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10-18-2015, 07:42 AM
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#1
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Guru
City: Houma, Louisiana
Vessel Name: M/V LUNASEA
Vessel Model: 45ft Bluewater Coastal
Join Date: Aug 2014
Posts: 529
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What Gear Ratio Do I Have ?????
How can I tell what the ratios are on velvet drives. When I put port in gear it moves boat more than starboard engine. What I am trying to say is with both in gear boat will turn to port.
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10-18-2015, 08:19 AM
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#2
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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If tags are gone or not readable, get a phototach and with engine idling in gear, shoot the engine crank pulley and prop shaft. Divide numbers to get your ratio.
Ask around the dock, many boat owners keep a phototach on board.
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10-18-2015, 08:20 AM
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#3
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Guru
City: Marathon, Florida
Vessel Name: Walkabout
Vessel Model: 1989 Sea Ray 380 Aft Cabin
Join Date: Jan 2012
Posts: 521
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There should be a metal plate on the gear that tells you.
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10-18-2015, 08:21 AM
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#4
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Guru
City: Solomons Island Md
Vessel Name: Fryedaze
Vessel Model: MC 42 (Overseas Co) Monk 42
Join Date: Sep 2011
Posts: 1,720
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There should be a name plate on the top with the ratio and series numbers. You may have to scape some paint. Not likely that they are different ratios.
Prop condition?
Engine RPM?
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10-18-2015, 08:26 AM
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#5
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Senior Member
City: louisiana
Join Date: Aug 2014
Posts: 234
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Hmmm....I would assume your transmissions are the same ratio. Your issue may be slip in the clutch on one tranny or a difference in pitch on one prop. A little time with a non-contact tachometer and a helper will help narrow it down.
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10-18-2015, 09:21 AM
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#6
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Guru
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
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The above phototach idea answers your question but What WOT will each engine hit? That might give a clue what's going on.
Everything can be weird on a boat but the usual suspect would be a bent or out of spec prop.
Keep it simple and look for the obvious stuff.
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10-18-2015, 12:18 PM
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#7
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Guru
City: Houma, Louisiana
Vessel Name: M/V LUNASEA
Vessel Model: 45ft Bluewater Coastal
Join Date: Aug 2014
Posts: 529
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Thanks Props just out shop but did this before having them redone. Will try phototach
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10-18-2015, 02:20 PM
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#8
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Guru
City: Melbourne, FL
Join Date: Dec 2014
Posts: 1,731
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Quote:
Originally Posted by kartracer
Thanks Props just out shop but did this before having them redone. Will try phototach
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You can make a mark on the flywheel and the driveshaft and turn either one a single revolution and see what your ratio is. It is probable that it you can either hand turn the prop shaft by hand with the coupler or a pipe wrench. Since it is a step down transmission, that would be easier than turning the engine over manually. If you want to turn the engine over carefully, (key off, power off, etc.), put a socket and pull handle on the front of the engine crank shaft. Usually there is a nut on the front crank holding the timing wheel / balancer / front pulley on.
Don't make the mistake my Dad made and leave the pull handle on the driveshaft when cranking the engine Big mistake and glad no one got hurt, except the Craftsman pull handle (twisted in a big U shape). No, he wouldn't use their warranty, assuming someone would ask how he screwed it up...
Stu
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10-18-2015, 02:30 PM
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#9
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Senior Member
Join Date: Oct 2007
Posts: 323
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Quote:
Originally Posted by kartracer
Thanks Props just out shop but did this before having them redone. Will try phototach
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some times in the older velvet drives one tranny is 2to1 and the other is 1.9 to one they do that to reverse the rotation when both engines turn the same way. they say that there is a 10% diff . not a big deal
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10-18-2015, 02:31 PM
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#10
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Guru
City: Gibsons, B.C., Canada
Vessel Name: Island Pride
Vessel Model: Palmer 32'
Join Date: Oct 2007
Posts: 4,409
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Quote:
Originally Posted by stubones99
You can make a mark on the flywheel and the driveshaft and turn either one a single revolution and see what your ratio is. It is probable that it you can either hand turn the prop shaft by hand with the coupler or a pipe wrench. Since it is a step down transmission, that would be easier than turning the engine over manually. If you want to turn the engine over carefully, (key off, power off, etc.), put a socket and pull handle on the front of the engine crank shaft. Usually there is a nut on the front crank holding the timing wheel / balancer / front pulley on.
Don't make the mistake my Dad made and leave the pull handle on the driveshaft when cranking the engine Big mistake and glad no one got hurt, except the Craftsman pull handle (twisted in a big U shape). No, he wouldn't use their warranty, assuming someone would ask how he screwed it up...
Stu
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That will not work with a hydraulic gear box. Without the engine running there is no hydraulic pressure to lock the clutches so turning the shaft end or the engine manually will result in no drive through.
Your suggestion would work with the mechanical boxes such as many Hurths where the clutches are locked with a mechanical toggle.
Best bet is per Ski's suggestion.
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