Gate Rudder

A read about gate rudders awhile ago, and now there's a couple Youtube videos. Two single screw ships were built in Japan to the same size, design and machinery except for the rudder. One has a single conventional rudder and the other with twin rudders alongside the prop with expanded movement ability. Besides enhanced rudder effects, they claim a 14% energy savings with the gate rudders in an early trial and now claim 20-30%.
I've used Kort nozzles and they give a lot more thrust with the same engine. The twin rudders confine the thrust and probably duct it like a Kort. I don't know what the rudder machinery looks like, complicated I'm sure. But if used with simple twin rudder machinery and just for the added thrust and energy savings it looks worth the effort for a 20% savings over the life of the vessel. You could run at the same cruising speed with lower rpm or cruise faster at the current rpm. On new builds, a smaller engine.

Sounds interesting. Wonder how it performs on smaller boats. And I hate videos with no voice.

It looks similar to the Kitchen rudder.

Never heard of this rudder configuration but looks interesting. I also have Kort nozzle experience and am not a fan, Yes they give more bollard pull and all but prefer open wheel propulsion.

I’ve talked about a cruder version for years. Just two rudders. One on either side of the propwash.

Just like w airplanes the propwash if passing over part of the boat can be a drag. The rudder is pulling the boat backwards when underway. The relatively high velocity of water over the boat’s rudder causes a lot of drag and that drag is pulling backwards on the boat. Imagine trying to hold onto a rudder holding it in the propwash or go 25 knots and thrust your rudder down into the water alongside. It’s a drag man

Also the propwash is not straight. It cones in on aircraft and may do so on a boat. And rudders that aren’t flat plates will experience some interplane drag similar to biplanes. Two pilings in a river have more than twice as much drag of one if they are close to each other.

Thanks very much for posting Lepke.

Nomad Willy said:

I’ve talked about a cruder version for years. Just two rudders. One on either side of the propwash.

Just like w airplanes the propwash if passing over part of the boat can be a drag. The rudder is pulling the boat backwards when underway. The relatively high velocity of water over the boat’s rudder causes a lot of drag and that drag is pulling backwards on the boat. Imagine trying to hold onto a rudder holding it in the propwash or go 25 knots and thrust your rudder down into the water alongside. It’s a drag man

Also the propwash is not straight. It cones in on aircraft and may do so on a boat. And rudders that aren’t flat plates will experience some interplane drag similar to biplanes. Two pilings in a river have more than twice as much drag of one if they are close to each other.

Thanks very much for posting Lepke.

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Good points. And seems like there's some merit to a ducted prop, essentially a rudder that wraps around the prop. Planes have these, too. However, in boating, not sure what the tradeoffs are.

Also, the flat rudder may not be the most efficient. The fishtail rudder certainly has better handling and my understanding that it doesn't significantly affect the speed..... but may at high speeds. Perhaps better for trawlers. The NACA 23000 wing in aircraft is similar, fat front and skinny back, but is not symmetrical, and has great performance characteristics.

Now, here's a question...... why don't we see more hydrofoil trawlers? Seems like once you get it up, it becomes fast and efficient?