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Propeller rotation - important?
Hi,
Recently my propeller threw off a blade. I ordered a new propeller from Michigan and today it arrived. BUT - my local dealer made a mistake: He ordered a right-hand propeller - but the old one was a left hand rotation! I just waited for four weeks - and really wouldn't like waiting another four weeks for another to arrive. So here's my question: Is it possible to reverse the direction of the transmission instead so I don't have to change the propeller? The engine is a Yanmar 6LP-STE and the transmission is a Hurth/ZF. And: Should I do it? I mean - Is there any drawbacks in changing rotation? Anders Denmark |
Propeller rotation - important?
Cheaper to exchange the prop for the correct hand than to replace the
transmission. Going to the opposite hand prop will also change the way your boat handles in close quarters. You can't find a used or loaner prop to get you by until the correct item arrives? |
Propeller rotation - important?
I just have the impression that some marine gears are built to run both
ways - so that props in dual engine configurations can be made to turn in opposite directions. In other words: I'm not talking about REPLACING the transmission but changing the rotation by basically exchanging forward with reverse... ...or is this nonsens...? :-) Anders "Gould 0738" skrev i en meddelelse ... Cheaper to exchange the prop for the correct hand than to replace the transmission. Going to the opposite hand prop will also change the way your boat handles in close quarters. You can't find a used or loaner prop to get you by until the correct item arrives? |
Propeller rotation - important?
"Anders Lassen" anders.lassenNEJTILSPAM (at)adr.dk wrote in message . .. And: Should I do it? I mean - Is there any drawbacks in changing rotation? Some transmissions, (as in some I/O units that I have had in the past) have their forward and reverse gears/clutches identical. An example was a Volvo I/O unit my dad had 30 years ago. You could move a part of the shift linkage from the left side of the belcrank to the right side, swap the prop and everything would be fine. There are also a lot of transmissions where the forward and reverse circuits are NOT equal. Velvet Drive transmissions are an example. The forward gear is much more robust and more efficient. Reverse involves more gears and the clutch is not anywhere near as robust. If you are not sure that your transmission is happy with either direction then you should not use the reverse pitch prop. I checked the Hurth web site and found the following bit of information: "These ratings allow full power through forward and reverse gear trains, unless otherwise stated." So, I believe the bottom line is that you need to check the model of your transmission! Your best bet would be to contact Hurth directly: http://zf-marine.com If you can't get a satisfactory answer, I wouldn't risk it. Rod |
Propeller rotation - important?
"Anders Lassen" anders.lassenNEJTILSPAM (at)adr.dk wrote in message . .. I just have the impression that some marine gears are built to run both ways - so that props in dual engine configurations can be made to turn in opposite directions. In other words: I'm not talking about REPLACING the transmission but changing the rotation by basically exchanging forward with reverse... ..or is this nonsens...? :-) Anders Nope, not nonsense, but may not be true of all transmissions. My 52 foot Navigator, powered by twin Volvo diesels is set up with one transmission running in reverse, compared to the other transmission. I've forgotten the transmission types, but they are made in Italy and are common on larger boats and yachts. Eisboch |
Propeller rotation - important?
My Volvo Penta 270 stern drive changes from R to L prop spin with a simple
change of the shifter rod and linkage. Don't know much about your engine combo, though. "Anders Lassen" anders.lassenNEJTILSPAM (at)adr.dk wrote in message . .. Hi, Recently my propeller threw off a blade. I ordered a new propeller from Michigan and today it arrived. BUT - my local dealer made a mistake: He ordered a right-hand propeller - but the old one was a left hand rotation! I just waited for four weeks - and really wouldn't like waiting another four weeks for another to arrive. So here's my question: Is it possible to reverse the direction of the transmission instead so I don't have to change the propeller? The engine is a Yanmar 6LP-STE and the transmission is a Hurth/ZF. And: Should I do it? I mean - Is there any drawbacks in changing rotation? Anders Denmark |
Propeller rotation - important? - Yes, it is.
