SigmaDrive experience

[Delfin]

Curious if anyone has installed one of these. It's a CV shaft coupler that will tolerate up to 3 degrees of misalignment. Not cheap for my boat, but aligning a 2500# engine is very, very time consuming.

So any experiences would be welcomed.

https://kingpropulsion.com/sigmadrive/

[a64pilot]

It works great, does everything it’s supposed to, you will notice a smoother driveline.
I’ve had mine since they came out I believe.
Engine alignment is transitory, you get it absolutely dead nuts perfect, then the mounts allow the engine to move and or your hull may flex slightly etc.
Try this measure or mark you engines exact position from one side of the enclosure, then get under way. That measurement will change, what causes it is the engine torques or the side of course because it’s spinning a driveshaft under load and the mounts allow movement.

With a Sigma drive you motor will move even more, because the shaft isn’t being bent trying to stop it.

I believe it may even be logical to run softer than normal mounts with a Sigma drive, which should absorb even more vibration.

What makes a Sigma drive unique is that it can accept thrust so no other bearings are required.
I believe it’s actually nothing more than a Rzeppa joint, which has been around for a long time, the front axle of Military trucks have Rzeppa joints

[a64pilot]

Only thing I’d caution you on is the bolts that actually clamp the Sigma drive to the driveshaft are grade 8 or equalivent, so they need to have a good rust preventative put on them to keep them from rusting

[Delfin]

Great feedback A64, thank you. They want over $5k for one that fits Delfin, but if it works could be justified a lot of ways.

[a64pilot]

Nothing from them is cheap, if you get it, it will look look like jewelry, which for that kind of money it should.

I got it trying to resolve a prop vibration, that I’m now pretty certain isn’t resolvable, however my driveline is now smooth as glass when I’m not operating in my vibe area.

I’m now certain my vibration is the result of turbulent induced flow due to my wide keels deadwood.
I can tie to a dock and it’s smooth as glass at all RPM’s but underway above 2000 I begin to get a vibe.

The Sigma drive should eliminate shaft alignment as an issue though, and seeing as how it’s run essentially with no angle it should last pretty much forever.

This is a Rzeppa joint, which I’m almost certain is what a Sigma drive is
https://images.app.goo.gl/vyH1qf8bTsxBwo228

[Delfin]

Yeah, I'm not sure it will fix the little vibration I get, but eliminating alignment issues seems like a blessing regardless.

[Chenega]

Originally Posted by Delfin

Curious if anyone has installed one of these. It's a CV shaft coupler that will tolerate up to 3 degrees of misalignment. Not cheap for my boat, but aligning a 2500# engine is very, very time consuming.

So any experiences would be welcomed.

https://kingpropulsion.com/sigmadrive/

I installed one on my last boat (Morris Leigh 30) and it solved a lot of vibration issues. I first replaced mounts, did alignment, then installed SigmaDrive. Pricey but it did the job...

[Bill O]

Interested in this thread with hopes to reduce some vibration we have in our drive configuration. Not sure it will fix it as I believe it is coming from the Maxprop blade on the deadwood. We have the proper tip clearance in the aperture and all the blades are in good shape. This issue started after we switched from a 3 blade fixed prop.
A64, I find it interesting the SD didn't fix your vibration issue completely. Was wondering if you have a Maxprop or some other flat bladed feather prop? It seems some of these issues maybe inherent w/these types of props.


Bill O.

[Islander53]

Sigma drive is well worth the money. I thought my engine was smooth before installing, I noticed a huge difference in noise and vibration reduction. Everything this company makes is really well engineered, like the autoprop! And their automatic shaft brake.


As noted above you need to protect it with t-9 or corrosion block. Not sure why they couldn't have used more corrosion resistant materials.

I did have one scare with the sigma drive, I had fouled my prop up with a crab pot and it spun the shaft free from the sigma drive and my prop shaft almost fell out of the boat. The sigma drive only uses a collet and compression to hold the shaft . No key
Since then I have added a hose clamp on the shaft so it cannot pass the packing gland.

