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07 July 2015, 21:44
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#1
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Member
Country: UK - Scotland
Town: Haddington
Make: Avon SR4
Length: 4m +
Engine: 50 Hp
Join Date: Apr 2015
Posts: 47
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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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07 July 2015, 21:58
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#2
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Member
Country: UK - England
Town: Royal Wootton Bassett
Length: 8m +
Engine: 250
Join Date: Jul 2008
Posts: 8,042
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SR4 30 Knots
Your under propped, you should hit 33-36 with a 50
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08 July 2015, 07:03
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#3
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Member
Country: UK - Wales
Town: St Davids
Boat name: Mellifera
Make: Avon
Length: 4m +
Engine: Outboard
Join Date: May 2010
Posts: 189
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Quote:
Originally Posted by whisper
Your under propped, you should hit 33-36 with a 50
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+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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08 July 2015, 07:31
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#4
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Member
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,292
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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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Member of S.A.B.S. West Country Division
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08 July 2015, 08:21
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#5
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RIBnet supporter
Country: UK - England
Town: Warwickshire
Boat name: Impulse
Make: Ribcraft
Length: 5m +
Engine: Suzuki 140
Join Date: Sep 2011
Posts: 1,020
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35 actually😉
Sent from my iPhone using RIB Net
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08 July 2015, 08:55
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#6
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Member
Country: UK - England
Boat name: Son of a Beach
Make: Avon SR4
Length: 4m +
Engine: Mercury 50hp
Join Date: Sep 2012
Posts: 130
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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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08 July 2015, 09:09
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#7
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Member
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,292
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Quote:
Originally Posted by AJ.
35 actually😉
Sent from my iPhone using RIB Net
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Nobber!!
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08 July 2015, 17:08
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#8
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RIBnet admin team
Country: UK - Scotland
Boat name: imposter
Make: FunYak
Length: 3m +
Engine: Tohatsu 30HP
MMSI: 235089819
Join Date: Sep 2005
Posts: 11,661
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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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08 July 2015, 17:44
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#9
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Member
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,877
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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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08 July 2015, 18:03
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#10
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Member
Country: UK - Scotland
Town: Haddington
Make: Avon SR4
Length: 4m +
Engine: 50 Hp
Join Date: Apr 2015
Posts: 47
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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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08 July 2015, 18:10
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#11
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Member
Country: UK - England
Town: Bristol
Make: Ribcraft
Length: 5m +
Engine: Yamaha
Join Date: May 2006
Posts: 4,292
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Quote:
Originally Posted by Mollers
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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Bet thats what the bloke who's tender you nicked called you or perhaps he used stronger words
and if anybody is propping for top speed then don't as mollers will hate it!
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Member of S.A.B.S. West Country Division
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08 July 2015, 18:26
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#12
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Member
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,877
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Quote:
Originally Posted by matt h
Bet thats what the bloke who's tender you nicked called you or perhaps he used stronger words 
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Which bloke, we have a busy tender loan scheme in these parts. It operates on the Boris Bike system.
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09 July 2015, 19:52
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#13
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Member
Country: UK - Wales
Town: St Davids
Boat name: Mellifera
Make: Avon
Length: 4m +
Engine: Outboard
Join Date: May 2010
Posts: 189
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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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