Water jet bow thrusters

[Robin]

Years ago I remember I think Vetus made bow thrusters that worked by pumping water jets instead of having a propellor in a tunnel. The obvious advantage was there was no need for the large diameter tunnel through the hull, just a couple of skin fittings, plus the pump presumably could be located farther away if necessary.

I haven't seen anything like this advertised for years, does anyone know if they are still made or even does anyone have one? This is inspired by another post about fitting a thruster on a 34ft boat rather than any real need as even with just 2 of us we manage easily enough with a responsive 41 footer.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[pvb]

No good for small yachts...

Yes, I remember seeing a water jet thruster advertised years ago, and it probably was by Vetus. Although they sound good in theory, they're really no good for smallish yachts. The problem is lack of efficiency. To get the same sort of thrust as a conventional thruster, but using small diameter outlet pipes, the pressure involved has to be huge, and the power consumed is much greater than with a conventional thruster - maybe 3 or 4 times as much! To reduce the power consumption with a water jet thruster, it's necessary to lower the pressure and increase the pipe size, but then you end up with the same size holes in the hull as with a conventional thruster. So it's a non-starter for smallish leisure craft. But for larger commercial vessels, it is a possibility.

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[Mudplugger]

Re: No good for small yachts...

Can understand the reasoning you give, but if one sticks a hose pipe in the water, powered by a 4hp pump, there is quite a lot of kick, ( experienced on the rare occasions, when trying to clean an E. coast S.C. slipway) From a purely personal point of view, I would have thought that there was sufficient thrust to push the bow, from say a 2" outlet. A 2hp reversable water pump is a lot easier to fit than a Bow-Truster! ...Tony W

<hr width=100% size=1>Tony W.

 

[Mudplugger]

Re: No good for small yachts...

Can understand the reasoning you give, but if one sticks a hose pipe in the water, powered by a 4hp pump, there is quite a lot of kick, ( experienced on the rare occasions, when trying to clean an E. coast S.C. slipway) From a purely personal point of view, I would have thought that there was sufficient thrust to push the bow, from say a 2" outlet. A 2hp reversable water pump is a lot easier to fit than a Bow-Thruster! ...Tony W

<hr width=100% size=1>Tony W.

 

[pvb]

Smaller diameter means...

Smaller diameter outlets limit the volume of water which can be shifted. In order to maintain thrust as the outlet diameter reduces, the pressure has to be increased significantly. You can only generate sufficient pressure with a mighty pump, which uses loads of power. It can be done, but to match the thrust generated by a conventional 2hp bow thruster, you might need a 10hp pump, which is a lot of amps at 12volts!

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[rich]

Re: Smaller diameter means...

How would an air comppresser work, big bubbles pushing the bow..

<hr width=100% size=1>http://www.jersey-harbours.com

 

[Robin]

Re: No good for small yachts...

Yes I think I see where you are coming from, but what I remember seeing was a standard offering in the Vetus catalogue, ie intended for leisure boats and had just a small skin fitting much like the loo outlet. Maybe it didn't work very well and didn't catch on. Idle curiosity really but it would be nice if someone out there had one at some time.


<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[ashley]

see here <A target="_blank" HREF=http://www.capsante.com/Pages/thruster.html>http://www.capsante.com/Pages/thruster.html</A>

<hr width=100% size=1>Live life to the fullest... think of all the people on the Titanic who passed up chocolate dessert.

 

[Robin]

Thanks, at least I know I wasn't dreaming that I had seen one! So far we have managed well enough without a thruster even with just 2 of us on a 41 footer but she is very responsive (the boat is too!) and it is surprising what can be done with warps and a bit of forethought.

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>

 

[philip_stevens]

Nigel Irons had one fitted to his high speed trimaran during the days of Peter DaSaravery's (spelling??) America's Cup attempt. I saw it in use when the trimaran came into Mylor Yacht Harbour. It appeared to work quite well.

<hr width=100% size=1>regards,
Philip

 

[alan]

Re "what can be done with warps and forethought" ............. were you still talking about the boat???

Alan.

<hr width=100% size=1>Alan Cloke

 

[Robin]

Assuming you did want a serious answer...

We are in a downwind berth with the prevailing wind, with just 2 of us on a 41ft boat and need to turn smartly getting in and out. We might therefore move the boat way back in the berth by using a spring line and easing other lines to match, lines with no load can be let off, the engine isn't needed to do any of this either. If we need help to turn the boat it can be done by rigging a (doubled for slipping) fore or aft spring and motoring forward or backwards as needed against this to swing either the bow or stern in/out as needed - leaning on stategically placed fenders.

Coming into our home berth we use a central spring line only, marked at the right length. Once attached the engine is put back in gear and the wheel over, the boat sits there nicely until all the lines are on. If going into a visitor berth we will have fenders and lines both sides including the centre spring (hopefully the finger is long enough to use it), we will if possible chose a berth that fits our prop kick, ie turn to starboard going in (port going out) and berth portside to.

There are lots of ways for different circumstances like leaving from quays or fore/aft piles or buoys. All it needs is a little thought beforehand as to 'action and reaction', ie if I let this go, or if I pull this what happens? This whole subject is a book in itself and the magazines fill their pages with it most months.

Robin

<hr width=100% size=1><font size=1>Sermons from my pulpit are with tongue firmly in cheek and come with no warranty!</font size=1>