[Delfin]

Originally Posted by Chenega

I installed one on my last boat (Morris Leigh 30) and it solved a lot of vibration issues. I first replaced mounts, did alignment, then installed SigmaDrive. Pricey but it did the job...

Those are lovely boats. Much obliged the the input.

[a64pilot]

Originally Posted by Bill O

Interested in this thread with hopes to reduce some vibration we have in our drive configuration. Not sure it will fix it as I believe it is coming from the Maxprop blade on the deadwood. We have the proper tip clearance in the aperture and all the blades are in good shape. This issue started after we switched from a 3 blade fixed prop.
A64, I find it interesting the SD didn't fix your vibration issue completely. Was wondering if you have a Maxprop or some other flat bladed feather prop? It seems some of these issues maybe inherent w/these types of props.


Bill O.

It’s an Autoprop and it works by centripetal force decreasing pitch and induced water flow increasing it.
So I theorize that when I approach 7kts that the prop is trying to increase pitch when not behind the keel, and decreasing it when it is, and this is causing my vibration. This constant pitch change, or attempted pitch change.
It may also be there with a fixed prop as the drag and thrust would change greatly when behind the keel, I’ve just not tried a proper fixed prop.
My boat came with a prop that was hugely over-propped, the engine of memory serves would only turn about 2600 RPM, and it is the prop pitch and diameter recommended by IP, so either that prop was reworked by a prop shop or this vibration is a function of my hull design.

What kills that theory is I’ve not heard of anyone else complaining about it?

Anyway my vibration is in my opinion definitely propeller based, and does not occur unless we are underway, as I said it’s glass smooth at any RPM if tied to a dock.

[Delfin]

Originally Posted by Islander53

Sigma drive is well worth the money. I thought my engine was smooth before installing, I noticed a huge difference in noise and vibration reduction. Everything this company makes is really well engineered, like the autoprop! And their automatic shaft brake.


As noted above you need to protect it with t-9 or corrosion block. Not sure why they couldn't have used more corrosion resistant materials.

I did have one scare with the sigma drive, I had fouled my prop up with a crab pot and it spun the shaft free from the sigma drive and my prop shaft almost fell out of the boat. The sigma drive only uses a collet and compression to hold the shaft . No key
Since then I have added a hose clamp on the shaft so it cannot pass the packing gland.

The lack of a key is one concern. My engine develops a lot of torque and while the prop is well protected behind the keel, I'm not sure I want to deal with that scenario mid ocean. I wonder why they done accommodate a keyway?

[a64pilot]

Originally Posted by Delfin

The lack of a key is one concern. My engine develops a lot of torque and while the prop is well protected behind the keel, I'm not sure I want to deal with that scenario mid ocean. I wonder why they done accommodate a keyway?

It’s a tapered fit, a lot like a lathe has, the lack of a key way is an advantage as if you get into a scenario that something has to give, it may slip, I say may as it may not too.
But one nice thing about the way it fits up is you can vary the seating depth of the shaft, meaning you can tuck the prop right up to where it’s supposed to be.
Those bolts I spoke of that are grade 8, they clamp the shaft by sliding the collar into an angle, the deeper it slips in, the tighter it grips the shaft.

[Delfin]

Originally Posted by a64pilot

It’s a tapered fit, a lot like a lathe has, the lack of a key way is an advantage as if you get into a scenario that something has to give, it may slip, I say may as it may not too.
But one nice thing about the way it fits up is you can vary the seating depth of the shaft, meaning you can tuck the prop right up to where it’s supposed to be.
Those bolts I spoke of that are grade 8, they clamp the shaft by sliding the collar into an angle, the deeper it slips in, the tighter it grips the shaft.

They want to know the taper of the shaft. How do you measure that with the needed precision?