Spherical thrust couplers for sailboats

SigmaDrive spherical shaft couplings are an easy way to reduce engine noise and vibration on a sailboat. With a SigmaDrive installed the onboard comfort is instantly improved and also the engine / transmission system protected. To show how this is achieved you can download a free report we wrote here SigmaDrive eBook.

This little report describes how noise and vibration can be caused by engine misalignments and how it transmits up through the boat into all the structures and shakes everything to bits purely because of the coupling system. It explains about the engine alignment, and those four rusty things under the engine which most people don’t realize actually push the boat along. Yeah, the engine mounts are a pretty important part of the boat.

We talk about that and then introduce SigmaDrive, which is our product that is a flexible shaft coupling system that you can install on the boat very easily that softens the shaft line, reduces the noise and vibration, and makes life onboard so much easier. It’s a simple thing to fit. It doesn’t require a mechanic. It doesn’t require critical alignments. It’ll protect your transmission, save you money, and it’ll make everything quieter.

But anyway, I just wanted to talk in this video, to talk a little bit more SigmaDrive, introduce who I am. Does that sound good? Okay. Let’s carry on then. So SigmaDrive. I like to think of SigmaDrive, it’s a spherical thrust coupler. Most of the other coupling systems, well, pretty much all of them on the market that move or have some movement system in them, are constant velocity type couplers. So they’re the joints that you’d see under trucks where they have the drive shaft comes down and bends. It adds some motion into the drive system to add some flexibility.

The problem with them… it’s not a problem, it’s just their limits, is that they can’t take a thrust load. So when you come to a marine environment, as we just said, the engine mounts… Propellor makes a thrust, the thrust goes up the prop shaft, comes in through the coupler to the transmission from the engine. So the engine is working hard.

Those four rusty things under the bottom of the engine are what actually drives the boat, and most people don’t realize that. They’re really, really important. And if you just replace one or don’t manage them or look after them, it can have serious impact on your alignment. The alignment will then affect your onboard comfort and it can affect the seals. It can affect so many things on the boat. So it’s really nice to pay attention to all this and understanding, which is what the ebook goes into, the sensitivity of the system.

So this is not a constant velocity joint. We call this, I would say it’s more like a ball joint can take a thrust load. Because inside here there’s a sphere, and the sphere itself is what takes the thrust load. So the thrust will come up the shaft and it will absorb through the coupling and you don’t need a thrust bulkhead now. The other systems like Aquadrive, you have to have a thrust bulkhead to take the thrust load, and then you can’t transmit the thrust because they use a rubber system. They’re rubber bearing squishes if you take a thrust load, so you have to have a thrust bearing system in. There’ll come a bit more of that later.

So the SigmaDrive, and I’ll just show you an animation on the screen now. So you can see that there’s a central sphere that’s taking… That takes the thrust load, and then on the quadrants you can see, and that’s actually ball bearings and those ball bearings are what takes the torque load. So the coupling in itself, it is like say, a ball joint or an elbow joint or something, that can take thrust untorqued. So it makes it very, very unique.

So that’s how SigmaDrive works. It’s very, very straightforward, very, very simple. There’s a lot of complicated things, very simply, but we won’t go into that just yet. There’s more in the report if you want to read it. So fitting one of these things, how does it work? Okay. So this is a system here we use at the boat shop and you can see the system because there’s like a ball joint. It can move, it’s actually three degrees either side. So it gives three degrees. If you imagine it spins round one rotation. It gives you six degrees full sweep, then it can be moved.

And if the engine’s out by three degrees, the shaft is physically bent. You can see it. And we’re talking on normal engine alignment thousands of an inch, critical alignment. So if this thing’s on, you can bounce around on on a sea wave, and it will not have any problems whatsoever. It’ll soften the loads and protect this little thing here.

So fitting it couldn’t be simpler. The unit, we’ve standardized it, so you can see on the back there’s different holes for different… Kanzaki, for Yanmar. And then we have different pilots depending on what transmission… A pilot, for those that don’t know, just seats the coupling on the output fans of the transmission so it’s centralized. It doesn’t take a load. It’s just an alignment tool that actually stays there.

Stud systems, four studs, slides on. And then the other side, this is empty at the minute. We come with a unique system. This is called a taper lock collar. The taper lock in engineering is a very, very efficient method of connecting something. And it uses a taper to squeeze a slot together. You can see that on camera. This is used on cruise ships, container ships, military vessels, but they would use a hydraulic system to do the same job. But the main point is it’s a keyless system. And you would say, “No, you need a key to drive it.” You don’t. The key puts a point load on the coupling. This one has a 360 degree grip. And it’s not designed to fail. It’s not supposed to be a drive saver or anything like that. This thing will grip like you have no idea. It’s awesome.

Anyway, you can see on camera there, there’s two different diameters on this one. We do these in a range of diameters, so we can specify the shaft from seven-eighth’s up to an inch and a half for this smaller coupling, SD55. Basically we would size this up for you, and then this would sit in here and then the propeller shaft would obviously go into here. As you can see on this one, it would then tighten up the bolts and then it would grip the shaft. And that’s pretty much the installation. The hardest part of the install is actually getting this to go over the propeller shaft. Obviously this is oversized.

