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09 May 2017, 17:24
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#1
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Member
Country: UK - England
Town: blackpool
Boat name: Fast Forward
Make: Scorpion
Length: 8m +
Engine: 315 Yanmar
Join Date: Aug 2006
Posts: 385
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Etec 250 ho economy
Have recently bought a 7.2 m Asis rib fitted with a 250 Etec ho outboard.The boat came with a ballistic 24" prop which although fast cavitated like mad.I bought a four blade Lexor 153-22 prop and set off for the Easdale Rib Rally.
The economy and performance of the engine was great. I cruised at 3000 revs and maintained 30 Kts ,no cavitation Chris who has an 8.5 m Scorpion with a 225hp Optimax used literally twice as much fuel as me.I opened the boat up to WOT and still got 5000 revs and 46kts I am a happy bunny. I really think for whatever reason 4 bladed props work very well on ribs
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It looks massive on the trailer,but tiny in a big sea!
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09 May 2017, 17:33
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#2
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Member
Join Date: Jun 2010
Posts: 2,934
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intested in the 4 blade thing myself but not sure what to do as it is an expensive test and would take a long long time to recoupe it from fuel savings.
is 5k the correct revs for an etec?
on my zuke 200 i get upto about 5950rpm (perfect for my engine) and i burn 0.8-0.9lpm in the cruise range, that equates to circa 24-28 knots and 3400rpm or so.
lately though i must admit to having taking a liking to cruising at 35 knots, cover a lot of ground but fuel consumption obviously takes a hit.
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09 May 2017, 17:45
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#3
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Member
Country: UK - England
Town: blackpool
Boat name: Fast Forward
Make: Scorpion
Length: 8m +
Engine: 315 Yanmar
Join Date: Aug 2006
Posts: 385
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Hi Xk59D
Think the engine would run a bit faster with a smaller prop, but it seems quite happy, plus the engine is working well under its max load.The power is there if I need it and the economy fantastic
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It looks massive on the trailer,but tiny in a big sea!
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09 May 2017, 19:36
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#4
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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: 12,178
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I'm a big believer in 4 blade props, I've had great results with them in the last 2 boats. The Mercury Rev4 takes a lot of beating imo, unfortunately it doesn't fit the DF140, so I'm running a Solas 4 blader.
Optimum RPM for the Etec is 5600 iirc, they do like to rev freely, you might actually get more top end & reduce the oil consumption with a smaller prop, plus the holeshot will improve.
__________________
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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09 May 2017, 21:06
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#5
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Member
Country: UK - England
Town: Wild West
Boat name: No Boat
Make: No Boat
Length: under 3m
Join Date: Jan 2008
Posts: 5,306
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[QUOTE=Pikey Dave;
Optimum RPM for the Etec is 5600 iirc, they do like to rev freely, you might actually get more top end & reduce the oil consumption with a smaller prop, plus the holeshot will improve.[/QUOTE]
I'd be surprised if this wasn't the case
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A clever Man learns by his mistakes..
A Wise Man learns by other people's!
The Road to HELL ..is Paved with "Good inventions!"
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20 May 2017, 13:07
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#6
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Member
Country: UK - England
Town: Truro-Cornwall & Brazil
Boat name: Bananas in Blue
Make: Humber Destroyer 5.5
Length: 5m +
Engine: E-Tec 115
Join Date: Jun 2007
Posts: 386
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I dropped 2" off the pitch on my Etec 115 and improved my cruising economy by about 15 percent while raising my wot revs by about 300 to the recommended 5650. WOT fuel consumption went from in indicated 46l per hour to 41 with no loss of top speed.
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20 May 2017, 21:50
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#7
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Member
Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: S/R5.4/regal3760
Length: 10m +
Engine: Suzukidf70 2x6lp 315
Join Date: Jul 2009
Posts: 4,027
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Quote:
Originally Posted by M.Thornton
Have recently bought a 7.2 m Asis rib fitted with a 250 Etec ho outboard.The boat came with a ballistic 24" prop which although fast cavitated like mad.I bought a four blade Lexor 153-22 prop and set off for the Easdale Rib Rally.
