Prop Shaft Systems.

Brian
I did see it. I do not like hydraulics for power applications. Losses are too much - about 2 to 3 times higher losses than electric. Hydraulic motors are best for compact, high torque applications where drive system inertia might be difficult to manage.

The stuff that Dave designed was primarily used for raise drills where the low inertia gave low impact stress on jamming - a necessity to protect the string particularly when the head is close to the drive. I think they still rank as the highest torque for size of any hydraulic motor. Something like 64kNm from a 500mm diameter motor.

The curved shaft has much lower drag than any hydraulic motor mounted underwater irrespective of how compact the motor is.

 

I'd agree with you, Rick, if you're looking at the kind of hydraulic drive one might piece together from readily available earth-mover components and such. But a dedicated hydrostatic transmission should be able to achieve a total power loss, from engine crankshaft to propeller shaft, of about 10-12%. That's very much on a par with a good brushless DC generator, controller and motor. Hydraulics, of course, are a very different field from electrics, and have their own set of potential pitfalls to watch for. But I certainly wouldn't reject them out of hand, especially for applications such as a sailing catamaran where it might be very desirable to have only one engine but two independently controllable sets of running gear.

For pure, optimal efficiency, of course, it will always be very hard to beat a simple mechanical shaft to a properly matched propeller. But there are many situations- auxiliary power on sailboats being a big one- where overall efficiency is less of a concern than the system's physical size, ability to adapt to changing load conditions, ability to survive nasty conditions, etc. (If sailing auxiliaries cared about drivetrain efficiency, they wouldn't have 12" folding props- drive efficiency is sacrificed in favour of low sailing drag.) In these situations, right now I think it's a toss-up between electric and hydraulic: the former being preferable when house loads are a significant fraction of the total, the latter being quite attractive for primarily propulsive applications.

 

Matt
I was comparing the curved shaft to a hydraulic drive mounted underwater. The curve shaft enables the prop to be pulled clear of the water so prop drag eliminated when sailing.

The hydraulic motor drive linked by Brian offers both drag when sailing and poor overall mechanical efficiency when motoring - neither desirable. The curved shaft has negligible losses when motoring and sailing.

There is no discussion regarding close coupled hydrostatic or hydrodynamic transmissions; different application.

I have engineered the curved shaft for my application so that it is robust and reliable. No other propeller driven craft could go where I go. The challenge is there to engineer it for other applications. If you want the best overall efficiency of a water propeller I doubt that you will find anything better.

Rick W

 

strut

Very intresting strut arrangement in Bodrum

Oktay Çemberci
İstanbul/turkey

 

Its a home-brew affair , a little bit of marine growth on that lattice will seriously obstruct the flow to the prop, would have been much better to have a V support with less area and better inline forces and a lighter structure.

 

As a stern gear supplier that answers many of the problems associated with noise and vibration, things to look at improving are.

1. Rubber cutless shaft bearings by their nature allow a shaft to flex. Rigid composite bearings elliminate some of this movement, this improves the situation.

2. A standard cutless bearing carrier is rarely checked to see if it is in alignment to the shaft line. P bracket or stern tube. Using a clearance fit composite bearing bedded on epoxy, the alignment of the bearing carrier can be checked as the bearing should be able to spin on the shaft and in the carrier. This is a very likely cause of your lecturers vibration issue along with the fact that he probably had a rubber bearing.

3. Run the shaft in a tube as we do with the Seatorque system, this gives cleaner water flow to the prop with the added support of extra bearings in the tube. Running in oil uses less hp so more gets to the prop.

The issue of alignment in a system where the rubber engine mounts take the thrust is not that relevant, th ereason being as soon as you put the drive in geart and thrust loads are applied the engine will move and pivot so however accurate you have been with the vessel at rest in our out of the water it will all go out of alignment when in use.

 

"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." -- Mark Twain

Tigawave
2. A standard cutless bearing carrier is rarely checked (who told you this? I have never heard of it not being checked!) to see if it is in alignment to the shaft line. P bracket or stern tube. Using a clearance fit composite bearing bedded on epoxy, the alignment of the bearing carrier can be checked as the bearing should be able to spin on the shaft and in the carrier. This is a very likely cause of your lecturers vibration issue along with the fact that he probably had a rubber bearing. (if you will erase your post, go back and read the thread, then post something of your sales pitch that is relevant to the discussion - I'll erase this post before anyone notices)

3. Run the shaft in a tube as we do with the Seatorque system, this gives cleaner water flow to the prop with the added support of extra bearings in the tube. Running in oil uses less hp so more gets to the prop. (Less horsepower than what? BTW, Is that Seatorque aluminum?)

The issue of alignment in a system where the rubber engine mounts take the thrust is not that relevant (Who is teaching you this? Every time there is a side load on a shaft, it is flexing and wearing out, applying side loads to whatever bearing is downstream, transmitting vibration to the hull through the mounts and gland, wearing out packing and wearing out the mounts) , th ereason being as soon as you put the drive in geart and thrust loads are applied the engine will move and pivot so however accurate you have been with the vessel at rest in our out of the water it will all go out of alignment when in use (The engine will move, yes, but the better it is aligned at rest, the smoother and more efficient while running)

 

Thanks for the comments Mark,

Maybe it's just the boats I see or work on? but you're entitled to your views.

Sorry for mentioning the product,

 

Seing as my last post was deemed too commercial on this subject.

I'll try again.

Did he have rubber bearings? I will assume so.
Rubber gives so any inclination for the shaft to move will not be resisted, the ability to maintain a suporting water film will be reduced as the gap will increase on one side of the shaft.

The secret to goo bearing operation is a thin film of water, to maintain this the bearing and hence bearing carrier alignment is cirtical to within tenths of a mm. Useing a rigid bearing with close tolerance deflection forces can be resisted far better than with a rubber bearing, when or if the water film breaks down under pressuer then you need a good run dry material before the water fil is established again.

Put a fine tolerance bearing finished as a clearance fit in a boat with the shaft chocked and you will find out how close the carrier alignment is, you should be able to spin it. Once this is achieved fix it in place with something rigid. You may be surprised at eth improvement in the system.

As others have said aircraft wouldn't fix a prop not in line with the airflow (bota boats are limited in how this can be fixed) but they wouldn't run the prop 2 m from the engine in rubber bearings either.