Category Archives: propellers

“MAN ES to provide propulsion systems for Canadian Coast Guard’s AOPSs” –Naval Today

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Three AOPSs at pier before the commissioning ceremony for HMCS Margaret Brooke (AOPV-431). Canadian Navy photo

Naval Today reports,

“German manufacturer MAN Energy Solutions (MAN ES) has received a contract to provide propulsion systems for two Arctic offshore patrol ships (AOPSs) for the Canadian Coast Guard.”

The Coast Guard versions of the Arctic Offshore Patrol Ships apparently have the same propulsion system as the preceding six Navy versions, but there are details about the propellers in this announcement that I had not heard before.

“Finally, MAN Energy Solutions will deliver 2 × MAN Alpha-branded five-bladed, bolted propellers that meet PC5 rules and which can even be exchanged underwater. These cater for higher cavitation inception speeds, possible shock impacts, and mission-critical conditions requiring additional redundancy, silent operation with minimal hydro-acoustic signatures, and suppressed underwater-radiated noise, the company highlighted.”

I don’t know what a “bolted propeller” is, but the idea that they can be changed without dry docking sounds like it might be useful, particularly on a vessel that operates in ice where we have had some experience with damaged propellers.

Innovation in Propellers

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Tip vortices – conventional versus Kappel. Tip vortices are tubes of circulating water that are formed at the tip as the propeller generates thrust.

Tip vortices – conventional versus Kappel. Tip vortices are tubes of circulating
water that are formed at the tip as the propeller generates thrust.

gCapatain has photos of a new type of propeller.

Although I have a hard time seeing it in the photos, this shape is similar in concept to the upturned wing tips that now common on commercial aircraft. Propellers are after all, really just wings that rotate around a central hub. Having seen this, I now wonder why we haven’t seen this before.

Diagrams of fluid flow over a airfloil section usually show a linear flow from the leading edge to the trailing edge, but actually there is also a span-wise flow that spills off the tips and creates vortices. They add drag and increase noise.

Photo: The air flow from the wing of this crop duster is made visible by a technique that uses colored smoke rising from the ground

Of course the reason the airlines use these devices is to improve fuel economy. The principle also works for propellers.