The economy and performance of the engine was great. I cruised at 3000 revs and maintained 30 Kts ,no cavitation Chris who has an 8.5 m Scorpion with a 225hp Optimax used literally twice as much fuel as me.I opened the boat up to WOT and still got 5000 revs and 46kts I am a happy bunny. I really think for whatever reason 4 bladed props work very well on ribs
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Sounds like your still overpropped which while the engine might sound happy in reality it's constantly overloaded, I'd be looking to switch down a pitch whilst a petrol 2 stroke will probably tolerate being overloaded better than say a diesel it still can't be good for it long term
Engines are better slightly underpropped rather than over
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20 May 2017, 22:12
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#8
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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: 12,178
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Optimum wot rpm for that engine is 5600 iirc
__________________
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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21 May 2017, 16:27
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#9
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Member
Country: Canada
Town: GTA
Boat name: Seabright
Make: Seabright
Length: 5m +
Engine: 50 HP ETec Tiller
Join Date: Aug 2010
Posts: 234
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22 May 2017, 17:42
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#10
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Member
Country: UK - England
Town: Gloucestershire
Boat name: Osprey
Make: Osprey Vipermax
Length: 5m +
Engine: E-tec 300 G2
MMSI: TBC
Join Date: Dec 2006
Posts: 4,021
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The new RX4 prop that is fitted to the E-TEC G2's is fantastic and will also fit the Gen 1 engines. Well worth a try if you can get hold of one to test. I would suggest a 22" for you engine / rib combo.
As already suggested 5000RPM at WOT is too low and you will reduce the life of the engine over the long term by "lugging" the engine like this.
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Chris Stevens
Born fiddler
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22 May 2017, 22:36
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#11
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Member
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 100hp Yam/150hp opt
Join Date: Sep 2003
Posts: 2,069
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Quote:
Originally Posted by M.Thornton
The boat came with a ballistic 24" prop which although fast cavitated like mad.
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Something not right there. Is there any damage on the prop? Worth sending it away to be checked for balance and distortion on any of the blades.
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22 May 2017, 23:10
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#12
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Member
Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: S/R5.4/regal3760
Length: 10m +
Engine: Suzukidf70 2x6lp 315
Join Date: Jul 2009
Posts: 4,027
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Quote:
Originally Posted by Searider
Something not right there. Is there any damage on the prop? Worth sending it away to be checked for balance and distortion on any of the blades.
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Not necessarily anything wrong with the prop if a big engine is over propped the prop can break away and cavitate
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22 May 2017, 23:17
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#13
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Member
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 100hp Yam/150hp opt
Join Date: Sep 2003
Posts: 2,069
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Quote:
Originally Posted by beamishken
Not necessarily anything wrong with the prop if a big engine is over propped the prop can break away and cavitate
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Yesssss, but unless the prop is inspected by someone who knows what they are looking at the OP won't know.
I'm assuming that the previous Owner spent £££ on that propeller and if it didn't perform properly they would have taken it back?
Irrespective of the old prop - the new one isn't right either. Rec RPM range is 5300-6000.
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23 May 2017, 00:11
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#14
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Member
Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: S/R5.4/regal3760
Length: 10m +
Engine: Suzukidf70 2x6lp 315
Join Date: Jul 2009
Posts: 4,027
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Yeh he needs to go down in pitch to bring the revs back up.
4 blade props are known for not being the fastest option but make up for the Loss of top end in other ways, the op dropped a pitch from 24 to 22 but went for four blades which has increased drag on the engine and he's still down on revs so next step would be to drop another pitch to gain revs and probably speed
He doesn't need to check his old prop to know he's still down on rpm
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23 May 2017, 12:30
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#16
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Member
Country: UK - England
Town: Southampton
Boat name: SMH Rib / War Shot
Make: Ribtec / Scorpion
Length: 4m +
Engine: 100hp Yam/150hp opt
Join Date: Sep 2003
Posts: 2,069
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Quote:
Originally Posted by beamishken
Yeh he needs to go down in pitch to bring the revs back up.
4 blade props are known for not being the fastest option but make up for the Loss of top end in other ways, the op dropped a pitch from 24 to 22 but went for four blades which has increased drag on the engine and he's still down on revs so next step would be to drop another pitch to gain revs and probably speed
He doesn't need to check his old prop to know he's still down on rpm
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My point about having his previous prop checked is that there may be a fault or some damage with it which is causing it to cavitate or ventilate.
If, for example, one blade is bent aft in relation to the others, as could easily happen if it had been grounded, this will mean that this blade has more pitch. It will be more highly loaded than the others and may cavitate.
WRT his new prop - yes, he needs to come down in pitch a little.
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