Use pressurized water as manuevering thruster?

[ldrumond]

Searching draws a blank.
Seem to remember that a number of years ago, Vetus listed in their catalogue, a thruster system for manuevering small pleasure craft that was based on a stream of pressurized water optained from a high capacity water pump. Water stream plumbed to thru hulls at "4 corners" somehow controlled by valves?
Probably a simple reason why I can't find any info on it.
Memory fails me, didn't / doesn't work -- right?

[SeaSpark]

Remember the system and a test report i once read.

It had one big disadvantage, efficiency was around 60% compared to a normal bow thruster. Advantages were, less drag from water in/outlets and more freedom in choosing a place for the pump. I wonder why Vetus does not sell the system anymore.

[FAST FRED]

www.omnithruster.com

These are for commercial work boats , not cheap, for 75 to 2200hp.

Better efficency , although a std prop is usually figured at 50% , in comparison these may be better.

FAST FRED

[SeaSpark]

http://www.ybw.com/forums/showflat.php/Cat/0/Board/pbo/Number/608109/an/0/page/8/view/collapsed/

Contacted a friend of mine with experience in this field, he remembered the Vetus sytem and knew it was discontinued becouse the pump had to be exactly matched with the hoses and nozzle. Changing lenght of hose or adding a bent in it affected the (poor from start) efficiency dramaticly. In practical applications this lead to systems with very poor performance.

[SeaJay]

These look pretty interesting to me...wondering if you couldn't modify a small jetski pump???

http://www.willdo.nl/

[kach22i]

These look pretty interesting to me...wondering if you couldn't modify a small jetski pump???

http://www.willdo.nl/
Great link, I've bookmarked it. I have a (air) bow thruster for a "on-paper" hovercraft design. The same problem of the bow thruster having to be almost as powerful as the main stern thruster/prop exist for hovercraft as well. Mass and momentum are a pain to shove around with effect.

[Frosty]

When I had a steel yacht I was toying with making a bow thruster from a small outboard motor gearbox. An appropriately sized tube with a flat on the top section to bolt the gearbox up to . It would then be a simple matter to attach a reversable electric motor to the shaft on the inside.

[rwatson]

This is an idea I have been interested in for a long time.
I remember seeing a film about a 30ft catamaran that used what looked like a garden hose outlet in the bow, to push the bow around, as it was very long and thin, and had a big turning circle.
My ideal would be a control stick like the ones on the new Volvos, that simply opened up the appropriate nozzle(s), and you went in that direction.
Might only need small nozzels for directional control, and one big propulsion one for the stern.
I thought if using the foot off a yamaha ject drive outboard motor for the pump. Very compact.
More ideas very welcome

[Sternwheel Rat]

I too am interested in this type of bow thruster. I am designing a sternwheel riverboat that will need bow and stern thrusters for close quarter manuvering. I thought about the waterjet because of the reasons stated above,{lack of drag, ease of placement, availability of water pumps, etc..} But a little research concluded this is not a viable choice, except on fairly small craft. I've decided to go with the standard thruster,{prop in tunnel, electric motor on top, mounted thru hull fore and aft}. I do plan to build my own, with an old foot off small outboard. Glad I'm not the only one who dreams up this kind of stuff.

[rwatson]

S Rat - did you look at the http://www.willdo.nl/ site ?
They have this sort of system up to 80 ft ?

[Sternwheel Rat]

rwatson, thanks for the link. First off, the largest they offer is up to 20m, {66ft.} and my plans are for 120ft. by 30ft. Then, it's powered by hydraulics, not the way to go, as far as I'm concerned. I've studied the options and decided on diesel over electric, so electric thrusters is what I'm looking at. I will need very powerful thrusters to overcome the wind effect on my "sailboat without a keel". The other problem I see is the pickup, straight down. This is a brown water boat, not a blue water boat, and I spend a lot of time in very shallow water. Picking up rocks and mud off the bottom sounds like a lot of costly repairs in the very near future. The through-side tunnel set up looks better, because not only do you get thrust on one side, but suction on the other!

[FAST FRED]

An electric start outboard that could be lifted clear of the water , between the hulls, would be the cheapest and simplest to install

.Push right is FWD , push left REV? (Reverse for the PC crowd.)

In some sizes the OB can be had with a deeper reduction gear case , and spin a larger propeller.

Hardly elegant but the thrust is substantial , and 20 to 100 hp system or larger would surely be less expensive than an in hull version.

FF

[Sternwheel Rat]

I have a home made bow thruster on my boat now. A Minn-Kota, 101 ft. lbs. of thrust at 36v. It works very good on 43 tons of sternwheeler. The problem is, I have to pull it out of the water manually, not very convienient from the pilothouse. And it takes up deck space. That's why I was thinking water jet, remote location, permanant placement, etc...
I'm leaning toward conventional now, prop inside tunnel driven electrically, mounted below water level, permanant.
If you've got the room, and don't mind dropping it in when you need it, an electric trolling motor makes a fine bow thruster, multi-directional as well!

[SeaJay]

Getting back to the idea of water jet nozzles...The WillDo Jet Thruster ( http://www.willdo.nl/ ) sure seems like slick solution but I can't help but think that this could be expanded upon and built using off-the-shelf components. Why not one honkin' central pump for multiple uses...bow thrusters, wash down, damage control etc? What sort of pump would be best? How do you calculate thrust generated by a water pump? Clearly there are losses in piping, fittings, etc...and what to use for nozzles? control valves? Any ideas?

[Sternwheel Rat]

I hadn't thought of using the Fire/Washdown pump for the thruster! That's a great idea SeaJay!
Now, I'm with you, how to valve it out?

[singleprop]

I personally think that jet thrusters are worth considering. Willdo is producing jet thrusters for tug boats, I believe that this size of boat need a lot of side thrust. If tug boats are using Willdo thrusters, then they are powerfull and reliable enought for a pleasure boat as well

You can talk to them directly and they can pretty much make ANY size thruster, directly coupled to an engine, hydraulic powered, electric powered or by V-belt.

I am quite sure that they can design a suitable jet thruster for a barge since this company comes from the land of barges (Holland).

By the way, they have a 250 KgF unit as well.....!!
Single prop

[riverliver2b]

Sternweel rat...in view of the size boat you are planning and your preference for diesel/electric propulsion, have you looked at splitting the sternwheel into two independently controlled halves? If so, I would be interested in your rationale for not going that route. Incidentally, I just bought a piece of property down in Mobile County with a 700'x50' canal off of Fowl River and am trying to decide what to put on it. I missed a heck of a deal on the 87' Jean Mary, if you are familiar with her. Would value any insights/suggestions

[SeaJay]

Sternwheel,

Have you got any further with your thruster project. I just had my unfinished 46' sailboat hull delivered. The bow is really not designed to handle a propeller driven thruster. By the time I move back to the point where I have enough depth to cover the tunnel, I've lost a great deal of leverage, and therefore the unit gets larger and I move aft a bit more...and I guess you can see where this leads.

