Jet or stern drives on 11m Rib?

[Alan Priddy]

Scary Des, I take your point but on you do not get big waves in a force 6-7 and the pacific's along with most rib's are ok in conditions that the winds will generate, in the right hands of course.In open sea in big seas Jet boats are bloody dangerous! Once the wave gets under the sponson the boat lifts and the jet cannot suck enough water to give sufficiant propulsion, the wave turns the boat sideways and you have a whole lot of poo on your hands. The next time it is blowing 50 knots of southerly wind on an out going tide, try and get around the needles in a jet boat and report on your experiances.

Alan P

[Scary Des]

Originally Posted by Alan Priddy

The next time it is blowing 50 knots of southerly wind on an out going tide, try and get around the needles in a jet boat and report on your experiances.

Alan P

Happy to do this if you can provide the boat

The naval expression ‘to stay on station’ means that the boat will be launched and used in a way that takes little account of the weather conditions (other than the usual). Pacific 22’s will still be launched in any sea state because it is the main (and sometimes only) rescue boat on a war ship.

With a jet you have to approach boat control in a different way to a propeller, throttling back as you would with an outdrive to prevent broaching results in a loss of directional control so with a jet you keep the thrust on and use the forward reverse control to hold position. In other word with a propeller you match revs to hold position with a jet you half drop the bucket to match thrust.

As I said I am not trying to start an argument I just want to under stand why you hold your views.

Incidentally did you know that the RNLI have order several jet boats?

[quinquarimarine]

Originally Posted by Pete7

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 ?

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In terms of power to weight ratio, performance and space the OBs now do win. The cost per mile works out about the same provided duty and VATrebate is in place. Other factors such as ease of replacement, leg or jet wear etc also come into play.

Critically the resale value of OBs after say 12 months use is very high compared to an IB.

The major drawback is obtaining fuel supply and it is for this reason that a number of our customers have set on IBs.

One f the difficulties with IBs is the limited number of suitable units on the market suitable for a production RIB. Yanmar and Volvo hold the lead at present but with units of 315hp a single installation is barely adequate to power a 10m (noting that if they were OBs twin 150hp would be adequate). Thus twin installations are required which on say a 3m overall beam gives very little space to play with. Worse is the cost of a twin IB of say £40k as oposed to £16k for twin OBs !.

I am no great fan of OBs and they have their share of downsides (we need to lug 250 galls on a busy day !!) but after many years of playing the cards they have won in our view.

The reference to the RNLI and jets I believe is for shallow water/estuary work and is one of the applications including close quarters handling when the jet will win every time.

Cheers

John.

[Pete7]

John, thanks, quite enlightening.

Pete

[David B]

Have had experience on this class which is 10 mt . all i can say on the thames in anything less than a ripple its superb , stop on a sixpence , walk sideways , turn like you would not believe........................put it in a sea and forget it stick with outdrives you will not regret it.

David

[Scary Des]

put it in a sea and forget it stick with outdrives you will not regret it.

David

That's not what the guys in poole are saying. It's also on 14mtr RNLI boat.

[David B]

Hey the guys in Poole you refer to perhaps do not use one every day !
feedback is the in word right now ..............

Whilst being in the RNLI I can tell you what the crews suggest and what actually happens is not the case ! we suggest a seating layout , an office suit decides to do it his way over a gin and tonic. Now thats not being bitchy its become a fact that there are to many suits in the RNLI and constructive comments from crew and feedback on equipment is not always listened too.

When you use one every day..........experience tells you whats good and whats not. I agree in certain classes of craft and I note somebody mentioned the new craft on trila in maine with the US coast guard jets have been very successful but they do have their down sides too

Simply e.mail tower lifeboat or gravesend crew and ask for their opinions on jets in a sea state

Who are "the guys in Poole " ?

I have

[Simon A]

Dyfed & Powys Police took delivery of a 11.5 m rib in 1999. Anyone have any knowledge of that one or any contact email addresses for any one/organisation using jets?

[Scary Des]

it's a Delta with twin 230 Yanmar and twin hamilton jet.