HAMILTON WATERJETS

[bob_tyler]

It was interesting that MBM compared shaft, outdrive and IPS but ignored Hamilton (the only ones I know of) Water Jet Propulsion, despite being in the Southern Hemisphere..

The three methods of propulsion involving propellors all protrude below the bottom of a boat and are therefore exposed to damage from flotsam. The waterjet has no such exposure to damage.

Have any forumites experience of waterjets. For example, maintenance problems, increase or loss of power compared to the various forms of props, freedom from damage by flotsam, comparative fuel consumption or any other points.

Reduced draft must also be an advantage.

Why have they not really caught on?

The only UK built power cruisers I can think of fitted with these are the Swordsman range.

Discuss?

 

[Ships_Cat]

Why have they not really caught on?

Must be a UK problem, but if so it would seem strange because Rolls Royce are a big maker of water jet drives (product name is Kamewa). Water jets are very popular in USA, Australasia and the Pacific at least, especially on commercial power cats. I think you may find that cost is an issue when it comes to pleasure boats and don't come into their own until boat speed exceeds around 25 knots.

I don't pay much attention to new builds in the UK but I am aware of 3 big water jet powered cats (commercial passenger) built there but exported to Caribbean.

John

 

[Talbot]

One reason that they are not as popular as they desrve, is the space requirement. The move has been very much towards outdrives where possible to maximise the internal volume, but the jet drive demands that the engine be even further foward in some cases than a conventional shaft drive. Thus not popular!

 

[Ships_Cat]

I don't think you will find that is a problem in the boats they are fitted in. Two reasons come to mind (taking Hamilton as an example) -

- As far as I know the smallest Hamiton unit has a power capability of around 260kW so we are not talking of very small vessels (and except for special situations such a running braided or heavy rivers, twin jets are common so maybe 500 kW) unless of high performance.

- The distance from the transom to the coupling on that unit is only 500 mm and it is usually possible to do without a gearbox so is a space saving from that omission.

I have been involved in the builds of number of fast high quality larger water jet powered vessels and some smaller ones (around 18 foot for adventure tourism, high performance with very high loads on board) and any extra space requirement is not an issue that I have ever come across.

Putting all that aside, they are not common on smaller pleasure boats except for special tasks such as running braided or heavy rivers, etc and I suspect the main reason is cost and best performance being at sustained high cruising speed (which smaller pleasure boats have no hope of keeping up in the sea).

{Edit: Cranky's general claim that they are less efficient than a prop drive is incorrect - as I have pointed out, they come into their own at boat speeds greater than around 25 knots, they are not a drive suited to slow vessels (except when manoeuvring when they are the best drive around, especially if dual, triple or quad).

If you are on the Solent, have a look at Red Jet 4, a water jet powered vessel (has 2 x MJP Swedish water jets) I am familiar with and in your backyard}

John

 

[cranky]

Had a lot of experience with PP Jets, Castoldi and Doughty in the late 70's, all very manouverable and very safe for rescue work and shallow water operation.
The down side was that the system is less efficient than a prop so the engine worked harder to produce the power resulting in higher fuel consumption.
In shallow operations gravel was easily picked up causing excessive wear to the impeller and sleeve, thus reducing efficiency even further.
We did a lot of trials with the police and fire brigade in London,
but these were thwarted by the amount of rope and polythene that was drawn into the impeller despite the weedrake over the intake, very difficult to clear unless you can lean over the transom to access the inspection hatches, so restricted to boats with a low freeboard.
The system was always treated with suspicion, which is probably why it has not caught on in a big way, except with jet skis and ribs of course!

 

[cranky]

With recent systems you may well be right, as I stated, my experience was in the mid 70's and was based on comparisons at that time with like boats and engines fitted with sterndrives and jets.

 

[fisherman]

Cygnus put a jet in a Cyclone for Gerald Northey in Newquay a few years back. The jet needed about 3000revs, so the Sabre 300hp had to be run a bit fast. We thought a step-up gearbox might be better. It had a PRM gearbox, although you can run with a carden shaft. This was to enable the intake to be blown clear of weed etc. We were shown a video of it doing about 30 kts through about ten inches of water (unintentionally!)

 

[thefatlady]

They've been around for a long time. Back in the early 50s, my father bought an Aquajet 4hp outboard. It was continually getting blockages on the cooling system. We still had it in the 60s, when I put on a Thames hire boat and broke the transom.

 

[fisherman]

Was that an Aurora Aquajet? We had one, almost useless.

 

[thefatlady]

Don't know, but this is the only picture of it I could find.

Thats me, my father and the outboard in a WW2 collapsible dinghy alongside the MTB I was raised on.

The outboard had a horizontal propeller so that it sucked up the water and threw it out of the back. It was slow, but would push a heavy load. It also had an exposed spark plug, as I discovered when I held it while my friend started it!

 

[fisherman]

The very same!