I think the better solution is to put some small water jets right up front. The WillDo units fit the bill, but I wouldn't be suprised if the total bill added up to $10k. I'd like to see what could be built from standard components and use the system for multiple uses as mentioned before. I don't think building it would be that hard, but I have no idea how to size it. I read somewhere that if 4 hp was required for a standard thruster, then 4 + 1hp (for hoses) at the pump would provide the necessary thrust. Anyone care to comment?

Regards,

SeaJay

[FAST FRED]

Anyone care to comment?

A few hours of practice will allow 95% or better of the manuverability of the bow thruster boat/

Save the complexity , save the hassles , space loss and $$$ and finish the boat as simply as can be done.

BESTITIS is a disease that grabs builders , and wastes years and buckets of ca$h.

For 1/1000 the cost of a thruster you can get a boat manuvering lesson.

There are no "nice to have" on a cruiser only MUST haves.

FF

[Sea Jay]

Fred.

I agree with your general idea that simple is better, and many of the ideas I am incorporating in this boat follow that philosophy. However, I sail on SF Bay and much of our limited dockage is subject to high winds and currents. As I will single-hand this boat much of the time, a little assist from a thruster on occassion doesn't seem to be out of line.

However, if you really want to get to the heart of the matter, if I wanted simple, I'd just go out and buy a boat. Building does not equal cost effective or simple! ;) The truth of the matter that it is the totality of the engineering solution required to design a boat that I love. We all noodle about in our own ways.

Fred, I've read a lot of your posts, you're a creative guy, so help me figure this out...what size pump do you think I'd need, and what off-the-shelf technology might be using similar valves?

Best Regards,

SeaJay

[FAST FRED]

"help me figure this out...what size pump do you think I'd need"

The "pump" will suffer as all pumps will from the skin friction of the delivery pipe , and the power required to get good thrust will go up about 50% with every slow bend in the delivery and about 90% for any 90deg changes.UGH!

Frankly if you want the least hassle and best most useful cruising boat , I would install a complete hyd system in the boat.

Then USED a windlass, used hyd bow thruster , huge hyd bilge pump and even powered sheet winches could help on the boat.

Tailing is EZ , sheet cranking is hard so if the hyd accumulator was hand pumped while sailing , tacking would be a snooze.

There are even hyd start setups for most diesels , so dead batteries might be a hassle for the entertainment system , but not a threat to the vessel.Same hand pump and accumulator as for sheet winches.

The best way to create a GREAT boat is to see what the big $$$ folks do on big boats , and scale the great reliable stuff down for use on your project.

A boat with keel cooling , a dry stack and full hyd is really hard to kill, and fantastically EZ to maintain.

And should you ever overload any system , no electric white smoke pours out , and NO REPLACEMENTS are needed.

FF

[FAST FRED]

If you are willing to give up the space for the equipment and large pipes, you might consider getting an old Ski Doo drive package and installing that.

The pipes would be the same diameter as the jet skis output and a valve like a carburetor plate could be cable operated to open on the side you need the thrust.

Since it would only operate a few min at a time fuel costs would be minor.

Perhaps it could fit under a forward bunk to save room, at docking speeds it would not have to have the water inlet facing forward.

FF

[Sea Jay]

Fred,

Excellent points. If you check out the Willdo system, it features hydraulic power. Here is the result of 20 hours of thinking while driving back and forth to Portland.

1. My original thought was a jet ski pump and it is still under consideration (without gas motor)

2. Is there such a thing as a reversible pump? Visualize a short length of 2" pipe in place of a standard bow thruster tunnel. Now plumb in this "two way" pump in the middle where the thruster prop/motor normally sits. Now there is virtually no friction losses due to long runs of pipe, and one less thru-hull. Suck water in one side and shoot it out the other. Even if such a pump doesn't exist, the thing can be configured with valves just like the Willdo. The point is that instead of running two rather large water pipes through the middle of the boat with all of the associated losses, you are running two smaller hydraulic lines ( with all of their associate losses). Absolute power effieciency is low priority. I've got lots of power and the thruster only runs for very short periods. My real problems is that a 6" tunnel just isn't going to work.

3.There are many things I like about hydraulics but I kept coming back to the fact that I wanted the windlass(s) to be indepentent of the engine, ie battery operated. It seemed logical to run an electrical foward thruster motor since I figured I'd put a couple of batteries up front to handle the windlass anyway. I thought about an accumulator, but don't know much about them, and how much capacity they have. If I had enough to haul the anchor without the engine (or could get it with a manual pump) we could be talking turkey.

4. I'm with you on the keel cooling. I have also given some thought to a dry exhaust, but I can't figure out where to locate it so that a) it doesn't interfer with the rig b) doesn't foul the sails, and c) where I don't have to breath the stuff while I'm in the cockpit.

Anyway Fred, thanks for the suggestions...we're thinking along the same lines.

Best Regards,

Sea Jay

[FAST FRED]

3.There are many things I like about hydraulics but I kept coming back to the fact that I wanted the windlass(s) to be indepentent of the engine, ie battery operated.

A windlass when working hard will require 100 to 200A for 10 or 15 min to be usefull. That would require about 1000 lbs of batteries if you do not wish to harm them in use. And don't forget the last 15% of recharge may take hours and hours!

4. I'm with you on the keel cooling. I have also given some thought to a dry exhaust, but I can't figure out where to locate it

The ones I have seen that worked well ran the exhaust up the mizzen mast.

If you have only one mast a standpipe about 6 or 8 ft tall must bring the hot gas past the halyard wincg working area.

The diesel smell will be 35 to 50 ft up.

FF

[TollyWally]

For modestly sized work boats hydraulics are the only way to go, power, power power! Ships with large AC generating capacity can use electrical power much as we would on land to great benefit. But in a battery/dc situation hydraulics are my choice.

[FAST FRED]

But in a battery/dc situation hydraulics are my choice.

Surely the answer today, BUT,

The modern aircraft hates the weight of a fixed hyd system , and the ease of battle damage rendering it ALL disabled.

Modern A/C practice is a power pack that runs on electric (with multiple paths for power and control) and powers the use item in place.

The load on the electric motor is fixed , so if the hyd stalls , there is no damage to the electric side.

AS surplus mfg capacity always drives prices down I would look for hyd/electric packages on better items like windlasses.

Advantage no fixed piping and pump/resevoir system , no hyd cooling required , and yet the delightful ability of Hyd to be overloaded with ZERO damage is kept.

The use of a 240 to 440V power supply would get rid of the huge heavy , costly DC cable requirement.

FF

[TollyWally]

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

[masalai]

Aowwwwww, this thread is annoying me, as FF suggests get the training and FORGET lateral thrusters.... Best option, stand at the stern and urinate, else get trained to use your existing power systems.... bloody shiver me timbers (I was going to use other adjectives, but remembered it is Sunday) you are supposed to be learning and becoming a responsible boatie, Go practice...

[rwatson]

Masalai - you must have been feeling liverish. All the training in the world won't prevent damage from gusting winds, adverse currents while manouvering a boat with a stern leveraged power source about 2 miles from the uncontrollable bow.

I feel the solution for this design dillema is a high powered water pump with its own small petrol motor, pushing sea water along galvanised steel pipes. The controls would be the equivalent of taps (one for port, one for starboard) that control the water jets exiting the hull close to the bow. Instinct tells me 1 inch pipe with a fire-hose nozzle would do the trick.

