Prop is spinning freely


Chris Likins
 

We have A54 #133. Today when sailing I noticed that the prop was spinning freely(in reverse) each time a wave would pass under us. It’s easy to see that the shaft brake is not engaging when the engine is in neutral or shut down. Referencing Bill Rouses book p.305, it reads that the hydraulic shaft OPENS the calipers when pressurized by the transmission. Currently the shaft is retracted into the piston at all times allowing the calipers to remain open. I understand that the calipers are supposed to spring shut on the disk when transmission pressure is lost on the shaft. I am a bit confused by this as there is no mechanical connection between the hydraulic shaft and the outer caliper. It seems like the calipers should close when the shaft is extended.. So my questions are
1. Can someone help explain this system in more detail? 
2. What position should the shaft be in when pressurized and not pressurized? 
3. Is it most likely a bad spring on the caliper? 
4. Most importantly for now.. Is it ok to allow the prop to spin freely for the duration of the passage or would it be better on the shaft if we remain in forward gear. 

Thank you for the help! 


Courtney Gorman
 

Easy fix
See where the plunger engages the brakes tape a quarter in this spot then all is well 
Also voyage will be much quieter 
Cheers 
Courtney 
Trippin 
54#101


On Jan 3, 2021, at 10:37 AM, Chris Likins <likinsca@...> wrote:

We have A54 #133. Today when sailing I noticed that the prop was spinning freely(in reverse) each time a wave would pass under us. It’s easy to see that the shaft brake is not engaging when the engine is in neutral or shut down. Referencing Bill Rouses book p.305, it reads that the hydraulic shaft OPENS the calipers when pressurized by the transmission. Currently the shaft is retracted into the piston at all times allowing the calipers to remain open. I understand that the calipers are supposed to spring shut on the disk when transmission pressure is lost on the shaft. I am a bit confused by this as there is no mechanical connection between the hydraulic shaft and the outer caliper. It seems like the calipers should close when the shaft is extended.. So my questions are
1. Can someone help explain this system in more detail? 
2. What position should the shaft be in when pressurized and not pressurized? 
3. Is it most likely a bad spring on the caliper? 
4. Most importantly for now.. Is it ok to allow the prop to spin freely for the duration of the passage or would it be better on the shaft if we remain in forward gear. 

Thank you for the help! 


Ken Powers SV Aquarius <ken@...>
 

Hello Courtney,

Chris is still having a problem.  Please write more about the procedure to correct the problem, I can't understand how to correct the problem.  Is your comment is missing punctuation.

"See where the plunger engages the brakes tape a quarter in this spot then all is well" 

Thanks!

Ken
Aquarius


Ken Powers SV Aquarius <ken@...>
 

On Aquarius we put her in Reverse to lock the shaft.  Would Chris be able to do this?  Or will it damage the transmission?

Ken
Aquarius


Alan Leslie
 

Chris,

There is a spring inside the brake caliper piston cylinder that is supposed to push the piston and keep the pads pressed against the brake disc when the engine is not running. The caliper is semi floating like a car disc brake
There is an adjustment bolt on the aft end of the the cylinder that allows you to increase the pressure on the spring. Adjusting this, may or may not help.
If the pads are badly worn, it won't help, you need new pads.
I had this issue when in the Pacific a few years ago and I solved it by adding an adjustment bolt on the forward caliper so I could make the brake just close.
It's quite a simple system really.
Cheers
Alan
Elyse SM437


Courtney Gorman
 

Where the plunger comes out of the cylinder to push against the brakes.  You tape a quarter to the spot on the brakes where the plunger contacts it this will increase the compression of the pads 


On Jan 3, 2021, at 4:33 PM, Ken Powers SV Aquarius <ken@...> wrote:

Hello Courtney,

Chris is still having a problem.  Please write more about the procedure to correct the problem, I can't understand how to correct the problem.  Is your comment is missing punctuation.

"See where the plunger engages the brakes tape a quarter in this spot then all is well" 

Thanks!

Ken
Aquarius


Sebti Lamya
 


 

Chris,

There is usually not a simple answer to your question. 

 The most common issues for non-braking are mechanical within the caliper mechanism. Non-braking is usually caused by the following in order of probability:
  • The caliper bushings will wear and cause misalignment and open calipers
  • The brake shoe pads will wear
  • The caliper frame may be loose on the hydraulic cylinder
  • The hydraulic cylinder spring may need adjustment
  • The hydraulic cylinder may need an overhaul
  • The caliper mechanical springs may be broken or defective
  • Or, something else I haven't thought of 
The most common issue for not releasing is hydraulic in nature.

