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Old 26 February 2014, 13:34   #1
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Country: South Africa
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Real World Testing 40hp 2 stroke vs 4 stroke

Hi

I've been a member on this forum for almost 10 years, posting very little, but rather reading and absorbing as much knowledge as possible. I have a passion for semi-rigids and have had one for the last 10 years, in conjunction with my fibreglass boats.

I did this real world test for my local South African Boat Fishing forum and thought that i would share my findings here.

Makes for interesting reading:


When the discussion of 2 stroke vs 4 stroke is raised, there are a few common well known theories that we mention. The general consensus amongst boaters is that a 2 stroke has better performance, whilst a 4 stroke offers better economy, but lacks the grunt or low down hole-shot of a 2 stroke.

I can attest to this theory, as when i still drag raced motorbikes at Killarney Race Track, my buddy's would run 400cc 4 stroke motorbikes against 250cc 2 stroke bikes, and the 2 stroke bikes would ANNIHILATE them!! We all knew that 2 strokes were faster, even though they had smaller engines.

With the advancement made by the modern outboard manufacturers, has the PEFORMANCE gap been made smaller or is there still such a big difference?

I was in the perfect position to test this. I had aquired a 5.0m Gemini Semi Rigid and had fitted her with a 40hp 3 cylinder pull start Yamaha 2 stroke. My wife wasn't too impressed being asked to pull start the motor, even though it started with half a pull!! So, i was asked to look for a motor with electric start. As luck would have it, a second hand Honda 40hp electric start tiller steer motor came my way, at a VERY good price, and i acquired the motor.

My tests were to determine the PERFORMANCE of the motors.

0-10 knots. I slipped the boat into gear, then idled for a minute or so and then opened the throttle completely. The time it took to get to 10 knots was then recorded. This was repeated 15 times, alternating runs WITH the slight swell, as well as against the slight swell. The average of these times were taken.

0-15 knots. I slipped the boat into gear, then idled for a minute or so and then opened the throttle completely. The time it took to get to 15 knots was then recorded. This was repeated 15 times, alternating runs WITH the slight swell, as well as against the slight swell. The average of these times were taken.

0-20 knots. I slipped the boat into gear, then idled for a minute or so and then opened the throttle completely. The time it took to get to 20 knots was then recorded. This was repeated 15 times, alternating runs WITH the slight swell, as well as against the slight swell. The average of these times were taken.

WOT (Wide Open Throttle). I made 4 runs, at full open throttle. Two runs were with the swell and two runs against the swell. The highest recorded speed on the GPS was taken.

Fuel consumption. I filled my fuel tank to the FULL mark. Did the testing runs and after the trip, refilled the fuel can to the FULL mark. Total fuel used was recorded as well as total distance travelled according to the GPS's trip meter.
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Old 26 February 2014, 13:36   #2
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Country: South Africa
Boat name: Born Wild
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Yamaha 40hp 2 stroke outboard

This motor belonged to a very good friend of mine and was in storage for the last few years. I took the motor to Anchor Boat Shop, who serviced her and replaced all the necessary seals, impellor, cleaned the carbs, etc, etc. For the test, i installed a new set of spark plugs. Motor was in very good working condition.

Model: 1995 Yamaha 40hp 2 stroke Autolube 3 cylinder long shaft
Weight: 75kg's
Displacement: 698cc
Prop: 12p Yamaha Prop

Boat: 5.0m Gemini Semi Rigid
Weight: 180kg's
Fuel: 25kg's
Safety Kit: 20kg's

Crew: 200kg's

Total Weight of Boat, Engine and Crew: 500kg's







0-10 knots. Average 5.1 seconds

0-15 knots. Average 6.1 seconds

0-20 knots. Average 7.5 seconds

WOT - Top Speed - 29.1 knots

Fuel Consumption. Distance Covered 8.40nm, Fuel Used 7.1litres = 1.18nm/ltr



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Old 26 February 2014, 13:40   #3
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Country: South Africa
Boat name: Born Wild
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Honda 40hp 4 stroke outboard

Because this motor is an electric start, i had to add a battery to the boat. My daughter insisted on coming along, so we had a extra passenger, even though she only weighs 15kg's........




Model: 2011 Honda 40hp 4 stroke 3 cylinder long shaft
Weight: 97kg's
Displacement: 808cc
Prop: 13p Honda Prop

Boat: 5.0m Gemini Semi Rigid
Weight: 180kg's
Fuel: 25kg's
Safety Kit: 20kg's
Battery: Deltec 60amp 15kg's

Crew: 215kg's

Total Weight of Boat, Engine and Crew: 552kg's









0-10 knots. Average 4.4 seconds

0-15 knots. Average 5.9 seconds

0-20 knots. Average 9.5 seconds

WOT - Top Speed - 28.4 knots

Fuel Consumption. Distance Covered 9.04nm, Fuel Used 4.1 litres = 2.2 nm/ltr






And after a hard days testing!!

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Old 26 February 2014, 13:41   #4
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Some issue's worth pointing out:

When i fitted the 40hp yamaha 2 stroke to the boat, she was mounted a tad bit too high. During tight turns, she would cavitate a bit. It didn't bother me and i left it like that. When i fitted the Honda 40hp 4 stroke, it was also mounted a tad bit high. The Honda however doesn't go down as far into the water as the Yamaha and i would get the odd occation of cavitation under acceleration. I will cut the transom down a bit and refit the motor, to eliminate this cavitation.