In my minds eye, I see a system where the pumps are running at full capacity , and the pumped sea water being squirted harmlessly straight down. When the helmsman wants to turn the bow, the water 'tap', closes the 'escape pipe' as it opens the port or bow jet.

It would be reletively easy to jury-rig a test setup to verify the efficiency of the setup before bulding it into the boat.

I have vivid recollection of seeing a documentary with a long 30ft hull being slowly turned with no more than the equivalent of a garden hose outlet.

The pump motor could be the same one for the onboard generator, to justify its purpose a bit more.

[masalai]

Well WTF did the likes of Chris Columbus, James Cook Willhelm Dampier and the myriad others who did not have even that much "reliable power"??? do you really NEED such? - - I have seen local trawler and other boat drivers do very well with a single prop....

[eponodyne]

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.

[Sea Jay]

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

[masalai]

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...

[FAST FRED]

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

[TollyWally]

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?

[rwatson]

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.)

[masalai]

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....

[FAST FRED]

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

[ACSarazin]

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

[FAST FRED]

slender speedster (10 meter)

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

FF

[SeaJay]

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

[SeaJay]

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

[SeaJay]

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.

[Guest625101138]

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
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.

[SeaJay]

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

[Guest625101138]

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.

.....

SeaJay

SeaJay
The basic relationship is:

Force = Pi/4 * Water Density * (pipe ID)^2 * (Flow velocity)^2

So taking a 40mm ID pipe you will need a flow rate of 27.8m/s to get 1000N (1000/9.8kgf say 100kgf or 220lbf).

The required static head to achieve this flow is 400kPa (40m) (58psi). The pump power is 9.3kW without any losses. I would think 15HP would go close allowing for losses. The volumetric flow rate is 35lps (555GPM). This is the sort of flow required for a fire hydrant.

I looked at possible pumps and it will need to be at least 3". The attached link shows what a 4" pump could do:
http://www.godwinpumps.com/images/pdfs/cd100m.pdf
This has more than enough grunt. The 3" pump is marginal.

There are many pump manufacturers. I just found this one as it had a good range of simple pumps. You can get some nice compact electric powered pump of similar size but I did not find one with performance curves available on the www.

The length and size of delivery pipe is also important. I would be really concerned with water flow above 8m/s in a pipe so you need to have a delivery pipe of at least 75mm (3") and keep it short to reduce losses. If the intention is to run a good distance then you should determine the pressure loss and you might find it makes sense to make it bigger. It is normal to go larger than the pump outlet by 20% or so.

So you can see it is possible and not all that unrealistic. There are some other points to consider though.

Ideally you will jet above the waterline as having the jet below waterline will create back pressure and reduce performance.

Water from the nozzle at 27m/s could do serious damage to any nearby small craft if directed at them. Remember if something is placed in front of the nozzle it will experience a steady impact force of 1000N. Would easily capsize a small dinghy for example. 555GPM going into a small boat for a brief period could swamp it. So streams should be directed downward and just above the waterline

Trying to keep the pipe sizes down results in high velocity. You probably want nice butterfly valves or similar to give good control. Solenoid valves will cause hammer.

The nozzle has to be secured in such a way to resist the thrust. It is effectively a point load on the hull so may need localised support. Probably no more than any high integrity through-hull fitting.

This shows the sort of engineering required. If you have access to good hydraulics (as in water) designer then it may be worth doing more detail and comparing with more conventional thruster. The bigger the area the less power for the same thrust.

A force of 1000N is not insignificant and you might find that going down a bit in required force would make for a more economic solution.

The forces and flows you are requiring are in the vicinity of a fire hose. These are usually readily available in industrial sites if you want to get a feel for what you will be doing. You may have already had experience with such equipment. I would never man a fire hose single handed. They can generate large forces and need to be treated with care.

One thing about this solution is that you are dealing with readily available industrial components. It is not one-off type stuff for the luxury yacht market. You do need to have it engineered reliably though.

Rick W.

[Sea Jay]

Rick,

Thanks for the detailed response. I'll spend some time with the numbers. However, the sizing you have arrived at would appear to push the system into the non-feasible range. (too heavy, too large of a pipe). But as you say, perhaps a smaller system would be suitable. Looking back at the Willdo system, I think they suggest the same thing. I see that they are recommending a system with only 60kgf and a 45mm pipe, and imply that their thruster works a little slower than conventional thrusters. With your information in mind, and reading their literature more carefully, I see where they disucss their "special thru-hull fittings". These likely are very important to their system performance.

However, you hit on my key concept that these components are off the shelf industrial units. Not to dismiss Willdo's work, but I'm betting I can come close. Anyway, thanks again for the input. I think I have what I need to start massaging the numbers.

Best Regards,

SeaJay

[Guest625101138]

I had a look through the Willdo literature. The numbers stack up with what I have given above. They look compact, well engineered and neat. The price is reasonable - EUR1360 for a 30kgf thruster would be hard to better. I also think there is merit in minimising the length of pipe as they have shown.

I feel a bow thruster would provide just about all you need. I could not think of many situations where you would need both bow and stern.

Rick W.

[SeaJay]

Rick,

I’ve spent some time with your formulas and have a much better sense of the relative forces involved in using pressurized water as a thruster. However I am now a bit uncertain as to how Willdo is achieving their published thrust performance numbers.

Using information from their site and your formulas, the 30 kgf model would have a velocity of 15.3 m/s (30+ mi/hr) and a flow rate of 300+ gpm. The 60 kgf model, which would be recommend for my boat, would have rates of 21.6 m/s (48 mi/hr) and 430 gpm. As you have noted, and other sources have confirmed, velocities of greater than around 5 m/s start to have an erosive effect on pipes. I can readily see the potential harm that could arise if these streams were misdirected.

Estimating a complete Willdo set up at around 4,000 Euros (6,300 USD), it does seem unlikely I’d better the price and actually not a bad deal. Especially considering that the price includes the hydraulic pump, which could then be used for other applications. (However, I’m open to suggestions if any of you mad scientists out there have one!)

Thanks again for all of your help. This has been a very informative exercise.

Best Regards

SeaJa

[Guest625101138]

Rick,
As you have noted, and other sources have confirmed, velocities of greater than around 5 m/s start to have an erosive effect on pipes. I can readily see the potential harm that could arise if these streams were misdirected.

Estimating a complete Willdo set up at around 4,000 Euros (6,300 USD), it does seem unlikely I’d better the price and actually not a bad deal. Especially considering that the price includes the hydraulic pump, which could then be used for other applications. (However, I’m open to suggestions if any of you mad scientists out there have one!)

Thanks again for all of your help. This has been a very informative exercise.

Best Regards

SeaJa

A pipe operating above 5m/s is typically not recommended for continuous use or long length. With a system that is going to do a few minutes a month at most it is not going to do much harm to operate at much higher velocity. The main limit will be extra drag with length. This increases power requirement. The nominated power may be with short hoses. At some point the allowable pressure in the hoses will limit thrust.

You could put the question of pipe length to Willdo. What is the maximum allowable length. What is the power requirement for a particular system with a given hose length. What is the maximum allowable pressure.