The quarter that Courtney refers to will usually solve the problem when the bushing is worn, or the brake pad is worn.

It is possible that the Italian-made Caliper you have is no longer made. If so, Amel will supply you with a new model that will work, but not necessarily fit without minor modification.

I believe that you can either leave the prop free spinning or place the transmission in gear to stop the spinning, however, I do not recommend either of those because I have not been able to verify the long-term issues, if any, in doing either.


CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Sun, Jan 3, 2021 at 9:37 AM Chris Likins <likinsca@...> wrote:
We have A54 #133. Today when sailing I noticed that the prop was spinning freely(in reverse) each time a wave would pass under us. It’s easy to see that the shaft brake is not engaging when the engine is in neutral or shut down. Referencing Bill Rouses book p.305, it reads that the hydraulic shaft OPENS the calipers when pressurized by the transmission. Currently the shaft is retracted into the piston at all times allowing the calipers to remain open. I understand that the calipers are supposed to spring shut on the disk when transmission pressure is lost on the shaft. I am a bit confused by this as there is no mechanical connection between the hydraulic shaft and the outer caliper. It seems like the calipers should close when the shaft is extended.. So my questions are
1. Can someone help explain this system in more detail? 
2. What position should the shaft be in when pressurized and not pressurized? 
3. Is it most likely a bad spring on the caliper? 
4. Most importantly for now.. Is it ok to allow the prop to spin freely for the duration of the passage or would it be better on the shaft if we remain in forward gear. 

Thank you for the help! 


 

For your information, I have seen all sorts of "fixes" for worn-out caliper bushings when performing Pre-Purchase consulting. This photo takes the Grand Prize Award of all I have seen. It includes a wooden clothespin and wire, both circled in red. The new owner of this SM replaced the calipers with a slightly different model caliper from the same Italian manufacturer as the original. Amel SAV provided the new caliper:
image.png

image.png
CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Mon, Jan 4, 2021 at 9:45 AM Bill Rouse <brouse@...> wrote:
Chris,

There is usually not a simple answer to your question. 

 The most common issues for non-braking are mechanical within the caliper mechanism. Non-braking is usually caused by the following in order of probability:
  • The caliper bushings will wear and cause misalignment and open calipers
  • The brake shoe pads will wear
  • The caliper frame may be loose on the hydraulic cylinder
  • The hydraulic cylinder spring may need adjustment
  • The hydraulic cylinder may need an overhaul
  • The caliper mechanical springs may be broken or defective
  • Or, something else I haven't thought of 
The most common issue for not releasing is hydraulic in nature.

The quarter that Courtney refers to will usually solve the problem when the bushing is worn, or the brake pad is worn.

It is possible that the Italian-made Caliper you have is no longer made. If so, Amel will supply you with a new model that will work, but not necessarily fit without minor modification.

I believe that you can either leave the prop free spinning or place the transmission in gear to stop the spinning, however, I do not recommend either of those because I have not been able to verify the long-term issues, if any, in doing either.


CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
View My Training Calendar


On Sun, Jan 3, 2021 at 9:37 AM Chris Likins <likinsca@...> wrote:
We have A54 #133. Today when sailing I noticed that the prop was spinning freely(in reverse) each time a wave would pass under us. It’s easy to see that the shaft brake is not engaging when the engine is in neutral or shut down. Referencing Bill Rouses book p.305, it reads that the hydraulic shaft OPENS the calipers when pressurized by the transmission. Currently the shaft is retracted into the piston at all times allowing the calipers to remain open. I understand that the calipers are supposed to spring shut on the disk when transmission pressure is lost on the shaft. I am a bit confused by this as there is no mechanical connection between the hydraulic shaft and the outer caliper. It seems like the calipers should close when the shaft is extended.. So my questions are
1. Can someone help explain this system in more detail? 
2. What position should the shaft be in when pressurized and not pressurized? 
3. Is it most likely a bad spring on the caliper? 
4. Most importantly for now.. Is it ok to allow the prop to spin freely for the duration of the passage or would it be better on the shaft if we remain in forward gear. 

Thank you for the help! 


