Jet Thruster

Has anyone had experience with a jet thruster. My stern has only a 9" waterline. So I can't find any stern thruster that will work in that shallow water. Ran across a Jet thruster that claims to work in a small amount of transom depth. All advice welcome.

Thanks

I'm not familiar with a jet thruster.
Side Power makes cowls for their stern thrusters that allow them to work in shallow water. I think they would allow you to use up to their 215 mm stern tunnel.
http://www.imtra.com/COLLATERAL/DOCUMENTS/ENGLISH-US/PRODUCTS/STERN_THRUSTER_COWLINGS2015.PDF

Many years ago Vetus sold a thruster that had a large pump mounted in the boat with hoses leading to thru-hull fittings on each side of the boat. Valves would direct the water to the side that needed thrust. Is this what you're calling a jet thruster?

Haven't used one or see one in use. However, I think it's a very interesting solution. There are a lot of variations on them and I'd definitely want to find someone experienced in the model I was considering, which could be a challenge. In an existing boat, you could have difficulty in being able to locate the part inside the boat.

There are other options for your situation too such as retractable thrusters.

Just looked up Jet Thruster. That is the same idea that Vetus was selling. I really like the idea. One time at a boat show I asked Vetus why they dropped it but I didn't get a good answer.

I suspect it takes more power to get the same thrust as a prop in a tunnel thruster. If you can generate enough thrust, it would certainly solve your problem.

Keep us informed on what you find out.

Dixie Life said:

Has anyone had experience with a jet thruster. My stern has only a 9" waterline. So I can't find any stern thruster that will work in that shallow water. Ran across a Jet thruster that claims to work in a small amount of transom depth. All advice welcome.

Thanks

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Please post the link to the jet thruster. Sounds interesting.

Alaskan Sea-Duction said:

Please post the link to the jet thruster. Sounds interesting.

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https://www.hollandmarineparts.nl/jetthruster/jt-30

The most common use for them has been ski and wake boats.

Here is a link to the size calculator for a Jet Thruster.
https://www.hollandmarineparts.nl/jetthruster/systems

I plugged in a 41 ft power boat with 15' height and it said they don't make one big enough.

HopCar said:

I suspect it takes more power to get the same thrust as a prop in a tunnel thruster. If you can generate enough thrust, it would certainly solve your problem.

Keep us informed on what you find out.

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It does, they try not to talk in terms of hp but in terms of thrust. Holland has a calculator.

I used their calculator for a 50' but rather tall boat and got this response

Warning!
Based on the information you have entered your vessel will need a stagnation pressure larger than the maximum of 90 Kgf (157 KGF).

Due to the specific properties of the Jet Thruster, in some situations the largest available system, the JT-90, may be a good solution for easier manoeuvring after all.​

So, for the Holland product size of boat seems to be a challenge. Now, not like they don't exist for large boats.

Bow thrusters - Veth Propulsion - Thruster Supplier

HopCar said:

I'm not familiar with a jet thruster.
Side Power makes cowls for their stern thrusters that allow them to work in shallow water. I think they would allow you to use up to their 215 mm stern tunnel.
http://www.imtra.com/COLLATERAL/DOCUMENTS/ENGLISH-US/PRODUCTS/STERN_THRUSTER_COWLINGS2015.PDF

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There is a significant amount of space needed (3-5") inside the boat LOWER than the tunnel bottom with Side Power thrusters. The motor and housing extends down on the inside. I JUST barely fit one in to my AT34 and it was quite a bit larger than the OP's 9" available.

I wonder if you could rig the Jet Thruster as an emergency bilge pump as well? That's a huge pump.

Too bad the rear thruster isn't steerable! Also, I can't imagine not having 90 degreel ells on the hardware so the hose does not risk kinking at the hull fittings.

Dixie Life said:

Has anyone had experience with a jet thruster. My stern has only a 9" waterline. So I can't find any stern thruster that will work in that shallow water. Ran across a Jet thruster that claims to work in a small amount of transom depth. All advice welcome.

Thanks

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This might be ok in 9 inches. I cannot measure now, but this is a Dickson hydraulic thruster.

This is jet thruster is really cool. But for the price of the bow/stern, I could have a yacht controller installed.


Yacht Controller - Wireless Remote Control of Your Yacht

Dixie Life said:

Has anyone had experience with a jet thruster. My stern has only a 9" waterline. So I can't find any stern thruster that will work in that shallow water. Ran across a Jet thruster that claims to work in a small amount of transom depth. All advice welcome.

Thanks

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The US Navy now uses them on our submarines for main propulsion because they are quiet and do not exhibit the same cavitation as propulsion.

NO, I am not giving away secrets.

jleonard said:

This might be ok in 9 inches. I cannot measure now, but this is a Dickson hydraulic thruster.

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We had one of those on our old trawler... We called it "The Toe Chopper" (or The Toe Cutter if Mad Max is your thing)

I saw jet thrusters in operation on a 110' yacht about 20 yrs ago. I don't know anything specific about the thrusters, but my observation of them in use convinced me then that I would see lots more like them in the future. NOT!. don't know why, maybe just too $$$.

https://www.hollandmarineparts.nl/

No experience and limited overseas agents, but I have this linked for my own possible use.

I looked at doing a jet Thruster but ended up going with an oversized side power unit and have been really happy (limited use so far). I met one guy with the current jet Thruster from Holland and he was happy with it, i think he had about a ‘45 foot trawler but similar design to my kk54. I think I can find his contact info if you get super serious about it.
Two issues I found was I couldn’t find a single person who knew much about them or installed more than one. Add to that it took about a month for the owner of Holland to call me back.
Secondly I’m not sure I like the idea of a semi proven system (talking about the install/Holland not the concept) running massive pipes through the boat. If you have an issue you could sink yourself before you even get to the throughholes.

Would love to hear if you go with one, I thought about it also for a get home capability.

AC

Thanks Art. I'd really like to find out what size thruster he had installed. Their website advised a JT70/90; the salesman is saying a JT50. Since he has about the same size boat as mine, his experience will be a great help.

I am surprised they didn't use a large radius elbow on the fittings because unless the hose is wire wound, it is likely to collapse and cause a flow restriction. An elbow would have turned the hose barb headed aft rather than a 90 degree bend in the hose to push it on the hose barb.

Also, you don't need 9 inches, in fact, the exit can be above the waterline with the same effect. You do need to make sure you have the intake well in the water though or it will cavitate.

A 90 will reduce the flow by about 50%.
A 45 will reduce the flow by 25%.
A sweeping hose will reduce the flow some mathematically amount. I will leave that to the math majors providing you provide the radius of the 'sweep'.

OldDan1943 said:

A 90 will reduce the flow by about 50%.
A 45 will reduce the flow by 25%.
A sweeping hose will reduce the flow some mathematically amount. I will leave that to the math majors providing you provide the radius of the 'sweep'.

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But a hard 90 large radius elbow will reduce it less than a collapsed rubber hose. that was the basis for my message.

stubones99 said:

But a hard 90 large radius elbow will reduce it less than a collapsed rubber hose. that was the basis for my message.

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If there is a collapse I would think it would be on the suction side.
BUT, the hoses do look like they are wire reenforced

They are wire enforced. Intake 3”, exh. 2”. The 2” will have only a positive pressure; a 90 will only reduce pressure by 10% as per specs.

Based upon Heat Transfer and Fluid formula, the output will be decreased a 90 will decrease it by 50% and a 45 will reduce the output by 50%.
Something about the friction.
I had a problem with a 90 in a sanitary line between the head and the sanitary tank and when changed to a 45 all the problems went away. The semi-solids were able to slide easier to the tank.