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Old 06 November 2017, 15:37   #1
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RNLI Rib & Jet Drive. Why not used?

Watched the 'Saving lives at sea' program we recorded.

Why don't the RNLI make greater use of jet outboards on their small Ribs? There would be no risk of incapacitating the boat when in bad seas near rocks and less risk of injuring someone in the water.

Makes perfect sense to me so why not?
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Old 06 November 2017, 15:56   #2
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They do use jets on the E Class.

Which Rib would you put the jet on? They seem to prefer to put the D Class in close to rocks. D Class is effectively a big SIB so you'd need an outboard jet. Also a lot easier to lift off the engine and replace it for an OB.

While it may be risky to say it... ...when did an RNLI boat ever hit someone with the prop? Quite how I have no idea given their apparent rescue method on Saving Lives @ Sea seems to be to chuck a crew member in at the first opportunity!

You can tilt a propeller outboard. If you have an under the hull jet... ...does parking it on sand etc cause issues?

The E Class also use solid tubes (foam filled). You could argue the same for tubes.
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Old 06 November 2017, 16:51   #3
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Quote:
Originally Posted by ShinyShoe View Post

You can tilt a propeller outboard. If you have an under the hull jet... ...does parking it on sand etc cause issues?
To clarify I was referring to 50-70hp outboards that can be tilted when landing on the beach.

In the program they didn't know if they could rescue someone clinging to the rocks because they had to go in backwards nose facing the waves. There was risk of the boat and crews lives if the prop were to strike submerged rocks and also risk of the prop cutting the person in the water.

I notice the fire brigade used prop guards on those 30hp Mariner engines for sale on the auctioneer site. Fitting these would be the least they could do?
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Old 07 November 2017, 01:05   #4
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Draw air a high speed air in rough water, suck pebbles and weed off the bottom in shallow water, very poor inefficient drive at low speed (eg towing?).

I've owned a jet boat (5mtr/165hp) and really.......not all they're cracked up to be.
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Old 07 November 2017, 02:33   #5
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I know that the RNLI have tested various combinations of boats and drive systems. Money is no object, so if jets would work better than they'd almost certainly be using them.

Jets always sound like a good idea for rescues but I suspect that the drawbacks simply outweigh the benefits.
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Old 07 November 2017, 02:54   #6
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Quote:
Originally Posted by Limecc View Post
To clarify I was referring to 50-70hp outboards that can be tilted when landing on the beach.

In the program they didn't know if they could rescue someone clinging to the rocks because they had to go in backwards nose facing the waves. There was risk of the boat and crews lives if the prop were to strike submerged rocks and also risk of the prop cutting the person in the water.
I think youíve fallen for the TV drama. It doesnít make good tv to say we had to follow all our training and pick someone up, itís far better to introduce an element of perceived risk. In big waves you want to be bow to them anyway as you have control, donít get swamped as easily and have an escape plan, surfing into the shore or capsizing trying to turn would have made great tv though.

I speak from experience that a low speed rock ding in shallow water is not usually terminal; and they carry a spare prop. If you get rope, stones or kelp jammed in a jet drive it may not be so simple.
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I notice the fire brigade used prop guards on those 30hp Mariner engines for sale on the auctioneer site. Fitting these would be the least they could do?
the fire service are probably using the guards to protect the prop from debris and hidden street furniture in floods rather than people. They are widely reported to ruin top speed (something that affects a lot of rnli responses) and handling (which might be just as tricky for close quarters handling).
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Old 07 November 2017, 03:12   #7
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Although I will admit I'm no expert, I did my RIB Safety boat qualification back int he summer so I've been watching the 'drama' on TV with interest. Many times the wife has asked why they were backing the boat in, what the line is for etc and I've been explaining it to her. Some thinks they have been doing so seem wrong from my own training but then again, RIBS are far more robust than people think. e.g. if both side tubes were fully deflated and only one engine was working, it would still carry on working.
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Old 07 November 2017, 05:04   #8
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Quote:
Originally Posted by Limecc View Post
In the program they didn't know if they could rescue someone clinging to the rocks because they had to go in backwards nose facing the waves. There was risk of the boat and crews lives if the prop were to strike submerged rocks and also risk of the prop cutting the person in the water.
Luckily rescues at sea are performed by RNLI Volunteers backed by years of experience and millions worth of our donations - not television production crews. I dread to think of the carnage that would be required to make a good Docu-rescue!

You/the presenter may have missed how the technique works:

The boat sets an anchor off the shore and uses the line to hold itself off while only one engine is used for fine positioning/reversing. The other engine is burning in neutral and is there to be used should the turning engine seriously ding something. The RNLI are not know for cutting up casualties.

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Old 08 November 2017, 16:34   #9
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I suspect jets would be a massive cause of failures a prop can survive far more low speed shallow abuse than a jet. Also jets are dangerous read the warning on the back of a jet ski next time your near one.. serious internal injuries may occur .....

The helms on life boats while mostly volunteers are able to safely do stuff in the worst conditions, we could only aspire to in mild conditions.

They go where no one else should and are trained and equipped to. They do use guards on some lifeguards boats used on beaches (Arancia) and some jet skis for fast response (RWC)
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