Chris Z expertly builds up the repair area
We are all very proud of the announcement today that Straight Line Marine (a division of High Seas Yacht Service) is now certified for American Bureau of Shipping (ABS) Cladding on Stainless steel shafts. Straight Line is the only machine shop in the State of Florida to be awarded this certification which is a testament to the skill of our master Machinist Chris Zylka.
Shaft cladding repair (otherwise known as a weld-over) is a machine shop process for repairing shafts with layers of welding. The process is explained in more detail in this technical article. When a shaft is worn or pitted with crevice corrosion the surface becomes hostile to shaft lip seals or cutlass bearings. The lip seal will leak continuously while a cutlass bearing will wear out prematurely.
Crevise Corrosion on Shafts will Destroy a Lip Seal System
Crevice Corrosion is a chemical phenomena that occurs in warm, stagnant salt water. The chemical properties change with time and corrosively attack the stainless steel. This problem is outlined in more detail in this white paper that explains the chemical reaction and possible preventative measures that a Captain can take.
Prior to Straight Line Marine becoming certified an ABS Class vessel that needed shaft cladding would need to ship the shafts outside Florida. Straight Line Marine will pick-up and deliver shafts in the South Florida area. This will save yachts a tremendous amount of time and money.
Congratulations to Chris Zylka for all of his hard work and accomplishments.
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Straight Line Marine is a machine shop dedicated to running gear and the art of repairing bent shafts and struts. When looking at bent shafts we often get the question – is it too bent to fix? The answer is simple – if it is not cracked then it can be straightened. A cracked shaft is not repairable (focusing here on stainless steel marine shafts) and must be replaced. A bent shaft can be repaired. We use a cold, hydraulic press process that does not alter the metallurgy of the shaft. It takes a lot of practice and time to straighten a shaft. Some shafts have metal memory and need to be checked hours or a day later. If the shaft is bent badly enough (over 1/2″) we will run a red dye crack test when the straightening is complete. Unlike this experience straightening bronze struts, we have not had a shaft crack during the straightening process.
It is hard to imagine a 4″ shaft bending almost 1.5″ at the prop taper and even more difficult to see in a picture. So here is a quick video showing one of our extreme projects. This shaft was out of a 112′ Westport that ran hard aground.
The bent shaft was not the only damage – the V-Strut legs were “waffled” as it was pushed straight up towards the vessel’s bottom. Straightening both legs took quite a bit of enginuity with a series of hydraulic presses. We did save the strut and reinstalled it with an optical scope alignment.
Bent strut from a 112' Westport
A poorly machined coupler taper on a shaft will definitely lead to vibration problems.
We are working through a few issues with a customer that has had persistent vibration problems on his 80′ vessel. Once the shafts were out and in the machine shop we noticed an obvious problem with one of the coupler tapers. As the shaft was rotating in the shaft straightener, you could see that the fine line where the taper blends into the shaft had a visual wobble. This is a sign of a taper that was cut off-center. A few measurements confirmed that the center hole used to hold the shaft centered in the lathe for machining was off 0.020″.
That means the pilot on the coupler was running out 0.020″ (which was confirmed by putting the coupler back on the shaft) causing the shaft to run-out the same. In our business 0.020″ is a huge number that is definitely one source of running gear vibration.
The remedy was relatively simple – put the shaft in the lathe and recut the taper. We had to use the steady rest in the lathe since the center hole was useless. By recutting the taper the coupler will fit a bit further down the shaft which, in effect, shortens the shaft length. Fortunately we had a little length to play with so the only other change involved moving the Spurs line cutter holding block. I will put up a post on this topic later.
Once the taper was recut the coupler was lapped on (the same way the prop was lapped in my prior post) for a perfect fit. The coupler had to be refaced but amazingly the pilot ran-out 0.001″ without any additional machining. The coupler was manufactured true.
A short video will help understand visually what we saw. Please excuse our amateur video editing – this is work in process.
Stay tuned for more info on this job and a final sea-trial report.
When shafts are in the machine shop for checking, straightening or repairing you should have the props and couplers lapped onto the shaft. Lapping the bore of the prop/coupler to the shaft taper ensures a 90-100% fit between the surfaces. If you are installing new propellers or there has been damage, this process becomes even more important. It is not uncommon to find a prop or coupler bore that is only touching in certain high points on the taper. A poor fit can cause the prop to be slightly off balance on the shaft. A poor fit with low contact is also more likely to become a loose prop at some point in time.
Lapping is the process of using a gritty paste between the two surfaces to allow them to grind together for a perfect fit. We prefer to lap while the shaft is in the lathe in order to take advantage of the shaft spinning and the overhead hoist to hold the heavy props and couplers. The process can also be done by hand while the shaft is still in the boat – but that is hard work and is less effective.
A video is worth a thousand words – here are two difference angles showing a lapping in progress.
Please give us a call when you are in need of running gear or shaft repair. Don’t waste money by having a machine shop only complete part of the job. Ask for everything to be lap fit.
Tiara 52 Runs Smooth
Another 50′ Tiara came to us with a vibration problem that was diagnosed as shaft whip. This particular model has too much distance between the strut bearing and the v-drive engine. This is exactly the same problem encountered and posted on another Tiara last year.
The solution is fairly simple – add another cutlass bearing to the stern tube. However, this can only be done if the latest alignment technology is used. Not all struts are aligned perfectly to the stern tube. You can get away with less-than-perfect strut alignments if there is no bearing in the tube and the engine is aligned properly. This is seen all the time when a shaft is not going through the center of the stern tube.
