Faulty images: issues to improve on[edit source]
File:Propeller-cased ship without hydrofoils.PNG File:Propeller-cased ship with hydrofoils.PNG
Out of scope. Drawing of non-existent installation which won't work. An indication of the level of the creator's sophistication is "Note that the water supply pipes need to have an cumulative equally large diameter as the propeller casing; thus when using 2 water supply pipes the diameter of a single pipe needs to be half that of the casing." If it worked at all, using two pipes, the diameter would need to be 0.707 the diameter of the casing to get the same supply as one pipe the diameter of the casing.
I didn't know this, never calculated it. Thanks for the heads-up. KVDP (talk) 13:45, 7 June 2010 (UTC)
In small sizes, this is analogous to a water-jet, which are less efficient than open propellers, but use steerable nozzles (rather than a rudder as shown here) to gain superior control and very shallow draft.
Hmm, I thought pump-jets were more efficient giving the notes at http://en.wikipedia.org/wiki/Pump-jet (see advantages and disadvantages), but I trust your correct here. Perhaps the wikipedia article is then best changed KVDP (talk) 13:45, 7 June 2010 (UTC)
In larger sizes this is comparable to a Kort Nozzle around the propeller, but Korts are relatively short -- a meter or two long at most. A Kort Nozzle provides a significant increase in bollard pull and efficiency at slow speeds, but they are not generally used in vessels faster than about ten knots. They are open front and back and do not have anything like the separate supply pipe shown here.
the supply lines were used to allow the water to enter from around the hull, if it was to be simply a single tube, the hull could obstruct the water flow coming in. KVDP (talk) 13:45, 7 June 2010 (UTC)
The drawing is not clear as to the source of the water supply for the propeller, but note that friction in the pipes would be considerable, reducing efficiency dramatically. Jameslwoodward 16:23, 6 June 2010 (UTC)
I worried about this too, however giving the wikipedia article I thought output was still higher than open propellers. Also, without an encasing, fish can not be protected from the propellers.
File:Ship compartment purposes.jpg The drawing shows a strange rudder mounting that won't work. Jameslwoodward