Counter rotating props

in one of the gearbox's..usually just a pump adjust to turn one of the boxs l/h to r/h.
unless you have perk's and then one of the engines might be counter rotating,which just means the engine its self runs backwards..
 
We have twin Perkins M135s.The gearboxes are 72C.One of the gearboxes is set up to run "backwards" and the prop on that shaft is handed to suit.
You may also find that the pitch on the props is also different due to internal forward/reverse ratios in gearbox.
When my boat was built somebody made a real pigs ear of the maths.Instead of removing pitch on one prop they had added it.
A post on here and some helpful info on what had gone wrong soon sorted problem and offending item was repitched from 22" to 18". by local workshop.
 
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moonraker 36 said:
do you have b/warner box's 1-1 ?
if so why the diff in prop pitch?
Click to expand...

B/W 71 1F, port box 1.91/1 stb box 2.1/1, port prop 22" x 23.5" pitch, stb prop 22" x 21.5" I knew they were different, I'm not that much of an anorak, I had to go and look in the bible for the specs, which just happen to be in the office here at home;);)
 
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SpottyDog5 said:
JFM -As simple as that ?
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Fundamentally, yes. There is the additional factor that F and R ratios might happen to be different, as others have explained above, but fundamentally yes one box works in "reverse". Engineeringly, the boxes are a bunch of well-made metal parts and are indifferent between running in F and R.
 
omega2 said:
Apparently contra rotation makes for better handling and a prettier wake shot, ours run both the same way i.e. left handed, steers straight as an arrow, even with the A/P off, no matter which way they run it.s just a matter of "learning" what the boat does in all situations.

http://www.youtube.com/watch?feature=player_detailpage&v=KqfZ6ZXl5pc
Click to expand...

Despite the contra rotating props etc my old c*w still leaps to starboard when going astern and as I berth portside it makes for all sorts of interesting conversations between me and the boat sometimes......
 
jfm said:
Fundamentally, yes. There is the additional factor that F and R ratios might happen to be different, as others have explained above, but fundamentally yes one box works in "reverse". Engineeringly, the boxes are a bunch of well-made metal parts and are indifferent between running in F and R.
Click to expand...
Thanks to JFM and the others for answering my question, most appreciated.
 
some g/boxs just need the internal hydrolic pump turning through 180 to change the rotation.
again some g/box will run in reverse no prob's,but others wont as the bearings when in revers can be different and wont take the thrust.
all depends on the box.
 
"some g/boxs just need the internal hydraulic pump turning through 180 to change the rotation."

thats the M/O in the Velvet drive G/box.
 
Other than the one simple explanation I really struggle with a heap of misconceptions is some of the replies.

"In one of the gearbox's..usually just a pump adjust to turn one of the boxs l/h to r/h.
unless you have perk's and then one of the engines might be counter rotating,which just means the engine its self runs backwards.. "

#1 Only applies to Velvet Drive reduction gearboxes not DD models. And the mere mention of a vessel blighting counter rotation Perkins brings tears to my eyes.

"ZF only run one way, so you will have one in reverse with a slightly lower ratio."

#2 ZF refer to rotation as Position A/Position B not ahead and astern, transmissions designated as such accept full power in both directions. As to different ratios, many ZF models including Roy’s ZF 85 A gearboxes have identical ratios in both position A and B.

"some g/boxs just need the internal hydrolic pump turning through 180 to change the rotation.
again some g/box will run in reverse no prob's,but others wont as the bearings when in revers can be different and wont take the thrust.
all depends on the box."

#3 Ebay spelling of hydraulic aside, point #1 applies.

"Despite the contra rotating props etc my old c*w still leaps to starboard when going astern and as I berth portside it makes for all sorts of interesting conversations between me and the boat sometimes...... "

#4 Regardless of propellers being handed or turning in the same direction a properly set up vessel should always track true when going ahead, and with handed propellers vessel should track reasonably well astern and if you are berthing port side to a kick of starboard engine only will tuck stern in neatly, no clue why vessel should be swinging to starboard, assuming of course that vessel has the convention of outward turning propellers.
 
latestarter1 said:
other than the one simple explanation i really struggle with a heap of misconceptions is some of the replies.

"in one of the gearbox's..usually just a pump adjust to turn one of the boxs l/h to r/h.
Unless you have perk's and then one of the engines might be counter rotating,which just means the engine its self runs backwards.. "

#1 only applies to velvet drive reduction gearboxes not dd models. And the mere mention of a vessel blighting counter rotation perkins brings tears to my eyes.

"zf only run one way, so you will have one in reverse with a slightly lower ratio."

#2 zf refer to rotation as position a/position b not ahead and astern, transmissions designated as such accept full power in both directions. As to different ratios, many zf models including roy’s zf 85 a gearboxes have identical ratios in both position a and b.

"some g/boxs just need the internal hydrolic pump turning through 180 to change the rotation.
Again some g/box will run in reverse no prob's,but others wont as the bearings when in revers can be different and wont take the thrust.
All depends on the box."

#3 ebay spelling of hydraulic aside, point #1 applies.

"despite the contra rotating props etc my old c*w still leaps to starboard when going astern and as i berth portside it makes for all sorts of interesting conversations between me and the boat sometimes...... "

#4 regardless of propellers being handed or turning in the same direction a properly set up vessel should always track true when going ahead, and with handed propellers vessel should track reasonably well astern and if you are berthing port side to a kick of starboard engine only will tuck stern in neatly, no clue why vessel should be swinging to starboard, assuming of course that vessel has the convention of outward turning propellers.
Click to expand...

all hail l/s...
 
"ZF only run one way, so you will have one in reverse with a slightly lower ratio."

#2 ZF refer to rotation as Position A/Position B not ahead and astern, transmissions designated as such accept full power in both directions. As to different ratios, many ZF models including Roy’s ZF 85 A gearboxes have identical ratios in both position A and B.

I stand corrected, only quoting what ZF told my mate, who had them in his Blythe Cat. He had fuel consumption differences.
 
Why are the ratios slightly different on pos. A and B on some gearboxes?

I never understood this as appart from the hydraulic shifting and clutch mechanism the gearbox is mechanical?
 
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