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Old 06 May 2004, 16:29   #1
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Country: France
Town: le palais
Boat name: agnhélie
Make: narwhal
Length: 6.7
Engine: YAMAHA 115 4 STROKES
Join Date: May 2004
Posts: 19
two strokes four strokes

from what i can read from you guys ,it seems than four strokes for the same amount of hp are less efficient than two strokes in terms of fuel savings;what's the truth,is any body able to give me figures about that
i am concerned about the silence at iddle ,cause i am fishing with the engine on
4 stokes are probably less performant than 2 stokes cause of their weight

it sounds fo me than 4 strokes was easier and cheaper to maintain tue or not
thanks for all of that
i am looking at 150 HP
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Old 06 May 2004, 16:38   #2
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Country: Ireland
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Boat name: XS-600
Make: XS-Ribs
Length: 6m +
Engine: Merc Optimax 150 XL
Join Date: Feb 2004
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Roll on the debate!!

It is my understanding that for fishing with the engine idling at low revs and trolling around at low speed a 4stroke will behave better, and so may suit your needs. Not sure about this though!!

Their are plenty of threads already, on this but I think it all boils down to personal preference, and what you want the engine to do.
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Old 06 May 2004, 16:43   #3
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Country: France
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Boat name: agnhélie
Make: narwhal
Length: 6.7
Engine: YAMAHA 115 4 STROKES
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i am not trolling i am mainly concern about fuel economy
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Old 06 May 2004, 16:46   #4
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Country: UK - England
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With the exception of the 90 and 130 honda fourstrokes an opti will use more fuel than a 4 stroke. It may not be much more but when the oil costs are added they are noticibly more expensive to run.

Have a look at suzuki 4 strokes, by far the best in my opinion at the 140 suzuki is quite a lot lighter than a 150 opti.
As for fishing, four strokes wont make the typical oily 2s troke smell at tickover and are quieter.
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Old 06 May 2004, 16:50   #5
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Country: UK - England
Town: Blandford / London
Boat name: Top Cat
Make: Scorpion 8.1
Length: 8m +
Engine: Yamaha F225
MMSI: 235020739
Join Date: May 2003
Posts: 124
Very occasionally my optimax (2 stroke) cuts out if it has been running slowly for a longish period of time 1hr +. It does have 500+ hrs on it but apparently it has always done it, it is a 1999 model. This not really worrying as 1 –2 squeezes on the fuel bulb and it restarts first time and then runs very sweetly again.

Just passing this information on as a four stroke maybe better if idling for long periods of time.
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Old 06 May 2004, 16:50   #6
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Engine: Mercury F60 EFI
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Not sure that 4/ are easier to maintain than 2/ though...I think the mechanical 'simplicity' of 2/ makes them easier if anything. Having said that...I wouldn't have a scooby-doo with either of them. Checking the oil is a far as I've been!
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Old 06 May 2004, 17:15   #7
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Country: Ireland
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Boat name: wizzard
Make: REDBAY
Length: 7m +
Engine: 225 optimax
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preferences

Its down to what you want, in a boat invariably you are going to be in situations where you need extra or immediate umph,This is important towing toys, towing boats, making a rapid manouvre etc etc, four strokes will do this, but strokers love this sort of driving.Four strokes as we know have valves and cam chains, sump oil , and sump or four stroke oil filters. Two strokes dont have valves cams , oil filters.Two strokes having less moving parts can rev higher, their lubrication is with the fuel, as far as the cylinders are concerned. Four strokes tend to rev a little less, are quiter, and obviously reuse their lubricant in the cylinders with scrapper or oil rings removing it each time.
As far as power is concerned in a stroker its done in two cycles, but fours need to preform two more.Easily a two stroke will give you that immediate umph, more readily than its heavier four stroke counterpart with matched hp.I am not talking about dfi, two strokes as I know they can be heavy.
In reality I prefer two strokes, for lubrication, power cycling output, smell, sound , rev range , simplicity , ease of maintaince, and immediate umph on tap.
If I wasnt running a fast rib, but say a harbour launch, where I needed a quiter engine, not immediate umph relative to a two stroke, good fuel economy, and I didnt want to buy two stroke oil,
and never reved hard, I would fit a four stroke.
I just happen to be a fan of two stroke motors, but there are some amazing four strokes out ther, with plenty of power, up in the big Hp ranges, its down to choice and needs at the end of the day.
The boat and your needs and driving style should dictate the motor you use.There are benifits to both and down sides to both.
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Old 06 May 2004, 17:45   #8
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Country: UK - England
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Engine: Suzuki 70hp 4* outbo
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In our diving club we have 3 Yamaha 2 stroke engines & 1 Suzuki 4 stroke. We have a 30hp Yamaha premix on a 4.5m Zodiac, this has been the most reliable of the Yamaha engines it is also the oldest. We have another Yamaha 30hp auto lube on an Avon 5m & a Yamaha 40hp auto lube on an Avon 5.2m. These two auto lube engines have been nothing but trouble, the carbs have had to be stripped down & cleaned 3 or 4 times every year because of blocked slow running jets. All three of these boats & engines tend to use almost 2 tanks of fuel in a typical days diving.
Earlier this year we got a Humber Assault 5.5 with a Suzuki 70hp 4 stroke, this is a lot quieter and runs a lot better at tick over for long times, no smelly exhaust fumes & a typical days diving has yet to use 1 tank of fuel (yes they are the same size tanks)
I know 4 stroke engines are heavier, cost more to purchase & you have to change the oil & filter regularly but from my own experience I know what we will be getting in future.
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Old 06 May 2004, 18:50   #9
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9 months ago i was going to buy a diesel or 4-stroke RIB.

The reasons for discounting diesel are numerous, but those for choosing an Optimax over a 4-stroke may help you here, particularly because i was looking for a 150ish HP unit.

Firstly there was a poor choice of 4-strokes at this size. I don't like Suzuki's, that's just me - i know the new engines are supposed to be good but but i still don't like 'em.

The next choice i could find in 4stroke was a Yam 115 unit, which was similar in weight to a 150 opti

The 150 opti was several thousand pounds cheaper than the 4-stroke

I don't need to idle for long periods of time

I do like skiing and hence loads of low end power

The optimax smartcraft gauges are superb, really, really superb - do not overlook this.

I'm not trying to persuade you 2-stroke DFI is the route for you, if you are going to idle for long periods of time it probably is not. I can guarantee you non-DFI 2-stroke is NOT the route to go, consumption and resale are very poor. For info i will probably be replacing my sailing club's safety boat engines with 4-stroke units, although there are no DFI engines of the 40hp size available i would still choose 4-stroke here if there were.

With 70 hours and 1500nm under my belt I can confidently say i can acheive a little under 1nm per litre. If i open the throttle loads i can dent this figure. 1500 miles have used 7 tanks (1600li) of fuel.

I hope that is of some help!
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Old 06 May 2004, 19:02   #10
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Country: Ireland
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Boat name: XS-600
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Engine: Merc Optimax 150 XL
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Quote:
although there are no DFI engines of the 40hp size available i would still choose 4-stroke here if there were.
There's a new Evinrude e-tec 40hp. These are direct injection. Just thought I'd post this for anyone looking at the smaller engine sizes. Looks a good engine too. No run-in, First service after 3yrs. If they had Smartcraft and made em bigger than 90 I'd have gone for one.
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