Danny and Yvonne SIMMS
 

Hi Bill,

Volvo recommend either freewheeling or in gear. However care needs to be taken that either forward or reverse gear is selected depending on which firmly stops the spinning, the wrong one will allow slow revolution of the shaft from partially closed clutches which of course will cause wear. How to know which? When sailing observe the shaft rotating, put it into gear, the correct one will produce a satisfying clunk and the shaft will stop, the wrong one will slow the shaft but not fully stop it.  

Regards

Danny

SM 299

Ocean Pearl

Mangonui New Zealand

On 05 January 2021 at 04:45 CW Bill Rouse <brouse@...> wrote:

Chris,

There is usually not a simple answer to your question. 

 The most common issues for non-braking are mechanical within the caliper mechanism. Non-braking is usually caused by the following in order of probability:
  • The caliper bushings will wear and cause misalignment and open calipers
  • The brake shoe pads will wear
  • The caliper frame may be loose on the hydraulic cylinder
  • The hydraulic cylinder spring may need adjustment
  • The hydraulic cylinder may need an overhaul
  • The caliper mechanical springs may be broken or defective
  • Or, something else I haven't thought of 
The most common issue for not releasing is hydraulic in nature.

The quarter that Courtney refers to will usually solve the problem when the bushing is worn, or the brake pad is worn.

It is possible that the Italian-made Caliper you have is no longer made. If so, Amel will supply you with a new model that will work, but not necessarily fit without minor modification.

I believe that you can either leave the prop free spinning or place the transmission in gear to stop the spinning, however, I do not recommend either of those because I have not been able to verify the long-term issues, if any, in doing either.


CW Bill Rouse Amel Owners Yacht School
 
Address: 720 Winnie, Galveston Island, Texas 77550 
 
View My Training Calendar


On Sun, Jan 3, 2021 at 9:37 AM Chris Likins < likinsca@...> wrote:
We have A54 #133. Today when sailing I noticed that the prop was spinning freely(in reverse) each time a wave would pass under us. It’s easy to see that the shaft brake is not engaging when the engine is in neutral or shut down. Referencing Bill Rouses book p.305, it reads that the hydraulic shaft OPENS the calipers when pressurized by the transmission. Currently the shaft is retracted into the piston at all times allowing the calipers to remain open. I understand that the calipers are supposed to spring shut on the disk when transmission pressure is lost on the shaft. I am a bit confused by this as there is no mechanical connection between the hydraulic shaft and the outer caliper. It seems like the calipers should close when the shaft is extended.. So my questions are
1. Can someone help explain this system in more detail? 
2. What position should the shaft be in when pressurized and not pressurized? 
3. Is it most likely a bad spring on the caliper? 
4. Most importantly for now.. Is it ok to allow the prop to spin freely for the duration of the passage or would it be better on the shaft if we remain in forward gear. 

Thank you for the help! 

 

 


 

Thanks for that, Danny. I was told the same thing by Yanmar. However, I am reluctant to repeat it because I assume it will depend on the transmission installed on the engine. And to further confuse the issue Volvo and probably others have moved to electric gear changing transmissions which I assume require the ignition to be ON.

This is the reason I don't recommend it. 😀

Best,

CW Bill Rouse 
Amel Owners Yacht School
+1 832-380-4970 | brouse@...
720 Winnie, Galveston Island, Texas 77550 
www.AmelOwnersYachtSchool.com 
Yacht School Calendar: www.preparetocastoff.blogspot.com/p/calendar.html


   


On Mon, Jan 4, 2021, 2:00 PM Danny and Yvonne SIMMS <simms@...> wrote:

Hi Bill,

Volvo recommend either freewheeling or in gear. However care needs to be taken that either forward or reverse gear is selected depending on which firmly stops the spinning, the wrong one will allow slow revolution of the shaft from partially closed clutches which of course will cause wear. How to know which? When sailing observe the shaft rotating, put it into gear, the correct one will produce a satisfying clunk and the shaft will stop, the wrong one will slow the shaft but not fully stop it.  

Regards

Danny

SM 299

Ocean Pearl

Mangonui New Zealand

On 05 January 2021 at 04:45 CW Bill Rouse <brouse@...> wrote:

Chris,

There is usually not a simple answer to your question. 

