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Old 11 September 2005, 12:40   #1
nik
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jet drives

Hello all,
I was wondering if any of you had experience of jet drives and what you thought of them.
I realise that there are pro`s and con`s. So to kick you off, here is a list of what I have been told about them.

Pro`s
safe (no mincer at the back), can be used in shallow water (no prop to damage), highly manoueverable, very quick stopping, no reverse gear to engage.

Con`s
more expensive to run, or less efficient, if they leave the water, they land "dead in the water" because the drive needs to refill with water. However it has also been put to me that these drives are usually found in larger boats therefore less likely to leave the water. I also know of an ocean dynamics rib in the scillies that ingested some seaweed and had to be towed back to port, I dont know how common that is.

And I have absolutely no idea about maintenance, but I am aware of some of the shortcomings of drive legs.

Thanks, Nick.
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Old 11 September 2005, 12:52   #2
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Hi, I looked after a Copy of a Hinckley Picnic boat for a guy last summer. It had a 300hp Yanmar driving a Hamilton jet unit. Didn't go much on it at all.It weighed around 2.5 tonnes and struggled to do 24 knts. This may have been due to a poor impellor set up, but was rubbish for the amount of HP.Don't be fooled by that shallow water guff. They hate shingle etc. and we also stuffed it full of weed. It took all afternoon to get it all out. The dump bucket would jam, which was scarey when going along side, as you then had no astern (brakes). The big plus is, as you say safety. Otherwise. not for me., I'll take a prop antime.
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Old 11 September 2005, 15:25   #3
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Quote:
Originally Posted by nik
Hello all,
I was wondering if any of you had experience of jet drives and what you thought of them.
I realise that there are pro`s and con`s. So to kick you off, here is a list of what I have been told about them.

Pro`s
safe (no mincer at the back), can be used in shallow water (no prop to damage), highly manoueverable, very quick stopping, no reverse gear to engage.

Con`s
more expensive to run, or less efficient, if they leave the water, they land "dead in the water" because the drive needs to refill with water. However it has also been put to me that these drives are usually found in larger boats therefore less likely to leave the water. I also know of an ocean dynamics rib in the scillies that ingested some seaweed and had to be towed back to port, I dont know how common that is.

And I have absolutely no idea about maintenance, but I am aware of some of the shortcomings of drive legs.

Thanks, Nick.
I have used jets for years and now run the 9 mtre Seawolf with twins of which we built.

You will not get quite get the same top end speed but the jet has no losses like a prop.

You have had a response from some one else running them down, obviously has had little experience of them.

Most jets will drive direct from the engine, but you can fit a gearbox giving you the option to back flush.

You have ultimate manoueverability with jets, you do not get that with props.

I am a proffesional boatman with some 30 years experience, and have used all sorts of combinations in boats.

If you would like to try out jets, PM me.
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Old 11 September 2005, 15:38   #4
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Quote:
Originally Posted by pressman
I have used jets for years and now run the 9 mtre Seawolf with twins of which we built.

You will not get quite get the same top end speed but the jet has no losses like a prop.

You have had a response from some one else running them down, obviously has had little experience of them.

Most jets will drive direct from the engine, but you can fit a gearbox giving you the option to back flush.

You have ultimate manoueverability with jets, you do not get that with props.

I am a proffesional boatman with some 30 years experience, and have used all sorts of combinations in boats.

If you would like to try out jets, PM me.
Dear oh dear, that old "I've been a boatman for 30 years" shit and so was my father and his, going back 300 years. It was my opinion. And,yes you obviously are far more jet experienced than I and more biased as you sell them. The boat I ran did have a reverse gear flush facility. I could have flushed it until christmas and it wouldn't have gotton the weed out. We had to remove the inspection plate and grab handfulls of it at arms length until we got enough out of the pick-up grid to allow flow.
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Old 11 September 2005, 15:44   #5
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Originally Posted by Mollulnan
Dear oh dear, that old "I've been a boatman for 30 years" shit and so was my father and his, going back 300 years. It was my opinion. And,yes you obviously are far more jet experienced than I and more biased as you sell them. The boat I ran did have a reverse gear flush facility. I could have flushed it until christmas and it wouldn't have gotton the weed out. We had to remove the inspection plate and grab handfulls of it at arms length until we got enough out of the pick-up grid to allow flow.
ok, each to their opinion,we're all entitled to that!! Dolphin boats do sell jet boats, also outboards and outdrive legs. whatever the customer requires.
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Old 11 September 2005, 16:00   #6
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and grab handfulls of it at arms length
dats cuz yew cawnish nobburs av gott verry shawt arrms.

