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Old 11-21-2007, 02:22 AM   #1
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water jet bow and stern thrusters

Has anyone out there got any experience with bow and stern water jet thrusters. Or companies that produce these systems....

I have only found one company with a complete system but don't know and cannot find more info about these systems:*** www.willdo.eu

Regards Singleprop
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Old 11-21-2007, 10:34 AM   #2
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water jet bow and stern thrusters

It would be interesting to know if waterjets have the same characteristic as aircraft jets, in that when power is applied there is a delay before any actual acceleration occurs. Unlike a propeller, which as it goes faster produces additional thrust right away that results in immediate movement. The delay with a waterjet thruster may not significant enough to be concerned about, but I strongly suspect a propeller thruster will move the bow or stern sooner and with a more positive action.

-- Edited by Marin at 11:36, 2007-11-21
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Old 11-21-2007, 10:54 AM   #3
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RE: water jet bow and stern thrusters

Ever seen a JetSki, PWC, or Jet boat "take off"? No lag time that I know of.

Check out http://www.omnithruster.com

Their thruster starts up and runs constantly (when you want it to be ready for use). It thrusts in both directions which cancels itself out, then it blocks water to a side causing an imbalance to push the boat. This way the thrust is up to full power at all times.

They also have nozzles you can direct 360 degrees. So you could drive the boat forward or backward as well as side to side. Could even drive the boat home in an emergency.

Another advantage to thrust from a water jet is that it works when you are underway. No cavitation such as a propeller thruster.

Mostly used on larger ships. Used also for holding position when working with underwater gear.

Very expensive.
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Old 11-21-2007, 11:48 AM   #4
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water jet bow and stern thrusters

">Ever seen a JetSki, PWC, or Jet boat "take off"? No lag time that I know of."

On the other hand, these craft are all fitted with waterjets for safety reasons. So it's not really possible to compare their performance to an identical craft with a propeller because there aren't any.

I was told by a co-worker who's big time into water skiing that one reason ski boats don't use waterjets is because they don't have the power and torque to get skiers up quickly.* Plus there's the issue of the big rooster-tail of water these drives tend to put out--- most skiers wouldn't want this in their face

There is an inherent acceleration delay in a jet (of air and I would assume water) because unlike a propeller, it takes some degree of time for the force of the jet to become strong enough to overcome the inertia of the airplane (or boat). A propeller is developing thrust immediately and this is immediately transmitted to the airframe (or hull). The same amount of inertia has to be overcome, but the propeller overcomes it faster. At least it does in an airplane. I don't know why it would be different in a boat.

Waterjet drives were not created because they performed better than props but because they offer operational advantages. Shallow water, safety, and applications like hydrofoils where props simply aren't practical to use are the main reasons behind waterjet drive. They are much less efficient than propeller drive---- the Boeing family of military and civilian jetfoils was good proof of that. The water propulsion system worked fine but it was incredibly inefficient, which is why the concept was eventually scrapped.

But I suspect that whatever performance and acceleration deficiencies may be inherent in waterjet drive are irrelvant for a thruster application other than it will probably take more drive power to achieve the same result with a waterjet that you get with a propeller. And in some ways, a conventional bow thruster IS a sort of waterjet in that it takes water into its tube and accelerates it out the other end of the tube with its propeller.

For large ships, it may be more efficient to use a smaller but much more powerful water accelerator (waterjet) to move the bow or stern than the much larger, slower-turning, propeller-in-a-tube that would be required to get the same amount of thrust. But I suspect that when it comes to small recreational boats like ours, the cost of the more complex waterjet system would prove to be quite high while not yielding much improvement over conventional bow and stern thrusters.

So, as Gene said, it probably all comes down to cost. If waterjet thrusters for small boats were economically competitive, we'd probably see more of them. The technology's been around for a long, long time.

-- Edited by Marin at 12:50, 2007-11-21
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Old 11-21-2007, 12:04 PM   #5
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water jet bow and stern thrusters

We have a Ominithurst a 200 sereices which is the smallest they make. Our thruster also has the forward thrust besides side to side. They are quite expesive, 70 grand, especially if the boat does not have hydraulics to begin with. The big advantages is the thrust can be run for hours at a time. I have sat up to two hour holding a costant position. They are mostly designed and used on larger work/commercial boats. On the PMM under Engines- thruster I posted a long post which is more in detail.

