Remote V drive alignment

baylabayla3288

baylabayla3288

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When measuring the engine - cardan shaft - gearbox - propshaft alignments on my Ferretti's remote V drive setup it turned out that the angles are too much out of spec. I have had some low frequency vibration that could be felt on the flybridge when accelerating. Also I have a resonance sound comming from the port transmission at approx 900 rpms. Due to these symthons we decided to do a thorough check of all the alignment angles.

Due to the remote v drive setup some special tools are needed and the work is a bit more complex compared to a straight shaft setup. We found that on both engines the in and out angles on the cardan jack shaft between the engine and the Twin Disc transmissions exceeded the spec. A 0,5 deg difference is allowed but we measured more than a degree. This will cause uneven rotation due to the universal joints used on both ends of the cardan shaft.

I'm told that these Twin Disc transmissions produce some gear clatter at idle but could the resonance be due to this missalignment? Anyone on the board who can comment this or have experience with the tolerances accepted by this type of drive setup much appreciated.

The low frequency vibration is most likely due to the propshaft misalignment we measured. Here a 0,6 mm gap was measured between the propshaft and the transmission flanges on both shafts. This is a large gap and it looks like it has been there form the beginning as the transmissions are firmly bolted to the hull and cannot be adjusted without drilling.

Here is a scematic picture of the remote setup looking from the side

https://goo.gl/images/dzlP1N
 
Hi
Sounds as if you know what you are talking about, which is a good start...
Although I have no experience of this transmission, I have a fair deal of experience when it comes to larger scale transmission and rotating machinery.
Just a few points worth considering;

It's worth noting that all rotating machinery has an event called the critical rpm. This is usually two points in the rev range that are close to at match the natural harmonics of the application, usually a lower and a higher specific rpm. It's perhaps worth a thought that this is what you are experiencing ? Has it always been like this ?

Another question perhaps....with regards to the gap you mentioned. Is this evident in the same location, even after you have rotated the shaft to a different location on the circumference of the coupling ?

Is there any back lash to be felt when trying to move the shaft/coupling by hand on the horizontal and vertical axis ?

Did you check alignment with a laser kit or DTI ?

Cheers.
 
baylabayla3288 said:
Due to the remote v drive setup some special tools are needed and the work is a bit more complex compared to a straight shaft setup. We found that on both engines the in and out angles on the cardan jack shaft between the engine and the Twin Disc transmissions exceeded the spec. A 0,5 deg difference is allowed but we measured more than a degree.
Click to expand...
Why are you saying that the alignment job is more complex? I mean, the most critical part with remote v-drives (or with remote gearboxes with embedded v-drive, as I guess is yours, since you mention that it's a Twin Disc) is the alignment of the prop shaft with the v-drive flange - which is what bears the thrust.
But as I understand, your misalignment problem is "only" related to the jack shaft.
And if so, it should be possible to fix that just by lowering/raising slightly the engine(s), playing with their mounts a bit - unless I am missing something.
Btw, is the 1 degree angle downward or upward?
My bet is on the first, which could simply mean that the engines lowered a bit compared to their initial regulation, due to compression of their mounts over time.
 
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Thank you QBhoy for your reply, here are my ansvers:

QBhoy said:
Hi

"It's worth noting that all rotating machinery has an event called the critical rpm. This is usually two points in the rev range that are close to at match the natural harmonics of the application, usually a lower and a higher specific rpm. It's perhaps worth a thought that this is what you are experiencing ? Has it always been like this ?"

The resonance noise has been there all the time during my ownership, 2 years and approx 200 hours. The boat has a bit less than 400 hours on the clocks now. The sound is not very pronounced and it is limited to 800 - 900 rpm in gear and on the port side only. This could also be the carracteristic of the gear box also as the port side is turning in the left hand direction. At higher speeds all is very smooth. My old boat had also a kind of hauling sound on the port side at similar low rpms which according to Volvo was due to the rotation direction, one more set of gears in use due to left hand rotation

"Another question perhaps....with regards to the gap you mentioned. Is this evident in the same location, even after you have rotated the shaft to a different location on the circumference of the coupling ?"

The gap is independent of the position of the shaft, allways at 7 o'clock so I guess a bent shaft is excluded. This is the same on both shafts.

"Is there any back lash to be felt when trying to move the shaft/coupling by hand on the horizontal and vertical axis ?"

No, all feels very tight however all flange bolts were loose on the cardan shaft flanges on both ends, could be due to the missalignment or somebody forgot to tighten them at some stage earlier.

"Did you check alignment with a laser kit or DTI ?"

For the cardan angles we used mechanical sticks where the two points have to meet. For the propshaft we used a feeler gauge.

Cheers.
Click to expand...
 
