Japanese liftable propellor shaft.

The sketch that rusty barge shows is of a different lifting prop system that I have seen on a small boat. This is pretty simple but maybe not as good for a large boat where tilting the motor might be difficult. A lifting prop with a U joint is not useful for continued propulsion because of vibration that would be introduced by rotational variation in prop speed. For that, you need a CV set up.

Was the Dispro set up used in other than fully extended position? I thought that the Dispro was mainly for rowing without the drag of prop and shaft.

 

Those are some interesting questions.
in Japan did they run up close to the beach with the engine running and the raised prop turning, or just coast in in neutral ?

A CV joint would be very susceptible to corrosion submerged a couple of foot underwater?

Would a rubber gaiter/bellows be enough protect the CV joint?

 

Here's neat little set up with bolt on rudder, but designed for surface drive.
http://www.lancingmarine.com/databook/files/index.html. Page: 16

Mounted on a jacking plate or bolted to the bottom of a lifting swim platform it could work nicely with submerged props.

 

A someone mentioned, an outboard drive powered by an inboard diesel and a hydraulic pump/motor may make sense for a boat that needs to run up on the beach. Careful attention to hydraulic pump/motor efficiency should mean that they are a net efficiency gain over gas engines. People run jet drives and they aren't efficient either.

 

Re surface drives, I was chatting to a guy who had a race boat with twin surface drives and he mentioned that the props Had absolutely no grip in the water at slow revs, he suggested carrying oars to berth the boat in the marina! At 40 kts plus they come into their own.

Jets are hopeless at slow revs too.

Hydraulic pumps lose about 20% efficiency.......

 

Just thinking of practical applications for this idea.

A lot of twin engines boats would like to run with one engine for economy reasons. Problem is with one prop dangling in the water flow it creates a lot of drag. Lifting one shaft/prop out of the water would increase efficiency by a lot, enabling economic single engine operation and a huge increase in range.

There are quite a lot of hulls with small prop tunnels: these would have enough room above the shaft to allow it to be lifted if the prop stuck out past the transom.

I can envisage a twin 250hp diesel twin engined s/d design that runs one engine at say 1500 revs/1.5 gal/hr at about 7 or 8 kts..........this would allow the operator to fill up with fuel at the cheapest bunkering location rather than the local rip off merchant!

 

Here is a link that suggests it is hard to beat an outboard engine if you need something suitable for predictable shallow water.

http://www.boatingmag.com/boats/boat-engine-comparison-outboard-vs-sterndrive-vs-jet-drive

 

Very interesting article: thanks for posting.
Hard to a beat a good outboard!

Motorboat monthly in the Uk did a similar test on 6 identical boats with Volvo, cummins and Yanmar diesel outdrives of 250 hp and 350hp: each boat was equipped with a super accurate fuel meter.


It was in the february 2012 issue: they charge for back copy's, but you can find them online if you google it !

 

I find it amazing that no one understands how the conventional propeller shaft in an automobile works and that includes Professional Engineers. The post of my NZ boat shows one approach I used when I Patented the "Vessel Pivotal Drive Shaft Mounting" c 1973. Why would you put the U/V`s outside of the hull in the water when everything can be fitted safely inside the hull? If you Google Pivotal Drive Shaft for boats, CAM.A.PROPULSION, and search www.bostdesign forum you can find much more info on a very practical shaft drive for boats. The pivoting action when the drive hits the bottom eliminates any damage to the drive which can be designed in so many configerations. It will take you anywhere a boat can float and you do not have to have big power and high speed to use dynamic lift to navigate shallow water.
www.youtube.com/watch?v=tT3M1DUz-6M Smat Drive

 

Hi Tom,

My googling skills ain't that great, but your u tube site has been taken down and I can find only a passing mention of your post on the forum.

what exactly is your drive, and what does it look like?

 

Tom, I know a number of engineers who know how conventional propeller shafts in automobiles work. Why do you claim no one understands?

 

If marine engineer's understood all of the possibilities of the conventional auto rear drive propeller shaft why have they never installed them in boats.they just tell me you can not do it but can not explain why. It works the same as in an auto with the propeller taking the place of the rear axle and wheels trailing behind the boat. The mechanical parts are the same (twin u/v joints) as what has been used in boats forever except they have been fixed in place with no provision to move up and down. A a tunnel for the shaft to move is no problem or water seals.

 

Tom, Are you saying that the shaft angles of both U/V joints don't have to be equal & opposite in order to drive a prop with no vibration?

 

jananese liftable propeller shaft

Hi rusty barge. The youtube site does work..well for me anyway. I have built dozens of different configurations of my pivotal drive simple ones just like a standard inboard install
and other designs just to experiment but I was building for my own use and not to try and impress anyone else. You can use a pivotal drive as a mud boat, Surface Drive or conventional sub surface drive with different options to steer the options are endless.Just build what you want.

 

japanese liftable propeller shaft

Take a look at a conventional shaft drive install with twin u/v joints and a sliding spline (c/v joint)
Motor at 10 degrees, each u/v joint at 5 degrees each = 20 degree shaft angle. The only reason the shaft can not move up and down is because it is fixed in place and always has been.The thrust bearing must be self aligning to allow the shaft to pivot. You need a shaft tunnel to allow the shaft to move.
There are other provisions of course . You can build all of this to suit your design. Just think of all the advantages there are many and you can do it your self.