I am surprise Gene did not mention, I had one, as he dools over the Ominithrust.
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Old 11-21-2007, 12:30 PM   #6
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water jet bow and stern thrusters

I believe that continuous operation is also the main advantage of a hydraulically driven conventional thruster as well--- the prop-in-a-tube type.

We used to charter a GB36 with a single engine and an electric bow thruster. Don't know what brand of thruster it was, but it was a fairly small one and I recall it had a warning label at the helm stating not to use the thruster for more than five seconds (or something similar) at a time. I assume this was to prevent overheating of the motor. Of course five seconds was generally more than sufficient for what we needed the thruster for, so it was never a problem. I've been told that not all electric thrusters have this limitation.

But my understanding is that a hydraulic thruster can be run forever or until the hydraulic pump fails, whichever comes first. Plus I assume hydraulic thrusters are silent in operation. The grinding sound of an electric thruster has to be one of the most annoying sounds in boating, particularly when operated by someone who insists on steering his boat with the thruster instead of the rudder(s). We have a few of these folks in our marina......
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Old 11-21-2007, 02:10 PM   #7
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water jet bow and stern thrusters

First off, I didn't look to see what these water jets are about. If they use an impellor to drive the water then they are really no different from a conventional thruster....although possibly remotely located. So in this regard I agree with Marin....they are theoretically the same.

And Marin, I don't think your comparison of jet engines is valid. The main reason turbine engines lag is due mostly to the rotational mass of the engine itself and how the combustion takes place. It just takes a moment for the fuel to become heat(energy) and then get things turning. If the engine is already "spooled" then there is mostly no lag. That is why it is procedure to have the engines spooled and stabilized by 1000ft on final approach(one of the criteria of a stabilized approach). You want the engines to be ready in the event of a missed approach.

Jet boats and jets skis do get up and go in a blinding fashion. The main reason water jet propulsion is not universal is that it is not efficient. If there is a need for it(like safety or shallow draft) then by all means. But f there is no need, then you are just throwing power out the window. I had heard somewhere in the neighborhood of 25%. Jet boats are not as efficient as jet planes for the same reason. The propellor(impellor) is only "working" on a small volume of fluid(air or water). A propellor aircraft is much more efficient than a jet for this reason as is an open prop on a boat versus a jet drive. There are also reasons due to turbulence in the tunnel but we'll keep it simple.

Sorry for the off topic but something tells me there aint no listmiester that is gonna scold me!!!
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Old 11-21-2007, 02:24 PM   #8
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RE: water jet bow and stern thrusters

I never said the Omnithruster was more efficient or even equal.

The advantage I stated was that it runs continuous.

The nozzles can be directed 360 degrees for side to side and forward & reverse thrust.

It can even propel the boat home in the event of main propulsion failure.

It can be used while the boat is at full speed. No cavitation problems.

Oh, and yes the pump/impeller is remote mounted and the nozzles are in the bow. There is a limitation to the distance because of losses in long runs. Requires three holes in the hull (intake and 2 jets).

I would guess that ships prefer this sytem for holding position because the jets run continuous and you control direction by imbalancing the flow. No starting stopping and reversing a propeller in a tube.

I am still figuring out if I can use my sawsall underwater to steal Phil/Fill's omnithruster

-- Edited by Gene at 15:26, 2007-11-21
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Old 11-21-2007, 03:12 PM   #9
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water jet bow and stern thrusters

John--- I know about the spooling up business and why with regards to jet and fanjet aircraft. But I sure seem to recall from somewhere (school, pilot training, NASA, here at work?) that in addition to the slower response times of turbine engines, jet thrust itself is "slower" in response. Or maybe they were saying the same thing you just did but in a different way.

Regarding bow thrusters, am I correct in assuming that a hydraulic thruster (prop-in-a-tube) is quiet compared to an electric thruster. I've never had the opportunity to hear a hydraulic thruster run, or at least hear what I knew was a hydraulic thruster run.
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Old 11-21-2007, 06:37 PM   #10
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RE: water jet bow and stern thrusters

Our electric thruster says not to exceed thirty seconds continuously. I don't exceed fifteen seconds, in order to maintain a good safety margin. It is plenty, as all I use it for is minute adjustment at the very end of a docking procedure. The only other use is when leaving our slip, as the fairway is very narrow.

