Jet Thrusters vs traditional tunnel

[krush]

Betcha I can make one out out of scraps for cheap:

https://www.youtube.com/watch?v=Gx93wqOb16s





https://www.youtube.com/user/hollandmarineparts/videos

 

[krush]

Another video: https://www.youtube.com/watch?v=lh8JnkDu3CA


and simple install https://www.youtube.com/watch?v=7pPzvpngkHM

Here's some interesting theory written in the comments:



Carmel Pule'
5 years ago
Looks like a good quality product, which it is of course. Attention has been devoted to everything of importance, gate valves close to the hull units, those pipe clips are of the best quality I have ever seen. It is amazing how much momentum a two inch diameter hose pipe can generate. Here is a question for the science or physics minded people. Would the thrust generated alter if the output nozzles were above or below the waterline? Above the waterline the jet exhausts in air surroundings while below the waterline it exhausts in water surroundings. The answers to this question should be interesting.

3


Jet Thruster
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Jet Thruster
Jet Thruster
5 years ago
Hi Carmel, the answer is a surprise to many people: More force/momentum/impulse is generated when expelling water above the waterline. Not much but a bit more. When generating thrust with a water jet, it's all about the flow and speed of the water which exit the nozzle. Turbulence near nozzle opening below the water line slows it down, above the waterline a few percent more thrust occurs. Our systems are designed to function below the water line. We recommend to place the nozzles max forward in the hull for a maximum arm of momentum towards the pivoting point of the boat.

 

[whoover]

I was thinking about something like this year's ago. Having one power unit and being able to send thrust where you want it is interesting. Running hoses through the boat could be tricky.

Walt Hoover

 

[Pascal]

It s an interesting system for small shallow boats but there are two concerns

First of all, the high number of hoses, clamps, fittings etc greatly increase the risk of disastrous failure. Second, i looked up the conversion from Kgf to hp and even their biggest unit only puts out 1 hp…. That’s way less than a conventional thruster.

I don’t see the big deal about the fiberglass work installing a conventional thruster. Yes it requires professional installation especially the tunnel drilling part but the glassing is no big deal and when you re done you get a solid maintenance free structure with zero chance of sinking the boat.

 

[cww]

What's all the hoopla with thrusters on hatts? I know they're all the rage on modern yachts, but by and large modern boats have shallow drafts, no keels, and a lot of windage, which makes them useful. Hatts are heavy and have a substantial keel, they pretty must just sit where you leave it until you use the engines to move it. They're all twin engines with large propellers, which makes for good response around the dock. I have never once felt that I needed a thruster on this boat, or wished I had one. Stabilizers are another story, however...those are on my wishlist.

 

[SKYCHENEY]

What's all the hoopla with thrusters on hatts? I know they're all the rage on modern yachts, but by and large modern boats have shallow drafts, no keels, and a lot of windage, which makes them useful. Hatts are heavy and have a substantial keel, they pretty must just sit where you leave it until you use the engines to move it. They're all twin engines with large propellers, which makes for good response around the dock. I have never once felt that I needed a thruster on this boat, or wished I had one. Stabilizers are another story, however...those are on my wishlist.

100% agree. I know of a couple of people that added thruster to Hatts shortly after buying the boat only to later admit that they rarely ever use them and shouldn't have spent the money on adding them.

 

[krush]

It s an interesting system for small shallow boats but there are two concerns

Second, i looked up the conversion from Kgf to hp and even their biggest unit only puts out 1 hp…. That’s way less than a conventional thruster.

First of all, the high number of hoses, clamps, fittings etc greatly increase the risk of disastrous failure................ and when you re done you get a solid maintenance free structure with zero chance of sinking the boat.

You are going backwards on your conversions. All that matters is thrust (force). Trying to equate HP to thrust is silly. Water jet, propeller, paddle wheel, they all produce thrust, and that is what ultimately moves the boat. You're comparison is ridiculous.

And I imagine a leaking seal on the shaft of a bow thruster could easily sink a boat. It may be less likely, but nothing is impossible.

 

[Pascal]

Since KgF is a unit which converts to HP, it is a valid comparison especially as that is what they provide… and obviously 90 KgF is far more impressive than 1 hp…

All the thrusters I have experience with have a sealed gearbox to which the motor is attached to. No shaft seal into the boat. In case of a leak water will get in the gear box but not in the boat

 

[whoover]

I feel there is a place for a bow or stern thruster but it is getting a bit silly. In our small club we have at least four boats around 34 feet with a bow thruster, also some of the scariest boat handlers in the place. A thruster is not a miracle cure for poor docking skills. My neighbor on a 40 Searay has both bow and stern installed by previous owner but he won't use them if I'm watching him.