Note the size of the inlet. This is the size necessary to avoid high suction loss as there is only around 15psi to play with in a small craft. I expect if you do the sums for this section of piping you will get a velocity under 5m/s.

Rick W.

[D Legendre]

Hello everyone,
New to this forum. I am in the process of building a 25 foot pilot type bass boat (displacement 3500 pounds) and just about to close the floor.
Been exploring this idea of a water jet thruster for a while and at this stage of building, have to decide if it's a go or no go with the whole thing.

I also believe that I can (maybe) better Willdo's price but also customize the controls to have some kind of directional control on the stern thrusters to move me away from the dock where depth is very shallow and could damage the prop on my outboard engine.

Rick,
Thanks for the formulae, I ran the numbers and come up with 215 GPM with hose ID 40mm and thrust of 15 KgF (according to Willdo). Maybe I missed something but can you tell me how to derive the required static head and pump power ? I would run on battery power alone and if the draw is too much, I will scrap the idea unfortunately.

Sea Jay,
I am curious to know if you went ahead with Willdo and how are their services after the sale ?

Thanks
Daniel

[Sea Jay]

Daniel,

I am not to the stage of construction where I need to purchase the unit however, I am providing the necessary access for future installation. With my uderwater profile I just don't have the room for a 10" tunnel so the smaller piping of the jet system is what is driving my decsion. Otherwise I'd just plan on a standard propeller type thruster with likely larger aftermarket support. Please keep me posted of your developments.

Best Regards,

Doug

[Guest625101138]

Hello everyone,
New to this forum. I am in the process of building a 25 foot pilot type bass boat (displacement 3500 pounds) and just about to close the floor.
Been exploring this idea of a water jet thruster for a while and at this stage of building, have to decide if it's a go or no go with the whole thing.

I also believe that I can (maybe) better Willdo's price but also customize the controls to have some kind of directional control on the stern thrusters to move me away from the dock where depth is very shallow and could damage the prop on my outboard engine.

Rick,
Thanks for the formulae, I ran the numbers and come up with 215 GPM with hose ID 40mm and thrust of 15 KgF (according to Willdo). Maybe I missed something but can you tell me how to derive the required static head and pump power ? I would run on battery power alone and if the draw is too much, I will scrap the idea unfortunately.

Sea Jay,
I am curious to know if you went ahead with Willdo and how are their services after the sale ?

Thanks
Daniel

You can apply Bernoulli equation. This assumes perfect conditions for the piping. The pressure ends up at 62kPa for your conditions. Resulting pump power is 0.85kW. Realistically more like 1.5kW accounting for losses. You need about a 6" pump doing 1500rpm. You might be able to find some pump curves. If your pipe is long and only 40mm diameter it will chew up a lot of power.

Rick W

[D Legendre]

Rick and Sea Jay,
Just got a reply today from Willdo. They talk about a pump and dc motor assembly with 40mm ID hose for my boat.
I have to tell you that I find 215 GPM is a lot of water for a little dc driven pump. My pump dc motor search so far is less than good. The biggest I found dc driven was in the 10GPM range. I am wondering if you have any better sources than I in this field.
I will probably end up looking at this challenge the other way around. Find the biggest pump dc motor available and use Rick's formulae to find how much thrust it can give with a 40mm ID hose. This will probably be my go no go answer.
By the way, Willdo tells me that their unit draws 300 amps with the dc motor they have. I wonder where this motor pump assembly comes from.
Any suggestions are welcome. I will have to make my decision soon and would be dissapointed to close the floor without the unit only to find out it could have been done later.
Daniel

[srimes]

for reference:

http://duckworksmagazine.com/03/r/articles/jet/drive2.htm

[Guest625101138]

Daniel
There are some very nice 240V pumps available like Davey but they do not come with 12V DC motor.

The biggest 12V stuff is for bilge pumps, solar circulating pumps and low voltage pond pumps. I doubt that you will find any in the size you need. I found a bilge pump that will produce about 2kgf for a fellow wanting to power a canoe in shallow water. Would not be much use for you.

You can certainly get low voltage motors that give you the required power off 12V but they are not coupled to small pumps. They are not sealed though so are not well suited.

The photos for the makeshift jet boat linked in the previous post gives you an idea of the sort of flow you will need. It is a lot of water. The jet will reach about 20ft high if directed upwards. Not quite a fire hose but still significant.

Rick W.

[D Legendre]

Rick,
Something bigger has to exist somewhere. Here is some info (attachment) from Willdo about a 20KGF 12 vdc driven pump. Looks nice and pretty compact too.
Does that give you any hints as of what kind of motor or pump type is used ?
Unless I am wrong, the 20KGF unit shows 12v, 2KW motor. In a previous email from Willdo, the rep talked about 300 amp draw. Some thing I don't understand is that 2000 watts / 12 volts = 166 amps , not 300 amps. Are they taking into account for losses or is my calculation wrong ?

Also, I seem to notice like a bypass tube on top of the unit.
If I can work this out, I would prefer having the pump going only on demand.
What I mean is I would not want the motor driving the pump all the time in a recirculating way until there would be a demand (opening a passage valve). Instead, I would like the motor to come on only when I would send a signal to the unit, then the motor would come on and the appropriate passage would open also. This would restrain the power demand I believe. Is that feasible ?
Thanks again for your insight and sorry for this long reply.
Seems to me the more I know, the more I find I don't know !
Daniel

[Guest625101138]

When we went through this previously we concluded Willdo represented fair value for the system. The nominated power of 2kW for a 20kgf system is certainly close. The electric motor is likely to be around 80% efficient so you have to allow for this. Electric motors will easily operate above their rated power for short periods. The 300A might be related to starting or the 14V you get from the battery when being charged. If the motor is directly connected then rpm will be linear with voltage and power will be cube relationship. Hence current will rise with the square of voltage.

Personally I do not like the idea because it requires through hull fittings below the waterline. The security of your boat is reliant on the security of all this plumbing. Think how quickly you can sink it if a line fails and it allows 200gpm into the hull. So with this consideration you want very reliable plumbing. The electric drive is not too difficult to do on the cheap. Model plane motors can get close to the required power on a 12V system:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142&Product_Name=HXT_80-100-B_130Kv_Brushless_Outrunner_(eq:_70-55)
These are not rated continuously but you only need burst power anyhow. You need an electronic controller because they a 3-phase motors. But the controllers are also quite low cost:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4316&Product_Name=hexTronik_PRO_120A_BESC_w/_PC_Programmability
I have a couple of smaller versions of these and they are outstanding value.

The issue with this stuff is that you need to separate the motor from any wet bits. Pump sealing is important. You can get magnetically driven chemical pumps but they start getting expensive.

Ultimately you get back to looking at Willdo as being fair price. There are a lot of considerations that they have already worked through. It is reasonable that they get something back for their development effort.

Rick W.

[CTSAUTOMATION]

Hi i have looked at the wildo range who recommended a 25kgf, el25 pump and controls which can be used in a force 6 . I have a 25ft motor boat and decided to build my own. I used skin fittings just below the water line with 3/4 fittings at the bow, ajustable flow 12v dc solinoids and a single cyclone pump in a y connector from the head pick-up (19mm pipe id). The flow was rated at 100lmin at 0,1m head. wildo sujested a 500lmin pump at 2-3bar.

