Jet Powered Ferry

[Bish]

"There's more to do on a Fuller's Cruise!!"

[mcdjl]

The Sea Cats and High speed ferries are also jet driven in the UK. The water jets which are used are a lot more efficient and generate higher speeds than propellors which is the main reason for their use. Its the same principle as Jet skis which have been around for much longer. As well as having a water jet pumping the water around these are often powered by a proper jet (though technically called a gas turbine).
The reason for the water being still will be that the yhave very little draught so not much water get pushed out of the way by them (depsite the huge plume of spray behind them).

[Pigeon]

mcdjl said:

powered by a proper jet (though technically called a gas turbine)

"Jet engine" is a subset of "gas turbine", not the other way around. A gas turbine used to provide shaft power is not a jet engine.

[OnTheOverrun]

The primary reason for their use on ferries is maneuverability and secondly fuel efficiency.

Ferries need to do a lot of very precisely controlled maneuvers with a minimum of fuss and crew - jets work 360 degrees and at zero speed. They are more efficient than props on shafts because they don't stick out so far and thus have far less drag.

http://www.boattest.com/Resources/view_news.aspx?N...

Here's a couple of the high speed ferries I use just about every week:

http://www.youtube.com/watch?v=sBKV_3OiUv0

http://www.youtube.com/watch?v=zCYF0gU7N-k

[tank slapper]

OnTheOverrun said:

They are more efficient than props on shafts because they don't stick out so far and thus have far less drag.

This is only true for high speed craft that travel faster than about 25 knots. Below that speed they are quite a lot less efficient that props.

[OnTheOverrun]

tank slapper said:

OnTheOverrun said:

They are more efficient than props on shafts because they don't stick out so far and thus have far less drag.

This is only true for high speed craft that travel faster than about 25 knots. Below that speed they are quite a lot less efficient that props.

I know. The boats in question do travel above 25kts.

[Glosphil]

In the mid-1970s during a visit to Moscow I travalled on a gas-turbine powered hydrafoil ferry with props. Very fast with amazing acceleration. Seemed to have a 2-speed gearbox - anyome know if this was the case? And if so, why?

[Semi hemi]

Glosphil said:

In the mid-1970s during a visit to Moscow I travalled on a gas-turbine powered hydrafoil ferry with props. Very fast with amazing acceleration. Seemed to have a 2-speed gearbox - anyome know if this was the case? And if so, why?

Mahoosive power is used to overcome the drag of the hull through the water then once up on the foil there is a lot less drag

[Glosphil]

Semi hemi said:

Glosphil said:

In the mid-1970s during a visit to Moscow I travalled on a gas-turbine powered hydrafoil ferry with props. Very fast with amazing acceleration. Seemed to have a 2-speed gearbox - anyome know if this was the case? And if so, why?

Mahoosive power is used to overcome the drag of the hull through the water then once up on the foil there is a lot less drag

Thanks. That makes sense. Although I do seem to recall a definite clunk as if a gear change was happening - however, it was 35 years ago so probably a faulty memory is to blame.

The 'boats' also approached the stopping places at a hell of a speed, slowing very late and dumping the hull back into the water to stop (plus reverse?)

Edited by Glosphil on Saturday 1st August 16:19

[Nickyboy]

I believe the NY Waterway ferries between Manhatten and Jersey are powered by similar means, they accelerate damn fast and when dock have it on full beans against the jetty before turning almost on a six pence and powering back into the Hudson. You can also hear what i thought was a whine of a turbine as it spools up

[Taffer]

Nickyboy said:

I believe the NY Waterway ferries between Manhatten and Jersey are powered by similar means, they accelerate damn fast and when dock have it on full beans against the jetty before turning almost on a six pence and powering back into the Hudson. You can also hear what i thought was a whine of a turbine as it spools up

The NY Waterway ferries, like most fast ferries, are turbocharged diesel engines driving a water jet. Even vessels up to the size of the Sea Cat use diesels, for economic reasons. A few ships do have gas turbines powering a water jet (Stena HSS for example), but with the rise of fuel prices they aren't as commercially viable as in the past (a couple of the HSS ferries were laid up a couple of years ago due to high fuel prices).

The current trend for marine propulsion is going back to the propellor, albeit in the azipod system, which has an electrically-driven prop on a pod that can be rotated through 360 degrees. No prop shafts inside the ship (so more space), more manouevrable than a prop/rudder combination, although still expensive to install and maintain.

[JVaughan]

The Sardinia Ferrys are Hydro Jets ... I believe they can almost half the crossing times of conventional ferrys.

There was a program on Discovery Turbo a while back that covered "The Fastest". I believe speeds of plus 50 knots were mentioned !!!