On Tue, 25 May 2004 18:37:27 +0200, "Anders Lassen" anders.lassenNEJTILSPAM (at)adr.dk wrote:
Hi, Recently my propeller threw off a blade. I ordered a new propeller from Michigan and today it arrived. BUT - my local dealer made a mistake: He ordered a right-hand propeller - but the old one was a left hand rotation! I just waited for four weeks - and really wouldn't like waiting another four weeks for another to arrive. So here's my question: Is it possible to reverse the direction of the transmission instead so I don't have to change the propeller? The engine is a Yanmar 6LP-STE and the transmission is a Hurth/ZF. And: Should I do it? I mean - Is there any drawbacks in changing rotation? Anders Denmark Hi Anders, I hope it will be not too late for a reply to your question. Rotation is not a your choice, but it is depending from the boat manufacturer designer. You don't specify WHAT kind of transmission you are using, but presuming you own a classic one comprising an Engine, a Marine Transmission, a Propeller Drive Shaft and a Propeller... ....you will have these problems... It is depending from engine rotation (LH or RH), kind of transmission gear (LH or RH, Forward Ratio and Reverse Ratio, Forward Torque and Reverse Torque, Internal Gears design etc.) Some technical details: Usually all engines are "LH" (seen from Flywheel side). Usually Forward is "direct drive" meaning that there are only TWO gears engaged... so Rotation of Propeller Shaft is inverted versus engine rotation ( LHRH=RH) ... so Propeller has to be RH . Reverse is done by THREE Gears... so Engine and Transmission Shaft have same rotation ( LHRHLH=LH ) so a RH Propeller rotates LH and does REVERSE. Where is the matter? You will have NEVER the same ratio Forward and Reverse: Forward has TWO Gears coupled together and transfers a lot of power (direct drive). Reverse has THREE Gears coupled together and the Second One is a small one rated (designed) for a limited Torque and use. So you cannot use "Transmission Reverse" for " Boat Forward". So, if you wish to use a "Reverse Propeller" you have to replace ENGINE with a RH one! Of course there are other options, but these are the most important ones. +++ Otherwise... if you have another kind of transmission, and specifically the one with Forward and Reverse similar to the one used on Outboards ( Three Bevel Gears Style with Cog Clutches ) there are no matters... Forward and Reverse have same Ratio, same Torque, same Cog Clutch.... so RH or LH are optional choices and are not involving any other part or performance... +++ The answer is exclusively depending from the parts involved in. I hope this could help you. Regards, WinXP PS.- I don't know who-where is your Supplier... but any decent Supplier has "a lot" of used Propellers available for speed tests or power test or saved or... so he "has to have" a decent one for emergency purpose... Important is it has same HUB and same Rotation... Pitch, Outer Dia and number of Blades is relative... By the way, it is a good idea to have a "replaceable" propeller on board... |
Propeller rotation - important? - Yes, it is.
the trust bearing is wrong.
