An Innovative System

[amateur mariner]

Hi everybody!

Can anybody tell me that is there is any solution for the shaft and rudder to retract once the boat s berthed in shallow waters.the size of the boat is around 20m and speed required speed is around 12kts.Does some special type of joint can solve this problem.Are there any types of systems already available in the market or what can be the solution?

Looking for your replies

Never seen such system.
Only jet propulsion or "pump jet" are the solutions I am aware of.

[gonzo]

The most economical solution would be either sterndrives or outboards

[amateur mariner]

There r several small boats which emply this type of method but the arrangement is not so heavy and is retracted by the individuals.I look to retract using some mechanical/hydraulic system. Sterndrives look to transmit power at different degrees but I dont want this.I just look to retract it once boat is stopped and then i am able to retract it fully out of water.


Can somebody help me out of this strange problem

[CDK]

Google for Arneson and/or surface drives.

[brian eiland]

Originally Posted by amateur mariner

Hi everybody!

Can anybody tell me that is there is any solution for the shaft and rudder to retract once the boat s berthed in shallow waters.the size of the boat is around 20m and speed required speed is around 12kts.Does some special type of joint can solve this problem.Are there any types of systems already available in the market or what can be the solution?

Looking for your replies

I might be able to help you with some ideas and suggestions. What type of vessel do you wish to place this on...new or used, power or sail, or motorsail

[Ken Johansson]

Dave Gerr has a description of a simple system for this in his latest book, Boat Mechanical Systems Handbook (p38). Not including retractable rudder though.
I think you either could go for Arneson drives as CDK suggests or design (have somebody design) your own system.

Are surface drives efficient for low speeds (12kts)?

The most economical is probably sterndrives as Gonzo suggests. Depending on the design of course, but in the top position you could usually put most of the driveleg out of the water. Just like on an outboard.

[marshmat]

Originally Posted by amateur mariner

Can anybody tell me that is there is any solution for the shaft and rudder to retract once the boat s berthed in shallow waters.the size of the boat is around 20m and speed required speed is around 12kts.Does some special type of joint can solve this problem.Are there any types of systems already available in the market or what can be the solution?

Yep. Here's a classic example, albeit smaller:
http://www.disappearingpropellerboat.com/history.html

The Volvo Open 70 racing yachts, among other high-speed classes, have similar retractable drivetrains, although not all can retract while running.

One option is to put a universal joint in the shaft, outboard of the stuffing box; suitable bearings on a pivoting bracket are necessary to handle the prop thrust. Another option would be to mount the whole driveline on a pivoting platform- probably more work, more complexity and more problems unless it's all above water, ie. a long-tail setup. Sterndrives, outboards and jets are all possible options as well.... although I might rule out jets if you only want 12 knots.

[brian eiland]

Here is a solution for variable rudder depth:
Rudder-in-a-drum

[amateur mariner]

Originally Posted by Ken Johansson

Dave Gerr has a description of a simple system for this in his latest book, Boat Mechanical Systems Handbook (p38). Not including retractable rudder though.
I think you either could go for Arneson drives as CDK suggests or design (have somebody design) your own system.

Are surface drives efficient for low speeds (12kts)?

The most economical is probably sterndrives as Gonzo suggests. Depending on the design of course, but in the top position you could usually put most of the driveleg out of the water. Just like on an outboard.

i have read in this book that this typ of system cant support powerful engines.I am looking to use around 200KW engine to fulfill my powerin requirements.My boat is around 15m and have approx 0.8m draft.

[amateur mariner]

Originally Posted by marshmat

Yep. Here's a classic example, albeit smaller:
http://www.disappearingpropellerboat.com/history.html

The Volvo Open 70 racing yachts, among other high-speed classes, have similar retractable drivetrains, although not all can retract while running.

One option is to put a universal joint in the shaft, outboard of the stuffing box; suitable bearings on a pivoting bracket are necessary to handle the prop thrust. Another option would be to mount the whole driveline on a pivoting platform- probably more work, more complexity and more problems unless it's all above water, ie. a long-tail setup. Sterndrives, outboards and jets are all possible options as well.... although I might rule out jets if you only want 12 knots.

I think using a universal joint seem to solve a problem.Can anybody help me out of the procedure of designing this.What all calculations need to be done for this.

[brian eiland]

Originally Posted by amateur mariner

I think using a universal joint seem to solve a problem.

Universal joint will not stand up to this type of thrust loading...remember the prop is pushing the whole of the vessel thru the drive train. Do some more searching....it's a scholastic project, right?

[marshmat]

Universal joints can't transmit the kind of axial loads a prop shaft must handle, not without being greatly oversized and/or wearing excessively fast. Usually, when a universal joint is placed in a shaft carrying axial loads, there must be a thrust bearing on the load side to handle the axial forces. If it's a pivoting system, the assembly carrying the thrust bearing obviously has to pivot about the centre of the universal joint.... take a look at a sterndrive's gimbal assembly and you'll see just how complicated a U-joint-inside-gimbal can get even for a fairly straightforward task.

[Kay9]

why not simply design a "tunnel hull for the prop and shaft?

K9

[brian eiland]

While you at it check out this "thompson coupling"

U-joint, CV-joint, Thompson coupling