ships or boats with two propellers, the starboard propeller is right-handed and the port propeller is left-handed. This cancels out the lateral drift.
With three propellers, the center one can be left-handed or right-handed.
The lateral drift (evolutionary effect) will inevitably occur, but only when stationary and can be counteracted with the rudder.

I don't understand how a boat can drift to the left or right if not due to the effect of the propellers.
If it's well-built, it's symmetrical, and if it's symmetrical, it goes straight.
The unwanted drift is due to leeway (wind), drift (current), or propellers.

I hope this helps.

bruced,
I have a slightly larger scale ELCO. I do not experience the pull that you speak of and my props all rotate in the same direction, as per the original ELCO's.