anders.lassenNEJTILSPAM (at)adr.dk wrote: Hi, Recently my propeller threw off a blade. I ordered a new propeller from Michigan and today it arrived. BUT - my local dealer made a mistake: He ordered a right-hand propeller - but the old one was a left hand rotation! I just waited for four weeks - and really wouldn't like waiting another four weeks for another to arrive. So here's my question: Is it possible to reverse the direction of the transmission instead so I don't have to change the propeller? The engine is a Yanmar 6LP-STE and the transmission is a Hurth/ZF. And: Should I do it? I mean - Is there any drawbacks in changing rotation? Anders Denmark Hi Anders, I hope it will be not too late for a reply to your question. Rotation is not a your choice, but it is depending from the boat manufacturer designer. You don't specify WHAT kind of transmission you are using, but presuming you own a classic one comprising an Engine, a Marine Transmission, a Propeller Drive Shaft and a Propeller... ...you will have these problems... It is depending from engine rotation (LH or RH), kind of transmission gear (LH or RH, Forward Ratio and Reverse Ratio, Forward Torque and Reverse Torque, Internal Gears design etc.) Some technical details: Usually all engines are "LH" (seen from Flywheel side). Usually Forward is "direct drive" meaning that there are only TWO gears engaged... so Rotation of Propeller Shaft is inverted versus engine rotation ( LHRH=RH) ... so Propeller has to be RH . Reverse is done by THREE Gears... so Engine and Transmission Shaft have same rotation ( LHRHLH=LH ) so a RH Propeller rotates LH and does REVERSE. Where is the matter? You will have NEVER the same ratio Forward and Reverse: Forward has TWO Gears coupled together and transfers a lot of power (direct drive). Reverse has THREE Gears coupled together and the Second One is a small one rated (designed) for a limited Torque and use. So you cannot use "Transmission Reverse" for " Boat Forward". So, if you wish to use a "Reverse Propeller" you have to replace ENGINE with a RH one! Of course there are other options, but these are the most important ones. +++ Otherwise... if you have another kind of transmission, and specifically the one with Forward and Reverse similar to the one used on Outboards ( Three Bevel Gears Style with Cog Clutches ) there are no matters... Forward and Reverse have same Ratio, same Torque, same Cog Clutch.... so RH or LH are optional choices and are not involving any other part or performance... +++ The answer is exclusively depending from the parts involved in. I hope this could help you. Regards, WinXP PS.- I don't know who-where is your Supplier... but any decent Supplier has "a lot" of used Propellers available for speed tests or power test or saved or... so he "has to have" a decent one for emergency purpose... Important is it has same HUB and same Rotation... Pitch, Outer Dia and number of Blades is relative... By the way, it is a good idea to have a "replaceable" propeller on board... |
Propeller rotation - important? - Yes, it is.
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Propeller rotation - important? - Yes, it is.
ah, you just might wish to remember that the prop MUST push against the prop
shaft which pushes against the thrust bearing to push the boat forward. Got to. In other words, the thrust bearing takes 100% of the horsepower developed by the engine. That is a lot. In forward. There is also a thrust bearing needed for going in reverse as well. However, as the horsepower used in reverse is much less and the time it is used is hugely less the reverse thrust bearing need not be anywhere near as big. Now, change the prop so the former reverse thrust bearing becomes the new forward thrust bearing and operates at 100% power over extended time the potential to trash that bearing becomes very real. Most people forget that the prop has to push against something to push the boat forward. That something is the thrust bearing. the trust bearing is wrong. snip Hi. It should be or should be not. It is depending from "direction" not "rotation": "Forward" is always forward so Propeller is always "pushing" the vessel. Usually is the "Propeller Shaft" to be supporting the pushing efforts. Gears and Clutches are supporting only the rotational torques. But in any way has to be examined the specific Driveline, application and purpose. Same thing for Gearbox engineering, drawing, performance and manufacturer technical choices... By the way in North Adria Sea and Lagoon of Venice all Clam Dredgers are operating in Reverse ! So a lot of fishermen are replacing rotation of Propeller just to operate Gearbox in "Forward"... ... other ones are "preferring" to operate in true Reverse as so the gear-ratio is wider than Forward one... In any way it is a good thing don't operate DIY on ANY vital parts of any kind ofvessel... Bye, WinXP |
Propeller rotation - important? - Yes, it is.