My system works in calm conditions at a very slow speed (ideal start) I am currently looking for a small pump that is close to the wildo spec. There pump is reversed engineered from bigger units used in the stena line oil rig support craft.

I am covinced that a good pressure pump may be better than high flow?

I used a wash down pump a hose and a rod to try this before starting work. since we only need a gentle nudge from time to time a small pump looks logical.

[kistinie]

Hi !

post a picture of your pump if you have !
Thanks !

[Guest625101138]

Hi i have looked at the wildo range who recommended a 25kgf, el25 pump and controls which can be used in a force 6 . I have a 25ft motor boat and decided to build my own. I used skin fittings just below the water line with 3/4 fittings at the bow, ajustable flow 12v dc solinoids and a single cyclone pump in a y connector from the head pick-up (19mm pipe id). The flow was rated at 100lmin at 0,1m head. wildo sujested a 500lmin pump at 2-3bar.

My system works in calm conditions at a very slow speed (ideal start) I am currently looking for a small pump that is close to the wildo spec. There pump is reversed engineered from bigger units used in the stena line oil rig support craft.

I am covinced that a good pressure pump may be better than high flow?

I used a wash down pump a hose and a rod to try this before starting work. since we only need a gentle nudge from time to time a small pump looks logical.

I am not sure I have understood what you mean but the following might help your understanding.

If you have a view that placing the nozzle below the waterline helps then this is incorrect. The best place for the jet to exhaust is just above the water level. I can appreciate this may create a problem for neighbouring vessels. However this is the reason jet boats discharge above the water level. It is more efficient.

The force you can generate with a jet is given in a post above. The power required to produce a given force increases as you increase jet velocity.

As a first approximation the least power as a function of thrust can be determined as:
Power = (4/pi/9/rho)^0.5 x Thrust^(3/2)/D in Watts

rho = 1025 for salt water
D in metres.

This relationship is the fundamental jet relationship. In practice there are pipe losses, rotor losses, lift losses and back pressure losses to contend with. In real life these will almost double the required power.

Point is the bigger the nozzle the less power required to produce a particular force.

Working out what you will get from a particular system is not very difficult. It is far better than just fiddling with hoses and pumps. Determine what is needed to do the job and then build it. It will still take a bit of development but at least you know where you are heading.

Rick W

[Ad Hoc]

"However this is the reason jet boats discharge above the water level. It is more efficient."

This is not strictly correct. Waterjet boats ideally discharge at the waterline, there is zero head. I have also never had KMW,LIPS,MJP, Hamilton et al ever suggest to me doing anything otherwise on any vessels I've designed too. Ive designed vessels ranging from KMW FF450 jets right up to KMWs 120 S series

[Guest625101138]

"However this is the reason jet boats discharge above the water level. It is more efficient."

This is not strictly correct. Waterjet boats ideally discharge at the waterline, there is zero head. I have also never had KMW,LIPS,MJP, Hamilton et al ever suggest to me doing anything otherwise on any vessels I've designed too. Ive designed vessels ranging from KMW FF450 jets right up to KMWs 120 S series

I have facts and science to back up the information I provide unlike others who provide unfounded claims to knowledge that is just nonsense.

The most significant development in establishing water jet technology was to set the discharge above the waterline. This results in very little head increase and is far better than dealing with the backpressure from an entrained stream.

Rick W

[Ad Hoc]

If you were to read what i wrote, you will see that is not what I'm saying. However if you feel so strongly then please tell KMW, LIPS, MJP et al, that they should change their recommendations and warranties of their equipment.

Ive been down this road with all of them before....their kit, their warranty.

I don't know how many water jet powered boats you have designed but whenever you have the centreline of the duct/shaft above the waterline, it becomes increasingly more difficult to prime!..hence why all the manufacturers recommend in line with DWL..regardless of what theories are out there.

[Guest625101138]

If you were to read what i wrote, you will see that is not what I'm saying. However if you feel so strongly then please tell KMW, LIPS, MJP et al, that they should change their recommendations and warranties of their equipment.

Ive been down this road with all of them before....their kit, their warranty.

I don't know how many water jet powered boats you have designed but whenever you have the centreline of the duct/shaft above the waterline, it becomes increasingly more difficult to prime!..hence why all the manufacturers recommend in line with DWL..regardless of what theories are out there.

I would like to see any picture you have of a jet powered boat where the discharge nozzle is underwater when the boat is operating at design condition.

Rick W

[Guest62110524]

I would like to see any picture you have of a jet powered boat where the discharge nozzle is underwater when the boat is operating at design condition.

Rick W

Rick Ad Hoc has been espousing his design virtues since he came onboard, he even claimed to have "talked' the British M.O.D, into changing from steel to al al, yet on the 3 occasions I asked him for his credentials, whom he had worked for, his name etc, he chose to ignore, as he is by myself: so do not fret my man, we are listening to you, as per

[Ad Hoc]

Rick

There you go again, you utterly fail to comprehend what has been written, and meander down pointless meaningless paths of your own choosing.

Where have i written "... where the discharge nozzle is underwater ..."..? please explain to me where this is in my text?..can't find it....oh dear!

Also if you are so 100% convinced that you have this all singing all dancing new theory, then you better tell KMW, LIPS MJP et all very quickly so you can make a killing on a patent. They have only been doing this for 30 odd years...clearly you have better resources than all of them combined.

Next time you're on a jet boat..ask the Capt to place loads of ballast on the bow, to make her bow down trim so the jets are above the waterline. Then ask him to engage...and listen to the racing as the pumps cannot prime!

Ah, since you're such an expert on jets, you know all about the KMW AWJ-21, but I'm sure you've told KMW that this is not possible as your are asserting incorrectly again.

For those with the intellegnce to read and deisgn vessels with waterjets, you see that it is an underwater discharge waterjet design with remarkable stealth characteristics. But hey who am I compared to someone who knows far more than all the waterjet manufactures in the world combined.!

[Guest625101138]

Rick Ad Hoc has been espousing his design virtues since he came onboard, he even claimed to have "talked' the British M.O.D, into changing from steel to al al, yet on the 3 occasions I asked him for his credentials, whom he had worked for, his name etc, he chose to ignore, as he is by myself: so do not fret my man, we are listening to you, as per

whoosh
This fellow Ad Hoc is bad news for the forum. He has killed some very useful input from contributors unwilling to challenge him on his pumped up claims.

He provides silly advice and has turned off a number of good forum contributors by his pompous stance. Taking any opportunity to put people down. I have not yet identified a single positive contribution or any useful advice.

If you go back through his posts it is like a train wreck.

Some examples:
He advised a fellow wanting to build a shallow mudflat hull that he needs to start with the hydrostatic head on the hull to determine how thick the sheeting should be. How useful is that?

He told Leo Lazauskas that he did not know what he was talking about when Leo advised depthofit that his model needed to be at least 1.5m long to get results valid for scale up design.

He has no idea of what Stitch and Glue construction is.

He has no idea who Dave Gerr is.

He believes the cross beams of a catamaran, point supported at port stern and starboard bow, will have zero moment to resolve.

He has no idea that the units for endurance limit of materials is a stress value.