Question - Why would you run a thruster when under way?
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Old 11-21-2007, 06:47 PM   #11
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water jet bow and stern thrusters

Our thruster is rated for 3 minutes continuous which should be plenty. If you are running a thruster for anything longer than short bursts on a small boat, then you most likely should not be running a boat.
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Old 11-21-2007, 07:29 PM   #12
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water jet bow and stern thrusters

The thruster on the GB36 we chartered was probably rated for 30 seconds like Carey's. Five seconds does seem like a pretty excessive limitation unless the motor was the size of my thumb.

As to Carey's question, I don't know why some people use their thrusters while idling through a marina at four or five knots. I can see where the steerable nozzles like Gene described would work while a vessel was moving forward or backwards through the water. But the forward motion of a boat would greatly reduce the purchase of a conventional thruster impeller on the water since it would be flowing past the openings in the tube which would make it more difficult to be pulled into the tube and expelled from it.

But there are boats that are operated this way in our marina. Their thrusters are grinding away through every turn in the fairways. Perhaps the skippers haven't been able to visualize the fact that you steer the back of a boat with the rudder(s) not the front. This isn't so obvious in open water but it's very apparent in close quarters. So perhaps they can't judge turns when it's the back of their boat that's going to swing around, not the bow, and are more comfortable when it looks like their boats are steering like their cars. Ironically, most of boats I see maneuvered this way are twins--- big Bayliner/Meridians, etc.
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Old 11-21-2007, 08:54 PM   #13
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RE: water jet bow and stern thrusters

Agreed, I don't know why anyone would want to use while underway either. I see those guys steering through the basin by thruster all the time. Very strange.

I don't even have a thruster, I can only dream. I was merely stating the advantages, be them useful or not.

The few hydraulic thrusters I have been around were all nearly silent. The guy in the slip next to me comes into the slip and sets the bow and stern thrusters on continuously. Then he can leisurely tie up his boat while it holds itself to the dock. You don't even know they are on except for the swirls of water near the bow.

I think they are quieter because the hydraulic motors run at a low RPM as compared to electric. So you can gear closer to 1:1 and use a prop with more pitch.

The electric spin at relatively high RPM and I think it is the gear set that makes all the noise. Or cavitation of the prop spinning fast. Not really sure.

In my steel boat with 8.5ft of draft I can hear underwater really well. Like a underwater microphone. It is really interesting to hear people's props as they pass. The thrusters are the loudest and sailboat props are second. Motor boats are not very loud at all. I assume the noise is relational to the efficiency.
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Old 11-21-2007, 10:20 PM   #14
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RE: water jet bow and stern thrusters

Like John Baker's, my thruster is also rated at 3 minutes continuous running. This thruster, my third, is of the same manufacturer and model as the previous two but is considerably quieter. The explanation given me, when I stated that fact was that the tunnel has been faired considerably, while the other two were not.
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Old 11-22-2007, 12:05 AM   #15
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water jet bow and stern thrusters

I've just assumed the noisy electric thrusters are that way because they have really noisy gearboxes and little or no sound-deadening in their mounting.

-- Edited by Marin at 01:06, 2007-11-22
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Old 11-22-2007, 07:00 AM   #16
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water jet bow and stern thrusters

It is probably both. Heck, I enjoy that noise.....the sound of decadence....sorry, this is my first bow thruster and it is on a boat that really doesn't need it so it makes me look like a skilled boat handler.....and lazy!!

-- Edited by Baker at 08:01, 2007-11-22
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Old 11-22-2007, 09:24 AM   #17
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RE: water jet bow and stern thrusters

Well the hydraulic thrusters are very quiet, they can not be heard from the out side.* There is a 6 second delay when changing the thrust direction as one tube opens and the other closes.* But 90% of the time that is not a problem being the Eagle responds slowly which allows the time.*

*
I find being able to vary the thrust is a big benefit, so I can thrust the Eagle in a 360 degree circle.* Like in out present slip faces East the exist is west, so I can thrust the bow around at the dock.* The big advantage was waiting long periods to get through the locks and or under bridges as we can hold the position for hours. **Other thruster would be dead.*

Why would thruster be used while under way.* Most long range trawelr have a emergency tiller incase the stearing goes out,*in that case the thruster could be used to steer the boat, and/or with the forwared thrust could be used*as a get home.*

*
That being said I would still prefer a standard in the tube/propeller type hydraulic thruster which would give the same results but simpler and less expensive. ****
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Old 11-22-2007, 07:41 PM   #18
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water jet bow and stern thrusters

Thrusters are very convenient ways to cheat when backing longer distances with a single screw. While one can turn the wheel lock to lock, thrust forward to straighten out and then lock to lock back and continue backing, a 2-3 second burst on the bow thruster will bring the bow as far as you'd like to keep on backing in almost a straight line.