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Propeller rotation - important? - Yes, it is.
fair winds, guy. As you point out, if the tranny is designed to take a prop
going either direction things are fine. ah, you just might wish to remember that the prop MUST push against the prop shaft which pushes against the thrust bearing to push the boat forward. Got to. In other words, the thrust bearing takes 100% of the horsepower developed by the engine. That is a lot. In forward. There is also a thrust bearing needed for going in reverse as well. However, as the horsepower used in reverse is much less and the time it is used is hugely less the reverse thrust bearing need not be anywhere near as big. Now, change the prop so the former reverse thrust bearing becomes the new forward thrust bearing and operates at 100% power over extended time the potential to trash that bearing becomes very real. Most people forget that the prop has to push against something to push the boat forward. That something is the thrust bearing. Yes, all these things are right ones. Question is: How has been designed (engineered) the Thrust Bearings Box ? (sorry I don't know its English code-name) Our ones are designed and manufactured with a couple of Heavy-Duty Taper Rolling Bearings, # 322xx, a couple of Rubber Seals for Lube and Water Cooling devices. Used in Clam Dredgers working in Reverse... they are tailored to be operating in both directions. Heavy-Duty Bearings in Forward and Light-Dutry ones in Reverse were used times when Bearings were very expensive... but actually it is a "poor" spare, requiring different machining on both sides, double the Stocks of spares on shelves and aboard. But they could be till existing... Glad to have meet someone involved in Technical matter. I'm a newcomer in this NG but I will visit it at least once a week. I hope to have some interesting questions to put to NG attention. Thank you for your time, WinXP. |
Propeller rotation - important? - Yes, it is.
Thanks for all your replies.
I've cleared things up this much: The transmission is designed to run equally fine in both directions. Ratios are almost similar. The transmission has two "modes" - A and B. A is the "normal" mode where the propeller-shaft runs in opposite direction of the engine. B is normally reverse - the propeller-shaft runs same way as the engine. Here's the funny thing: From the factory, the boat is delivered with a LH propeller - which means that the transmission has to run in the "B"-position to have the boat move forward - i.e. reverse of "normal"! I called the Norwegian factory to ask why. They replied that "the boat liked the LH propeller the most"! (Don't know what that means.) So it all narrows down to this: Assuming that transmission is not an issue - are there any "hull-issues" that should imply that a given hull simply "runs better" with a LH instead of a RH - or vice versa? Anders Denmark "JAXAshby" skrev i en meddelelse ... fair winds, guy. As you point out, if the tranny is designed to take a prop going either direction things are fine. ah, you just might wish to remember that the prop MUST push against the prop shaft which pushes against the thrust bearing to push the boat forward. Got to. In other words, the thrust bearing takes 100% of the horsepower developed by the engine. That is a lot. In forward. There is also a thrust bearing needed for going in reverse as well. However, as the horsepower used in reverse is much less and the time it is used is hugely less the reverse thrust bearing need not be anywhere near as big. Now, change the prop so the former reverse thrust bearing becomes the new forward thrust bearing and operates at 100% power over extended time the potential to trash that bearing becomes very real. Most people forget that the prop has to push against something to push the boat forward. That something is the thrust bearing. Yes, all these things are right ones. Question is: How has been designed (engineered) the Thrust Bearings Box ? (sorry I don't know its English code-name) Our ones are designed and manufactured with a couple of Heavy-Duty Taper Rolling Bearings, # 322xx, a couple of Rubber Seals for Lube and Water Cooling devices. Used in Clam Dredgers working in Reverse... they are tailored to be operating in both directions. Heavy-Duty Bearings in Forward and Light-Dutry ones in Reverse were used times when Bearings were very expensive... but actually it is a "poor" spare, requiring different machining on both sides, double the Stocks of spares on shelves and aboard. But they could be till existing... Glad to have meet someone involved in Technical matter. I'm a newcomer in this NG but I will visit it at least once a week. I hope to have some interesting questions to put to NG attention. Thank you for your time, WinXP. |
Propeller rotation - important? - Yes, it is.