But this is supposed to be an interference fit, so it’s a very, very tight fit, and it’s really hard to get on sometimes. Once it’s in, before you tighten everything up, the unit comes with these little wafers, and these are supposed to, once it’s going, there’s four of them and you can lock it off. Oops. There you go. You kind of get the idea. You can lock it off so that the ball joint is true.

Then once you’ve done that, when you align it, you can back off the bolts at the back, pull the sigma dial off, and you put feeler gauges in so you can align it. Although it is very flexible, we’ve designed a way to align it, even if you wanted to. The nice thing about it is, like I said, you don’t have to rely on critical alignment anymore. You can eyeball it with a rule or a piece of tape, or however you want to do it, and the SigmaDrive will be fine.

The shelf life on these things, or the working life we should say, for small vessels, these go to about 75 horsepower. So you’re looking at about 35, 40 foot, 45 foot boats. These you’re looking about 12 to 15 years. It is a wearing part. So they will have different lifespans depending on how hard you load them and how much you work them, and obviously how much of an offset you put on them.

But in general, they’re designed to be very, very low maintenance. They’re pre-filled with grease. And pretty much every time you do a major haul up, once every five years or something, you can take them apart and regrease them. But it’s a sealed system. It’s not designed to be maintained, kind of like the sealed batteries or something. And they work great. They’ve been around for 10, 15 years, got tremendous reputation in Europe. And they’ve been in the US about three or four years. And obviously we’re the distributor for them, so we’ve got some good stories and some really, really solid people that are just in awe of these things and how they quieten everything down and how they just make life onboard so much better.

So that’s how it comes. And you can see, we have different sizes. The majority of sailboats are going to be… So this is a four inch flange, and this is a five inch flange. This is the next size up. So this is SD55, and this is SD100. The ratings, 55 stands for… It’s a metric system, apologies. 55 Newton metre thrust, and 100 Newton metres of… Sorry, torque. 55 Newton metres of torque. 100 Newton metres of torque. So it’s relating to the performance of the system. This one is seven-eighths up to inch and a half, and I think this one’s inch and a half or inch and a quarter up to two inches, I believe. Well, don’t quote me on that.

Now then, if… And once you get to the crossover point, kind of like a 50-foot boat, depending on the engine, you may have, the boat is within the torque range of the units, but the diameter is wrong. So we have a series of adaptive flanges. And we can send you drawings, and it’s actually in the report, where you can actually modify the four inch flange to fit on the five inch coupling. And the nice thing is because they’re completely hollow, you don’t need to turn shaft.

And this is the other interesting thing about them. Normally, with a coupling, you’d trim the shaft to fit it. Like an Aquadrive, it’s got to be short to fit the thrust bulkhead. Then you’ve got to have an intermediate. None of that. You don’t need the key wear. You can have a shaft made and just leave it rough, just sham for the edges. As long as you can slide it into the coupling, everything else is completely hollow, which just makes installation a dream. You can install it in the water.

If you have a PSS, it gets a bit lively. If you have a shaft lug, it’s a piece of cake. You back off the shaft, tighten it up, and then it’ll steer. But if you have a PSS, you’ve got to break the seal and you’ve got to keep it managed. I mean, I would say 30% of the people that buy SigmaDrive have a PSS system. And a lot of them do it in the water. It’s not uncommon sort of thing. And it works a great little system.

But there was another… There we go. And then we have another system, a different type of adaptive flange. So if you have a V-drive system, typically the V-drive the output flanges of the transmission, the bolts are threaded. So this one here, you would drop bolts on this side, and then you would clamp it to here. And then the bolts become captive. And then you can screw the bolts in with an open-faced spanner into the output flange, the transmission.

So for the same SigmaDrive, here’s just two adaptive flanges. We have various different cog configurations. We can go small for seven-eighths shaft diameters and have three bolts. And we can do custom stuff as well. It’s a little bit… There’ll be an increase in the price, but it’s totally doable.

But anyway, in review, that’s SigmaDrive. It’s awesome. You should buy one. But anyway, to get one, I need a few things from you. Read the report. It’s very, very useful, and it’s a great source of information. To fit a SigmaDrive, we pretty much need to know the engine, make and model, the transmission, and this is really important, the transmission make and model. Now these are always rusty. And this one here is no exception. The plate’s gone off the top because we need to know the output flange, and the output flange is critical because it can make the difference of an adaptive flange or just a straight fit, depending on what it is.

So once we have the transmission, we can then size the diameter, and then we need to the shaft diameter. And once we have all these things, we can size the SigmaDrive. Everything’s pretty much manufactured. It’s CNC, manufactured in massive batches. So it’s on the shelf. All we have to do as much up the taper lock collar to the right SigmaDrive to the right pilot. We stick it all together in a box. It comes with the grease. It comes with all the lubricants, Loctite, everything you need just to put it on. And you can spend, I would say about an hour, and you should have a new coupling system on that will soften the shaft line, kill your noise and vibration, and make having drinks on deck a pleasurable experience again.

Anyway, my name is Dr. Roderick Sampson. Thank you very much for watching. I hope you download the ebook. Have a run through it. And then if you’d like to put some details in for a quote, we’d love to hear from you. Thanks very much.

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