 The most common issues for non-braking are mechanical within the caliper mechanism. Non-braking is usually caused by the following in order of probability:
  • The caliper bushings will wear and cause misalignment and open calipers
  • The brake shoe pads will wear
  • The caliper frame may be loose on the hydraulic cylinder
  • The hydraulic cylinder spring may need adjustment
  • The hydraulic cylinder may need an overhaul
  • The caliper mechanical springs may be broken or defective
  • Or, something else I haven't thought of 
The most common issue for not releasing is hydraulic in nature.

The quarter that Courtney refers to will usually solve the problem when the bushing is worn, or the brake pad is worn.

It is possible that the Italian-made Caliper you have is no longer made. If so, Amel will supply you with a new model that will work, but not necessarily fit without minor modification.

I believe that you can either leave the prop free spinning or place the transmission in gear to stop the spinning, however, I do not recommend either of those because I have not been able to verify the long-term issues, if any, in doing either.


CW Bill Rouse Amel Owners Yacht School
 
+1 832-380-4970 | brouse@...
Address: 720 Winnie, Galveston Island, Texas 77550 
 
View My Training Calendar


On Sun, Jan 3, 2021 at 9:37 AM Chris Likins < likinsca@...> wrote:
We have A54 #133. Today when sailing I noticed that the prop was spinning freely(in reverse) each time a wave would pass under us. It’s easy to see that the shaft brake is not engaging when the engine is in neutral or shut down. Referencing Bill Rouses book p.305, it reads that the hydraulic shaft OPENS the calipers when pressurized by the transmission. Currently the shaft is retracted into the piston at all times allowing the calipers to remain open. I understand that the calipers are supposed to spring shut on the disk when transmission pressure is lost on the shaft. I am a bit confused by this as there is no mechanical connection between the hydraulic shaft and the outer caliper. It seems like the calipers should close when the shaft is extended.. So my questions are
1. Can someone help explain this system in more detail? 
2. What position should the shaft be in when pressurized and not pressurized? 
3. Is it most likely a bad spring on the caliper? 
4. Most importantly for now.. Is it ok to allow the prop to spin freely for the duration of the passage or would it be better on the shaft if we remain in forward gear. 

Thank you for the help! 

 

 


Mark & Debbie Mueller
 

We have a ZF-25 2.0 transmission, the service manual states:

3.5
Sailing or moving in tow
Rotation of the propeller while the boat
is sailing, being towed, or anchored in a
river, as well as operation of the engine
with the propeller stopped (for charging
the battery), will have no detrimental effects
on the gearbox.
IMPORTANT
When the boat is sailing (engine
stopped), the gear lever must be in zero
pos-ition. Never put the gear lever in the
pos-ition corresponding to the direction
of travel of the boat.
Locking the propeller shaft by an additional
brake is not required: use the gear
lever position opposite your direction of
travel for this purpose.

Hope this helps until you can get the break repaired.  Reference page 33 of the attached manual.
--
Mark Mueller
Brass Ring  A54


Karen Smith
 

Mark,

I think you are mixing up the ZF25M transmission and the ZF25. The document you reference is for a ZF25M, not the ZF25.  This has been a common source of confusion on the forum, since both of these are the common transmissions used in many Amel boats. The similar model numbers for two very different machines has always been an issue.

This is my understanding of this un-necessarily complicated issue:

The ZF25M is a smaller, lower horsepower rated, transmission that shifts mechanically. I believe none of these transmissions were ever fitted with a shaft brake, because none was needed.  The ZF25, even though it has a very similar part number, is a very different beast.  I doubt the ZF25M and the ZF25 have any parts in common.  The ZF25 is a higher horsepower rated, hydraulically shifted, transmission.  As far as I know (and this might not be correct) the Volvo TMD22 engines all had ZF25M and the Yanmars all had ZF25.  Note that these model numbers changed when the original Hurth brand was bought out by ZF.

As the document you quoted points out, the ZF25M can free-wheel without damage, other than routine wear on bearings and seals. With a normal fixed prop or a MaxProp, putting it in reverse will lock the rotation.  The AutoProp is a different story.  It rotates in the opposite direction when free-wheeling, and needs to be put in FORWARD to lock it.  The rule for operation should be “Do not allow the transmission to free wheel while in gear—ever.”  If the prop rotates while in reverse, put it in forward.  And the other way round.