"JAXAshby" wrote in message ... There is also a thrust bearing needed for going in reverse as well. However, as the horsepower used in reverse is much less and the time it is used is hugely less the reverse thrust bearing need not be anywhere near as big. Now, change the prop so the former reverse thrust bearing becomes the new forward thrust bearing and operates at 100% power over extended time the potential to trash that bearing becomes very real. Either I am not following what you are saying or I am envisioning something totally different. As you said, the thrust on the shaft must be countered someplace, and that someplace is the thrust bearing(s). The thrust will either "push" or "pull", it shouldn't matter which direction the shaft is rotating. If you attempted to drive the boat by having the propeller in front, like an airplane, then the shaft will be pulling and the thrust bearing surface associated with "pull" will bear the brunt of the load. But I didn't think this is what we were talking about. I know that several models of Velvet Drive transmissions don't care which direction the input and output shafts turn, as long as they turn the same direction in "forward". You can have a Left Hand and Right Hand rotating engine turning Left Hand and Right Hand props and the transmissions don't care. If you attempted to have the Left Hand engine turn the Right Hand prop, however, then the transmission would be using the "reverse" clutch for forward which is not nearly as robust as the "forward" clutch and you would likely have reliability issues. The web page for the Hurth transmissions indicated that many of their models were capable of full engine horsepower in either "forward" or "reverse" operation. I don't know if that really means you can use them for reversing the rotation for counter rotation or not. There are many outdrive designs that has the drive shaft come down and drive two gears, one towards the front and one towards the rear. A "dog" or cone clutch will engage one gear or the other, which will make the prop shaft turn one way or the other. The clutches are identical and the thrust is carried on the shaft bearing (not the gears) so it doesn't matter if the gear more towards the front is considered "forward" or not. Rod |
Propeller rotation - important? - Yes, it is.
Assuming that transmission is not an issue -
are there any "hull-issues" that should imply that a given hull simply "runs better" with a LH instead of a RH - or vice versa? Anders Denmark I've lost track of the boat in question. The issue could well involve "operator" ease or senses such as the steering station location to the side, which can be a factor when docking. Some people just have a "feel" that a particular rotation works better or feels better to them |
Propeller rotation - important? - Yes, it is.
On Mon, 7 Jun 2004 23:03:19 +0200, "Anders Lassen" anders.lassenNEJTILSPAM (at)adr.dk wrote:
Thanks for all your replies. I've cleared things up this much: The transmission is designed to run equally fine in both directions. Ratios are almost similar. The transmission has two "modes" - A and B. A is the "normal" mode where the propeller-shaft runs in opposite direction of the engine. B is normally reverse - the propeller-shaft runs same way as the engine. Here's the funny thing: From the factory, the boat is delivered with a LH propeller - which means that the transmission has to run in the "B"-position to have the boat move forward - i.e. reverse of "normal"! I called the Norwegian factory to ask why. They replied that "the boat liked the LH propeller the most"! (Don't know what that means.) So it all narrows down to this: Assuming that transmission is not an issue - are there any "hull-issues" that should imply that a given hull simply "runs better" with a LH instead of a RH - or vice versa? Anders Denmark Yes, it is. Venetian Gondola is operated by a "single" oar in the RH side: to go straight it is shaped asymmetrical. The LH side is more curved than the RH side. Oar turns to left... shaped side turns to right... = straight line. Same thing happens to a single propeller boat: the reaction to propeller rotation tries to turn boat to right or to lift direction. To go straight forward you have to compensate time by time. To avoid this any Boat Designer has an its own "trick"... maybe a different shape of the hull... maybe a slight "off-center" centerline... maybe a different tank in one side... maybe battery pack.. maybe something else... It could be "calculated" or it could have been found during the first tests of the boat... Right now we are "blueprinting" several propellers for an all new power boat that doesn't wish to plane... Of course for the Boat Manufacturer is cheaper to replace several propellers than get away a full set of boat moulds... This is the way: Test... no good... modify... test... no good... replace... test... maybe... adjust a bit.. test... go! Cheer! WinXP |
Propeller rotation - important? - Yes, it is.
