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Old 15 October 2009, 02:40   #1
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Second Trip in our Searider and a few Questions :)

Hi All

Apologies in advance for more questions - I just can't help myself

1. We went out again yesterday - Chichester Harbour across to the IOW and back - fantastic . We had the boat planing for most of the way at 20 knots. So once you have the boat planing is there any value in increasing engine power (apart from going faster) as this is the most fuel efficient point of the RIBs performance?

2. It was a great feeling skipping across the tops of the waves and only when we slowed did we feel the swell. Should a RIB be planed regardless of wave conditions - I think what I mean is - assuming the skipper is competent (I'm not yet!!) is the safest use of a RIB to be planning or if the weather is bad then going over/through the swell/waves is the safest option - does that make sense??

3. Does anyone know much about the Yamaha Pro engines - ours seems very reliable (75hp) but more fuel hungry than we have experienced with our four stroke 60hp. I'm sure there are lots of threads working through fuel consumption but is there a simple formula to work out fuel capacity vs distance or do you need to try it and see then work out an average yourself?

4. Last question - honest. Some interesting MOD activites going on while we were off IOW - first of all a ship let of a large white smoke flare, a Sea King helicopter (I think) then arrived hovered and the smoke instantly stopped. Next the Sea King appeared to "land on the water" or at least it's wheels were touching and finally we watched to Lynx helicopters patrol the same area. We were to far away to see markings clearly or actual activity. Any ideas what they were doing/practising?

Once again thanks all

Jxx
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Old 15 October 2009, 04:46   #2
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Hi, planing is the norm. How fast is up to you and the sea conditions. It is possible the wave size and length will produce conditions which are too uncomfortable or dangerous for you to mentain planing speed so you have no option but to slow down. But, it's your boat and you can travel at whatever speed you prefer. If pootling along is what you fancy doing, why not?

There are fuel consumption guestimate formulae but the only one that matters is your own consumption so best to do some testing at various speeds and see what's good for your combination.
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Old 15 October 2009, 04:55   #3
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You'll find it takes more throttle to get onto the plane than to stay on it. ie once on the plane you can reduce the throttle to save fuel and still maintain planing speeds.
In the same way you may have to reduce speed if its rough sometimes incresing your speed can give a better ride, all depends on the size and distance between waves.
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Old 15 October 2009, 06:30   #4
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Great boats aren't they!

1. Best economy for the hull is achieved when the boat is fully on the plane - about 20 knots for the hull. Going faster will be less efficient - but may be more fun!
The engine will also have a rpm range where it is operating in its mid range power band where the economy will be best. This is probably between about 3250 and 4000 rpm. Once above 4000rpm its thirst will increase.

2. Go at whatever speed feels comfortable or safe. There are certain conditions - short sharp chop for example - where it may be more comfortable to go faster and skip across the tops of the waves rather than riding up and down over them. However, when that slightly larger wave appears you may find yourself going skywards out of control and having a hard landing. Keep your hand on the throttle at all times and be ready to back off if needs be. You'll get to know what feels best.

3. I don't know much about Yamaha Pro 75hp engines but would bet on it being a detuned 90. My SR5.4 with a 90hp 2 stroke used to do a bit under a litre per mile at about 22-25 knots. I would expect yours to be similar. About twice the consumption of your 60hp 4 stroke is what you should expect?

4. Sounds like they were picking up a diver? You can subscribe to QHM local notices on their website and this gives all sorts of info on exercises when they need people to keep clear.

Have fun :-)
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Old 15 October 2009, 13:50   #5
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What revs do you achieve with the throttle wide open (WOT) and a normal load?
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Old 16 October 2009, 02:49   #6
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Thanks All - Searider - yes they are extremely good RIB's for the money I could'nt be more impressed

A detuned 90hp - sounds interesting can you detune the detune and make her 90hp again??

Jizm - not sure we've yet opened the throttle right up - but she planes at 20knots running at 3400 revs

Thanks again

J
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Old 16 October 2009, 03:15   #7
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I think the gearboxes have a restriction in on the 75's, this is what we got told when we got them.
I would have thought the carbs would have needed different jets too though?
Sating that on the little 50cc and 125cc scooters you could move the restrictor and off you shot, it made the difference between 30mph and 50mph.
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Old 16 October 2009, 04:52   #8
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what does the engine look like> does it have Yamaha in big white letters and two small diagonal stripes. not much other decoration?

By the way well done on buying the best first time boat you can
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Old 16 October 2009, 05:00   #9
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Thanks RW - but the credit has to go to you guys here on Ribnet - having asked the question the answer came back loud and clear BUY A SEARIDER 5.4M or maybe a Humber

Really chuffed with her

You can just see the engine here:



J
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Old 16 October 2009, 05:26   #10
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Quote:
Originally Posted by Knot Yet View Post

Jizm - not sure we've yet opened the throttle right up - but she planes at 20knots running at 3400 revs

Thanks again

J
Sounds about right, maximum throttle operating range is between 4500-5500rpm.
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