Jet Drive for 10m tour boat - weed and shallow water solution needed

So I am planing to build a tour boat - See this post for more details

The boat will be 10m long with 3m beam, needs to transport 15-20 people in shallow water but sometimes on lakes filed with weed (fresh water weed) with cruising speed of 40-50 km/h and low speed manoeuvrability. I will be build of aluminium most likely.

I am researching if a jet propulsion would be suitable for that. Until a few days ago I was convinced that it will not work but since I have seen the videos with Phantom Jet boats I thought I might give it a chance here and ask.

Will this system work for a boat as large as this one?
What is the secret behind this boat? - I have seen the recessed intake on the boat bottom but is that all there is to it?



The other requirements for the boat where - shallow draft and low wake just like the M-hull or the Inverted V hull. Any idea about that?

If weed goes in the turbine how do you take it out? Or is this going to be shredded and expelled? How does that affect the longevity of the Jet pump?

What about reversing a boat in a weed infested canal?

These are just a few questions at this moment as I have no experience wit the Jets I can't say if they are dumb or not but I'm sure I will find out soon )

Thanks,

Daniel

 

Hi Daniel,

In short: yes, jets can be a good option for high speed applications in shallow waters. There are, however, quite a few ways to screw it up. The jet pump supplier should be involved fairly early in the design process, before the hull shape is finalized. Their engineers see requirements like yours all the time and can help to ensure that you'll end up with a hull and drive that are appropriately matched.

At the scale you're talking about, the jet drive suppliers would likely be Hamilton, Ultradynamics, etc. instead of the Mercury Sportjet and American Turbine pumps used by Phantom. Be prepared for the sticker shock of upgrading to these commercial-grade pumps.

Speaking in very general terms, jets tend to be less susceptible to weed-related problems than outboards or sterndrives, but they can still suck up enough weeds to stall the engine. There's often a cleanout port in the top of the intake duct that extends above the waterline and can be opened while the boat's in the water.

Rocks, sand and other hard materials will do a fair bit of damage to the drive if sucked up. I suppose fishing line could damage the seals, and strands of floating rope are of course an excellent weapon against PWCs (if sucked in, they wrap around the shaft and jam the thing up). So they're not impervious to damage, but are arguably more likely to survive impact and sucking-stuff-up than a typical outboard.

 

Hy Mat,

Thank you for the reply. In general I am not concerned about the floating ropes and fishing line because there's little or none where I operate the boats. The main concern would be the the vegetation. As the boat is heavier than the Phantoms it will have more draft so the weed will be closer to the intake... also take off will be slower and that's the moment when the vegetation can be sucked in and stall the engine. This is my main fear.

In the 70's they have build some jet boats here in the Delta that could go anywhere using a 250 hp v6 engine... the only problem was excessive weed that stopped the boats in the middle of lakes. I know the technology was primitive compared to today's turbines but I had to ask. Jet drives fascinate me and they are so practical.

What about the noise? Are they noisier than conventional propulsion? Dumb question again but..

What is in general the price of a Hamilton turbine for a 300hp Diesel? I have no clue about that either but I guess putting out the gear box and shaft etc would make it "buyable".

I wish I had a jet boat near me somewhere to go and test it... but I guess this is the price to pay if you like pioneering stuff...

 

Monofilament fishing line is a killer...also plastic bags. If these affect your area of operation make sure the jet manufacture is aware and installs defenses.

 

Monofilament fishing line might be a problem sometimes as they lie floating around sometimes and plastic bags... where on earth there is no plastic bag problem ...

I know high speed boats suffer from plastic bag problems and if one comes to the intake of a jet propulsion it's fly time for all on deck at 40km/h. What kind of defences are there for such situations? Can you use a rope cutter on a jet propeller? That would help even with the weed but I guess it messes up the whole efficiency and all...

