Rudder angle

[Derek Warner]

Hi Pd's

Decoy was designed with fine under water lines especially at the stern and I am sure she was a near
universal [Scottish] design for screw or paddle - so from this basis my 1:25 scale version has a rudder
some 85 mm long x 80 mm deep in the water

Many of the snaps of Australian paddlers show the rudder hard over and in some cases greater than 90
degrees from FWD & AFT. So with that on board I plan to trial both a 90 degree included swept angle,
and if that doesn't turn her enough, increase the included swept angle to 180 degrees

No I know we have a contingent on the twin engine = twin steer capability, however Decoy had a single
engine & this is the planned path I have chosen

Does any PD have any experience with increasing the rudder swept angle in an attempt to improve steerage?

Any comments for or against greatly appreciated

Derek

[Dai Powell]

Hi Derek,
I am not so well up on "swept angles" but if you are
referring to 90 degrees to the centre line of the boat I would think
you would have a damned good water brake with a bias in the
direction of steer. Anything, from at the most 45 degrees is going
to have a retarding effect, I believe 30-35 degrees is the normal
max,
However have fun, a parachute hung over the appropriate side would
be very effective if "streamed" just aft of the paddle on the side
of choice,............Dai Powell

[Mike Mayhew]

Dereck me old mate, Rudders are funny things,there is a limit to their maximum angle of efficiency after which they cease to help the turning movement and become a brake. In normal marine practice a standard "barn door" type rudder, ie/ hung by its leading edge, will have a working swing of 35 degrees each side of amidships. Since this was discovered, there have been a constant desire to get more leaverage into a turn and the "Becker" rudder was invented. This has two blades one attached aft of the other , like a door hinge, and the aft section turns as well as the whole unit thus creating a curved effect and thrusting the water almost 90 degrees. In your case the Murry River steamers had chains attached to the rudder on a 2:1 pully basis rather than a tiller.I have studied hundreds of photos and sketches and also noted that the rudders were hard over when alongside. I have it on good authority that this was so that it could not get damaged and gave more quayside space when loading etc. Remember there were hundreds in their 'hay day' It seems that the chains were slacked off. Also you will require to make the rudder area slightly larger in a model to get the real effect, I have to add 1/3rd to my 1:12 scale sailers, and Adelaide will have a larger rudder at 1:24 scale Hope things are getting back to normal Down Under and the weather is a bit cooler. I am making fittings for ADELAIDE in resin and white metal which I will be exporting to Float a Boat along with some of the rest of my fittings.
Wishing you all the very best, Waverley Mike.

[Derek Warner]

Well Dai, Harry & Mike responded & thanks for this - like snip
>I agree that anything more than about 35-45 degrees is simply
>going to create a lot of drag on the "vessel".
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>but if you are referring to 90 degrees to the centre line of the
>boat I would think you would have a damned good water
>brake with a bias in the direction of steer. Anything, from at the
>most 45 degrees is going to have a retarding effect
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>Rudders are funny things, there is a limit to their maximum angle
>of efficiency after which they cease to help the turning movement
>and become a brake
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
funny thing is, they all say the same thing!!! - now I do understand
the functionality differences between screw & paddle [also remember
doing three point turns in the pool with my 1.8 metre BHP Iron Prince
twenty years ago] where from a vessel at rest, the screw would provide
a concentrated flow of high velocity water directly over the angled rudder
& thus the stern of the vessel would be displaced relative to the opposite
angle of the rudder

From all this I agree that a rudder hard over on a paddler would act as a
brake/retarding effect/create drag etc, but this when applied to a moving
vessel must not only have the effect slowing but also turning the vessel

I am still many months away from river trials but will keep all posted

regards Derek

[Leighton]

Derek,
Regarding the angle of the rudder(s) somebody once mentioned to me
that there is a difference to the angle of the rudder if it is
behind the stern paddle wheel or in front?
Can any PD enlighten me why it should be so?

[Joe E Brown]

The main thing about sternwheel rudders is just common sense. The
main rudders (forward of the wheel) have a long slope to it and
almost touches the hull to keep drift from wedging into the rudder.
Also they're long to aid in repelling the wave thrust to the side
when backing. Otherwise the boat would be washing the current under
the hull without much turning movement. The back of the rudder is
usually curved to match the wheel, again to keep from getting drift.

The monkey rudders are usually barely under the water because, when
pushing forward, the thrust of the water go upward and washes the
rudders about 3/4 of the way up. There is such thrust there that the
rudders don't need to be very big even when going slow. The monkey
rudders tend to be fairly straight in the front for it is so shallow
drift tend to roll under the rudders.

[dragoncity]

Derek,
no matter how BIG ( long, high, deep, deflection angle) you make your rudder
it wont be big enough !!

I have observed, and tested, a number of rudders on my P.S Industry and came
to the above conclusion, one rudder was 120mm long ( and looked really
stupid) and even it did not do a good job of steering the boat.

In the case of the DECOY however, I think you may be surprised at how
effective it might be as you do have a nice 'hull exit' shape and good water
flow.

Maybe bow thrusters, as suggested previously by Mike Mayhew, are the answer
after all !!! Keep them slooow and nobody will know :-)

--
Brett S Hallett