How much better are 4 strokes fuel consumption

[martin33100]

Hi, we may get another RIB in the future, our old RIB had a Merc 90 and our current boat has a Yam 70, both 2 stroke.
I like the reliability and how simple they are to look after but if we buy a newer RIB it’s probably going to have a 4 stroke on it.

So my question is in the real world do the 4 strokes actually use far less fuel when comparing like for like power wise?.

Our next RIB will be around 5.5-6M ish.

[Pikey Dave]

Originally Posted by martin33100

Hi, we may get another RIB in the future, our old RIB had a Merc 90 and our current boat has a Yam 70, both 2 stroke.

I like the reliability and how simple they are to look after but if we buy a newer RIB it’s probably going to have a 4 stroke on it.



So my question is in the real world do the 4 strokes actually use far less fuel when comparing like for like power wise?.



Our next RIB will be around 5.5-6M ish.

If you’re comparing a modern efi 4 stroke to a similar HP vintage carbed 2 stroke, then it’s night & day. The 2 stroke will use at least twice the fuel of the 4t probably even more. However, if you’re comparing the 4t to a modern DI 2 stroke, then in the real world, there’d be little if anything in it.

[Livid]

Yeah that's my experience too, we have a 40 4stroke and 40 2 stroke and the 2stroke is at least twice as thirsty. It is however a lot more reliable and cheaper to maintain so it depends if you use it enough to justify the fuel savings over the yearly maintenance costs

[Fenlander]

I know this experience is on the small side hp wise but...

I went from a 15hp 2-stroke to a 20hp efi 4-stroke a few years ago (and back again but that's another story) and managed about 50% extra distance at slightly greater speeds. For me the greatest benefit was the greater range for a given tank size.

[jeffstevens763@g]

The only offering I have is on our long trips with gurnard he had a 25 two stroke on a 420 sib I had a 25 four stroke on a 3.65 sib I was 15% better off but if you equal the boats and weight I think more the 10% worse for the two stroke.

[Limecc]

Originally Posted by martin33100

So my question is in the real world do the 4 strokes actually use far less fuel when comparing like for like power wise?.

Evinrude etec direct fuel injection two strokes are at least as good if not better than a four stroke. Caloundra Marine videos on YouTube usually include the fuel consumption in their comparison reviews. If buying a new outboard, would be on my shortlist.
https://youtu.be/tZvIw83uZgY

[69cmw]

Originally Posted by Limecc

Evinrude etec direct fuel injection two strokes are at least as good if not better than a four stroke. Caloundra Marine videos on YouTube usually include the fuel consumption in their comparison reviews. If buying a new outboard, would be on my shortlist.

I thought Evinrude stopped making outboards [emoji848]

[Livid]

Yeah as of a few weeks ago they have so I wouldn't recommend buying one unless you're willing to roll the dice

[martin33100]

Thanks the reply’s guys, if we use the RIB like our last one we may do a lot of towing ie water sports so I guess a DI 2 stroke may give us the best of economy and power?.
However if the right RIB comes up for sale with a 4 stroke on it I am not that bothered about the servicing costs as my labour is free.
I am one of the maintenance techs at Southampton Container terminals and I did my apprenticeship building Diesel engines so I don’t mind having a go at most things.

[Pikey Dave]

Originally Posted by martin33100

Thanks the reply’s guys, if we use the RIB like our last one we may do a lot of towing ie water sports so I guess a DI 2 stroke may give us the best of economy and power?.

However if the right RIB comes up for sale with a 4 stroke on it I am not that bothered about the servicing costs as my labour is free.

I am one of the maintenance techs at Southampton Container terminals and I did my apprenticeship building Diesel engines so I don’t mind having a go at most things.

Having owned boats with both DI 2 strokes & 4 strokes, my experience is that there’s much more “grunt” with the 2 strokes & neglible difference in fuel economy. The 4 stroke cost of ownership is much higher, due to the (imo) excessive servicing requirements.

[Maximus]

I've owned many 2strokes over the years.....but things move on and I do prefer 4strokes overall ...I find them much more economical... I like the quiet running....no oil to worry about...and if you've ever followed 2strokes at Sea for a period just hope you've enough Gee Gees to overtake..( especially a twin set up)
The Trick with any engine choice for a RIB ...is to match the engine Size (Power) to the Hull AND loading expected Then prop it properly!... to get the performance your after
As for 2strokes v Four I can only speak from my experience

I've trialed/raced 250 HO g2 Tws strokes (on a LIGHTER Newer RIB!) ...against my own set up 6.8 RC with 250 Df in hole shot tests over a few hundred yards...
Result NOTHING in it!!!...not even 1/2 a Boat length.
Now that's a real world test!
"Hole shot" for me is paramount....but topping out at 48knots in a Heavy layup Ribcraft 6.8 isn't too shabby...I could possibly improve on top end....but Grunt and Holeshot punch may suffer.
Try some different combinations...but ultimately get the engine Size/choice/set up/prop/..RIGHT and you'll get the best out of you're chosen package regardless

[martin33100]

Thanks for the advice guys, our old RIB was an Avon Adventure D560 and it went well with a Merc 90 2 stroke.
Ideally our next boat will be similar size or up to 6M, however prices are very very high at the moment.

[Searider]

I had an Avon 5.4m Searider with a carb 2 stroke Mariner 90.
Changed to a 6.5m Scorpion with 150hp Optimax - a boat probably 75% heavier and the fuel consumption was about the same at a litre a mile.
(better than a litre a mile at below 25knots).
Very happy with my Optimax.

I considered all engines when our Opti got to 900hrs and 15 years old.
Sea trialled a 150hp Selva 4 stroke which felt very weak in comparison with the Opti.
Liked the look of an E-tec.
However, bought another Opti when a good deal came up on a low hours one.

If money were no object I'd probably consider one of the new mercury 4 strokes 150hp or the V6 175hp simply because we do more low speed coaching now and the Opti is a bit loud!

Now that E-Tecs arent being made I'd probably avoid those.
Tohatsu TLDI is the same tech as Optimax and worth a look if the price is right.