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23 May 2013, 06:40
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#1
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Member
Country: UK - England
Town: wolverhampton
Boat name: patches & blue bird
Make: avon searider
Length: 6m +
Engine: twin 75's & 90
Join Date: May 2009
Posts: 131
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twin outboards?
As previous posts, next project is a 6mtr ish rib with twin 90s on the back.... Question is do you have to have one normal 90 and one counter rotating 90 to give a better drive as would there be to much "screw" effect from 2 normal 90s or is the answer just to fit non feedback steering to offset the screw effect so you dont feel any "pull" on the steering.... Whats the general opinion,thanks
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23 May 2013, 06:54
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#2
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Member
Country: UK - England
Town: Isle of Wight mostly
Make: Regal
Length: 6m +
Engine: Mercruiser
MMSI: 235911246
Join Date: Oct 2012
Posts: 188
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Just fit left hand and right hand props, which will give you the best result
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23 May 2013, 07:24
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#3
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Member
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 11,865
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Quote:
Originally Posted by fatboyrib
As previous posts, next project is a 6mtr ish rib with twin 90s on the back.... Question is do you have to have one normal 90 and one counter rotating 90 to give a better drive as would there be to much "screw" effect from 2 normal 90s or is the answer just to fit non feedback steering to offset the screw effect so you dont feel any "pull" on the steering.... Whats the general opinion,thanks
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You might struggle to find a counter rotating 90hp outboard, they don't usually start until 115hp
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Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: Don't feed the troll
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23 May 2013, 07:26
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#4
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Member
Country: UK - England
Town: West Sussex
Length: no boat
Join Date: Oct 2002
Posts: 3,872
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We installed twin Mercury 90 ELPTO (2 stroke) on our Parker 650. The 4 stroke engines were just too heavy. The 90 HP engines do not have counter rotation so just install standard engines. the performance is very good.
We first installed Mercury twin 60 HP 4 stroke , the weight was OK but poor performance
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Andre
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23 May 2013, 07:36
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#5
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Member
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,667
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Quote:
Originally Posted by solent spence
Just fit left hand and right hand props, which will give you the best result
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Errr that might be fun if one of them doesn't have a counter rotating gearbox.....
As Andre says, ref. the size but if you really feel you need symmetry have a dig around the microfiches. Some manufacturers carried gearboxes across that sort of HP range, so you may find you can take a couter rotating gearbox off a 115-ish & park it on the bottom of the leg of a 90.....
Will need some research tho'.
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23 May 2013, 07:39
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#6
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Member
Country: UK - England
Town: West Sussex
Length: no boat
Join Date: Oct 2002
Posts: 3,872
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If I am not mistaken the counter rotation begins from 135 HP upwards
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Andre
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23 May 2013, 07:42
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#7
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Member
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 11,865
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Quote:
Originally Posted by Andre
If I am not mistaken the counter rotation begins from 135 HP upwards
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Etecs start at 115
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: Don't feed the troll
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23 May 2013, 08:25
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#8
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Member
Country: Other
Town: Stanley, Falkland Is
Boat name: Seawolf
Make: Osprey Vipermax 5.8
Length: 5m +
Engine: Etec 150
Join Date: Mar 2006
Posts: 3,726
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Quote:
Originally Posted by 9D280
Errr that might be fun if one of them doesn't have a counter rotating gearbox.....
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Very manoeuvrable, will turn on a sixpence
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A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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23 May 2013, 09:15
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#9
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,053
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Quote:
Originally Posted by bogmonster
very manoeuvrable, will rotate madly on a sixpence
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ftfy
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23 May 2013, 09:22
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#10
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Member
Country: UK - Channel Islands
Town: jersey
Boat name: Martini II
Make: Arctic 28/FC470
Length: 8m +
Engine: twin 225Opti/50hp 2t
MMSI: 235067688
Join Date: Jun 2005
Posts: 3,030
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With hydraulic steering and a bit of transom offset it would be fine. There's twin 200s around with both std rotation without problems.
Advantage is you don't have to worry about problems with the inherently weaker counter rotating gearbox.
Sent from my portable speaking device using Rib.net
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23 May 2013, 09:40
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#11
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Member
Country: UK - England
Town: Isle of Wight mostly
Make: Regal
Length: 6m +
Engine: Mercruiser
MMSI: 235911246
Join Date: Oct 2012
Posts: 188
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Quote:
Originally Posted by BogMonster
Very manoeuvrable, will turn on a sixpence
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Haha, correct. Should have said "and gearbox"!
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23 May 2013, 09:45
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#12
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Member
Country: UK - England
Town: West Sussex
Length: no boat
Join Date: Oct 2002
Posts: 3,872
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Quote:
Originally Posted by Pikey Dave
Etecs start at 115
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I had Mercury in mind
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Andre
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