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Old 03 September 2007, 13:51   #1
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Jet-powered

Hi,
I am looking at a jet-powered rib. I have already read the only other thread I found re. jet-powered boats, but there are still a couple of questions that I would like to find answers to.
What kind of consumption would I be looking at here? I thihnk that this boat has a largish diesel as its power lump.

Is it possible to "convert" the boat to outboard/inboard as the case may be?
Not that I am thinking of doing this, but it is nice to know what is possible.

I hope that these questions are not stupid, but I really know very little about jet-powered units.

Tx.
Rupert.
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Old 03 September 2007, 14:17   #2
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A bit more info would be useful
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Old 04 September 2007, 04:25   #3
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http://www.rupertmarine.com/en/

Take a look at this with your name
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Old 04 September 2007, 09:15   #4
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Quote:
Originally Posted by rupert View Post
Hi,
I am looking at a jet-powered rib. I have already read the only other thread I found re. jet-powered boats, but there are still a couple of questions that I would like to find answers to.
What kind of consumption would I be looking at here? I thihnk that this boat has a largish diesel as its power lump.

Is it possible to "convert" the boat to outboard/inboard as the case may be?
Not that I am thinking of doing this, but it is nice to know what is possible.

I hope that these questions are not stupid, but I really know very little about jet-powered units.

Tx.
Rupert.

I think I would be able to help with a bit more information - we make a 1.7 litre 120hp diesel waterjet RIB - 6 metres overall and should use 27 LPH flat out, but in reality it uses around 10 - 12 litres per hour! It seats 5 with a big rear deck over the engine compartment, and we've fitted a "Monster Tower" to it for wakeboarding and with the 10" jet it will pull big guys up on a wakeboard with a great wake.

The hole in the bottom of the boat will be a handicap to fitting a conventional drive, as well as the wrong shaped one in the transom - the engine will be too far forward as well - a lot of work to convert to a conventional drive!

Not sure if that helps, but you might be able to use some of that as a comparison!
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Originally Posted by Zippy
When a boat looks that good who needs tubes!!!
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Old 04 September 2007, 12:02   #5
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Thanks.

Thanks guys. I really wish I had more info, but I just learned about these power units surfing around on the web and wanted to learn more about them.
I do seem to remember that the power unit was a diesel, quite big if I remember rightly, and that it why it struck me that it might drink a lot of juice.
Am just wondering whether they are better than ob/ib, I guess.
Rupert.
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Old 04 September 2007, 17:22   #6
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Water jet power isn't as efficient as normal props - prob about 20% difference. In smaller lighter boats it does have a few problems in rough weather - the pump can suck air instead of water which will reduce thrust.

Having said that they give you far more control - you can do a full speed stop without breaking anything - they are great in shallow water and for safety - and they are much kinder to the engine.
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Old 05 September 2007, 05:25   #7
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Revenger have just supplied a 32 which has had a 480hp Yanmar fitted,Hamilton water jet said it would do a max of 47 knots,imagine their amazement when the customer reported 52 knots !! Very nice unit though,very well engineered.
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Old 05 September 2007, 05:41   #8
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Quote:
Originally Posted by codprawn View Post
Water jet power isn't as efficient as normal props - prob about 20% difference. In smaller lighter boats it does have a few problems in rough weather - the pump can suck air instead of water which will reduce thrust.

Having said that they give you far more control - you can do a full speed stop without breaking anything - they are great in shallow water and for safety - and they are much kinder to the engine.
Although they are less efficient overall, a lot of commercial shipping use jets as they are more efficient at a specific speed, vary that speed and the efficiency drops off. Small diesels in RIBs or sports boats have the advantage of weight over say, a jet ski as they don't come out of the water as much - our 6 metre boat went over the Cowes for Ribex in a good force 6 without any problems!

Our diesel will go from 36 mph to facing the other way in not much more than its own length! The two week points of a conventional drive are the two 90 degree bends in the drive and the forward neutral reverse parts - a jet drive is direct permanent drive (some larger boats do have a clutch) or just through some gearing to get the revs of the impeller right making them less complicated and therefore much more reliable. (10 - 12 litres an hour doesn't do any harm either!)

Petrol jets tend to be quite uneconomical although the later Seadoo models are much better than they used to be!
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Originally Posted by Zippy
When a boat looks that good who needs tubes!!!
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