And what country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance? Let them take arms. The remedy is to set them right as to facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.
Wednesday, December 25, 2019
I didn't know you could adjust the pitch on a giant ship's propeller.
Also take a look at 'Azipods'. That is the propulsion system nearly all modern dynamically-positioned ships use (originally developed for icebreakers). A fixed pitch propeller unit that can rotate around 360° to provide thrust in any horizontal direction.
Azipods are usually electric motor driven. a lot easier than shafting and gearboxes to transmit power to the propshaft. the bearings are what impressed me the most. truly awesome! Issue with variable pitch props on ships is the blades are usually the most efficient at only one rpm/flow rate of water. so, the only cause for changing pitch is to reverse with out stop/start the drive motor. very different fluid dynamics than that of constant speed props on aircraft.
We had a 65ft sailboat in the yard over the summer that had a prop like that. Had no transmission, you just featherd the prop for reverse. Real pain to work on. The little sailboats have what's called a Maxi Prop, does the same thing but with engine rpm.
All the US Navy Destroyers, Cruisers, LSD's, LPD's, have controllable pitch screws. LCS (both variants) have steerable water jets. LHD's, LHA's, and CVN's have fixed pitch screws.
I think that most of them are these days.
ReplyDeleteAlso take a look at 'Azipods'. That is the propulsion system nearly all modern dynamically-positioned ships use (originally developed for icebreakers). A fixed pitch propeller unit that can rotate around 360° to provide thrust in any horizontal direction.
ReplyDeleteAzipods are usually electric motor driven. a lot easier than shafting and gearboxes to transmit power to the propshaft. the bearings are what impressed me the most. truly awesome!
DeleteIssue with variable pitch props on ships is the blades are usually the most efficient at only one rpm/flow rate of water. so, the only cause for changing pitch is to reverse with out stop/start the drive motor.
very different fluid dynamics than that of constant speed props on aircraft.
We had a 65ft sailboat in the yard over the summer that had a prop like that. Had no transmission, you just featherd the prop for reverse. Real pain to work on. The little sailboats have what's called a Maxi Prop, does the same thing but with engine rpm.
ReplyDeleteIf you can't reverse the engine--and you can't reverse a turbine--you'd better be able to reverse the prop.
ReplyDeleteAll the US Navy Destroyers, Cruisers, LSD's, LPD's, have controllable pitch screws. LCS (both variants) have steerable water jets. LHD's, LHA's, and CVN's have fixed pitch screws.
ReplyDeleteThey can't get enough sailors who can drive "stick", therefore an "automatic" prop.
ReplyDelete