With the addition of a cutlass bearing, the alignment is critical. On this project we did find one of the struts to be out of alignment to the stern tube. Therefore the strut had to come down and be realigned properly. While the Optical Scope system was set up, both v-drive engines got a precision alignment.
Tiara with a Strut Removed
V-drive alignments can be very complex. With the output coupling under the engine, the adjustment to the engine mounts can be intuitively opposite. It is very easy to get confused and move further out of alignment. Fortunately the Optical Scope simplifies the process and gives absolute confirmation when the engine is aligned properly.
Of course, the project was not complete until the customary sea-trial. All was smooth and the customer was very happy.
The vessel is now for sale and the listing broker is promoting the difference between a High Seas “fixed” Tiara and others still on the market.
If you have a shaking Tiara please give us a call for a free inspection and quote.
PSS Seal Refreshed and Ready to go
PSS Seals are found on many of the pleasure yachts. The PSS Seal system is a “face” seal that relies on the pressure between a carbon face stationary to the stern tube and a stainless steel face on the ring installed on the shaft.
Maintenance on these seals is pretty straightforward. If the shaft is out we will usually reface the stainless steel ring in our machine shop. A smooth, flat face, free of debris, is required for a solid seal. The carbon face is inspected for chips or cracks. If cracked they must be replaced. Finally, we inspect the bellow hose for cracks or other signs of wear. The bellow hose acts as a compression spring to keep the carbon against the stainless steel. If the bellow hose is aging, it will lose the spring effect and not apply enough tension. This is sometimes noticed if the seal leaks when throttling up the engines. Depending on the engine mounts, the engine will shift forward under prop load which eases the pressure between the stainless steel and the carbon. If the bellows is not compensating then leaking will occur. PSS recommends replacing the bellow hose every seven years.
Finally, during installation the stainless steel ring is compressed a distance, per the PSS manual (it varies with shaft diameter). Notice in the picture the sharpie mark on the shaft showing the position of the ring in the neutral state prior to compressing the bellows.
PSS Seal are very effective and easy to maintain. Give us a call if you have any questions or concerns with your shaft seal system.
Prop, Shaft and Rudders on a 61' Marlow
The new owner and new Captain on a beautiful 61′ Marlow came into the yard. The vessel had a major vibration that was most noticeable when driving from the lower wing station.
After removing props we went through our standard running gear inspection process – checking shaft run-outs, bearing clearance, seals and engine mounts. The running gear all checked out within spec so no need to pull shafts and create a big bill.
The rudders were extremely loose with up to 0.125″ of play and slop in the tiller arm pins. This was clearly a source of vibration with the prop wash rattling the rudders around.
Marlow’s were built using cutlass bearings as lower rudder bearings. We believe that allows too much play and premature wear. The lowers and uppers were replaced with Tides Marine UHMW bearings. The machine shop re-bushed the tiller arms and made new pins for the tie-bar. New Tides Lip seals and back together – all nice and tight. We only traveled a hundred yards in the New River before the Captain declared the problem solved. A month later he sent us the following update:
“Hi Chris, Thought you should know that the boat is running better then the day we bought her, thank you. Less noise etc. And we can actually run over 1400rpm with out breaking plates. ”
Next time you have a vibration, try to listen closely to your rudders. Don’t assume it is a shaft or alignment problem. And make sure you use a contractor that will take the time to inspect before tearing apart. We saved this owner a tremendous amount of money by recommending a “pass” on a full shaft job.
- Centa Coupling Disassembled Exposing Roller Elements
Tis the Season for working on torsional couplings. This particular unit came out of a 75′ Sunseeker with a ZF V-drive and Cardan shaft configuration. Similar to the last post on Vulkan Couplers, this unit is attached to the flywheel and designed to take the various torsional loads that are transferred between the drive-line and engine.
Creative PhotoShop work on a Classic Rybovich
You may have already seen this picture in circulation and we need to clear the air. This was a little humor along with some creative work on Photoshop.
This 1974 Classic 75′ Rybovich Motoryacht (one-of-a-kind) is meticulously maintained by her owner and is very “original”. During a recent haul-out for repower and transmission work we re-aligned the struts and will finish the engine alignment when everything is done in the engine room.
Thanks for all the “kind” words of encouragement from those that thought we suggested destroying a Classic. Also, I do not plan on engaging in a debate on the merits of Mercury vs. Yamaha in this application.
Vulkan Couplers have an Out-put Bearing in the Housing
Vulkan coupler are one of the most common found on mega-yacht sized vessels. This torsional coupling is found between the gear box and the engine and serves to dampen the torsional loads coming from the engine flywheel. A polyurethane element (see second photo) acts as a gear “bumper”. This particular Vulkan model was removed from a 87′ Ferretti with a ZF v-drive gear box and a Spicer cardan shaft.
The call first came in when a distinct thump was heard from that engine. The diesel mechanics checked out their end and determined it was int he drive train. That is when we get the call.
It was apparent that something was wrong when you could stand over the engine side of the cardan shaft and lift the assembly slightly – a worn bearing. With this version of a Vulkan there is a large bearing that is part of the bell housing assembly. This supports the weight of the u-joints on the cardan.
Vulkan Coupler Torsional dampening element
The Cardan and Vulkan have considerable weight and were, of course, in some tight places. You could say this job took more brawn than brains.
The job does require the right tools and training. The flanged coupler in the first photo must be removed from the shaft in order to replace the assembly on the housing. The coupler is hydraulically fit on the shaft. To remove and replace requires a high pressure pump and the right fittings. Any other removal process (force, heat) will definitely damage the assembly beyond repair.
Vulkan Couplings – another High Seas Yacht Service specialty.
