waterjet bow thruster

zt260

zt260

Well-Known Member
Joined
5 Oct 2007
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378
www.ashmouldings.co.uk
i am thinking of maybe installing a mini electric water jet thruster from www.willdo.eu i was wondering if anybody has any experiance with these and if any issues have arisen,sorry if this has been asked before.it would be fitted on a 28ft maxum single engine,i am looking at the 30kgf model.

ashley
 
Hi,

A company called B and B auto marine are fitting or are just about to fit the system to a boat in Yorkshire I beleive. Havent got the tel number but if you struggle to find it I have it somewhere.

Mike
 
i spoke to willdo yesterday and they said they had just sold there first mini system am guessing it maybe to the guys you mention,do you know if its at york marina as that is were my boat is.

ashley
 
A friend was short of space so fitted a water jet thruster.

It is only partially successful in that the jet still needs to be fitted at depth ( where the greatest water resistance is.)

My guess is the advantage of being able to fit a thruster to a small boat is lost as there will be insufficient depth at the bow.

It is no good having a powerful jet of water skim over the surface, there will be no significant push.
 
Mike i can get Phils number from Simon at acaster thats where i bought the boat and come to think of it i think it was you that surveyed it last august.

ashley
 
The design of the thruster you show has a further design fault( unless not shown in the diagram).

In order to get a powerful jet you need a large pick up, blasted out of a smaller hole.

The one you show is a 28 mm hole in and out.

There will be a vortex created like water down a plug hole.

this thruster needs to be fitted deep and your maxum will be very shallow draft at the bow.

I recommend a lot of research prior to ordering.
 
This diagram shows a large water pick up located on the bottom of the hull.

ENcover1.jpg


Which from other information on the site looks to be around 180mm in diametre.
 
Why? Surely outlet depth is irrelevent. I thought it is just Newton's 3rd law at play: "Every action has an equal and opposite reaction". So, if you chuck a load of water in one direction, a force will be produced, and move the bow, in the opposite direction. Exactly the same principal as the water jet main propulsion drive. When these jet boats are at speed, the water jet outlet is above the water.

All IMHO, not wishing to start an argument (debate maybe) or anything!!
 
Jez, thanks thats makes better sense but complete loss of the suction .

Jerry

The deeper you go the greater the water resistance.
A few inches make a huge difference.

That is how the Paddle wheel effect works on a prop that pushes to the side.


If you blast a jet of water to skim a surface it will barley push, may as well blast a hose into the air.

If the same jet is 2 ft under there will be a good push.

That is why I am concerned at the thought of putting one in the shallow bow of a maxim sports cruiser, there will be a few inches of depth only.

Any quoted figures need to be read bearing this in mind.
 
The one i am looking at is the mini electric which i dont think has the large intake hole just the 2 small holes,i appreciate what you are saying regarding depth of location,i need to check my boat for location/installation points first.
 
The whole idea of a jet drive is that it can be placed anywhere, top od deck if need be but where the jets exit is crucial.
The jets need to be well submerged.

An outdrive planing sports boat will barley manage a few inches at the bow where you need to put it.


I could be wrong, but I think you need to see one working on the surface before you fork out several gel coat repairs worth .
relying on being told it produces 4 hp of thrust at 3 meters could be misleading.
 
From the Hamilton Jet website:

HamiltonJet Waterjet History

In the early 1950s, when Sir William Hamilton began experimenting with marine jets, he followed the lead of the most successful invention to date, the American Hanley Hydrojet. Using a round centrifugal water pump that drew in the water and expelled it through a steer able nozzle under the boat, he was able to achieve an encouraging but unspectacular speed of 11 mile per hour.

A slight modification to expel the jet stream above the waterline proved the turning point in marine jet propulsion, increasing speed to 17mph and eliminating all underwater appendages. Waterjet propulsion was at last truly successful and the Hamilton Waterjet was born.
 
He he...fun you could have with an out-of-the-water waterjet bow thruster. Great for squirting kids in dinghys /forums/images/graemlins/grin.gif
 
A good explanation of why from a poster on boatdesign.net:

"To understand why most waterjets have the nozzle above the on-plane waterline, let's take a look at where the thrust of a waterjet comes from.

Ignoring for the moment the internal components, a waterjet is a classic example of Newton's laws at their simplest - for every force, there is an equal and opposite reaction force. Force is the product of mass times acceleration, or put another way, the rate of change of momentum.

To apply a forward force on the boat, the waterjet accelerates a large mass of water in the opposite direction. In early prototypes, with the output nozzle underwater, this posed a problem. Water is dense and incompressible, so the outlet stream quickly encountered a lot of back pressure from the surrounding water. It's very hard to get a high flow rate at a high speed with the surrounding water resisting the output stream (momentum = mass * velocity). Thus it quickly becomes very difficult to give the water leaving the jet a significantly greater momentum than the water around it.

When we move the outlet above the water, this picture changes. Air is compressible and about 600 times less dense than water, and so presents very little back pressure. Now it's not nearly so difficult to get the outlet flow to have both a high volume and a high speed, thus the change in momentum of the water through the pump is higher, thus the force is higher."
 
Well that leaves me somewhat confused to say the least.

Was only saying what my friend had discussed with me after he had fitted his.

Perhaps he needs to raise his and not lower it /forums/images/graemlins/confused.gif

Or perhaps your are discussing high speed jets that accelerate more the faster they go but the scoop effect will not work here as we are looking at slow speed jets /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

Not making any sense to me at all.
 
got to remember the one im looking at uses the outlet tube as the inlet tube so both tubes need to be under water,there is a part in their brochure that hints that they dont necessarly move the boat fast which isnt a problem,just got to check that i can locate them idealy5/6 inches under the waterline and forward enough
 
We had dealings with wildo recently, & whilst the equipment supplied turned out to be unworkable on our boat, they are nice guys to deal with & a refund was forthcoming without any problem, less transport costs etc, obviously.
 
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