MapisM said:
Why are you saying that the alignment job is more complex? I mean, the most critical part with remote v-drives (or with remote gearboxes with embedded v-drive, as I guess is yours, since you mention that it's a Twin Disc) is the alignment of the prop shaft with the v-drive flange - which is what bears the thrust.
But as I understand, your misalignment problem is "only" related to the jack shaft.
And if so, it should be possible to fix that just by lowering/raising slightly the engine(s), playing with their mounts a bit - unless I am missing something.
Btw, is the 1 degree angle downward or upward?
My bet is on the first, which could simply mean that the engines lowered a bit compared to their initial regulation, due to compression of their mounts over time.
Click to expand...

Hi Mapis,

Yes, it is actually not too complicated, there are just more components to be aligned. In my case both the prop shafts vers transmission flanges and the cardan angles need to be re-aligned as there is also 0,6 mm gaps on the prop shaft flanges. On the Ferretti the angle between the engine and the transmission is set to 5 degrees. The problem is that the angle between engine and cardan is one degree less than the angle between the transmission and the cardan, this difference should be less than 0,5 degree according to MAN &Twin Disc specs. What makes it a bit more complicated is that the solidly mounted transmissions have to be moved to align with the propshafts. Luckily we are talking mm and this can be done by drilling the mounting holes slightly owal.

Wether this will have an effect on the low frequency vibration at medium speeds and the resonance remains to be seen. At least these corrections should improve the life expectancy on the transmission components.

Here is some more I found on the topic:

http://www.sbmar.com/articles/aligning-u-joints-on-a-remote-v-drive/
 
baylabayla3288 said:
the solidly mounted transmissions have to be moved to align with the propshafts.
Click to expand...
Mmm... This is more surprising, because I can't think of any reason why the v-drive & prop shaft alignment could change over time.
In other words, this suggests that the alignment was slightly wrong from the beginning, i.e. the factory installation.
Not that this can't happen, but it's a bit surprising for a builder like Ferretti, anyhow.
Did you try getting in touch with their customer service and check what they have to say?
And in which year was the boat built, out of curiosity?
 
MapisM said:
Mmm... This is more surprising, because I can't think of any reason why the v-drive & prop shaft alignment could change over time.
In other words, this suggests that the alignment was slightly wrong from the beginning, i.e. the factory installation.
Not that this can't happen, but it's a bit surprising for a builder like Ferretti, anyhow.
Did you try getting in touch with their customer service and check what they have to say?
And in which year was the boat built, out of curiosity?
Click to expand...

I'm a bit surpriced too also by the fact that we have exactly the same misalignment on both prop shafts. Maybe there was a problem with the jig they used during manufacturing. I'm the second owner of the boat and it was built in 2001. Nothing points in the direction that there would have been a grounding of any sort, all looks original. Unfortunately my experience with Ferretti customer service is that they are not very helpful with boats of this age anymore. I will send them an inquiry though.
 
baylabayla3288 said:
Unfortunately my experience with Ferretti customer service is that they are not very helpful with boats of this age anymore.
Click to expand...

Tell me about it. They dont want to know in my experience

I can't add anything to this thread but I'm interested to read it because I have a similar V drive set up on my Ferretti
 
Bouba said:
Can you replace all the couplings with flexible ones, then alignment is not so critical
Click to expand...

Hi and tx for the comment.

I thought about that at some point as well but now it seems that it will be relatively easy to move the engines and transmissions into position to eliminate the angular problems all together. Also all components including the shafts, u-joints and couplings are in good condition so no need to replace anything. Flexible couplings would nevertheless be a good solution but for this kind of remote v drive configuration new resonance calculations would be needed to ensure that the whole thing does not selfdestruct.

To be fair towards Ferretti the engine - transmission alignment is mentioned in the manual as standard maintenance however the propshaft - fixed mounted transmssion should not need any adjustment after initial installation if done right.
 
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Just to let you know Alexandra is in the back in the water and the first 40 nm are behind. The good news is that she is running very smooth now. The low frequency vibes that could be felt on the flybridge when accelerating is gone, this was probably due to the propshaft gear box missalignment. Also the boat is clearly smoother across the whole rev range which is probably achieved with all cardan angles being in spec now. Only the resonance sound from the left transmission at 800 - 900 rpms can still be heard albeit clearly muted. I beleive that this is more related to the characteristics of the remote v drives. This noise can only be heard inside the boat and with the transmission at operating temperature and in forward gear. As this is the port side transmission there is one more set of gears involved producing the left hand rotation, this could cause the different behaviour between port and starboard I think.

Would be interesting to know if any of you out there who have the same remote V setup have experience any resonance noises at these lower rpms
 
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