The ZF25 relies on the hydraulic pressure generated by the rotating input shaft (from the engine) to shift.  If the engine is not turning, it will always be in neutral, and neither forward nor reverse can be engaged no matter what the position of the shift lever.  Therefore, the prop will always spin when the engine is not running.  Most hydraulic transmissions require the engine input shaft to be turning to pump the fluid internally to lubricate the moving parts. The ZF25, however, is allowed to rotate with the engine off.  It will be noisy, and add routine wear to the bearings and seals. There is no way to stop the rotation without a shaft brake.

Here are the rules:

If you have a Volvo with a ZF25M transmission:
  • Sailing in neutral is acceptable with any propeller. The prop WILL spin with a fixed prop or an AutoProp, and MIGHT spin with a MaxProp. While spinning, the prop is noisy and adds routine wear and tear to the bearings and seals. 
  • With a MaxProp or a fixed prop, you can sail in reverse and the prop will not turn. This is acceptable.  
  • With a fixed prop, if you sail in forward, the propeller will spin, and the transmission will be damaged quite quickly.
  • With a MaxProp, if you sail in forward, the propeller MIGHT spin, and if it does the transmission will be damaged quite quickly. 
  • With an AutoProp, you can sail in forward and the prop will not turn. This is acceptable.
  • With an AutoProp, if you sail in reverse, the propeller will spin, and the transmission will be damaged quite quickly.
If you have a Yanmar with a ZF25 transmission,
  • With any propeller, the shaft can spin when sailing. This is acceptable, again, other than the noise and additional routine wear on bearings and seals.
  • The only way to stop this rotation is to use a shaft brake.


Bill Kinney
SM160, Harmonie
The boat is in Charleston, we are in Antigua finishing up a delivery.


Danny and Yvonne SIMMS
 

A great reply Bill. Best explanation Ive seen. However I am going to drop a curly one here. I have a Volvo and a ZF 25M gearbox and an auto prop.For reasons I have not discovered it will sometimes lock in reverse, sometimes in forward. I have to observe the shaft spinning and engage one or the other. The correct selection will exhibit a satisfying clunk and the shaft stops dead. The wrong results in a soggy almost stop, in which case obviously I change to the other. It is random, so I just take care and always check.

Kind regards and wishing you all the best for the new year.

Danny

SM 299

Ocean Pearl

On 11 January 2021 at 14:18 "Karen Smith via groups.io" <karenharmonie@...> wrote:

Mark,

I think you are mixing up the ZF25M transmission and the ZF25. The document you reference is for a ZF25M, not the ZF25.  This has been a common source of confusion on the forum, since both of these are the common transmissions used in many Amel boats. The similar model numbers for two very different machines has always been an issue.

This is my understanding of this un-necessarily complicated issue:

The ZF25M is a smaller, lower horsepower rated, transmission that shifts mechanically. I believe none of these transmissions were ever fitted with a shaft brake, because none was needed.  The ZF25, even though it has a very similar part number, is a very different beast.  I doubt the ZF25M and the ZF25 have any parts in common.  The ZF25 is a higher horsepower rated, hydraulically shifted, transmission.  As far as I know (and this might not be correct) the Volvo TMD22 engines all had ZF25M and the Yanmars all had ZF25.  Note that these model numbers changed when the original Hurth brand was bought out by ZF.

As the document you quoted points out, the ZF25M can free-wheel without damage, other than routine wear on bearings and seals. With a normal fixed prop or a MaxProp, putting it in reverse will lock the rotation.  The AutoProp is a different story.  It rotates in the opposite direction when free-wheeling, and needs to be put in FORWARD to lock it.  The rule for operation should be “Do not allow the transmission to free wheel while in gear—ever.”  If the prop rotates while in reverse, put it in forward.  And the other way round.

The ZF25 relies on the hydraulic pressure generated by the rotating input shaft (from the engine) to shift.  If the engine is not turning, it will always be in neutral, and neither forward nor reverse can be engaged no matter what the position of the shift lever.  Therefore, the prop will always spin when the engine is not running.  Most hydraulic transmissions require the engine input shaft to be turning to pump the fluid internally to lubricate the moving parts. The ZF25, however, is allowed to rotate with the engine off.  It will be noisy, and add routine wear to the bearings and seals. There is no way to stop the rotation without a shaft brake.

