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Old 30 October 2007, 21:22   #1
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Country: Australia
Town: old bar
Boat name: efo
Make: avon
Length: 4m +
Engine: yam60hp 2stroke
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new to ribs

hey everyone im used to fast ski boats but decided to try a samll rib,,for sum fun,,bought a s/h avon 4.25 seasport with a 60hp feto 2stroke yam,,had a standard 17 alloy prop which found a semi submerged floating stump(teach me 4 going out 1st day after a few days rain) on 1st day out,,did see 103kph on sounder,,and thort shit ey,,this goes ok,,bought a ss sloas 13x 19 and saw 110kph on sounder,,,grabbed gps to check and saw 61.7 knots,@5400 wot..seeing engine was on lowest setting on transom i lifted it 1 hole,,now am seeing 65knots,at 5600rpm@wot,,following tide,,64.6 anytime,,boat luves lots of trim to sit on plank,,and will run 3000rpm b4 popoising,,am going to try 1 more hole up,b4 installing a cav plate dolefin and starting all over again with engine heights,,seems to me small to med size RIB boats do respond to ski boat type setups,,any advice as to porting or carb setups and timing would be appreciated,,cheers all happy RIBBING
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Old 31 October 2007, 04:10   #2
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65 Knots in an Avon Searider sounds like you may need to check your GPS?

Chris
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Old 31 October 2007, 06:28   #3
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Quote:
Originally Posted by Chris View Post
65 Knots in an Avon Searider sounds like you may need to check your GPS?

Chris
65kph sounds more like it even that is pretty good!
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Old 31 October 2007, 08:39   #4
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Country: Australia
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lol

have anuther gps that i use in car,,will take that as well next time then will have 3 speed checkers,,gotta say it dont feel like that speed,,as in the ski boat you knew you was travelling,,and 65ks well i ski at that speed so know its quicker,,anyone know anything about the yammy 2stroke 60hp feto engine,,
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Old 31 October 2007, 09:08   #5
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65Knt that is 120kph!!! or 75mph are you having a laugh?
I thought 40 mph was more like the speed!
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Old 31 October 2007, 11:44   #6
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Well I can just crack 40kt/65kph with 115hp so if somebody overtook me with a 60hp outboard doing 65 knots I would be right royally p****d off but at the same time rather impressed
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Old 31 October 2007, 13:23   #7
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Check the power to weight ratio. I have a SIB not much smaller than that which does 25mph on a 15hp.

Remember 60hp is a pretty big engine for a 4.25 and it's a true RIB.

Avon = 390lbs
Engine 200lbs
Crew say 170lbs
fuel 40lbs
Total weight - say 800lbs - power to weight is 13.33lbs per hp.

Then compare it with something like a Ballistic with an ETEC 250 - I am guessing about 1400kg or 3080lbs. Power to weight is 12.32lbs per horsepower - not that much different.

Still over 60kts does seem a little high..........
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Old 31 October 2007, 16:06   #8
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The sea sport is a very shallow V unlike the Searider so should be a bit quicker, however, if truble is getting 60+Knots in an over engined 4.25 Avon, fair dinkum
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Old 31 October 2007, 19:40   #9
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cant personally see that speed from that set up, given the data you supplied, at best around 48 knots, in order to achieve 65 knots you would need more like a worked 26p prop and that's assuming a crazy gear ratio, and that's more than amazing given the type of craft but anyhow happy crazy boating
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Old 01 November 2007, 12:32   #10
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We dont even get that speed with race tuned 50s on thundercats which weigh nothing and are cats so you have the wind tunnel. I think something is a miss here.
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