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Old 09 May 2017, 16:24   #1
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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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Old 09 May 2017, 16:33   #2
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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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Old 09 May 2017, 16:45   #3
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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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Old 09 May 2017, 18:36   #4
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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.
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Old 09 May 2017, 20:06   #5
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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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Old 20 May 2017, 12:07   #6
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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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Old 20 May 2017, 20:50   #7
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Quote:
Originally Posted by M.Thornton View Post
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
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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Old 20 May 2017, 21:12   #8
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Optimum wot rpm for that engine is 5600 iirc
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Old 21 May 2017, 15:27   #9
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This is a good site for all things ETEC.
For example:

150 HP WOT is only 5100 RPM, could use some advice please - Barnacle Bill's Marine Supply
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Old 22 May 2017, 16:42   #10
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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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Old 22 May 2017, 21:36   #11
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Quote:
Originally Posted by M.Thornton View Post
The boat came with a ballistic 24" prop which although fast cavitated like mad.
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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Old 22 May 2017, 22:10   #12
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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.
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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Old 22 May 2017, 22:17   #13
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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
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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Old 22 May 2017, 23:11   #14
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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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Old 23 May 2017, 00:22   #15
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If an engine can reach its max rpm it shouldn't make a huge difference what boat or weight it is, its more about reaching its max rpm with the correct prop.

This site has very accurate fuel comparisons on most engines, you can opt for litres or gallons at the top of the page, simply click on the outboard you need to check.Evinrude Etec 25 - 50 - 75 - 90 - 115 - 150 - 225 - 250 - 300 hp HO Outboard Fuel Consumption Chart GPH MPG Test & Specs | Portable 3.5 - 4 - 6 - 9.8 - 15 hp
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Old 23 May 2017, 11:30   #16
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Quote:
Originally Posted by beamishken View Post
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
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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