CLUTCH PLATE/DRIVE PLATE/DRIVE DAMPER
Whichever name you want to know it by, this out-of-sight, little known, sometimes misunderstood, integral part of the drivetrain on our boats can ruin your day and cruise if not maintained. For purposes of this article, we will settle on the name Drive Damper, since it best describes its function and location.
WHERE IS THE DRIVE DAMPER?
Located in the bellhousing between the engine and transmission, the medium pizza-pan sized drive damper is usually bolted to the flywheel of the engine and spline connected to the transmission. Its purpose is to absorb or dampen the torsional impact and noise of the power stroke from the engine. Without the drive damper, the continual pounding of the engine’s explosive power strokes could cause transmission chattering and possible damage to the transmission.
WHAT IS IT AND HOW DOES IT WORK?
Composed of two separate discs that are connected by flexible springs, or Teflon or polyurethane pucks, the flexible connection between the two discs cushions the engine’s torque impact. Both diesel and gasoline engines need drive damper plates to protect the transmission and eliminate gear chatter, especially at low RPM. Drive damper plates come in a number of varying sizes and torsional rigidity. The correct drive damper is sized to the horsepower and torque of the engine. Some plates use laterally mounted springs for shock absorbing, others use several puck-shaped flexible donuts between the two discs.
THEY DON’T LAST FOREVER!
Because of their location between the engine and transmission, it is impractical to inspect drive damper plates. Inspecting them requires nearly as much time and effort as replacing them. It is sometimes possible to visually check them with a borescope or through vent holes in the bell housing; however, this cursory view may not reveal their entire condition. The normal service life of a drive damper plate is 2,500 to 3,500 hours. Usually the shock absorbing connection between the two plates is the point of failure.
WHAT HAPPENS WHEN THEY FAIL?
At best, when a drive damper plate fails, it effectively acts as if the transmission is in neutral; with no forward or reverse capability. At worst, broken metal pieces of the plate scrape, score, and damage other bell housing or drive train parts. No matter what, you won’t be going anywhere with that engine and transmission.
WHAT IS INVOLVED IN REPLACING THEM?
The drive damper plate part varies in price from 250 Euros to 850 Euros . However, the process for replacing it is quite involved and labor adds to the cost. The transmission needs to be removed from the engine. To provide the needed space, the prop shaft must be pulled back, which is usually done when hauled out. Occasionally, removing the shaft coupling from the transmission provides enough space to remove the transmission. In many instances, the aft end of the engine must be supported before the transmission is removed.
Unless you are supplying your own labor for the job, the cost of the part becomes a very small part of the cost for this repair and replacement project. However, given the undesirable consequences of a failure while cruising, it is a small price to pay to replace these parts before their service life expires.
Pros and Cons and
Why you need to stay on top of maintenance
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GETTING TO KNOW YOUR S-DRIVE UNIT:
First things first is to make clear that Sail Drive isn't exactly the accurate term.
The right term is S drive as from the shape of the input - output drive shaft( propeller shaft) through the reverse gear box ,That's giving you from the engine into gearbox then down through the leg and then finally out to the propeller shaft , an S shape outline of the direction of input and output rotational force.
If you're in the market for a new or recently built sailboat, odds are good that it is equipped with a saildrive system vs. a conventional shaft drive set-up.
Basically a sail drive set-up is much like an outboard engine’s mid and lower section projecting through the boat’s hull. It’s a bit different in the sense that unlike an outboard engine or inboard/outboard (IO) set-up, the engine exhaust is not exiting the boat via the drive leg, but rather through the hull just like with a conventional drive system. However, raw-water intake for engine cooling is drawn up through the saildrive leg, just as with an outboard.
The flexibility of the saildrive configuration on a new hull design is compelling. The fact that the engine and drive system form essentially a single unit eases installation, and by design can keep weight “out of the ends,” which is always desirable with sailboats.
With the saildrive, the weight of a shaft, stuffing box, and propeller are moved forward, almost under the engine. Further, the propeller’s angle of attack is more parallel to the surface of the water, which will enhance efficiency and help to minimize traditional prop-walk characteristics common to conventional drive configurations. There's also a wide variety of folding or feathering propellers available for saildrives -- also desirable for the sailing crowd aboard modern designs with relatively flat underwater surfaces aft of the keel that can accommodate saildrive systems. (One of many examples is the the Hanse 545.)
One thing is clear: boatbuilders are embracing saildrives in a big way. Of the saildrive makers, and there only five that I’m aware of as of this writing, two are preeminent, at least here in Europe: YANMAR and VOLVO PENTA . Beta Marine, Lombardini and Nanni offer saildrives, but their market share is so small that there is not much known about them from a global perspective. When we compare the two majors, things shake out a lot like it does with cars: Some people love Land Rovers, some like Fords.
