Prop shaft, what am I looking at?

[ben2go]

I'm not as up to date on drive systems to turn a prop. The few straight inboards I have worked on the prop shaft is connected directly to the rear of the transmission and it handles the thrust load. All were on ski/wakeboard boats under 26 feet.


Over on the "Interesting Boats" thread, there was posted a homebuilt Glenn L model with a straight inboard. The prop shaft thrust seems to be taken up by a pillow block bearing. (I didn't think pillow block bearings could be used as thrust bearings.) With a truck style slip splined driveshaft turning the prop shaft by way of U-joints. I believe this was done so engine/transmission placement isn't critical to align with the prop shaft. Am I understanding what I am seeing correctly? There's gotta be a better way.



I can see this set up becoming a nightmare on maintenance and cost. I grease the driveline on my truck enough to know that even though I don't have to crawl under the boat to do it, I still don't want to have to deal with pulling floors and spinning the shaft to get the U-joint zerks facing up. I want to believe that the cutlass bearing and stuffing box will hold the prop shaft in place when the driveshaft has to be removed to replace the U-joints, another maintenance task I dislike on my truck. The whole system just seems overly and unnecessarily complicated.

 

[Nomad Willy]

Aqua Drive

Oh .. I take it back.
I’m quite sure the thing that appears to be a pillowblock bearing is just that. Have one in my Willard.

But the black thing fwd just behind the gear is not an Aqua Drive. My best guess is an Evolution Drive.

Looks like the very soft “Cushy Float” Aqua Drive engine mounts. They are good but alow a lot of fore and aft engine movement but w this drive the green thing aft is also (my guess) a thrust bearing. It’s big enough to have two tapered thrust bearings inside of it.
I suspect many boats here (more or less by accident) have a thrust bearing (not designed as such) that just has a ball bearing. My Willard is such a boat. I’m looking down my nose at the engineering aspect of it. Tighten down the set screw and the ball bearing takes the thrust. Set screw loose and the prop shaft and the inner race of the ball bearing become a bearing. But the grease fitting sends grease into the bearing, not to the shaft/inner race interface.
As I said I’m looking down my nose at this practice. Not sure how widespread it is either. May be quite common. How many of you have seen a pedestal bearing used in this way?

 

[Lou_tribal]

Aqua Drive

Oh .. I take it back.
I’m quite sure the thing that appears to be a pillowblock bearing is just that. Have one in my Willard.

But the black thing fwd just behind the gear is not an Aqua Drive. My best guess is an Evolution Drive.

Looks like the very soft “Cushy Float” Aqua Drive engine mounts. They are good but alow a lot of fore and aft engine movement but w this drive the green thing aft is also (my guess) a thrust bearing. It’s big enough to have two tapered thrust bearings inside of it.
I suspect many boats here (more or less by accident) have a thrust bearing (not designed as such) that just has a ball bearing. My Willard is such a boat. I’m looking down my nose at the engineering aspect of it. Tighten down the set screw and the ball bearing takes the thrust. Set screw loose and the prop shaft and the inner race of the ball bearing become a bearing. But the grease fitting sends grease into the bearing, not to the shaft/inner race interface.
As I said I’m looking down my nose at this practice. Not sure how widespread it is either. May be quite common. How many of you have seen a pedestal bearing used in this way?

I have a very similar setup on my boat and it has worked fine for the last 24 years so I guess it is not too bad. The pillow block bearing is just that, followed by a double cardan shaft. Not sure about the last black part,don't have this.
After some research I found out that this setup is mainly use in fishing boat, more than in recreational ones.
As you mentioned it allows for some flexibility in the coupling.
About the greasing part it has never be a problem for me, I grease everything 2 or 3 time a season and the shaft is easy to rotate by hand.

L

 

[Insequent]

There are two critical aspects here. First, marine gearboxes typically have thrust bearings in them. Which is why truck/auto gearboxes are not suitable, unless you have an external thrust bearing. Secondly: shaft support, bearing alignment and engine alignment must be essentially perfect to avoid vibration. Engine mounts need to be high quality also. Such alignment is not always easy to achieve. The u-joint etc options can be an appealing alternative despite potential maintenance chores as they provide some tolerance for engine movement (softer mounts) and hull flexure.

My own boat has 2" shafts that are 12'11.5" long. There are 3 bearings: one at the prop, one on an intermediate external strut and one in the stuffing box. There is a coupling on the end of the shaft hard bolted to the gearbox flange. I'm amazed, and delighted, that the guys in the yard got it all aligned so that there is not a trace of vibration.

 

[ben2go]

Thank you all for helping me understand it all. I knew the thrust loads had to be taken up by something somewhere. I understand the reason for the large automotive style drive shaft and U joints.

 

[Lepke]

In my experience it's better to have 2 U-joints or none. A single only helps in one axis. Alignment needs to be nearly as perfect as with no U-joint.

 

[menzies]

Not an aqua drive. I have them on Sonas, You will see them fixed to a brace in the hull so as to transfer the vibration to the hull and not the engine, The engine can then sit on softer mounts therefore reducing noise.

I'll take a pic next time on the boat.

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