 

Don't go jet it's not for your application. Ok ish at high speed but don't ever slow down and hope to restart ,high intake suction will cause blockages in weed and damage in silt in shallow water.
it's not just stalling the engine thats the problem it gets your cooling long before that. Trolling and displacement speeds are almost as bad. Getting back on the plane in very shallow water ,whatever the seabed,is difficult without causing damage ,ok if you are racing .but not under your circumstances .The jet featured has a lowering weed grill ,and the wise owner will order the optional weed rake ,both supplied for a reason. Noisy jet boats are nomally just not properly silenced ,underwater exhausts are discouraged as they add to cavitation in reverse. A reverse cut thread on the shaft is thought to prevent monofilament winding in and cutting the shaft seals

 

Im not completely aware of the design of the shaft seals on a jet. I only see them from distance when being serviced at the shipyard. . On a normal ,say...bow thruster, the monofilament line gets between the prop and the shaft seal and eats the seal out. Plastic bags do the same thing. It would be important to ask the jet supplier how they defend their shaft seals. Plastic is normally a problem when docking or maneuvering at slow speed in polluted harbours. Once up and running it shouldn't be a big consideration. Ask the jet manufacture for guidance. One problem with a jet is that you cant see whats happening inside the tunnel without actually opening up the inspection and having a look. A well designed inspection hatch is important. The jets mentioned like Hamilton are top equipment. perhaps they have liturature on the net.

 

You might contact these folks: http://www.bentzboats.com/commercial_sample.htm

They built three of the larger passenger jet boats operating in my area, "Big Blue", "Sommer Star" and "Orca Odysea"

While not designed for weeds, they are about the right size for your requirements, with shallow draft, and very fast.

 

Well Anthony I am afraid you are correct about this and this is also my fear. There are so many pros and cons that make almost impossible to chose a different type of propulsion than the traditional propeller with its shortcomings and all.

Seeing that Phantom boat made me think again about jets and their advantages for such application. As I said I have no experience what so ever apart the few jets on the Danube I consider ancient dinosaurs. They did their job thou for many years...

Should I go then for tunnel props? What is your advice.

@MatthewDS - Thanks for the link, interesting boat builder, I will ask maybe they know better. Do you see them on water? Are they noise? Have you ever heard of their problems? ... Sorry but I had to ask .

Thanks

 

I have never ridden in, or worked on those boats, but I used to work in the marina that the tour boats operated out of. In the beginning, I believe they had some trouble with blown out the engines, I assume as a result of inexperienced captains pushing them too hard.

They are somewhat noisier than a non-jet powered boat of the same size, due to the drives being so close to the surface, but I'm not sure if it would be noticeable when running.

 

My knowledge of tunnel props is limited ,If you are lucky Baeckmo, CDK et al will chime ln , if not PM them ,Common sense suggests that with that much weed in the water,they will probably knit rope out of it.

 

I can say straight away that most of the water jets not tolerate aquatic vegetation. This applies particularly to the classic water jet with a conical nozzle. What would you not say, quite insensitive to the grass, water cannons do not happen. There are just less sensitive and more sensitive. Для того, чтобы ходить по траве требуются особые подходы и решения.

You should be alert to the possibility that the efficiency of propulsion that can walk on grass, will be slightly lower than usual. But it's inevitable price to pay for the convenience of not thinking about grass.

If interested, I'll try to describe all that I know of a solution.
They are not so much.

 

If the water is too shallow or vegetated for a jet, it's probably also too shallow or vegetated for a sterndrive, outboard or conventional inboard.

Folks who live near mud flats have created drives specifically for this application- tunnel mounted, swept-blade surface props that can work on the mud and that shed weeds. Ultimately, though, if the water is so shallow you can't use a jet, you should probably be thinking of an air propeller or even a hovercraft.

 

Well SKR as you see I am interested in any good viable solution so I'm all ears if you have experience with such propulsion systems and hulls. As they say an optimist is a poorly informed pessimist. I know that weedless propellers are less efficient that's why I was trying to avoid them for high speed.

@MatthewDS -thanks for the info it is good to know because there is a lot of theoretical info and so few facts from the field. I would like to talk to a person that owns a Phantom just for a second opinion...

@anthony goodson - my current boats go well in the weeds but the only problem we have is with the cooling system, luckily we have some iron cast old tractor engines one them and they can run without water for a few minutes without harm... in the past 20 years we had no problem. I am thinking about keel cooling but that rises other problems.

 

The water level we would need to navigate in summer is 60cm to 1m often packed with vegetation. I wouldn't worry about mud thou as 60 cm of water is plenty for such flat bottom boat.