Here are the rules:

If you have a Volvo with a ZF25M transmission:
  • Sailing in neutral is acceptable with any propeller. The prop WILL spin with a fixed prop or an AutoProp, and MIGHT spin with a MaxProp. While spinning, the prop is noisy and adds routine wear and tear to the bearings and seals. 
  • With a MaxProp or a fixed prop, you can sail in reverse and the prop will not turn. This is acceptable.  
  • With a fixed prop, if you sail in forward, the propeller will spin, and the transmission will be damaged quite quickly.
  • With a MaxProp, if you sail in forward, the propeller MIGHT spin, and if it does the transmission will be damaged quite quickly. 
  • With an AutoProp, you can sail in forward and the prop will not turn. This is acceptable.
  • With an AutoProp, if you sail in reverse, the propeller will spin, and the transmission will be damaged quite quickly.
If you have a Yanmar with a ZF25 transmission,
  • With any propeller, the shaft can spin when sailing. This is acceptable, again, other than the noise and additional routine wear on bearings and seals.
  • The only way to stop this rotation is to use a shaft brake.


Bill Kinney
SM160,  Harmonie
The boat is in Charleston, we are in Antigua finishing up a delivery.


Beaute Olivier
 

Hello Bill,

all you wrote is correct.
There has been some SM2000 with VOLVO engine and ZF25 hydraulic gear-box, with the same shaft-brake system as on the YANMAR engine.
Some of these SM2000 are fitted with a prop shaft alternator which requires a solenoid valve system in order to keep the prop spinning while the engine is OFF. When in use, the solenoid valve keeps the pressure in the shaft-brake cylinder.

Happy New Year.

Olivier.

On Monday, January 11, 2021, 10:12:40 AM GMT+1, Danny and Yvonne SIMMS <simms@...> wrote:


A great reply Bill. Best explanation Ive seen. However I am going to drop a curly one here. I have a Volvo and a ZF 25M gearbox and an auto prop.For reasons I have not discovered it will sometimes lock in reverse, sometimes in forward. I have to observe the shaft spinning and engage one or the other. The correct selection will exhibit a satisfying clunk and the shaft stops dead. The wrong results in a soggy almost stop, in which case obviously I change to the other. It is random, so I just take care and always check.

Kind regards and wishing you all the best for the new year.

Danny

SM 299

Ocean Pearl

On 11 January 2021 at 14:18 "Karen Smith via groups.io" <karenharmonie@...> wrote:

Mark,

I think you are mixing up the ZF25M transmission and the ZF25. The document you reference is for a ZF25M, not the ZF25.  This has been a common source of confusion on the forum, since both of these are the common transmissions used in many Amel boats. The similar model numbers for two very different machines has always been an issue.

This is my understanding of this un-necessarily complicated issue:

The ZF25M is a smaller, lower horsepower rated, transmission that shifts mechanically. I believe none of these transmissions were ever fitted with a shaft brake, because none was needed.  The ZF25, even though it has a very similar part number, is a very different beast.  I doubt the ZF25M and the ZF25 have any parts in common.  The ZF25 is a higher horsepower rated, hydraulically shifted, transmission.  As far as I know (and this might not be correct) the Volvo TMD22 engines all had ZF25M and the Yanmars all had ZF25.  Note that these model numbers changed when the original Hurth brand was bought out by ZF.

As the document you quoted points out, the ZF25M can free-wheel without damage, other than routine wear on bearings and seals. With a normal fixed prop or a MaxProp, putting it in reverse will lock the rotation.  The AutoProp is a different story.  It rotates in the opposite direction when free-wheeling, and needs to be put in FORWARD to lock it.  The rule for operation should be “Do not allow the transmission to free wheel while in gear—ever.”  If the prop rotates while in reverse, put it in forward.  And the other way round.

The ZF25 relies on the hydraulic pressure generated by the rotating input shaft (from the engine) to shift.  If the engine is not turning, it will always be in neutral, and neither forward nor reverse can be engaged no matter what the position of the shift lever.  Therefore, the prop will always spin when the engine is not running.  Most hydraulic transmissions require the engine input shaft to be turning to pump the fluid internally to lubricate the moving parts. The ZF25, however, is allowed to rotate with the engine off.  It will be noisy, and add routine wear to the bearings and seals. There is no way to stop the rotation without a shaft brake.