The Honda motor is 22kg's heavier than the Yamaha 2 stroke. I also added a battery to the boat, which weighed 15kg's. Furthermore, i took my daughter with, which was another 15kg's of extra weight, which i did not have on the initial test with the Yamaha 2 stroke motor. The second test was thus done with 52kg's extra weight.

The Yamaha 40hp 2 stroke had a 12p prop on and the Honda 40hp 4 stroke had a 13p prop on. I have requested a 12p loan prop from Honda Somerset West and they have ordered one for me. I will redo the entire test when the 12p Honda prop arrives.
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Old 26 February 2014, 13:43   #5
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Initial Verdict

Performance:

I was convinced that the 40hp Yamaha 2 stroke would outperform the 40hp Honda 4 stroke by a large margin. When i took into account the 10% increase in weight in the second test, i was even more sure that the difference would be much greater, in favour of the 2 stroke Yamaha.

However, when i started comparing the data, i was very surprised to see that the Honda 4 stroke was actually FASTER during the 0-10knots test!! The Yamaha 2 stroke 40hp did the 0-10knots test in an average of 5.1 seconds, whilst the Honda 4 stroke 40hp did it in an average of 4.4 seconds. That makes the Honda 40hp 4 stroke 12% FASTER in the 0-10knots test.

During the 0-15knots test, the two motor are very close to each other, with the Honda 40hp 4 stroke being marginally faster, at 5.9 seconds compared to 6.1 seconds for the Yamaha 40hp 2 stroke. The Honda 40hp 4 stroke is thus 3% FASTER in the 0-15knots test.

During the 0-20knots test, the Yamaha 2 stroke 40hp was CONSIDERABLY faster, completing it in an average of 7.5 seconds, whilst the Honda 4 stroke 40hp did it in 9.5 seconds. Here, the Yamaha 2 stroke 40hp was FASTER by 21% in the 0-20 knots test.


Top Speed:

The Yamaha 40hp 2 stroke had a top speed of 29.1knots, whilst the Honda 40hp 4 stroke had a top speed of 28.4knots. That makes the Yamaha 40hp 2 stroke 2% faster on top speed. What is however impressive is that when testing the honda, the boat was 52kg's heavier.


Fuel Consumption:

The Yamaha 40hp 2 stroke used 7.1 ltrs of fuel to cover 8.40 nm, which equates to 1.18 nm/ltr. The Honda 40hp 4 stroke used 4.1ltrs to cover 9.04nm, which equates to 2.2 nm/ltr. The Honda 40hp 4 stroke is thus 46% LIGHTER on fuel when compared to the Yamaha 40hp 2 stroke. No surprise here, as that is what we all expected.


Conclusion:

This is NOT what i expected. I went and did a bit more research and found that Honda has BLAST on their motors ( Boosted Low Speed Torque, or BLAST, improves acceleration at low speeds. A quick movement of the throttle control activates the BLAST® system, advancing the ignition curve aggressively. "Hole Shot" is vastly improved as more horsepower gets the hull up on plane quicker. - as per honda website) This explains why the acceleration from 0-10knots and 0-15knots actually exceeds that of the 2 stroke Yamaha. The two stroke however keeps on powering on, when the BLAST system on Honda stops, which is why the 0-20knots is so much quicker for the Yamaha 2 stroke.

Not only has the newer generation 4 stroke caught up to it's 2 stroke counterparts in holeshot/low down acceleration, it has actually surpassed them!!

The fuel consumption figures are also not a true reflection of things, as most of the time the motors were tested at WOT, which is where a 4 stroke offers its worse fuel economy. If one was to cruise at 16-20 knots, the consumption would be MUCH better for the 4 stroke. Regardless, the economy is still BRILLIANT, saving you 46% of fuel at a MINIMUM.

Note:
I am in no way affiliated to either Yamaha or Honda. I do however have to say a BIG thank you to Neil and Dudley at Anchor Boat Shop for assisting me in rigging my boat with the Yamaha, as well as for their years of PHENOMINAL service!! GREAT guys and they will try their utmost to assist ANY boater. I can HIGHLY recommend them for all your Yamaha needs. Similarly, Jeremy and Andre and Honda Somerset West also offered AWESOME service and i have to thank them as well for assisting in the installation of the Honda motor to my boat. GREAT guys and would also recommend anyone wanting Honda's to go visit them. :mrgreen: :mrgreen:
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Old 26 February 2014, 14:20   #6
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Awesome post
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Old 26 February 2014, 14:28   #7
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Good post but a 1995 2s vs 2011 4s isn't a fair test. 2s tech has come on leaps and bounds too!!
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Old 26 February 2014, 14:32   #8
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Yes,really interesting post. Massive difference in Fuel Consumption and therefore boat-range.
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Old 26 February 2014, 14:35   #9
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As I've said before, I love my Honda 50. I was aware of the BLAST technology, though was a little sceptical as to how well it would work, but must admit that it seems to jump onto the plane when you whack the throttle open, and the fuel economy is exceptional.

PS. When you do the re-test, will you leave sleepy-head ashore so the only weight difference is the engine/battery?
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Old 26 February 2014, 14:38   #10
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Brilliant test but agree with HP .. It s not a fair test.. I dont mean that in a bad way so appologies i it came over like that.. Fantastic detail and effort!
I would like to see a test on a like for like set up.. A big well done for doing it!!
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