Use pressurized water as manuevering thruster?

Vessels docking in San Francisco in the age of sail had no bow thrusters, unless I make a grave mistake.

One modification i would like to see more of in the pleasurecraft world is "flanking rudders," usually installed in pairs forward of the propellor. They work best when installed on twin-screw boats; and obviously would not work worth a hoot on a full-keeled sailboat.

But I can tell you from personal experience that when a brownwater tugboat crosses up the throttles and the rudders (Port engine ahead, starboard engine astern; starboard your steering rudders, port your flanking rudders) it can be walked absolutely sideways. I mean straight abeam. Play with them a little and with some practice you can come charging into the dock and hang off a little bit and draw squares with the boat.

 

Masalai,

I've been sailing for 35 years without a thruster and know how dock a boat. I didn't write to this forum to learn how to dock, I'm trying to learn how to engineer a water jet thruster. Do I need one? No. Nor do I need an automatic transmission on my car, but you know what, I have one and I like it. What's the problem? I'm not freakin' Columbus, I'm just an old guy who wants to back out of Sam's, on a busy Saturday, in a heavy surge without a lot of drama. I thought these forums were a place where a guy could bounce around ideas, not be told how he should or shouldn't equip his boat. Hell, I might just turn the thruster on an spin around in circles just because I can.

If you can help me find a solution, great, otherwise, I can live without the the editorializing.

SeaJay

 

I suppose I am a bit of a pedantic "purist" and see no point, - - something like the self parking car, - - parallel parking is fully "hands off" automatic, on a range of cars recently released in Australia. - - - - That to me, means, it is time to stop driving on the roads, as the calibre of drivers will deteriorate to the level of technology support. Can you see where I am going with this?

Sorry for ramming an uninvited view, leave the writing on the wall, but, please do not implement it, as the calibre of the recreational sailor will surely fall swiftly into incompetence.... as has the calibre of the domestic car driver...

 

Doesn't it take more electrical power to drive an electrohydraulic winch then it would to drive the winch by electrical power alone?

Depends on weather the 12v dc wires were REALLY the right size .

A 240+ setup would have almost no voltage drop , the battery setups frequently show 9 or 10v while in operation.


Look carefully at any fire monitor , a 1 inch hole is fed by 4 inch pipe to get the volume and pressure .

The jet ski would need its output diameter kept to the outlet as the ski pump moves large volumes but will not like a nozzel restricting the output.

Might be easiest to mount a 40 hp outboard on the bow pulpit sideways and remote the shift and throttle to the cockpit.

Might get 500 or more pounds of thrust with the right prop.

And you can stick it on the dink when not docking in 6K currents with 45K crosswinds.

FF

 

I am not trying to be argumentative, but even if using welding cable for wire, I would think that using electricity to turn an electric motor to turn a hydraulic pump to turn a hydraulic motor to turn a windless would use more electricity than using electricity to turn an electric motor to turn a windless?

 

Go for it SeaJay - or they will have us back to square riggers and steering oars. Where the hell did all those historic wrecks come from? - lack of thrusters I tell you!!!!

To test my theory, get hold of a small petrol agricultural pump, attach a 1 inch pipe and a decent nozzle, and point it to starboard, and drop the other end in the water.
I bet if you fasten the nozzle to the handrail at the bow, and start the pump , you will be spinning in circles beautifully. You will have to do the sums to see if you can make it work with battery power.

A simple experiment to save thousands buying it in from the dutchman.

In the future, I have a vision of a joystick arrangment that drives 4 such nozzles, push it forward, go forward, pull it back, go back, push it sideways, go sideways. or a combination of all.

Then we can sit in the harbour entrance and spin till we are sick. hey, a bit of sneaky sidways thrust ought to make that windward mark so much closer -( chuckle.)

 

YollyWally, I recall some detailed advice on cable sizes for specific anticipated loads for a distance and in essence, any deviation to a lighter cable is fraught with danger of overheating and consequent fire... http://www.outbackmarine.com.au/ although Australian has good info - have a dig around in the wireing/circuit boards sections etc.... Sorry not much good but definately do your homework/research first - a fire on board does not often give one a second chance....

 

I would think that using electricity to turn an electric motor to turn a hydraulic pump to turn a hydraulic motor to turn a windless would use more electricity than using electricity to turn an electric motor to turn a windless?

Thats not the point as weather it takes 2.5kw or 2.8kw to run the windlass is of no consiquence

Weather the unit fails and white smoke pours out of an electric windlass motor that needs to be imported from gondwalla land ,
\ or if it simply stalls the hyd motor and no damage happens is the point.

A cruiser that can operate at 100%,, 100% if the time is the goal, not .2kw

FF

 

This may perhaps be fantasy (at present) or subject for a new thread, but is there such a thing as a small cycloidal propeller for use as a bow thruster? Obviously not for retro fitting to existing vessels, the application I have in mind is a slender speedster (10 meter) with a surface drive.

Tony

 

slender speedster (10 meter)

If you want FAST , drag counts, so a liftable or housing thruster would be first choice.

FF

 

Ok, here is the pump type I was talking about.

http://pump-distributor.com/products/index.cfm?

fuseaction=pump_model_detail&product_id=9493&series_id=490

This isn't large enough, but the principal is pretty straight forward. Mount it up front and poke a hole out each side you're in business. I'm with Fred in that reliability is the issue, not effeciency. This is strictly for short term intermittent use. One manufacture of conventional bow thrusters recommends a unit of 7.5 hp for a boat my size so that's probably the motor size I'm looking at. That unit creates 275 lbs of thrust in a 10" tunnel. The tunnel size is where I'm having the difficulty, and actually since a 2" jet could be located very far forward, I might be able to down size the motor a bit.

Now I'm off to find a heavy duty industrial model. If anybody knows of such an animal, let me know!

SeaJay

 

Sorry, I messed up the link. Just type "reversible" in the search window and it will get you there.

 

Check out this baby! Appropriately named the Wild Thing!

http://www.watson-marlow.se/pdfs-global/b-spx10_15-gb-01.pdf

If that won't spin your top, nothing will. But in this case, I think Masali is right...a bit of overkill.

 

The basic physics that govern the engineering of a jet thruster are quite simple.

A couple of examples:

Lets say you determine that 1000N is the required thrust. (This is what a strong adult male could exert when pressed while holding a moring line).

With a 20mm nozzle like a fire hose the water would need to be ejected at 55m/s. The is a very high velocity - a seriously powerful fire hose. The sort of thing that takes two or three firemen to control. The power required to do this without any system loss is 18.5kW. In reality you would need a high pressure pump with about 30HP.

Lets say you now go for a small thruster with a 100mm nozzle. To generate the same 1000N. The exit velocity drops to 11m/s. Still fast but not extraordinary. The required power drops considerable to only 3.7kW. Lets say about 6HP once you allow for losses.

So the nopzzle size is important. Making it smaller requires much more powet.

I can give you the equations if you are interested.

So a hose will do the job but you need lots more power than if there is a decent size thrust port.

Rick W.

 

Rick,

Thanks for the input. I would most definately like to see the formulas. As a starting point, I find thruster manufacturers recommending 275 lbf and 100 kgf of thrust for a boat my size. I was thinking about running the necessary pipe diameter up to the thru-hull...not sure how I would incorporate a nozzel, but that detail can be worked out later.

First I need to see how much water I must move through a 1-1/2" or 2" pipe to achieve this amount of thrust. I came across this discussion last night, but have not had the time to look at it carefully.

http://www.eng-tips.com/viewthread.cfm?qid=217997&page=1

I would be interested in your comments.

Best Regards,

SeaJay