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Old 05 April 2004, 08:40   #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, 08:50   #2
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Simon
What is your application?
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Old 05 April 2004, 09:35   #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, 09:39   #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, 10:58   #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, 12:06   #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, 16:18   #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, 04:02   #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?
Des
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Old 06 April 2004, 04:09   #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, 11:41   #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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