On Mon, 7 Jun 2004 14:52:14 -0700, "Rod McInnis" wrote:
"JAXAshby" wrote in message ... There is also a thrust bearing needed for going in reverse as well. However, as the horsepower used in reverse is much less and the time it is used is hugely less the reverse thrust bearing need not be anywhere near as big. Now, change the prop so the former reverse thrust bearing becomes the new forward thrust bearing and operates at 100% power over extended time the potential to trash that bearing becomes very real. Either I am not following what you are saying or I am envisioning something totally different. As you said, the thrust on the shaft must be countered someplace, and that someplace is the thrust bearing(s). The thrust will either "push" or "pull", it shouldn't matter which direction the shaft is rotating. If you attempted to drive the boat by having the propeller in front, like an airplane, then the shaft will be pulling and the thrust bearing surface associated with "pull" will bear the brunt of the load. But I didn't think this is what we were talking about. I know that several models of Velvet Drive transmissions don't care which direction the input and output shafts turn, as long as they turn the same direction in "forward". You can have a Left Hand and Right Hand rotating engine turning Left Hand and Right Hand props and the transmissions don't care. If you attempted to have the Left Hand engine turn the Right Hand prop, however, then the transmission would be using the "reverse" clutch for forward which is not nearly as robust as the "forward" clutch and you would likely have reliability issues. The web page for the Hurth transmissions indicated that many of their models were capable of full engine horsepower in either "forward" or "reverse" operation. I don't know if that really means you can use them for reversing the rotation for counter rotation or not. There are many outdrive designs that has the drive shaft come down and drive two gears, one towards the front and one towards the rear. A "dog" or cone clutch will engage one gear or the other, which will make the prop shaft turn one way or the other. The clutches are identical and the thrust is carried on the shaft bearing (not the gears) so it doesn't matter if the gear more towards the front is considered "forward" or not. Rod Hi Rod. You are right... we are right else. All problems are regarding: what kind of Transmission you are reversing. Clutches and Gearbox:: Good HD ones have same clutch for Forward and Reverse. Some ones have not... so Forward has to be forward, engaging only two gears. So it requires a propeller rotating reverse than engine. Reverse has Three Gears and the central one (idler) is a very small one, rotating on a small Roller Bearing or equivalent one. Gear Ratio between Driven Gear and Idler Gear (the small one) is usually in the ratio of 3:1 This is meaning that with boat engine rotating at 2,000 rpm the Idler Gear is rotating at 6.000 rpm! With boat engine rotating at 4.000 rpm... Idle Gear is rotating at 12,000 rpm ! (By the way: Why Transmission Gearboxes are using Oil Coolers?) So best solution for twin engines boat is to have one engine RH and one LH. So best solution to "reverse" propeller... is to replace Engine !!! Bevel Gear Gearbox has no problem to rotate Forward or Reverse... but they are on Outboards... Thrust Bearing: Old ones or cheap ones are assembled with two different Thrust Bearings: Heavy Duty for Forward, Light Duty for Reverse... Good new ones have Two identical HD Thrust Bearings both for Forward and for Reverse... so no matter in which direction they are mainly operated (not rotating).. You are right else: Forward is always Forward... no matter is RH or LH... There has been a bit of confusing details. Sorry for this. Bye, WinXP |
Propeller rotation - important? - Yes, it is.
The thrust will either "push" or
"pull", it shouldn't matter which direction the shaft is rotating. what happens is this. if the driven gear (the prop gear) in the lower unit is in the foward part of the unit it has a large, easy to use surface to be put to use as the thurst bearing. One the other hand, if the driven gear is in the back (i.e. closer to the prop than the driving gear/drive shaft). This means both gears get in the way of providing a large, easy-to-use bearing surface. All of which means unless the design engineers have some compelling reason to make the tranny drive in either direction they will otherwise just use the available thurst bearing surfaces as is, using the easiest for forward. |
Propeller rotation - important? - Yes, it is.