But for many sailors, questions regarding saildrives abound. Are they a better choice over conventional drive systems? What about the rampant tales of excessive corrosion? How about a rubber boot in the bottom of the boat to keep the water out? What are the advantages and disadvantages of using a saildrive system? Can you easily retrofit a saildrive to your older boat as part of a repower? Let’s work through answering these questions.
LOWER INITIAL COST, QUIETER
Boat builders can certainly save money on installation by using a saildrive system. With no shaft or strut required, engine installation is as simple as dropping a drive leg through a hole in the bottom of the boat and sealing it up with a rubber bladder.
My experience during on-the-water test comparisons has shown that saildrives run significantly quieter and with less vibration than conventional shaft systems. Less noise and vibration are things that make life on board a much more pleasant experience when motoring. Engine and shaft alignment procedures are no longer a part of the maintenance regimen, also a plus. But what about some of the other maintenance concerns?
THREE MAJOR MAINTENANCE AREAS OF CONCERN
There are really three major issues that a boat owner needs to think about when it comes to saildrives: the integrity of the watertight seal around the drive leg, ensuring that the seals that keep the oil in and the water out of the gear mechanisms are doing their job, and combating corrosion.
KEEPING THE WATER OUT
The matter of the gaiter, or boot, that seals the perimeter of the drive leg to the boat’s hull is one that, if neglected, could cause a boat to sink. In fairness, both Yanmar and Volvo drives employ a double seal with a water alarm system that will notify the boat owner if the outer seal begins leaking. Recommended replacement intervals for this rubber seal range from five to seven years between Yanmar and Volvo Penta, and both manufacturers consider this service a dealer-only procedure. Many boat owners have gone much longer than this before replacing the seals, but one has to wonder if an insurance company would pay a claim for a sunken boat if the service interval had been ignored by the boat owner. Certainly, this is a good question to ask an insurance agent before something like this happens. Both Yanmar and Volvo provide an “aqua sensor” that will sense water leakage if this bladder begins to leak, but periodic inspection of this critical rubber seal at least every two years is of the utmost importance. Without question this is one of the most important not-to-be-ignored service items related to the saildrive system. Depending upon how difficult engine access is on a given boat, replacement of the bladder and associated service parts can cost in the neighborhood of 1,000-1,500E.
As for the drive leg seals that keep the seawater out and the gear oil in, periodic checks of the transmission oil level and looking for any discoloration (milky white color) will indicate if problems exist.
It is recommended that the gear oil level be checked before each use, so any problems should show up rather quickly. Unfortunately, repairs needed here are going to require hauling the boat for seal replacement. Again, it is recommended that trained service personnel take on this task. Basically the task of resealing a drive leg is not much different than seal replacement on an outboard engine leg, and should have a repair frequency at any given time able , when out of the water, so to save the costs of going bad during the season and having to take the yacht out of the water adding costs.Every second year changing output shaft seals is always a good practice.
Changing the transmission oil is recommended at 100- to 250-hour intervals depending on the specific drive, and both Yanmar and Volvo provide methods for accomplishing this task without hauling the boat out of the water.
CORROSION CONCERNS AND SOLUTIONS
Corrosion is perhaps the most frequent issue associated with modern saildrive units. There are a few different causes for premature or excessive corrosion on these units, and if certain guidelines are followed, problems can be eliminated.
The number-one thing to remember about these drives is that the anodes on the units are engineered to provide corrosion protection for the drive only! Manufacturers recommend anode replacement every 100 hours, but it is of absolute importance to remember that this recommendation is based on some important assumptions that only the boat owner can maintain control over.
The first step in ensuring that your drive’s anode(s) provide good service is to make sure that any of the factory original paint on the drive leg that gets scraped off gets touched up. Also, you need to be certain that the anode material is appropriate for the water your boat stays in most of the time. The standard zinc anodes won’t do the job in fresh water and may even fail in brackish water. For brackish water use aluminum alloy anodes, and in fresh water magnesium alloy anodes are the best choice. Anodes should be replaced when they are 50-percent depleted.
Volvo electrically isolates their drives from their engines to minimize the chance of any electrolytic, more commonly known as “stray current” corrosion, occurring. Yanmar does not, and so one of the potential issues here occurs whenever your boat is plugged into shore power. Without electrical isolation, any boat plugged into shore power is connected electrically to all of its dock mates via the green grounding wire in their shore power system. This connection creates a galvanic cell and means that your boat’s anodes may actually end up protecting one or more of your dock buddies. This is a sure-fire way to deplete your saildrive’s anodes too quickly. The next bit of metal in the galvanic food chain once your drive anodes are depleted is the drive case itself. A galvanic isolator installed in the shore power system will prevent this from happening.
