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Old 07 July 2015, 16:44   #1
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SR4 30 Knots

Well had a good day at North Berwick on Sunday . First run in calm waters gps was reading 30 knots with my 50 on the back and rev sitting at 6k could have went more but my sensible head kicked in..............

Looks like I have the RIB BUG!!!
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Old 07 July 2015, 16:58   #2
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SR4 30 Knots

Your under propped, you should hit 33-36 with a 50
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Old 08 July 2015, 02:03   #3
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Quote:
Originally Posted by whisper View Post
Your under propped, you should hit 33-36 with a 50

+1

If you are hitting 6000 rpm with throttle to spare get a prop with more pitch. What is on there at the moment?

I have a 15" on mine and see about 35 knots flat out.
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Old 08 July 2015, 02:31   #4
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Thats duff info. with the right balance and prop you should be able to achieve 39
I had a 10.5 x 15 four bladed spitfire prop on mine and 39.4 was its best on slack water. Aj hits 34.5 with his 40 two stroke again with the same design prop!
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Old 08 July 2015, 03:21   #5
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35 actually😉


Sent from my iPhone using RIB Net
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Old 08 July 2015, 03:55   #6
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Since I've had my carbs cleaned out and my Mercury 50 is running well I also get 6k indicated on my rev counter. However given that when the engine is off it indicates ~1k rpm I'm unsure whether the rev counter is reading well. Waiting for some calm water to do some top speed testing. I'll also have a poke about to see what the fitted prop is and how this compares to the spare that came with the boat.
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Old 08 July 2015, 04:09   #7
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35 actually😉


Sent from my iPhone using RIB Net
Nobber!!
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Old 08 July 2015, 12:08   #8
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Tim, it is common for tach to show the rpm when the engine was turned off. If you have a key turning to on (but not as far as start) will normally reset it.
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Old 08 July 2015, 12:44   #9
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Don't prop for top speed, that's hairy chest medallion wearing shit. Any tosser can put the throttle on the end-stop on a flat calm day and take pics of the GPS.
Real men prop for grunt. Our's will do 32knts WOT with a 14 3/8 s/s prop. It leaps onto the plane and is as punchy as ferk in any kind of sea.
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Old 08 July 2015, 13:03   #10
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Cheers Guys ..

Think I will leave the prop on for the now, seems to pull okay with 2 people plus an auxiliary motor as well.
Only upgrade looking to do is fit BOAT BACK REST STAINLESS STEEL NEW Backrest seat back handle ideal for RIB BR1 | eBay

Thanks again for all the wise words.
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Old 08 July 2015, 13:10   #11
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Don't prop for top speed, that's hairy chest medallion wearing shit. Any tosser can put the throttle on the end-stop on a flat calm day and take pics of the GPS.
Real men prop for grunt. Our's will do 32knts WOT with a 14 3/8 s/s prop. It leaps onto the plane and is as punchy as ferk in any kind of sea.
Bet thats what the bloke who's tender you nicked called you or perhaps he used stronger words

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Real men prop for grunt
and if anybody is propping for top speed then don't as mollers will hate it!
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Old 08 July 2015, 13:26   #12
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Bet thats what the bloke who's tender you nicked called you or perhaps he used stronger words
Which bloke, we have a busy tender loan scheme in these parts. It operates on the Boris Bike system.
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Old 09 July 2015, 14:52   #13
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I don't have ptt so I can't change my trim on the go but all I meant was if the outboard is revving at 6000 and there was still some throttle left a bigger prop would be the way to go.

I think I have my boat fairly well balanced but not got near 40 knots yet. I only have a standard ali prop though and not enough ribs around these parts to compare it to.

Out of interest where do most others place their weight around the boat? Mine is a bit twitchy at 30 knots plus unless fairly calm.
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