Thrust Bearing Source

[tunnels]

Originally Posted by armstpat

I'm just about to start building a 25 foot Carolina Skiff. I want to use a thrust bearing and short shaft to the engine. Does anyone know where I might purchase the thrust bearing?

I remember reading this post some time ago and just found it again !!
Ok all boats need thrust bearings !! the shaft need to have the thrust bearing mounted inside the boat so no push or pull is taken on the gear box which in turn is transfered to the engine and its mounts and so onto the engine barers !!
True most all marine gearboxes have built in trust bearing the take the push and pull but a proper thrust bearing mounted onto a beam that is fixed directly to the barers the the motor is mounted on means your engine mounts will last almost for ever .
For the do it your selfers ,automotive gear boxes and motors are not set up or built to take trust forward or backwards . Also automotive engine mounts at not made to take trust either up and down and a little back and forward ok but nothing like what it will be when the propellor is pushing the whole weight of the boat and in reverse pulling !!!.

[tevake118]

Originally Posted by FAST FRED

" I really wanted to use a thrust bearing as I wanted to go with a diesel."

IF your diesel will be using a marine transmission , the thrust bearing is built into the transmission.

NO extra bearing is required.

Hi Fred: Please confirm: I hhave this Hurth mounted to a 2 cyl. Deutz sitting in my garage for 39 yrs waiting for me to get my catamaran built. Now's the time, and I was going to use an (expensive) Aquadrive..You say this tranny has a built in thrust bearing. well, the cut away diagram in: Marine Diesel Engines by Nigel Calder, p. 157, shows an "output shaft thrust bearing". Does that mean all I need is a coupling adapter, a CV-jointed shaft, and the propshaft/strut? tevake118

[Tigawave]

You can't use a CV coupling (aft of the thrust bearing) unless it is the hydradrive marine joint as this is the only one that will take the thrust loads.

The thrust bearing CV coupling (from the propeller forwards) first takes all the thrust loads on a bearing bolted to a bulkhead, then you have a fixed point with only torque and engine movement to deal with. This can be dealt with by a double CV joint.

If you are using the simple set up (where thrust is taken on the bearing in your gearbox) then you can have a flex coupling but shaft should be in alignment and any engine movement is taken up with the flexibility of the shaft and/or any coupling with movement.

If you like the idea of the aquadrive there is a better and also cheaper system using the same principles known as the hydradrive made by the same company that makes the marine joint The company is Power train in Norway, whi have earnt their reoputation over years of supplying transmission systems.The hydradrive is or was much cheaper than the aqua drive last time I looked. http://powertrain.no/index.php/en/

Hope it all goes well and you get on the water soon.

[CDK]

All marine gearboxes can take thrust, but ultimately the engine mounts transmit it to the hull so these have to be large and stiff to prevent axial movement. These forces should not be underestimated.

Starting the power train with a separate thrust bearing block allows for softer engine mounts and all kinds of flexible couplings to reduce noise and vibration.

[Landlubber]

"Starting the power train with a separate thrust bearing block allows for softer engine mounts and all kinds of flexible couplings to reduce noise and vibration."

YES...this is by far the best way to set up marine engines, it allows strong and simple thrust to be delivered to the hull in strong mopunts, and also simple engine mounts that can then of course reduce engine vibrations to almost nothing. Using CV like the Thompson joint then truely make a very comfortable system.

[keysdisease]

The OP was asking about this thrust bearing for a 25ft boat

[Landlubber]

Yes, the system is exactly the same, big or small versions.

[tevake118]

Thanks Guys, Now I understand that it is necessary to have a thrust bearing block bolted to the hull, and CV axle between Hurth flange and TB; then, in my case, for the provision of a retractable prop-shaft cum prop and strut(on aft crossbeam of a catamaran), either a Thompson coupling or the Norwegian 'powertrain' between the thrust bearing and the prop shaft(riding on brass or plastic bushings in an encasing tube) then some kind of distal seal (cutless) and finally, the propeller. Since the total swing of the "long-shaft" would be about 15 degrees, I would split the difference: i.e., the engine mounted at 8 degrees(on elastic mounts), and the thrust bearing with its double CV axle at 4 degrees to the engine; then, because of their designed axial- load carrying ability, the Thompson or powertrain com prop shaft at a further 3 or 4 degrees deflection. Is that right?

[MikeJohns]

Relevant to this thread

Smaller vessel thrust bearings.

[tevake118]

Sorry, this was my first time replying to a thread; if I understand correctly, we want to keep all replies relevant to the question the op started with. If someone wants to ask a question - like I did - that wouldn't respond directly to the original query,then I should start a new thread...is that correct?

[MikeJohns]

Originally Posted by tevake118

Sorry, this was my first time replying to a thread; if I understand correctly, we want to keep all replies relevant to the question the op started with. If someone wants to ask a question - like I did - that wouldn't respond directly to the original query,then I should start a new thread...is that correct?

You probably can't start a new thread yet but if you want to carry on we can have a look here or you can carry on on the thread I started linked above.

Do you have sketches of your proposed installation ?

[Boat Design Net Moderator]

Originally Posted by tevake118

Sorry, this was my first time replying to a thread; if I understand correctly, we want to keep all replies relevant to the question the op started with. If someone wants to ask a question - like I did - that wouldn't respond directly to the original query,then I should start a new thread...is that correct?

Welcome to the forum tevake118.

Just to flesh out what Mike has already said above, for questions about issues/concepts/equipment that is common to many boats, it's best to search first to see if there is already an existing thread where the question would be on-topic, and if there is more than one, choose the one which is the best fit. If there isn't already a thread that is a good fit or if it's an in-depth or unique question that would be confusing to intermingle with a more general topic, new members are able to start a new thread (it's the PM system that is not activated until you have 5 posts.)

[FAST FRED]

A thrust bearing should be built into your Hurth , IF it is a marine tranny.

A lifting shaft setup was done for far simpler decades on low powered boats that were brought up on a beach at night.

The use of a CV joint was unheard of , a simple truck U joint was all that was required.

A U single joint has no problem with thrust IF the shaft is lined up correctly.

The hard part is holding the prop end of the shaft in position with good repeatibility.

A bit of miss alignment only causes the prop blades to operate at a slightly different speed during each revolution. perhaps a noise problem , usually not.