The boat in question is a 33 feet semiplaning motorboat. Controls/rudder to
the starboard as well as seating arrangment. Engine Yanmar 6LP-STE, transmission Hurth HWS 630 A Anders I've lost track of the boat in question. The issue could well involve "operator" ease or senses such as the steering station location to the side, which can be a factor when docking. Some people just have a "feel" that a particular rotation works better or feels better to them |
Propeller rotation - important? - Yes, it is.
"JAXAshby" wrote in message ... what happens is this. if the driven gear (the prop gear) in the lower unit is in the foward part of the unit it has a large, easy to use surface to be put to use as the thurst bearing. I am not sure I am following: are you saying that the thrust is transfered from the output shaft to the gear, and then from the gear to the housing? I am having a hard time picturing that design. I have only had one lower unit (a Volvo Penta from about 30 years ago) completely apart enough to become intimately familiar with it, but the exploded views of other lower units, including my 2000 Mercury outboards, appear to be very similar. On the lower units I am familiar with, the prop shaft enters the lower unit housing through an oil seal and fairly good sized bearing. This bearing is also the thrust bearing for forward. I had thought that it was also the thrust bearing for reverse, but I would not swear to that (memory is a little foggy). The shaft continues into the housing, passing through a beveled gear. This gear uses the prop shaft as a bearing surface, it does NOT attach to or drive the shaft directly. Continuing on the shaft passes through the "dog clutch", which IS splined to the shaft. The clutch can slide easily forward and back but turns with the shaft. Continuing on the shaft passes through the other gear (which spins on the shaft, just like the first gear) then continues on to the second bearing. The two gears MUST be the same size, at least in diameter and number of teeth because they both have the same center (the prop shaft) and both must engage the same gear. Therefore, forward and reverse ratios are always the same. When the engine is running, the three bevel gears (one on the main drive shaft, two on the prop shaft) are all turning. When in neutral, the clutch is positioned between the two bevel gears, not engaging either one. To engage a gear, the clutch is moved either forward or aft, engaging one of the bevel gears that is rotating about the prop shaft, forcing the prop shaft to turn in that direction. Ideally, I would think that the two bevel gears would be totally "floating" on the prop shaft so that there would be no movement at all with respect to the driving gear. If the thrust was transferred through the shaft to the forward gear when the boat was in "forward" then there would be some amount of movement of the gear forward. As the thrust surface wore, this gear would move farther and farther forward. As it moves it will change the engagement with the gear on the driveshaft and before long you would end up with a stripped gear. As I said, I can't say if all outdrives are built this way, but the Volvo Penta I/O I had 30 years ago was, and I am pretty sure my Mercury outboard is like this as well. Rod |
Propeller rotation - important? - Yes, it is.
Subject: Propeller rotation - important? - Yes, it is.
From: "Anders Lassen" anders.lassenNEJTILSPAM(at)adr.dk Date: 06/08/2004 12:23 Pacific Standard Time Message-id: The boat in question is a 33 feet semiplaning motorboat. Controls/rudder to the starboard as well as seating arrangment. Engine Yanmar 6LP-STE, transmission Hurth HWS 630 A Anders May be part of the reason. Since you have a controls/steering to stbd, you will get the best view during docking when docking stbd side too. For a single screw boat with the LH prop, docking is normally much easier when docking stbd side rather than port side too, as Good Ole Mr. propwalk will tend to pull your stern into the dock when backing. Shen |
Propeller rotation - important? - Yes, it is.