He suggested to an experienced aluminium fabricator that the fabricator had no idea about controlling distortion in aluminium boat construction.

Have a look at this thread to see how this AH fellow can kill useful contributions:
http://www.boatdesign.net/forums/multihulls/designing-structure-38-catamaran-25944-2.html
Who would bother to continue to contribute when you get this sort of response. I hope Ernie returns. Look at the put-down for TYD in post #6.

Rick W

[Guest62110524]

YES, I am quite distressed abt it, I simply could not let it go, the fellow is quite plainly a fabricator of the first magnitude
I would implore you to contact Jeff, I have had no end of people contact me over this
By the times he is online, I suspect he is unemployed, a sad individual living some dream in his head
i think the best thing is ignore as I do, pretty soon ostrasim works
Trouble is, some people may listen to his nonsense and take it as Gospel, particulary boat builders who are coming into al al
And he tried lecture myself abt distortion after 29 years building al al

[Ad Hoc]

Rick

see you have done it again..you fail to address the issue you raised. You just ignore them when countered, and don't answer the questions posed as you consistently say must be answered by others when reciprocating.

Perhaps you should practice what you preach!

[Guest625101138]

...Where have i written "... where the discharge nozzle is underwater ..."..? please explain to me where this is in my text?..can't find it....

You wrote:
"Waterjet boats ideally discharge at the waterline, there is zero head."

For it to have zero head it must be below the water level or are you going to deny this basic physics. Of course it could be minutely thin and infinity wide I guess but I believe most would agree this is not how they are built.

Rick W

[Guest625101138]

Rick

see you have done it again..you fail to address the issue you raised. You just ignore them when countered, and don't answer the questions posed as you consistently say must be answered by others when reciprocating.

Perhaps you should practice what you preach!

In your mind you may believe you are the most important person in the world requiring an immediate response but I was responding to someone who makes useful contributions - something I cannot find from anything you have posted.

Rick W

[Ad Hoc]

Zero head means on the waterline when designing jet powered boats.

second, "...discharge above the waterline.." your words. This means the cone and hence the shaft line is above the static waterline. So, as stated above, you better tell KMW et al that they have been designing waterjet incorrectly, not me. Secondly tell them how easy it is to prime their jets when the shaft-line is above the waterline as that is where you wish to place their unit in your design.

Also you said " ..I would like to see any picture you have of a jet powered boat where the discharge nozzle is underwater..."

I gave you a reference which you obviously havent not bothered to look at or know about. Since you're a fan of cutting an pasting. Just cut and paste it into google, under MKW...you'll see the boat which you claim cannot be done. (Not so good at cutting and pasting as you cannot even copy my text correctly, you have used someone else's in your haste to reply above).

So, unless I am mistaken you clearly have the edge on KMW, LIPS et al, and you must have designed so many waterjet units that the whole world now uses them and that "normal" waterline discharge jets are grossly out numbered by your discharging nozzle above water.

[Ad Hoc]

It is a pity that this thread has gone down such a petty trail. Since, most of what you wrote was fine...but when you sprouted on about the usage of waterjets, it needed rectifying.

However you clearly feel that you have cornered the market on waterjet units and every other manufacturer is wrong and you are the worlds authority on waterjet units with your successful above dwl pumping units, given what you are saying above. Since that is your corollary.

[Guest62110524]

as we know ad hoc means
improvised or impromptu. so that abt sums it up

[Guest625101138]

Ad Hoc
I could find hundreds of videos and photos of jets discharging above the water level but since you referenced KMW I thought the proof would be more compelling to you if I chose a ship, which I believe is fitted with KMW jets.

Watch this video till the very end (once it is at design cruising speed) and tell me what you see. And then answer this simple question "Are the jets operating in free air above the water level?"
http://www.youtube.com/watch?v=V_TMaTBW1ho

Once you have provided the correct answer I would appreciate acknowledgement that you were wrong. I know that is wishful thinking but it should at least make you stop posting your nonsense to this thread.

Rick W

[Ad Hoc]

These jets are not above the waterline.

When you design a vessel with a waterjet, the shaft line is in line with the static dwl. When the vessel si underway, once speed has been attended, the transom is ventilated; that means it is clear and dry. So when you look down, just as in this video, it looks like it is above water. But in profile view, the shaft-line is on the waterline..ie zero head...it is not ABOVE!

[CTSAUTOMATION]

sorry no pics but if you google cyclone pump from jabsco you should find it.

[Guest625101138]

.......... When the vessel si underway, once speed has been attended, the transom is ventilated; that means it is clear and dry. ....

Ad Hoc
FINALLY YOU HAVE GOT IT.

It took a long time but you finally understand what I pointed out in my original response to CTSAUTOMATION. If you want efficient operation the jet must discharge in free air - not under the water.

If you do not appreciate this then the simple test is to get a hose at full bore and compare the thrust to restrain it in free air compared with the situation when it is plunged beneath the water surface.

Rick W

[Ad Hoc]

When you design a vessel with a waterjet, the shaft line is in line with the static dwl., how does that related to...."...Ideally you will jet above the waterline ...."

You truly have a bizarre set of definitions, such as what is a waterline, and you consistently do not try to establish assumptions or facts before you rush off like a bull in a china shop...not to mention ignoring your own assertions like vessels with waterjets below the waterline which you claim cannot be done etc.

[Guest625101138]

Ad Hoc
I am happy that you now acknowledge that the jet needs to discharge in free air for best efficiency. That was all I was pointing out to CTSAUTOMATION - remember he had set his below the waterline where it will lose thrust due to entrainment.

My concern is that it took so much nonsense to convince you of this. As long as CTSAUTOMATION appreciates the salient point - water entrainment in the jet stream will reduce thrust.

Of course the practicality of a high velocity discharge jet in free air near the bow of a boat in a marina may be a concern. However the flow will droop and a flush nozzle will likely have a slight downward trajectory to start with.

Rick W.

[Ad Hoc]

"...My concern is that it took so much nonsense to convince you of this..."

I'm sorry, but it is you who has been talking nonsense, because you do not use the same definitions as everyone else. A waterline is simply that, a waterline, measure form the deepest location of the hull to the location of the water where the vessel is floating....where does it say, it is taken from the bottom of the transom....????

You need to use the correct terminology first before you rush off into technical discussions. Which you consistently fail to do on this and other posts.

Buy a book on terminology..then maybe people may understand what you are talking about...whether it is nonsense or not.

[Guest625101138]

"However this is the reason jet boats discharge above the water level. It is more efficient."

This is not strictly correct. Waterjet boats ideally discharge at the waterline, there is zero head. I have also never had KMW,LIPS,MJP, Hamilton et al ever suggest to me doing anything otherwise on any vessels I've designed too. Ive designed vessels ranging from KMW FF450 jets right up to KMWs 120 S series

Ad Hoc
You obviously cannot read what I write - maybe you can read my quote that you posted.

I cannot see any mention here of waterline in the quote I made regarding efficiency.

The waterline was quoted in the Hamilton jet history. If you have a problem with them using the term waterline inaccurately then take it up with them:
http://www.hamiltonjet.co.nz/hamiltonjet_waterjet/waterjet_history
For my mind I know what they meant. If you want to be such a pedantic fellow then have a go at them. They may appreciate your insight more than I do but then I doubt it.