eyve bin onn de pis wiv sum ov yorr lott an ther ands downt seam too reech ther fkin pokkits.

gArf
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Old 11 September 2005, 16:04   #7
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That's coz weez rite on at gettin' you English to stick your 'ands in your own pockets! Tiz Cornish enterprise.
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Old 12 September 2005, 03:32   #8
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Have used them a lot. OK they do block occasionally (mainly idling about in harbours) and you can loose power if the intake comes out. BUT... if you have one set up properly to the boat you will never want to drive anything else. It is in the harbour where they are great and shallow work - you really can turn on a sixpence and with a little practice go sideways. Real fun when you have mastered it. Unblocking is normally easier if you simply open the inspection cover.
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Old 12 September 2005, 03:40   #9
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You're right Rodin, with experience, great fun. We never had a lot of luck or fun with the "Hinckley". I did the "jet" thing in Westport, South Island, NZ in a 15ft Aluminium thing with a tuned 7.4ltr lump driving a 2 stage Hamilton jet. It genuinely scared me shitless! Apparently Shotover river in Queenstown is a bit "over done" now. The boats are so big it's like a jet bus ride.
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Old 12 September 2005, 07:00   #10
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Quote:
Originally Posted by Mollulnan
Dear oh dear, that old "I've been a boatman for 30 years" .
As it happens experience does usually bring knowledge, small experience usually brings the relevant amount of knowledge.

I drive Jet boats and Prop boats for a living and have a couple of thousand of hours on props and nearly a thousand on Jets type so heres my view.

It depends on what you want your boat to do?

The versatilty and moanouverability that a jet brings will never be able to be achieved with a Propped boat. The jet drive is safer and more reliable. but less fuel efficient. Therefore is mostly suited to the commercial and rescue world.

Outboards and stern drives are great cos they go faster and require less power to get you going
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Old 12 September 2005, 08:13   #11
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What are jets like in rough seas? Do they lose grip and cavitate like mad? I suppose a lot depends on the size of boat though.
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Old 12 September 2005, 08:23   #12
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Our jet drive boat weighs 4 tonnes so it doesn't come out of the water that easily and we have found it fin ein Rough seas. when it does come out of the water it doesn't seem to flounder upon splash down!

The boat I drive in the North Sea is a 12 metre 10 ton Rib and again that dosn't come out that easily.

If the weather blows up this week I'll take the Avon out and se what happens in a rougher sea
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Old 12 September 2005, 09:33   #13
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If the weather blows up this week I'll take the Avon out and se what happens in a rougher sea

I think i'll have to come too, so as I can keep an eye on you
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Old 12 September 2005, 09:37   #14
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You are most welcome
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Old 12 September 2005, 23:45   #15
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Quote:
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The boat I drive in the North Sea is a 12 metre 10 ton Rib and again that dosn't come out that easily.
I imagine that would take some doing to launch that monster throught the air


nik,

What sort of engine power range are you thinking of? There is one interesting variation of the traditional jet outboards called the jetpac

There is also a very simple but neat 55hp outboard that is a hybrid of a prop & jet drive that the U.S navy on their 16 foot SIBs. Unfortunately this system is only made for 2 stroke OMC engines. There is a description of these at smalloutboards.com I am quite curious how the performance of this compares to that of a conventional prop system. Here are some pictures of it.
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Old 13 September 2005, 02:49   #16
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I'm sure either Mercury or Yamaha make a jet drive outboard, sounds like you could have a lot of fun with a drive like that!
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Old 13 September 2005, 08:13   #17
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Like this?

It's a yam but is I think the 115 block, less apendage drag than the curious US military job.
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Old 13 September 2005, 08:44   #18
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And here is a Mercury. These jet pumps come from the same manufacturer in the States and are made to fit most outboard brands

The jets are most suited for shallow water ie shallow rivers or for the emergency services when operating in flooded areas

we have recently supplied to our Dutch distributor our Parker 510 rib with jet outboard for rescue services. will try and get some pictures
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Old 13 September 2005, 09:33   #19
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whilst deciding what rib to buy I spoke to a top end manufacturer about jet drives thinking that they are safer than a prop which they are when stationery or going very slow but his response was that in anything less than 7m it was not advisable as you lost a certain degree of steerage at low speed in addition if you hit someone at speed the hull is going to kill them before they get minced in the prop
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Old 13 September 2005, 11:35   #20
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Just a thought- has anyone tried fitting a jetski engine into a small rib? I was daydreaming yesterday about the possibility of fitting a 120hp seadoo lump into my sr4 (just for the hell of it...y'know...)
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