On Tue, 8 Jun 2004 13:45:09 -0700, "Rod McInnis" wrote:
"JAXAshby" wrote in message ... what happens is this. if the driven gear (the prop gear) in the lower unit is in the foward part of the unit it has a large, easy to use surface to be put to use as the thurst bearing. snip The shaft continues into the housing, passing through a beveled gear. This gear uses the prop shaft as a bearing surface, it does NOT attach to or drive the shaft directly. Continuing on the shaft passes through the "dog clutch", which IS splined to the shaft. The clutch can slide easily forward and back but turns with the shaft. Continuing on the shaft passes through the other gear (which spins on the shaft, just like the first gear) then continues on to the second bearing. snip When the engine is running, the three bevel gears (one on the main drive shaft, two on the prop shaft) are all turning. When in neutral, the clutch is positioned between the two bevel gears, not engaging either one. To engage a gear, the clutch is moved either forward or aft, engaging one of the bevel gears that is rotating about the prop shaft, forcing the prop shaft to turn in that direction. snip As I said, I can't say if all outdrives are built this way, but the Volvo Penta I/O I had 30 years ago was, and I am pretty sure my Mercury outboard is like this as well. Rod Hi Rod. Your "Throat Bearing" is this one: continues on to the second bearing. This Bearing supports ALL the load to "push" the boat in Forward. It is usually of special shape, design or material (no tech data here). In Reverse your Thrust Bearing is the opposite one, near the propeller. Usually it could be of the same drawing of the opposite one, but many times it is different for performances and bore diameter. It supports ALL the load to "pull" the boat in Reverse. Bevel Gearboxes with Cog Clutch have no matter to rotate Forward or Reverse. +++ Now get a look to drawings: Usually the second bearing (Forward Thrust one) is placed in a solid body... meanwhile the first one (Reverse Thrust one) is placed in a removable flange... ALL the Reverse Thrust is supported by the three or four screws or the Snap Ring fixing this flange... no matter the size or kind of this bearing... Your specific one could be slightly different, but this is the standard in Outboard Propeller Shafts, any Brand. +++ Boats with on line Propeller Shaft (s) have a different Thrust Bearings but the standard one is similar to this one: Samewhere, along the Drive Line, is fixed one HD Thrust Bearing Box ( It has to be "rigidly" fixed to the boat !). Inside there are at least two HD Bearings (notice: NO standard "Ball Bearings" but specific ones...) sized to support heavy loads for a long time... (for years or for presumed boat lifetime...). Small ones are lubed by Grease, but good ones are Forced Lubed with a Gear Pump and are Forced Cooled (Lube and Case) with heat exchangers. Standard Vessels are "going forward" for the main time... but other ones (e.g. Clam Dredgers) are not: they operate in Reverse! So, standard Thrust Bearing Box could have "differently" sized Bearings for Forward and for Reverse. Other ones have same bearings in both sides. +++ Vessels with twin engines and twin drivelines are using engines with opposite rotation: LH & RH. In this way ALL components of the two Drivelines are working rightly and exactly in the same way, with same components an spare parts. This is depending from the Marine Gearbox concept (any Brand, as standard). Inside Gearbox there are TWO Shafts: Input & Output (plus a third small one for Reverse Idle Gear). On Input or Output Shaft are placed TWO Hydraulically Operated Multidisc Clutches ( ...sounds familiar "Twin Disc"??)... First one is for Forward (and adequately sized) and is "directly" coupled with Gear in Output Shaft: so Torque is roughly transmitted to Propeller in Forward. Notice that rotation of Propeller in Forward is always OPPOSITE to the engine one: Two Gears engaged: LH RH Gearbox Ratio in Forward is depending from these gears ratio. In Reverse you need for THREE Gears: LH RH LH. So you have to interpose a third Gear: the small idler one. Obviously the other two cannot be anymore of the same diameters of the Forward, so Reverse Ratio is ALWAYS different from Forward one (slightly, but different). Now all Torque in Reverse is transmitted by means of the "small" Idler one... so... Notice that Reverse rotation is the same one of the engine one. Notice that standard diameter of Idle Gear is two or three times less than main ones... .... so it rotates TWO-THREE times speedier than engine rpm ! With engine at 3.,000 rpm it could be rotating up to 6,000-9,000 rpm! Now you acknowledge why Marine Gearboxes are using large Heat Exchanger and Heavy Forced Lube... By the way... during the use... your Outboard Gearbox is fully "immersed" in fresh water.... +++ I hope this could help. Bye, WinXP |
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