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Old 12 November 2002, 13:47   #1
DJL
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FourStroke vs TwoStroke

Here are my findings on the topic, they will only really apply to mid range engines, as there isn't the option of hightech 2-strokes, such as optimax.

Situation: I recently changed from a Mercury 60HP 2-stroke (100kg) to a Mercury 60HP 4-stoke EFI (112kg)

Noise: The fourstroke is much quieter throughout the RPM range. A normal conversation can now take place at full throttle.

Top Speed: Surprisingly my top speed has increased by 1/2knots. I am using the same pitch/dia prop. The engines do however have difference gear ratios/WOT engine speeds Ė leading to the prop on the fourstoke spinning slightly faster.

Power: Acceleration seems very similar (probably due to the EFI), although itís difficult to tell though because you donít have the raw power sound that you get with a 2-stroke. The boat performs much better at low to medium planning speeds, the fourstroke doesnít labour and drink large amounts of fuel like the 2-stroke. The fourstroke is also very nice in rough weather, the smoothness of the power makes for a more comfortable ride when working the throttle. Having said that you do need to move the throttle further as the power is spread more evenly over the rev range. It will be intresting to try waterskiiing / ringing.

Fuel Consumption: Its hard to say at the moment because the engine is being run in and the RPM had to kept low and varied. However for the first time in the life of the boat a full payload of fuel kept the boat going for two days, even though similar hours/miles were covered. Will have to wait until I cruise normally for accurate figures.

Starting/Idling: Mainly down to the EFI and computer control, the engine starts first time, applying choke and throttle automatically. Over the first few minutes as the engine warms the revs drop to an idle speed of about 800rpm.

I am very surprised about how the fourstroke performs. I was ready to except a loss in performance for the fuel savings but I havn't needed too. From my experiences this weekend I have no idea why a 2-stroke would be bought over a 4-stroke Ė apart from initial cost. The 4/ is clean, quiet, more efficient, smoother, has loads more torque at low speeds and is just as powerful. Although they do feel quite difference to drive, I much prefer the 4/, and Iím not just say that cause I just bought one. I just hope Iím still happy after the bill for the first service.
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Old 12 November 2002, 14:39   #2
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I knew you would not be dissapointed.

Enjoy.
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Old 12 January 2004, 12:56   #3
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Daniel,

A year on and are you still chuffed with your engine? I have the same but yet to get it out on the water - yet to even run it in! Also, after your season, how have you fared with water sports and particularly fuel consumption? We have similar size boats so your knowledge would be very useful to me!

Thanks, Robert
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Old 12 January 2004, 13:43   #4
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Well done for dredging that thread up, Robert - you must have set one of those bleeping devices on your computer to remind you a year down the line

Seriously, though, it's a fascinating subject and particularly pertinent in my case since I'm currently dithering over whether to fit a Suzuki 50 Efi 4-stroke or Evinrude E-Tech direct injection 2-stroke to my 4m Searider. It should be pointed out though that a lot of Daniel's comments about 2-strokes are not necessarily applicable to direct injection technology.
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Old 12 January 2004, 15:02   #5
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PD wait too see about the E-tecs. If heard only good things about them, they are tiny! weight very little, should give comparable fuel consumption but wait for them to be throughly tried and tested before buying.
The fourstroke is a safe bet.
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Old 12 January 2004, 15:44   #6
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after my visit to london boatshow, all the gumf says that optimax, hpdi etc etc are very fuel efficient and the figures the suggest compare with 4stroke. But i have a friebd who has a modern 2strke rude and although it is very cheap on fuel he seems to be constantly putting oil in it. Surely that outweighs the cost making 4stroke a winner again??

ta gt
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Old 12 January 2004, 16:02   #7
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The engine has been great and even without the fuel savings it would have been worth the money. Generally its nice just to have an engine thatís quiet and starts instantly. Plus the extra few knots ain't bad either.

Fuel consumption has decreased by about 35%, giving around 2 to 2.4 nmi per litre. If you push it hard, 5500->6000 RPM it drops to around 1.7/1.8nmi per litre.

Water sports have been great - I started to learn how to wakeboard this yeah. The boat has loads of pull in it, in fact you have to be quite gentle with the throttle, much more so than with the old two stroke. Its also noticeably easier to get the ring on the plain too. I do have a stainless prop now though.

It was interesting to read what Pitkis wrote in the gallery about the Finnish Atlantic 21 being fitted with a pair of Mercury F60s. I will be intesting to know how they get on with them.
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Old 12 January 2004, 16:37   #8
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Quote:
Originally posted by gtflash
But i have a friebd who has a modern 2strke rude and although it is very cheap on fuel he seems to be constantly putting oil in it. Surely that outweighs the cost making 4stroke a winner again??
Quicksilver 2 stroke oil adds about 4p per litre - a saving of £1 per tank of fuel used (25L)
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Old 13 January 2004, 05:34   #9
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Do the maths

Most rib users are weekend warriors, and then mostly in the summer, spring and autumn. so the average boat only goes out for two days a week say for 30 weeks a year (bull, it's more like 15 weeks a year). Check your logs and you'll se what I mean

If your cruises average a 100 miles a day that's 3000 miles a year tops. The difference in performance betwen a two stroke Opti and a 4 stroke is marginal say + or minus 5%. given that you get about .8 of a ltre per mile and that 4 strokes were marginally more fuel efficient and adding a further !% for 2 stroke oil.

The four stroke 3000 miles at . 8 litres per mile = 2400 litres
The two stroke (opti) 3000 miles at .84 litres per mil = 2520 litres
So the 2 stroke on 3000 miles pops 120 more litres of fuel.

Thats about £90:00 a year extra in fuel for a 2 stroke. if your 4 stroke was just a grand deared than the new technology 2 stroke then you are only going take 12 years to recover that grand

If on the other hans you are a Dive Club, River Police, Sail Club
or small ferry operator then 4 stroke has got to be a winner if you are doing slow speed stuff all the time.

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Old 13 January 2004, 05:59   #10
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Stuart I am in agreement with you and there were many threads debating this issue I remember this one

2 vs 4

In general I think if economy and weight are the only (or the major) issue, then it does not worth the trouble of buyng a 4 stroke which is more expenssive than a 2 stroke.
If however, there other issues such as less noise, slow speed at long periods of time i.e. dive club as you mentioned (that's it really can't think of anything else) then a 4 stroke is a serious consideration.

In any case I am sticking with 2 stroke engines whatever else is going on (call me old fashioned and all that)

PS I think that 100 miles average a day for a private individual is quite a bit (as you say the very VERY max). Better do your sums for about 40-60 miles tops.

PS Is it also correct in saying that in smaller engine size (50-110 bhp) there is not a big (or not at all) difference in consumption?? Just asking
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