Rudder plate on outboard

[Tim M]

I've just seen this on ebay; it's a 25hp outboard with a "ruderplate" fitted. I've never seen one of these before, and was wondering what it was for, and whether it might actually work. I assume it improves steering. I'd consider getting one of these for a coaching launch I am responsible for; this is 7m long but has an outboard fitted near the middle (to reduce wash) bu is a pain to steer, in that it doesnt!
Can you get them off the self?

Tim:

[gingercoastie]

I do not see what difference a rudder plate on an outboard would make.


Rudders work by redirecting the flow of water. An outboard already does this by turning itself. Therefore a fixed rudder on a moveable outboard is useless, as it does nothing to alter the flow of water.

I think

[MeMe]

Originally Posted by gingercoastie

I think

......agree "I think"

[Hightower]

The only reason I can see is that it could be used for directing a boat when not being powered by the prop, ie: where the outboard couldn't be raised out the water on a yacht or something.

[Searider]

Used a lot on the inland waterways. (I spent some of my mis-spent youth on the Thames)

Slow speed = not much thrust = not much to redirect therefore rudder needed.

How often do we need to coast into a lock doing half a knot in our ribs?

Have seen an item called an "addarudder". Consists of two rudders side by side aft of the propeller mounted on a pivot on top of the cavitation plate. Designed to improve steering at low speeds but hinges up at speed to reduce the extra drag that would otherwise be caused.

Good idea for the coaching boat I reckon.

[wavelength]

Therefore a fixed rudder on a moveable outboard is useless, as it does nothing to alter the flow of water

ah!- but when you go to neutral you have virtually no steering, only the rudder effect of the leg/skeg, but fix a rudder to it and now you can still steer as long as you are making way thru the water. An inland waterways thing-not something you would want on anything that will be doing anything much more than a crawl along a ditch-oops sorry canal

[gingercoastie]

I stand corrected

[wavelength]

I stand corrected

never the intention you goin to ribex again alex ??????????????

[Slaphead]

I fitted one of those rudder plates to my Colvic Seaworker.It was attached to an Enfield sterndrive driven by a 2.2 BMC diesel.With the boat being a round bilge displacement hull steering was rubbish at speeds under 2 knots.
The rudder plate was a double plate that sat aft of the prop on either side and bolted onto the cavitation plate.It was spring loaded and lifted at around 3 -4 knots when you had steerage but dropped again at speeds below 3 knots and still provided steerage.
I think it made a big difference at close quarter handling.Cost about £130.

[Searider]

Originally Posted by Slaphead

I fitted one of those rudder plates to my Colvic Seaworker.It was attached to an Enfield sterndrive driven by a 2.2 BMC diesel.With the boat being a round bilge displacement hull steering was rubbish at speeds under 2 knots.
The rudder plate was a double plate that sat aft of the prop on either side and bolted onto the cavitation plate.It was spring loaded and lifted at around 3 -4 knots when you had steerage but dropped again at speeds below 3 knots and still provided steerage.
I think it made a big difference at close quarter handling.Cost about £130.

That's an "addarudder"!

[gingercoastie]

Originally Posted by wavelength

never the intention you goin to ribex again alex ??????????????

Not this year, I will be cruising the beutiful Isles of Scilly

[phillnjack]

The ADDARUDDER is not a duel blade rudder.
Addarudders were single ruders.
they had a fitting that went on the front of the outboard or outdrive and then two rods that went over the cavitation plate to the rudder assembly.

Do they work ? yes very very well.
Do they lower performance ? not unless your looking at microscopic differences.
Acceleration if anything is better with one, as more directional thrust.

I had one fitted on a boat that done 42 mph without it.
when fitted it still done 40 to 41 mph and the steering improved ten fold.
The boat became much safer and more usable at slower speeds.

At slow speeds it was fantastic, even when not under power i had steering.
You do not get any wander at slow speeds like all outboards and outdrives give.

At high speed the steering is also much more responsive.

Many people had these fitted to boats on the thames during to 70's.

The twin rudder set ups were not as good and a lot of them fell off or got damaged too easy.
they were very weak compared to the original addarudders.




phill

[Mollers]

Originally Posted by phillnjack

The ADDARUDDER is not a duel blade rudder.
Addarudders were single ruders.

Thanks for that info.

And thanks for resurrectinga 5yo thread.