I, for one, applaud technical questions
Well it is the questioner who should applaud the answerer if the answer is good and yours seems to be good. Thank you.
Shipbucket is a place where artists, engineers, seafarers, ship spotters and everything in between all have their place, and even clash every now and then, so asking these kind of questions is no issue, there will always be somebody who knows more of the subject
I've come to the right place then.
The disadvantages of an VSP are low efficiency at speed (or even inability to reach that speed) primarily,
OK. My internet search indicated that 18 knots would be considered a fast top speed for a VSP propelled ship - which would be too slow for a "Global Combat Ship".
and large draft and ship design impact second.
Well if it is too inefficient for high speed then other issues are besides the point.
the advantages are very good control at low speed, low noise levels (due to lower rotation speed indeed) and a large amount of torque for a given amount of engine power.
in short, this gives advantages when used as main propulsion on tugs, minesweepers and low speed patrol vessels,
That was the bit I understood before I got here.
but completely unsuitable for transports, cruise ships or combatants because of their inefficiency and inability when going fast.
Understood now.
in these cases, the VSP could potentially see use as auxiliary or maneuvering thruster. development of an cyclodial rudder for example allows it to be used as such.
Cycloidal rudder
There's no Wikipedia article for "Cycloidal rudder" yet, though "Voith Cycloidal Rudders" is listed as a product of
Voith Turbo.
ENCYCLOPEDIA OF SHIP TECHNOLOGY - Voith Cycloidal Rudder
The Voith Cycloidal Rudder is based on the Voith-Schneider Propulsor. It has a rotor casing that can rotate about a vertical axis, with two axially parallel rudder blades or hydrofoils projecting from it. Fundamentally, there are two different operating modes: passive and active. In the passive mode, the VCR acts as a conventional rudder and is used for this purpose when the ship is cruising. The active mode is used at low speed, e.g. in port. The VCR is then a high-precision source of propulsion when manoeuvring.
No images in that article, so here are a couple.
But not too many pictures of real cycloidal rudders showing up on an image search.
As a scientist, this impressed me -
SNAME Transactions, Vol. 110, 2002, pp. 299-306
Development of the Cycloidal Rudder for Very Maneuverable Combatant Ships
OPERATIONAL ASPECTS OF CYCLOIDAL RUDDER FOR WARSHIPS
The dual mode of operation of the VCR provides a number of key properties that are important for warships. These ships must have very high sustained speed capabilities for tactical reasons, but must be able to linger on station for long periods with very low power consumption and minimal signatures.
Conventional rudders in today's warships are designed to produce sufficient rudder forces with small inflow speeds. At high vessel speeds, the rudder area is oversized because of the squared dependence of rudder force to speed and this produces additional appendage resistance. As a consequence of the alternative modes of operation of the VCR as active rudder (slow speed) and passive rudder (cruising speed) the required rudder area can be designed for service speed much smaller. Especially for higher speed combatants this significantly reduces the appendage resistance of the rudder. Due to the reduction of rudder area acoustic noise radiation will also be influenced positively.
Redundancy of propulsion and steering by installing the VCR, which is completely independent from the main propulsion is also important for a Navy vessel's safety and survivability. In case of loss of main propulsion, the active mode of the VCR is emergency propulsion securing full maneuverability and guarantees take home capability.
The VCR may not only act as emergency propulsion but also as a 360-degree vectorable propulsion system for slow-speed operation. With full thrust in any direction achievable even at zero ship speed, the VCR effectively gives the combatant ship unprecedented maneuverability.
During patrol, low noise radiation operation is important. On a vessel with VCR, main propulsion may be completly shut down during patrol and active VCR may propel the vessel, resulting in much lower radiated noise.
High maneuverability is of major importance if a combatant has to cross mine fields in clean corridors. With a VCR this maneuverability is available from a low noise and non-magnetic propulsion device. As with the VSP for special applications VCR will be available in special non-magnetic reinforced and re-silent versions. More than 90 % by weight can consist of non-magnetic material. Special gear technology will assure silent operation. The design of the VCR will be based on the proven design of the VSP. The shock resistance of the VSP has been proven in full scale shock tests.
With the maneuvering capabilities of the VCR, movement astern, turning on the spot and lateral movement with stepless transition inside harbors and alongside piers is possible. This is of major importance in harbors without adequate tug fleets. With the VCR ships can safely execute difficult maneuvers, which previously would have required the assistance of tugs. The VCR gives the combatant what amounts to its own built-in, directly controllable tug for precise maneuvering. Implications for maneuvers like man-overboard recovery are obvious.
Finaly, an unusal capability is avioable with the VCR - stabilisation. Unlike fin-stabilizers, VCR's allow roll stabilization even at zero ship speed, and without detracting from the propulsion and steering capabilities. The thrust direction of active VCR may be electronically controlled to oppose roll motion. As thrust direction can be varied quickly and precisely excellent platform stability allows ROV operation, array deployment and recovery and helicopter launch and recovery in sea states much higher than today's operational limits.
Advantages of the VCR for combatant ships include:
- Low resistance rudder for high speed operation.
- Improved maneuverability in comparison to conventional propulsion arrangement.
- As VCR is main propulsion for low speeds CP- propellers may be replaced by FP-propellers.
- Redundancy of propulsion and steering (take home capability)
- Roll stabilization even during stand-still of vessel is possible.
- Shock resistance, low magnetic signature, low acoustic signatures.
The VCR, an ideal complement to advanced propulsion systems, is now available for specification in the next generation of warships.
So that was published in 2002. The "Global Combat Ship" design is dated here as "Late 2011 and early 2012" which from the perspective of 2002 is when, I presume, "next generation warships" would be being designed.
In other words, why does the Global Combat Ship type 26 design not use a cycloidal rudder? Why were the GCS type 26 designers reluctant to employ the cycloidal rudder?
Is this something I can berate the Royal Navy about - being slow on the uptake of new technology?
It has been recently revealed that the
Royal Navy are having huge problems with the engines in their type 45 destroyers.
This comes after
well documented problems with the Royal Navy's Astute class hunter-killer submarines.
So I would not be surprised to unearth something wrong with the design of the GCS type 26s they are about to build on the Clyde.
Well of course conventional rudders "work" so using them is not proof of a disaster in the making like the type 45 and Astute subs, but conventional rudders are no longer "state of the art" so it's a further sign of an systemic issue with the Royal Navy's defence procurement and prime contractors.