Interesting article on outboard stats

[Flex]

Read a boat review at boat point, they did a review on a 60 e-tec(the review is a few years old now).

What struck me as very odd was the stats they produced when comparing different engines.

heres the text'

On a 4.8m Stacer 469 Easy Rider bowrider, spinning a 15-inch pitch stainless steel SST prop and pushing 830kg, the demo E-TEC 60 outperformed a Yamaha F60C on a Horizon 4750 Sea Breeze displacing 800kg. When trolling at 650rpm it averaged 4.3km/h using 0.6lt/h, compared to 4km/h and 0.8lt/h for the F60C at 700rpm, although vibration levels were higher. It planed us at 21.5km/h and 3100rpm, and cruised at 34.1km/h and 4000rpm using 7.9lt/h, compared to 31.4km/h and 7.7lt/h at the same revs. No prop ventilation occurred through full-lock figure-of-eight turns at these revs.
The wide open throttle averages were 53.6km/h and 5800rpm using 19.4lt/h,


whereas the F60C averaged 50.1km/h and 19.2lt/h at 5650rpm.


But a carbie Merc 60 on the same hull, spinning a 14-inch alloy prop and pushing 750kg, averaged 5.6km/h and 2.1lt/h while trolling at 850rpm. It planed us at 23.4km/h and 2800rpm, and cruised at 4000rpm averaging 46.7km/h and 10.5lt/h. The WOT averages were 65.3km/h and 24.6lt/h at 5300rpm. So for top end performance, the Merc 60 has it all over the E-TEC 60!

So going by those stats if you did alot of long distance cruising running around 4000rpm. the old school carby is the best option.

At 4000rpm
e-tec- 34km/h at 7.9L
carby yamaha 4 stroke 31km/h at 7.7L
Merc 46km/h! at 10L


Is the mercs superior speed solely due to the props on each outboard? and gearcase sizing? 12km/h difference is a damn lot for such small outboards.
or the test results are incorrect or im interpreting them incorrectly

[FNQCairns]

That's the right speed for the merc at that rpm, the Yam would need to be running a 10 or 11p prop - so it reads as incorrect, the e-tec should be running at 31kph but the WOT is all wrong for the pitch.

The one's that ring fully true are the merc and the e-tec but mainly because the pitch is known, would need to know what prop the yam is using on to make good and easy sense of it.

heading to bed now but it all looks screwed up the e-tec should only do 44kph or so at 5800 wit hthe 15p...it's all a mess.

cheers fnq

[Flex]

FNQ mind if I ask what formula you use to work out speed given for pitch/hp etc?

[FNQCairns]

Hi flex just one of the propeller calculators (using 10% slip)on the net through google, had to search up the leg ratios also, hope I got it all right I was pretty blury eyed when I read your post and it sparked an interest.

cheers fnq