Japanese liftable propellor shaft.

Hi All,

Read this post by 8ball: page 32 about Japanese fishing boats:

http://www.boatdesign.net/forums/at...l-efficiency-fuel-savings-fishing-vessels.pdf


"An installation with liftable propeller with external universal joint
This installation is common in Japan on boats that operate from beaches with no surf. The engine is fixed and there is a conventional shaft line with stuffing box and bearing to the inside of a tunnel. A universal joint made of stainless steel or bronze permits lifting of the propeller. This is done with a liftable vertical strut that carries the outer bearing. The rudder is lifted separately and makes this installation less suitable for beach landing with heavy surf, which requires that the propeller and rudder be raised quickly."

Googled myself to death and can't find a single boat in Japan with this arrangement, or any information on the i'net.

Any idea's?

 

The closest I could find to this arrangement is this set up in NZ....

Looks like a jacking plate attached to the prop shaft with lifting twin rudders.
Photo 1: shaft lifted.
Photo 2 : shaft lowered.

 

Commercial operations in the uk and Ireland use shafts, jets and outboards; nobody uses I/O with a few exceptions. ( Botnia patrol boats).

Jets cost a kings ransom, think of a number and quadruple it.
Outboards only seem too power the smaller inshore vessels and fast ribs.
Shafts are a firm favourite with all operators: cheap to rig, zero maintenance, super cheap spares.....

....but hang down below the hull with twin set ups, and are VERY vulnerable to damage. ( hence many choose jets over shafts)

A shaft system that could be raised In shallow water would make real sense, and cost a fraction of the cost of jets.

 

Some design thoughts.

The swim platform looks like a likely candidate to attach 'P' brackets to carry the cutlass bearings. The props will have poke out further than the transom so that they can be raised to the waterline or above.

Hyraulic swim platforms are already available, and wouldn't need much strengthening to carry the weight of two prop shafts with props.

Would The UV joint need to be located externally outside the hull as close as possible to the end of the prop tube, or closer to the prop's end?

 

Rustybarge, thanks for the link, it is a very practical guide.

 

There's an entire FAO publication on the BOB drive (Bay of Bengal). I have a copy but I don't have the time or equipment to scan it in. Assuming I can find it which, right at the moment, I can't.....

Anyway, same author as the pdf you refer to above so should be findable. Worth while, there are full details of engines, drive systems etc complete with all sizes and scaled drawings needed to build them.

PDW

 

In the "Fishing Boats of the World #3", pp 383, ISBN 0 85238 043 7, published by the FAO, you will find some tech info as well as a few simple scetches and further references.

 

Also look into the Disappearing Propeller Company commonly known as Dispro. Several links to get you started:
http://www.dippy.ca/how.htm
http://www.boatdesign.net/forums/at...orld-s-first-trimable-shaft-drive-dispro1.jpg

 

I found it very interesting and informative: I am not a NA and learnt a lot of new stuff. So many of us get the concept and general arrangement wrong, and all the small details and engineering right!!!

 

This looks like a very interesting concept for third world countries, and should world really well with a small diesel. But mounting the engine and shaft on a pivot that exits the boat through a flexible rubber bellows that sits below the water line; a Merc outdrive nightmare waiting to reappear?

Could it work with 250hp diesels?

Notice the engine tipping with the prop shaft.

 

I will try and have a look.

 

Thanks very much, yes now you're talking.
This is getting very close to the concept:

The UV joint is located outside the hull in the water, there is no rubber bellows to leak, and the engine stays fixed in position.

What sort of UV joint could survive in salt water?

 

Calling all Japanese forum members: Please could you go down to the beach and take a quick photo of all these fishing boats with lifting prop shafts.

I would be very interested to see how they have engineered their systems.

Thanks in advance......

 

I don't understand why you have such a problem with inboard outboards. Have you owned any.

 

I've never had a boat with I/O.

I'm often look in on the MBM forum in the UK, and I've often read horror stories of Merc and Volvo outdrives self destructing.

Most often mentioned is:
Ingress of water.
Corroding lift and steering rams.
Corrosion of the alloy casings.
Worn and Fractured gear sets.
Main dealer only service items; DIY not possible.
Replacing the rubber bellows every year.
Complex UV joints.

In other words: $$$$$$$ every year, year in year out, for ever and ever!

Shafts: replace cutlass bearing once in a blue moon.