Ducted propellers?

[quinten1231]

So I have been thinking (day dreamin) on how I would go about building my boat in the future, and I was wondering if anybody has ever tried to use a Ducted propeller to increase speed and efficiency, ofcourse in combination with a suited propeller for ducting?

On slower displacement hulls the differences in thrust between ducted/ non-ducted are easily 20-30%, ofcourse I am speaking here of large commercial vessels such as cargo/tankers(250+ft) and tugboats, etc

I know it is not traditional of a Launch but since everybody seems to talk alot about how to obtain maximum efficiency and speed I thought I might bring up the topic, plus, its underwater so no significant change of design.

I also dont believe it would apply much to real steamlaunches since they are long and narrow, but I was more thinking of small tugs, dinghies etc (displacement hulls)

So that was basically my thought today, but let me hear your thoughts on this

Regards Quinten

[boatbum]

Quinten,

The launch I am designing will use a Kitchen or Kitchner rudder. Basically a adjustable duct to allow directional thrust and reversing with out reversing the engine. Such rudders allow speed control, reversing and the ability to spin the boat on it's axis instantly. I wonder why they never stayed in vogue. Just google it and you'll have more info than you can digest on the subject.

Keith

[fredrosse]

"I wonder why they (Kitchen rudders) never stayed in vogue. " While very novel and clever, they do have an efficiency cost, and going forward they will virtually always cause a loss of propulsion efficiency.

They can be a good solution to allow a non-reversable engine to function (forward/reverse/steering), but it is generally more efficient to just use a reversing gearbox for an IC Engined boat, or simply direct drive for reversable steam engines. if gearboxes or reversing engines are not available, then they might be a logical choice, but in today's world, they are generally just an interesting novelty.

[quinten1231]

Keith

The kitchen rudder, as mentioned before, is rather inefficient and is more of a novelty.
Although the design makes for an interestint setup and conversation material, it just does not contribute to efficiency.

I was actually thinking more of a real ducted propeller (kort nozzle) where the tapered duct together with a well suited tight fit propeller, created more thrust and therefore more speed and efficiency on displacement hulls.

Ofcourse the duct and propeller have to be carefully calculated, not just place a duct around it which is randomly tapered.

Something along the lines of the pic posted below, ofcourse much smaller scale and larger tolerances, pfcourse it will not be a cheap setup, but that is a relative term with steamboating I suppose.

Regards Quinten

[boatbum]

Quintin,

I'm not sure I agree that Kitchen rudders are ineffiecent, but I digress, Kort nozels do make quite a difference in tractive effort and are popular on tug boats. I'm not sure how much gain it would supply to a small propeller on a steam launch however. Give it a try and record your results, would make an interesting thread for the forum.

Keith

[Oilking]

http://www.submarineboat.com/kort_nozzles.htm this page has some info on small Kort nozzels. Wickipedia also has a concise description of the promary nozzel types and application.

The kitchen rudder went the way of the Dodo once reverse gears became available for small marine engines. However the modern jet drives reverse in much the same manner by dropping a diverter into the pump discharge redirecting it forward.

Dave

[Lopez Mike]

Let's see. With a power plant that will never see 4% thermal efficiency you are worried about propeller stuff? If it were me, I'd put a lot more effort into insulation and feed water heating.

Not that it isn't possible to have the wrong prop on a boat but if you stay within reasonable bounds, I suspect that the efficiency gains from exotic setups are likely to be illusory.

In my home waters there is a fair amount of weed and kelp and such. A nozzle of any sort looks like a wonderful chance to end up rooting around down there in cold water getting things cleared out.

Mike

[dhic001]

Paul Eaton here in New Zealand has put a Rice nozzle on his steamboat, but the boat isn't finished yet. Paul is on this forum, andwill no doubt be able to give a lot more information when he sees this. Will be very interesting to see how it works out.
Daniel

[quinten1231]

Mike

I wasnt really thinking of efficiency in the sense of reducing fuel consumption, but more in the sense of solely improving the efficiency of the propeller.

Basically, trying to get the power you currently have and convert it into thrust.

The whole point of subject is to see whether ducted props on a smaller scale would make as much of a difference as thoseon larger vessels, and whether it would be benifical to place one.
Ofcourse it would be less efficienct since it would not be professionally made, but I suppose it can make a significant difference.

Luckily where i will sail i do not have to worry about weeds etc.

Regards Quinten

[Kingsley]

Quinten,

I know of one steamboat with a ducted propeller, it is called Juno (details in the SBA register here :
http://www.steamboatassociation.org.uk/ ... Id=1117882)

I seem to remember the owner saying that he didn't think it was any more efficient in practice but that it was very good at picking up plastic bags which were almost impossible to remove when afloat.

Kingsley