Model Boat Mayhem

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Tightening the turning circle  (Read 858 times)

KitS

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 528
  • Getting back into the hobby after years adrift...
  • Location: Lydney, Glos. UK
Tightening the turning circle
« on: September 16, 2021, 10:38:15 pm »

If a boat won't turn sharply enough is it better to increase the rudder throw or fit a larger rudder?


Or is there any other methods that will do the job?


I've already got twin throttles and motors so I can go astern on one engine at slow speeds but that's not really practical when the boat's zipping along a bit.  :((
Logged
Regards
Kit

BrianB6

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,123
  • I'm not sure if I can get up from here
  • Location: Melbourne
Re: Tightening the turning circle
« Reply #1 on: September 17, 2021, 03:53:58 am »

It depends on your rudder shape and design.  I had to change my Cervia's rudder into a part balanced one to get better steering.
Logged

RST

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,877
  • Location: UK
Re: Tightening the turning circle
« Reply #2 on: September 17, 2021, 04:47:01 am »

....many many things I could question here before any kind of valid response.  Think about it:  You already have one very good answer of your own volition also unless you are of the more recent Colin MacRae fraternity.
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,023
  • Location: Blackpool, Lancs, UK
Re: Tightening the turning circle
« Reply #3 on: September 17, 2021, 09:12:11 am »

What kind of boat is it?
Logged
"With the right tool, you can break anything" - Garfield

KitS

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 528
  • Getting back into the hobby after years adrift...
  • Location: Lydney, Glos. UK
Re: Tightening the turning circle
« Reply #4 on: September 17, 2021, 09:42:45 am »

It's a 34" RAF Hants & Dorset launch with two 550 type motors, and the rudders are already balanced to an extent. Both are directly astern of the the props by about 7-10 mm.
Logged
Regards
Kit

GG

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 299
Re: Tightening the turning circle
« Reply #5 on: September 17, 2021, 10:18:40 am »

KitS,
        Have you looked at the thread "Rudder Rules"  on in the Tutorials section?  It might have some relevant information.


Glynn Guest
Logged

justboatonic

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,522
  • Location: Thornton Cleveleys
Re: Tightening the turning circle
« Reply #6 on: September 17, 2021, 11:00:11 am »

It's a 34" RAF Hants & Dorset launch with two 550 type motors, and the rudders are already balanced to an extent. Both are directly astern of the the props by about 7-10 mm.
If it isnt fitted already, fit something like an ACTion twin motor mixing esc that SLOWS the inside prop in a turn. This will make any boat turn smoother and better than messing with the rudder.
 If you have escs that just give the same throttle to each motor in a turn, you'll always end up with a bigger turning circle due to the inside prop pushing against the turning momentum introduced by the rudder.
Logged

Subculture

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 4,060
  • Location: North London
    • Dive-in to Model submarines
Re: Tightening the turning circle
« Reply #7 on: September 17, 2021, 11:08:31 am »

Ensure you have a good 35 degrees of throw each side of neutral.

Twin motors should ideally be spinning the props outwards when going forwards.

If that is the case, and the turning circle is still inadequate, then you can look at throttle biasing and/or increasing rudder area.

Circlip

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 3,846
  • Location: North of Watford, South of Hadrians wall
Re: Tightening the turning circle
« Reply #8 on: September 17, 2021, 11:35:02 am »

What is the turning circle in relation to the full size at speed? If you need a steering based "Kipper box", it's the wrong model. Sadly scale does not scale as far as speed is concerned in the toy world. Just watched a vid of the river class minesweeper, bobs about like a cork and the speed shown would make John Luc Pickard hang on BUT looks good when vid slowed down.


  Regards  Ian.
Logged
You might not like what I say, but that doesn't mean I'm wrong.
 
What I said is not what you  think you heard.

KitS

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 528
  • Getting back into the hobby after years adrift...
  • Location: Lydney, Glos. UK
Re: Tightening the turning circle
« Reply #9 on: September 17, 2021, 03:20:27 pm »




 Have you looked at the thread "Rudder Rules"  on in the Tutorials section?  It might have some relevant information.



I have now Glynn, thanks for the tip. That thread didn't show up in my original search.  :((


It does have lots of useful information and confirms my supposition that the model is inadequately ruddered for its power and length etc.




Ensure you have a good 35 degrees of throw each side of neutral.

Twin motors should ideally be spinning the props outwards when going forwards.

If that is the case, and the turning circle is still inadequate, then you can look at throttle biasing and/or increasing rudder area.





Yes, they both go a bit more than 35 deg, and both props are turning outwards at the top when going forward.






What is the turning circle in relation to the full size at speed? If you need a steering based "Kipper box", it's the wrong model.




Good question, as I have no idea what the turning circle of an H&D was back in the day. The model needs about 20 ft to make a 180 deg turn at 7/8 throttle currently.


I don't need a twin throttle setup, but I wanted to try one to see how it works. I'm building a much larger, and slower, model which hopefully will have a similar setup, but with a bow thruster as well, and I wanted to do a smaller model as a test bed.