Of course the benefits are wonderful when getting in and out of narrow slips into narrow fairways. My boathouse requires backing to port to get headed the correct direction out of the marina. My left handed prop isn't real happy to do that, so once I get the nose almost clear of the boathouse the thruster swings the bow around quickly and efficiently. I have practiced going in and out without the thruster and it can be done. But why jockey around when the solution is so easy?

I guess I'll feel guilty about using my thruster when I see the twin engine folks routinely land on one engine as if it's no big deal. Most times I hear the broken twins calling for dock help before they enter the breakwater. And if it's windy they want an "easy" slip to temporarily park in until the wind dies down. Obviously not every Captain is like that but a large number are.

Thrusters are here to stay, at least on my boat.
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Old 11-23-2007, 08:35 AM   #19
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water jet bow and stern thrusters

Since when did this thread become about feeling guilty about using a thruster? I guess if the purists had their way (i.e., using no technological advancements at all), we'd still be in dugout canoes.

I'm one of the guys with twins, a planing hull and a huge amount of vertical surface area (that acts like a sail) to sweat when windy... which is most of the time on the water. I use my thruster whenever I need it, and don't apologize to anybody. Granted, it only takes a short burst to move the amount I need to move... but that's what it's for.

Landing on one engine? If it was my starboard engine, no problem... as that's the one that runs the steering pump, giving me relatively easy rudder control. If I only have the port engine, and the wind is blowing at the slightest, I'm one of the guys that's going to be calling Vessel Assist to help me get in my slip... and I'm not ashamed to admit it. I've done it w/o the benefit of the hydraulic steering before, and it's neither fun or safe.

Better to get help getting in than allowing the wind to grab me and slam me into the dock or my neighbor's boats when I've limited maneuverability. The $100 tip to the Vessel Assist pilot is money well spent... just ask my insurance company.
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Old 11-23-2007, 03:30 PM   #20
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water jet bow and stern thrusters

The challenge faced by a twin operator docking with one engine is a whole lot different than the challenge faced by a single operator docking with his only engine. In terms of propulsion, the only issue a single operator has to deal with is prop walk. His center of thrust is aligned with the centerline of his boat. The twin operator docking with one engine has his center of thrust offset--- sometimes by quite a bit--- from the centerline of the boat. This produces a pivoting or yawing moment that the single operator never has to deal with. Depending on the design of the boat, this yawing moment can be suprisingly strong. A single operator who thinks that running a twin on one engine is the same as running a single should try it sometime. Not much apparent difference at cruise in open water, but when it comes to maneuvering, it's two different worlds.

Depending on the wind and current conditions and the maneuvering requred to get to a specific dock, it may be extremely difficult if not downright impossible to get the twin running on one alongside without assistance. And if the winds are blowing hard or there are other considerations that, if the boat was not docked exactly right, could result in damage, the prudent twin skipper will elect to go to a dock that's easier to get into.

As for the single-engine (or twin-engine) operators that pooh-pooh thrusters and imply that skippers that have and use them are less than skilled, I would be willing to bet that if the Magic Thruster Fairy installed one on their boat one night, they would be using it the next time they took the boat out. I think it's a good idea for a skipper, particularly one with a single-engine boat, to learn to maneuver and dock without the thruster simply because the day may come when the thruster doesn't work. I think depending totally on a thruster to be able to dock--- or steer in the case of the folks who maneuver through marinas on thrusters alone--- is limiting and will put the skipper at a disadvantage should the thruster roll over and die or is not enough to overcome the conditions.

One of the best boat handlers I know personally is Carey of this forum. His single-engine lobsterboat has a bow thruster, and while he has stated he uses it when he needs it, I can't recall a time when I've heard it go off. He's fit his boat into some pretty tight places without needing the thruster and he obviously understands both the theory of docking and how his boat responds to specific conditions. But if a situation arose where a burst of thruster might make the difference between damage and no damage, he'll use the thruster. And I doubt that any of the many people who know and boat with Carey would think "What a wimp," if he did. It would just be seen as the smart thing to do under the circumstances.



-- Edited by Marin at 16:39, 2007-11-23
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