Here are the rules:

If you have a Volvo with a ZF25M transmission:
  • Sailing in neutral is acceptable with any propeller. The prop WILL spin with a fixed prop or an AutoProp, and MIGHT spin with a MaxProp. While spinning, the prop is noisy and adds routine wear and tear to the bearings and seals. 
  • With a MaxProp or a fixed prop, you can sail in reverse and the prop will not turn. This is acceptable.  
  • With a fixed prop, if you sail in forward, the propeller will spin, and the transmission will be damaged quite quickly.
  • With a MaxProp, if you sail in forward, the propeller MIGHT spin, and if it does the transmission will be damaged quite quickly. 
  • With an AutoProp, you can sail in forward and the prop will not turn. This is acceptable.
  • With an AutoProp, if you sail in reverse, the propeller will spin, and the transmission will be damaged quite quickly.
If you have a Yanmar with a ZF25 transmission,
  • With any propeller, the shaft can spin when sailing. This is acceptable, again, other than the noise and additional routine wear on bearings and seals.
  • The only way to stop this rotation is to use a shaft brake.


Bill Kinney
SM160,  Harmonie
The boat is in Charleston, we are in Antigua finishing up a delivery.


karkauai
 

Bill K,
Thank you for this clear explanation of the Hurth/ZF transmissions. I haven't read this anywhere before and have never understood why my helm has a sign that says in French, not to put in reverse while sailing. When I switched from AutoProp to be MaxProp, I read that I should put in reverse until it stopped turning, then back to neutral. I have just finished a maintenance of the Autoprop and reinstalled it to see how it performs compared to the MaxProp.  I now know that if it turns while sailing, it is safe to put the transmission in forward, but not reverse.

Now for the next question...
When I repowered from Volvo TMD22 (78HP} to Yanmar 4JH4HTE, (110HP), I was assured by the Yanmar dealer and mechanic (Danny Ramos in Fajardo; top Volvo mechanic in the Caribbean at the time) that the existing transmission was ok to reuse.  It has had no problems after ~1200 hours using the MaxProp.  But now I am worried that it may not be quite up to the job.  Does anyone have thoughts or recommendations about that? 

Should I just replace it with a new, more
robust one? If I use the Z25F, that means adding a shaft brake, right? Are there other robust mechanical transmissions that wouldn't require the brake? Any downsides to that?

Or have the transmission inspected, and put it back in if everything looks OK?

Or, with 1200hours already on the transmission with the new engine, just assume it is Ok and leave it alone?

Thanks again Bill K, your post is a game-changer for me!

Happy New Year, everyone!
Kent & Iris
Kristy
SM 243





--
Kent & Iris
KRISTY
SM243


Juan de Zulueta
 

Dear Kent,

I have changed my engine for a yanmar 4jh4hte 6 years ago. Since my Super Maramu was built in 1990, It had the old transmission installed on it. Amel recommandation was to change the transmission to the new one more robust. My engine has now 1800 hours, since we have a mechanical transmission we don t need the brake.
Amel told me at that time that if I had the new transmission installed there was no need to change it.
Since your super Maramu is number 243 I believe you should have the new version installed on your boat.

Juan de Zulueta
Super Maramu 32
Ophélie X

Envoyé de mon iPhone

Le 11 janv. 2021 à 11:59, karkauai via groups.io <karkauai@...> a écrit :


Bill K,
Thank you for this clear explanation of the Hurth/ZF transmissions. I haven't read this anywhere before and have never understood why my helm has a sign that says in French, not to put in reverse while sailing. When I switched from AutoProp to be MaxProp, I read that I should put in reverse until it stopped turning, then back to neutral. I have just finished a maintenance of the Autoprop and reinstalled it to see how it performs compared to the MaxProp.  I now know that if it turns while sailing, it is safe to put the transmission in forward, but not reverse.

Now for the next question...
When I repowered from Volvo TMD22 (78HP} to Yanmar 4JH4HTE, (110HP), I was assured by the Yanmar dealer and mechanic (Danny Ramos in Fajardo; top Volvo mechanic in the Caribbean at the time) that the existing transmission was ok to reuse.  It has had no problems after ~1200 hours using the MaxProp.  But now I am worried that it may not be quite up to the job.  Does anyone have thoughts or recommendations about that? 

Should I just replace it with a new, more
robust one? If I use the Z25F, that means adding a shaft brake, right? Are there other robust mechanical transmissions that wouldn't require the brake? Any downsides to that?

Or have the transmission inspected, and put it back in if everything looks OK?

Or, with 1200hours already on the transmission with the new engine, just assume it is Ok and leave it alone?

Thanks again Bill K, your post is a game-changer for me!

Happy New Year, everyone!
Kent & Iris
Kristy
SM 243





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Kent & Iris
KRISTY
SM243