I bought a couple of slightly larger rudders at Deans Marine's event today, so I'll give them a try soon.
Logged
Regards
Kit

Netleyned

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,011
  • Location: Meridian Line, Mouth of the Humber
    • cleethorpes mba
Re: Tightening the turning circle
« Reply #10 on: September 17, 2021, 04:56:06 pm »

If you have a programmable radio,
There should be a mixer programme.
Before large build changes, see if you can
Programme a mixer to give you 60% or less
motor on rudder input.
Inboard motor on a turn slowing to 60%will give a tighter turn and costs nowt if your radio is capable
Ned.
Logged
Smooth seas never made skilful sailors
Up Spirits  Stand fast the Holy Ghost.
http://www.cleethorpesmba.co.uk/

KitS

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 528
  • Getting back into the hobby after years adrift...
  • Location: Lydney, Glos. UK
Re: Tightening the turning circle
« Reply #11 on: September 17, 2021, 05:58:17 pm »

I'm afraid I don't, not on a boat frequency anyway.


But I've installed the larger rudders, which both turn 35 deg either way, and I'll try it tomorrow.
Logged
Regards
Kit

Martin [Admin]

  • Administrator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 21,230
  • Location: Peterborough, UK
    • Model Boat Mayhem
Re: Tightening the turning circle
« Reply #12 on: September 17, 2021, 06:17:33 pm »

It's a 34" RAF Hants & Dorset launch with two 550 type motors, and the rudders are already balanced to an extent. Both are directly astern of the the props by about 7-10 mm.

Interesting, see:   https://www.modelboatmayhem.co.uk/Modellers/Christian-Sheppard/1ndex.htm


Logged
"This is my firm opinion, but what do I know?!"    -   Mayhem FaceBook Group!

CGAux26

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 656
  • Location: Deep in the heart of TEXAS (Tomball)
Re: Tightening the turning circle
« Reply #13 on: September 17, 2021, 10:33:41 pm »

You can add a fish tail (I think that's what it is called) to the trailing edge of the rudders.  It's piece of " brass angle, soldered or epoxied on.  Adding that made my Springer spin on its beam ends.
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,023
  • Location: Blackpool, Lancs, UK
Re: Tightening the turning circle
« Reply #14 on: September 18, 2021, 09:58:59 am »

A launch turning in about 6-7 times its length at speed would probably be deeply uncomfortable for the crew.  Overdoing speed when turning tends to result in either the boat leaning out, and, in extremes, flipping as a result, or digging in the inside side. 
Speed and behaviour in models do match the real thing very closely, that's why test tanks have been so useful over the past centuries.  What passes many modellers by is that scale applies differently to different parameters.  Distances are linear, areas use the square root of the scale, as do speeds, and volumes and power the cube root.  Real world water doesn't scale, it remains water.
Once the optimum rudder setup has been found, that's it.  If it turns adequately at low speed, any high speed improvements will need to come from motor control and will probably involve differential power, either manually via two sticks of automating the process using a mixer, either in the boat or in the transmitter.  Adding bits to the rudder will create extra drag which won't matter at low speed, but will prevent the high speed turning problem by preventing the high speed in the first place.
Logged
"With the right tool, you can break anything" - Garfield

KitS

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 528
  • Getting back into the hobby after years adrift...
  • Location: Lydney, Glos. UK
Re: Tightening the turning circle
« Reply #15 on: September 19, 2021, 06:44:24 pm »

Fitting the two new rudders I bought at Deans Marine on Friday has improved the turning circle of my ASR launch no end. It doesn't exactly turn in its own length but it's much less likely to ram to bank when when approaching a mooring now.  :-)


And having put new props, couplings and other running gear aboard, it's quite a bit faster too.


RESULT!  :-))
Logged
Regards
Kit

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,023
  • Location: Blackpool, Lancs, UK
Re: Tightening the turning circle
« Reply #16 on: September 20, 2021, 09:21:58 am »

Some before and after pictures would help no end.  OK this case is solved, but the question will arise again for somebody else.
Logged
"With the right tool, you can break anything" - Garfield

KitS

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 528
  • Getting back into the hobby after years adrift...
  • Location: Lydney, Glos. UK
Re: Tightening the turning circle
« Reply #17 on: September 20, 2021, 12:07:10 pm »

The only pics I could provide are those of the relative areas of the early and late rudders.


Trying to take pics of the boat circling with a two stick throttle and a rudder borders on the impossible............
Logged
Regards
Kit

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,023
  • Location: Blackpool, Lancs, UK
Re: Tightening the turning circle
« Reply #18 on: September 20, 2021, 05:36:18 pm »

The only pics I could provide are those of the relative areas of the early and late rudders.


Trying to take pics of the boat circling with a two stick throttle and a rudder borders on the impossible............
Before and after of the rudders, we can take your word that one was OK, the other less so.
Logged
"With the right tool, you can break anything" - Garfield
Pages: [1]   Go Up