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Old 05 April 2004, 07:40   #1
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Jet or stern drives on 11m Rib?

We are currently in the process of having an 11m Rib built. Does anyone have any thoughts/experience of stern verses jet drive of a boat that size.

At the moment jets look better for maintainance but there is concern about the handling in larger seas.

Thanks
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Old 05 April 2004, 07:50   #2
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Simon
What is your application?
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Old 05 April 2004, 08:35   #3
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Jet or stern drive Where and What

Private use travelling abound south west, down to the top of Biscay, Channel Islands, Scillies etc.

A to B stuff but in all conditions
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Old 05 April 2004, 08:39   #4
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Application

Quote:
Originally Posted by Brian
Simon
What is your application?
Private use travelling abound south west, down to the top of Biscay, Channel Islands, Scillies etc.

A to B stuff but in all condition
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Old 05 April 2004, 09:58   #5
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May I assume that Simon A. is Kitesurf as well?

Two points:
1. I know of a Redbay Stormforce 11 (Awesome Explorer owned by Andy Micklewright) which has twin Yanmar 300's with Bravo 3 legs which suits it ideally and which presumably will fit your application well. I am told that jet drives "lose" 20-30% of their power in driving the waterjet, but are ideal for amazingly close manouvering like entering caves for example. So if going this route you might want to select a larger engine. Several around at about 450hp.
Still, Bay of Biscay? two engines?

2. On your kiting foray. At least 3 large ribs (maybe 4) will be returning via the Scillies from S. Ireland on the weekend of the 22/23rd May. See
www.biboa.com
Cruising
and S/W Ireland page for details, if that ties in at all with your schedule.
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Old 05 April 2004, 11:06   #6
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Dont do it. A Rib with jets in big seas = suicide. ask Bear Grylls if you dont believe me! Alan P
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Old 05 April 2004, 15:18   #7
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Stern vs Jet

Agree with Alan P.

The question is why 11m.

If it is a question of space then do remember that the engines/drives will take up 1/1.5m at least.

So is the decision purely diesel vs petrol - please think hard.

Thus if petrol a 10m with OB will provide at least as much deck space as an 11m.

If your basis is on sea conditions favouring an 11m then do consider what the basis mould was and look at comparisions of block, prismatic etc coeficients.

We have poduced 10 and 11m vessels and favour OBs given all considerations. Note that the UK jet ribs, Ocean Dynamics, are now turning to OBs. And stern drives for serious commercial work - a big question investigated by many!

Sounds like the old case of you will be damned if you do and damned if you dont! and it only leaves us with sail or warp drive. !

Cheers

John
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Old 06 April 2004, 03:02   #8
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John / Alan P
Not claiming to be an expert or anything but wishing to understand this issue further, can you explain why Halmatic / RN have gone away from outdrives to jets on their ship to ship boats. The RN has been using outdrives for over 20 years on a considerable number of boats (400+) and in 2000 they changed to Hamilton Jets on the mark 2 Pacific. If anyone has the time and money to research the benefits it must be the Navy so why are you so opposed?
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Old 06 April 2004, 03:09   #9
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Alan / John this is quite interesting, are you therefore saying that modern injection outboards are a cost effective alternative when compared to the complexity and cost of bulding inboards and jets, assuming a commerical operator can get the tax back on petrol ?

And what was the problems with Bears Jet Rib going across the Atlantic ? I appreciate there is a small loss of efficiency with a jet, but would have thought the lack of 90' gearing of a stern drive and underwater props would make a jet a viable option particularly given the problems with stern drives and big inboards diesels, or have I missed something ?

Pete
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Old 06 April 2004, 10:41   #10
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I have heard that there may be a problem with broaching in aboat of that size as there is nothing acting as a rudder. It has been suggested that skegs could be put underneath but I thought this would affetc the handling when manouvering what about drying out?

Just for info we are looking at twin 315hp

And the problem with petrol is carrying all those cans!
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Old 06 April 2004, 14:52   #11
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Yo!! on petrol v. Diesel Simon.
I have always maintained the winning argument for diesel is availability, not price/tax or anything else.
It's fine for the Ramsey Islands guys where typically they operate out of a fixed base, but in your case finding/filling with petrol at say Duarnanez, Carteret, Deaville etc.??
Even in the Scilly Islands it's a pain.
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Old 07 April 2004, 00:59   #12
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jets v's stern drives

I run a 6.0m diesel jet and have no problems, even in big seas. yes she may lose drive occaisionally, very occaisionally. But she is very controllable in rough weather enables you to put the boat where you want. If you do go down the jet route, I would go Hamilton and ensure you can back wash the jet in case of blockage, ie carrier bags. I feel that even with the threatened disappeareance of red diesel I would much rather have a simple diesel lump chugging away behind me than a high tech outboard, thats my opinion...

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Old 07 April 2004, 08:04   #13
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If we go the jet route we will go for hamilton jets. Is there any advantage to a 3 jet set up which will put the middle jet lower down?

It has to be a deisel! I have spent too long carrying petrol in taxis in Audiernne to fill up 80 gallon tanks on a petrol rib.

I have been offered a trial on both stern and jet before we make a decision by the company we are talking to so I will post my experience as and when, but a trial is obviously limited and so I appreciate all feed back.

Thanks
Simon
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Old 07 April 2004, 11:47   #14
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The problem happens in big seas and in fairness the navy only operate their pacifics as support craft and not ocean going craft.The problem with the jet is it does not like going sideways once it has broached on a big wave and has a habit of capsizing (or nearly) which is what happened a couple of years ago on an Ocean Dynamics boat in Wales. Not to mention an 11 metre off of the Mull of Kintyre and Bears boat across the Atlantic etc etc. But then again if someone would like to correct me?

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Old 08 April 2004, 02:54   #15
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Thanks Alan
That's the kind of thing I was looking for. The extra maintainace of sterns doesn't seem as bad compared to flipping it.
The boat will have a full cabin specifically so it can be used in all weather conditions. Any similar size Ribs (11M) anyone knows of and the set up/make/power of stern drives would helpful. We want to have a top speed of 40-45knots and cruise at 30 and a range of 350 miles minimum and ideally 450?

Simon
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Old 08 April 2004, 03:47   #16
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Quote:
Originally Posted by Alan Priddy
The problem happens in big seas and in fairness the navy only operate their pacifics as support craft and not ocean going craft.
Alan P
Alan
Just to pick you up on a point.

The Pacific 22 is designed to Ďoperate in the open sea at any time of the yearÖ.. remaining on station in sea state 6 to 7í so I think it is disingenuous to say that they are not ocean going.

I come back to my original point, the Navy have an enormous budget to develop these boats and would not choose jets without justification, so for you to say that jets are no good in a big sea seems to contradict the Navy's findings. I could accept that an 11m boat behaves differently to a 6.5m boat or that hull shape or weight has an effect but to say that jets loose power and broach is dismissive of their abilities. I am not trying to pick a fight I just donít understand and would like to know more.

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Old 08 April 2004, 04:01   #17
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By the way, the US coast Guard have just taken on a P32 mark 2 with jet and find that operating in the surf or tight wave frequency they can turn in the trough between waves, try that with a leg!
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Old 08 April 2004, 06:22   #18
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Quote:
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... try that with a leg!
Des
Easy. Put on a good quantity of lock and open the throttle firmly. Be ready to back off or you may not be able to unwind it!
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Old 08 April 2004, 06:27   #19
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Easier with a jet
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Old 08 April 2004, 06:30   #20
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