IMPORTANT : the antifoul paint IF you use for the drive or propeller to be DESIGNED for Sail Drive Alu. Drives.
Antifoul paints have minerals into their chemistry that if not appropriate they add into corrosion .
This is why sometimes you see this pitting effect on antifouled drive units or propellers. Common mistake many do is to use the hull's antifoul paint for the drive units. BIG NO!.
I personally don't recommend antifoul on drives or propellers unless used specially designed certified brand products applied ONLY in spray form or HVLP technique for even layering.
Also, keep in mind that accessory bronze folding or feathering propellers, which are popular especially with racing sailors, can add a rather substantial mass of extra metal to your drive and make for extra hard work for the anode(s) and clutch disks. This very addition will require that anode consumption be monitored carefully until you establish a known service interval with your drive’s anodes.
Also folding or feathering blades need to be regularly cleaned and maintained as can stuck from barnacles or antifoul, making the drive running unbalanced leading to all the bad consequences following that effect.
BOTTOM LINE ON SAILDRIVES
So, which is better, the saildrive or a more conventional set-up with a shaft, stuffing box, and propeller? This is a really tough question to answer. From a user's perspective, better weight placement, improved motoring performance, and reduced noise and vibration make the saildrive the clear winner. From a maintenance perspective, I think the conventional set-up will always win out. Neglecting prescribed maintenance procedures and intervals with saildrives is going to cost you big. The conventional drive configurations are much more forgiving in this regard.
STUFFING BOX BASICS
SEAL THE DEAL BETWEEN THE BILGE AND SEA
Since the year 2000, most new boats have come equipped with shaft seals that require no packing, but inboard powered boats built before then have traditional stuffing boxes with packing.
All stuffing boxes work on the same basic principle: Rings of special wax-impregnated flax packing are wrapped snugly around the prop shaft and stuffed into a hollow packing nut that is screwed to the outside of the stuffing box housing. Tightening this packing nut squeezes and compresses the packing material around the shaft to form a watertight seal, even when the shaft is rotating. And except for a slow drip, the seal is watertight. A lock nut screws around the housing and tightened against the packing nut to keep it from losing as a result of vibration.
Proper maintenance will preclude:
STUFFING BOX BASICS
When a stuffing box starts to leak excessively, you should tighten the packing nut until the leak stops. This may be all that is required, but each time the nut is tightened, it squeezes and compresses the packing further, forcing it tighter around the shaft. As the flax packing compresses and the fax wears away, the chance of shaft damage increases. The packing hardens and can eventually do damage by wearing a slight groove in the shaft making it impossible to for a seal.
REPLACING THE PACKING
Once the flax packing wears down, it’s time to replace it. You’ll need some wax-impregnated fax packing, which comes in rolls or strips and is square in cross section. Its width measures 1/8 to 5/8 of an inch. The size you need depends on the space between the shaft and the inside of the hollow packing nut.
Before you get started, you will need a couple of wrenches to loosen and tighten the nuts. One wrench is a traditional pipe wrench, and the other is a spanner designed for a sink drain. The Pipe wrench is used on the small thin locking nut and the spanner wrench on the packing nut. When loosening the nuts, the two wrenches are moved towards each other. When tightening the nuts, the wrenches are moved away from each other.
Start by loosening the locknut. Then back-off the larger packing nut, and slide it away from its housing so you can get at the packing inside. Dig out all the old packing with a thin screwdriver or a bent piece of stiff wire, but work carefully to avoid scratching the shaft. Make sure you remove all the layers of packing.
If you are having trouble breaking the nuts apart, due to corrosion, use a little penetrating oil. Be very careful not to get near any engine or transmission seals. Penetrating oils will eat engine seals and may cause catastrophic failure for the seal.
Cut a piece of new packing just long enough to wrap around the shaft with no overlap. Stuff this ring of packing carefully into the hollow packing nut, then cut a second piece of packing the same length. Wrap the second length around the shaft, and stuff it in against the first layer, staggering the joints in each layer. Add enough additional layers to fill the packing nut completely, and then screw it onto the threaded sleeve of the stuffing box. Tighten firmly by hand, and then use a large wrench to give it an extra half turn.
CHECK THE PACKING
Start the engine and put it in gear. Let it run for two minutes to see if the box leaks. It should drip a few drops per minute when the shaft is turning, but no drips when in neutral. If it does, give the packing nut another half turn and check again. Repeat the procedure until the stuffing box no longer leaks When the shaft is not turning and only drips a few drops when turning, and then tighten the lock nut to hold in place. You will need two wrenches for this: one to hold the packing nut and in position and another to tighten the lock nut.
All traditional stuffing boxes require water for lubrication. If the box is allowed to drip, it allows for excellent cooling, longer shaft life, less opportunity for crevice corrosion and less opportunity for trapping air and running the box totally dry and cooking it.