Walt Hoover

 

[Bob Quinn]

I feel there is a place for a bow or stern thruster but it is getting a bit silly. In our small club we have at least four boats around 34 feet with a bow thruster, also some of the scariest boat handlers in the place. A thruster is not a miracle cure for poor docking skills. My neighbor on a 40 Searay has both bow and stern installed by previous owner but he won't use them if I'm watching him.

Walt Hoover

"Thruster Shame" I think it's a thing.

 

[krush]

Since KgF is a unit which converts to HP, it is a valid comparison especially as that is what they provide… and obviously 90 KgF is far more impressive than 1 hp…

All the thrusters I have experience with have a sealed gearbox to which the motor is attached to. No shaft seal into the boat. In case of a leak water will get in the gear box but not in the boat

So force is the same as power, it just converts easily? LOL! KgF is a FORCE, and HP is, well, POWER. They are completely different unit and are not "converted". This is primary school physics class.

Power is work done per unit of time. Work is a Force X distance. Therefore Power is (Force X Distance) ÷ Time.

Force is a vector, power is a scalar.


And what is on the top of that gearbox....does it have a vent? So water leaks into the gearbox that is below the waterline. Water fills up gearbox, because pressure outside failed gearbox seal is greater than pressure inside gearbox. Gearbox fills up with water and pressure in gearbox is now greater than pressure outside of gearbox, and then what happens?

 

[Pascal]

So force is the same as power, it just converts easily? LOL! KgF is a FORCE, and HP is, well, POWER. They are completely different unit and are not "converted". This is primary school physics class.

Power is work done per unit of time. Work is a Force X distance. Therefore Power is (Force X Distance) ÷ Time.

Force is a vector, power is a scalar.


And what is on the top of that gearbox....does it have a vent? So water leaks into the gearbox that is below the waterline. Water fills up gearbox, because pressure outside failed gearbox seal is greater than pressure inside gearbox. Gearbox fills up with water and pressure in gearbox is now greater than pressure outside of gearbox, and then what happens?

Have you used a bow thruster? Have you ever troubleshot one? Have you ever repaired one? Replaced a gear box?

 

[krush]

Have you used a bow thruster? Have you ever troubleshot one? Have you ever repaired one? Replaced a gear box?

Have you ever taken an elementary physics class, let alone a major engineering design course? Water sill flow from high pressure to lower pressure if seals fail. Full stop, end of story.

 

[Pascal]

Have you ever taken an elementary physics class, let alone a major engineering design course? Water sill flow from high pressure to lower pressure if seals fail. Full stop, end of story.

Thank you for answering my question.

 

[krush]

Thank you for answering my question.

Your question is deflection from your own arrogance and ignorance. It has nothing to do with the topic at hand. I've repaired, oeprated, modified, and even redneck rigged a little on every type of system you will find on a vessel (well, a big boy vessel). EVERYTHING

Any hole below the waterline has a potential to sink the vessel. No matter how you like to two-step around it with non-sequitur or red herrings.

 

[SKYCHENEY]

Your question is deflection from your own arrogance and ignorance. It has nothing to do with the topic at hand. I've repaired, oeprated, modified, and even redneck rigged a little on every type of system you will find on a vessel (well, a big boy vessel). EVERYTHING

Any hole below the waterline has a potential to sink the vessel. No matter how you like to two-step around it with non-sequitur or red herrings.

Bow thrusters only leak on sailboats

https://www.myhanse.com/bow-thruster-leakage_topic11520.html

 

[Pascal]

Your question is deflection from your own arrogance and ignorance. It has nothing to do with the topic at hand. I've repaired, oeprated, modified, and even redneck rigged a little on every type of system you will find on a vessel (well, a big boy vessel). EVERYTHING

Any hole below the waterline has a potential to sink the vessel. No matter how you like to two-step around it with non-sequitur or red herrings.

Talk about arrogance …

As such an experienced engineer, it s surprising that you don’t understand that a high pressure water systems with multiple hoses, clamps and connectors is more prone to catastrophic failure than a sealed gearbox. Sure a seal could leak but it’s extremely rare and will be minimal.

 

[krush]

it s surprising that you don’t understand that a high pressure water systems with multiple hoses, clamps and connectors is more prone to catastrophic failure than a sealed gearbox. Sure a seal could leak but it’s extremely rare and will be minimal.

The discussion had nothing to do with " multiple hoses, clamps and connectors is more prone to catastrophic failure". It is obvious more houses, a pump, and various connections provide more components that can fail. However, there is valve on every through hull to isolate--but I never said this was a "safer" or "better" system.

You claimed that traditional bow thrusters can't leak inside the boat and can't sink the vessel. Another thought, there is no isolation valve on a bow thruster to close off the outside water if(when) a seal does fail.

 

[q240z]

That looks perfect for the sailboats shown in the first video.

At my old yacht club, there was only one exception to the rule that sailboats returning to slips is closer to crash-landing than docking. The one sailor who was skilled in docking was a former Navy yard commander. All the rest, including every visitor, would benefit from having systems like that.