Author Topic: Single screw tugs with multiple rudders  (Read 1989 times)

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Single screw tugs with multiple rudders
« on: October 20, 2014, 23:10:00 »
A few days ago I posted this item on another thread on this forum -

"If your tug has a single screw and fixed kort nozzle, with multiple rudders, then I would suggest that the original vessel was a Towmaster design by Burness Corlett & Partners.  This design was a variation on their Hydroconic hull design, and was intended to meet demands by tug operators for increased manoeuvrability at a time when Voith-Schneider and Schottel drives were still in their infancy.

Adelaide Ship Construction (in Port Adelaide, South Australia) built one vessel in the 1970's with as many as 7 rudders - 4 forward of the nozzle, and 3 aft of it.  But I don't know which tug had this very complicated arrangement - anyone else know of this tug?

I have seen references to "shutter rudders" on one website - I think this might be another term for a similar arrangement."

I've since found a bit more info on this rudder arrangement, which may be of interest to some members.

As far as I can tell, Burness Corlett & Partners were the original developers of the Towmaster system utilising a fixed Kort nozzle with multiple rudders.  However I have also found several references to a similar US system - but obviously not combined with BC&P's hydroconic hull form.

The combination of the hydroconic hull form and Towmaster multiple rudder system gave tugs of that period greater bollard pull per horsepower than available from other tugs of the period, along with greater manoeuvrability.

During the 1960's, a British company by the name of Hydronic Pty Ltd applied for a US patent for method of increasing thrust from a tug's propeller by installing directional vanes within the Kort nozzle and behind the propeller, to straighten out the screw race, thereby imparting greater thrust into the water.  The synopsis of the patent application contained a discussion regarding the tug's manoeuvrability.  Paraphrasing that synopsis -

There are several methods to steer a (single screw) tug which is fitted with a kort nozzle -

1.  Use a steerable, directional nozzle.  But this requires an increase in the tip clearance between the propeller tips and the inner surface of the nozzle, which results in some loss of thrust, which is the main reason for using the nozzle in the first place.

2.  Use a system of one or more conventional rudders behind the nozzle.  Multiple rudders gave greater manoeuvrability while running ahead.  But in either case there is no effective steering while moving astern.

3.  Adding multiple rudders, either side of the propeller shaft, ahead of the kort nozzle, gave improved steering while operating the tug in reverse.

So now I know why the tug I mentioned in the first post had 7 rudders.  But I still don't know which tug had this complex system.  If anyone knows of this tug please reply on this forum.



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Re: Single screw tugs with multiple rudders
« Reply #1 on: October 24, 2014, 09:46:35 »

     Hi Dez.
  Google this one,  LLOYDSMAN Tug  Yard no 509
  Built 1970  By Henry Robb Shipyard Leith  Scotland.



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Re: Single screw tugs with multiple rudders
« Reply #2 on: October 24, 2014, 14:43:08 »
That LLoydsman is certainly a big tug - and very reminiscent of the Smit LLoyd 3000 class of the same period, except for being of only a single screw.

It's interesting that Llyodsman was designed by Burness Corlett & Partners, but there is no mention of it being of their hydroconic hull design - it probably wasn't, as my understanding is that these hydroconic boats were only built by one yard at Appledore in the UK.

Lloydsman is certainly much larger than the tug built in Adelaide with the 7-rudder Towmaster system - I don't remember which tug it was specifically, but she would have only been in the 100 - 110 ft size range.