If you care to apologise for you misinterpretation you may gain a little credibility.

Rick W

[Ad Hoc]

"If you have a view that placing the nozzle below the waterline helps then this is incorrect.....this is the reason jet boats discharge above... It is more efficient."

Hmmmm..lets me see..waterline, and oh yes, mentioning boats..wow, so you go from a waterline referring to boats to er...something completely different in one sentance....oh yes...and there it is too....effecinecy!...so there you have it.

Reading between the lines you cannot be a professionally trained naval architect. Because there is never is bizarre changing the definitions to suit owns own bizzaro views. It is clear and absolute.

Definitions are the first thing one learns....you chop and change and select at your peril. You may think you know what you're talking about...but it is clear to others with formal training that you do not know such correct terminology and their exact definitions, nor when to use them.

"If you don't say what you mean, you wont mean what you say..."

[Guest625101138]

"If you have a view that placing the nozzle below the waterline helps then this is incorrect.....this is the reason jet boats discharge above... It is more efficient."

Hmmmm..lets me see..waterline, and oh yes, mentioning boats..wow, so you go from a waterline referring to boats to er...something completely different in one sentance....oh yes...and there it is too....effecinecy!...so there you have it.

Reading between the lines you cannot be a professionally trained naval architect. Because there is never is bizarre changing the definitions to suit owns own bizzaro views. It is clear and absolute.

Definitions are the first thing one learns....you chop and change and select at your peril. You may think you know what you're talking about...but it is clear to others with formal training that you do not know such correct terminology and their exact definitions, nor when to use them.

"If you don't say what you mean, you wont mean what you say..."

Ad Hoc
Now you are in the gutter. Selective quoting to try to put words on paper that I never intended - incredibly childish and very poor form. I hope others will see how silly you really are.

You have proven yourself to be ignorant on many issues that you claim to be expert in and now you are showing that you will act dishonestly to try to score a point.

Rick W

[Ad Hoc]

So in other words, you don't stand by what you are saying when exposed to being misrepresenting and misleading others when definitions that ahve no place in text books etc.

Thanks for that.

Very unprofessional....still haven't my Qs anwsered too....!!

[cor]

Enough arguing, for best efficiency water jets should discharge into free air.

[CTSAUTOMATION]

Hi guys my point was in reply to earlier on in the threads about bow manouvering thrusters only not propulsion. Wildo quoted me a system that would install 40mm pipe (inch and half i think- swimming pool size like mine) and suggested the outlets to be 100mm below the water line. I made the decision to go smaller as i felt they had over sized the system for a bow thruster. I only need a gentil-aid to help berth my boat not spin on its axis. The pump they use is a similler one to a davis swimming pool pump (240v not 12vdc) I am considering using a swimming pool pump 500lmin at 6 bar and rewind the motor to 12vdc. I know a local motor rewinder who can do this for me. I am interested in your valid feedback. On the wildo web site you can see the installation examples of a jet below the water line. I feel this is for boat comfort in tight berthing situations as to not disturb other users.
Best regards gentlemen.

[Guest625101138]

The large 100mm nozzle will reduce the exit velocity and thereby reduces the entrainment. So efficiency loss is not as great.

The hazard of high velocity discharge above the waterline has been discussed previously on this thread at post #46. The reduced efficiency of underwater outlet has to be weighed up in these terms.

The flow power is 4.8kW at the stated design conditions. This will require motor power of 6-7kW depending on the pump efficiency. This is very high power for a 12V system. Will require a current of 600A.

If the motor is 240V induction motor you will not be able to run it directly from 12VDC even if rewound.

The pump is high pressure for the application. With that pressure at the pump you will have something like 30m/s at the nozzle in open air. The open air thrust will be 24kgf - reasonable. With it being underwater the entrainment loss will be significant but it will still work. I cannot give you a number. If you played around with nozzle size you should find there is an optimum but it is not something I can calculate.

If you have a swimming pool pump to trial then do some simple tests at a pool. You can measure thrust in open air and compare with under water. You can easily play with nozzle sizes to see what gives the best result.

Rick W

[CTSAUTOMATION]

cheers rick i think the 12v to 230v convertor is proberbly best way as the motor at 12v would require too large a current. The basic trial as you said would be to measure the force at the outlet nozzle in the pool and out. A crude sping balance and bucket would give some idea i think at the underwater outlet in the pool. I was thinking of the same spring balance test in pulling the boat at the jetty if you get the idea. Seems a bit rocket science but should give some ideas. i have flow ajustment at the skin fittings on the boat (in the solinoids body) to trim out the best results. I also looked at central heating booster pumps used in open systems. Thanks for the advice. regards TF

[Guest625101138]

If the pump operates at rated conditions the inverter will be a monster - maybe USD1000+. Going from 12V down to 240V is obviously 20 times so the current is 20 times higher. It will need to be a big battery to hold up for a minute or so of operation.

When you do your pump test on 240V you could also take a current reading. The 12V current will be roughly 20X for the same result.

Will be interested in you results.

Rick W

[Ratch]

Although this thread is a bit dated I am interested in the subject and would like some feedback on my idea.

I am looking at installing this pump http://www.catpumps.com/select/pdfs/333.pdf (pump) or one very much like it for a water maker. My thought was to utilize to also power a bow thruster and fresh water deck wash.

If I install a deck fitting I will have a supply of water at 800psi @ 10 lpm give or take or if you like a high pressure salt water gerni. Now if I use two solenoids one for each port and starboard clamped to a pole on the bow with each nozzle pointed in the appropriate direction I am thinking I should have an effective bow thruster (not that it is really needed) for a 36 foot boat.

I have attached a rough sketch.

Parts list:
Clamp
Pole
High pressure flexible hose
Some fittings
2 x solenoids
Cable and switches

[Guest625101138]

Ratch
The link does not produce anything for me.

If you run at 800psi and 10lpm you will get about 1.7kgf - not a lot. You can measure this with a small Gerni. You can certainly feel the thrust but it is not tiring to restrain. I cannot see it doing a lot on a 36' boat against a bit of a breeze.

You will also have quite a weapon. The nozzle velocity will be around 100m/s. That will throw a long way when exiting a streamline nozzle. Would not want it pointed at me.

Rick W

[CTSAUTOMATION]

Hi Ratch, looks okay, i would be a bit worried about the alli body in the pump as it would need a good rinse after the salt water use. If you were to try it just below the water line you would move the bow at its pivitol point as i have tried this with a similair set up. I used a 24ft boat and a deck wash pump 11 bar max. it did indeed move the boats bow. Only good for manovers and not propulsion. However small moves at slow speed is what is recommended in berthing. I am considering a good pump myself on a sale or return basis, if i can find a good supplier. good luck, regards TF

[CTSAUTOMATION]

Hi guys i managed to do a successful test today and have been able to move the boat with the small pump 100lmin. the movement is very slow and in a reverse or aft direction as well as port or starboard, I think this is due to the outlets being in the tip of the bow as it curves round. I am getting a 240v swimming pool pump 500lm 6 bar. I will be trying it next week. keep you updated. TF

[drmiller100]

Hello,
Under the jet propulsion forum I have a recent thread where a spreadsheet is posted by another gentleman.
In it is a spreadsheet which converts horsepower (and hence watts) to thrust force given speed of the boat and size of the discharge nozzle.

For low speeds such as a thruster would have, I would suggest you use a large flow per minute at a very low pressure to maximize thrust.

Further, if there is an engine on board, I would suggest a hydraulic pump mounted to the engine, combined with a water pump mounted to a hydraulic motor near where you needed the thruster. It might be cheaper and more convenient then an all electric system.

[Richard01]

Rick W, thanks for your clear and professional explanations.
I'd like to look at the Willdo combi jet thruster (ie stern and bow) for a 48 ft heavy sailboat ..guess 80-100kgf is about right.
On the point that you get more thrust if discharging into air vs underwater....You said you could not calculate how much more but would you hazard a guess?.
My thinking is that by having the nozzles just above the waterline aimed slightly downwards you'd reduce the number of underwater hull fittings and get a higher thrust that would offset the negative effect of the downward angle? it might be a bit noisy but would not be any risk to nearby boaters.
I presume Willdo realise that thrust is higher above water but have traded off more safety and quietness against a higher power requirement.
The boat has a 100hp Volvo engine so a direct connected waterpump via a toothed belt and magnetic clutch as Willdo proposes would give plenty of power ... and one would only generally only use the thrusters in neutral. A concern could be the transverse force applied to the engine main bearings by the toothed belt drive.
Would you have any comments?

[Guest625101138]

.........
On the point that you get more thrust if discharging into air vs underwater....You said you could not calculate how much more but would you hazard a guess?.
My thinking is that by having the nozzles just above the waterline aimed slightly downwards you'd reduce the number of underwater hull fittings and get a higher thrust that would offset the negative effect of the downward angle? it might be a bit noisy but would not be any risk to nearby boaters.
I presume Willdo realise that thrust is higher above water but have traded off more safety and quietness against a higher power requirement.
The boat has a 100hp Volvo engine so a direct connected waterpump via a toothed belt and magnetic clutch as Willdo proposes would give plenty of power ... and one would only generally only use the thrusters in neutral. A concern could be the transverse force applied to the engine main bearings by the toothed belt drive.
Would you have any comments?

I have Googled long and hard for something that gives me the back pressure on a nozzle. It is a process of entrainment and is a function of nozzle velocity of course. I have not been successful in finding data on it or the physics involved. I know it was a fundamental step in making modern high speed water jets efficient. You can do a simple test with a hose and a bucket of water to get an indication. At the relatively high velocities of these thrusters I expect you would lose 20 to 30% of the thrust by submerging it - that is a guess.

I also have a severe dislike for underwater fittings so I agree with with your approach. Actually it is not the fitting but more often what is connected to it. A slight downward angled jet will lose very little in the side thrust and should be safe to other boats.

I doubt that a properly tensioned toothed belt tension would cause any concern for a motor shaft for the sort of power take-off required.

Rick W

[Richard01]

Thanks Rick

[kistinie]

I doubt that a properly tensioned toothed belt tension would cause any concern for a motor shaft for the sort of power take-off required.

Rick W

Belt fly planes used for reduction mainly
No worry !

[Richard01]

hi Kistinie
Your reply was a bit cryptic...could you explain please

[mudman]

I think that this pump will do the job. Run it off of the engine while in neutral.
http://www.catpumps.com/pumpdetail.cfm?PumpID=251&link=1
Don't know the price, but I'm sure that it's up there.

Just thinking out loud here, but what about hydraulic rams with a plate that may come off of the sides of the hull on a hinge. Kinda use them like a fish tail, or a whale tail to................ Nevermind. Paddlewheel thrusters?......Naaaaaa.

I like the idea of a reversible inline pump in the middle of a pipe that runs from starboard to port. Sucks on one side and pushes from the other. Need a high volume pump.

Pressure losses would not be very great through full port valves and fittings. I can run some pressure drop calcs, but pretty much what ever the head pressure is, It will be maybe 10 psi less at the outlet, depending on line size and pipe material. Fiberglass or PVC has a far lower Delta P than steel pipe.

[Richard01]

mudman ... "idea of a reversible inline pump in the middle of a pipe that runs from starboard to port." would't work unless you had big diameter suction pipe on one side and small diameter nozzle on other with pump in between. I suppose you could do it with a reversing pump and some non return valves ie a big suction opening on each side as well as a nozzle on each side.......might as well just go for a conventional tunnel thruster.

the flap idea...whale tail .....is interesting....

[kistinie]

hi Kistinie
Your reply was a bit cryptic...could you explain please

Oups...Sorry for delay

Toothed belt have more than 95% efficiency and some amateur planes use these belts for reduction on engine pulling more than 150 HP.
Harley davidson use belt too
So i do not see why it couldn't drive a pump safely.
Just think to have a protection as theses belts are extremely dangerous for hands, clothes...

[Guest625101138]

Oups...Sorry for delay

Toothed belt have more than 95% efficiency and some amateur planes use these belts for reduction on engine pulling more than 150 HP.
Harley davidson use belt too
So i do not see why it couldn't drive a pump safely.
Just think to have a protection as theses belts are extremely dangerous for hands, clothes...

So you are in agreement with what I stated in post #98?

Rick W

[kistinie]

Of course !
Didn't changed my mind !
These belts are the best solution for home made devices.
Reduction ratio can be adjusted, no vibration transmitted and medium cost
Sorry if my first post wasn't clear enough

Almost all you dreamed to know about belts... is here ;)
http://www.sdp-si.com/D260/D260cat.htm

[plebusmaximus]

Apologies for not reading the whole thread.

What about triple bilge pumps or similar?

[altramp]

The thread seems to have run out of steam. I would be interested to hear more about the results of the home made trials.

Great informed discussion - it has certainly helped me

What I took away from the discussion is that ideally we need a large diameter exit and ideally a reversable pump to reduce the valve and pipe work. For recreational yachts the answer is starting to look like a prop in a tunnel in the bow....

On large boats where there distance between the exits is large maybe there is some benefit from using a single pump instead of several thrusters.

[Guest625101138]

Actually I witnessed the trial of water cannons on a tug recently. The system is designed to produce 1300Cu.m at 12bar to operate through 3 cannons. Do not know the bore but the throw with 30 degrees elevation was about 150m.

The 32m long vessel moved at 1 to 1.5 knots into a slight breeze. They have measured 2 kts in calm conditions.

It will take about 600kW to produce that flow and pressure so demonstrates the poor performance of a high speed jet as a slow speed thruster.

You are right about the large diameter. For slow speed maneuvering you ideally move a lot of water slowly if you want efficiency.


Rick W

[SeaJay]

If you haven't been to the Willdo site lately, check this out...

http://www.willdo.eu/index.php?subject=180

Here is exactly the configuration I was talking about. It simply sucks water from one side and pushes it out the other. The size seems limited at this point, hence the "Mini" name, but I think the principal is sound. I doesn't suprise me that they developed the pump themselves. After completing Par's "Pump Thrust 101 Course", I didn't find any off-the-shelf equipment that seemed to fit the bill.