Fuel consumption on a 650 vs 700

Dissko · 04 June 2020, 08:43

Hi there all, i am considering a XS650 with 150hp or a 700 with 175/200. What would the, rouhgly, difference be in fuel consumption? I know it`s depending on how you drive, but anyway. Thanks!

Obsidian · 04 June 2020, 08:52

For example a Yamaha...

150HP @4000RPM will draw 23 litres per hour
175HP @4000RPM 26 lph
200HP @4000RPM 36 lph (32 @3500 maybe better comparison)

Figures from: https://www.boat-fuel-economy.com/ya...umption-liters

36valley · 04 June 2020, 08:57

Can't comment on the difference, but my XS650 with a Suzuki 150 does 1.2nm to the litre cruising at around 25 knots.

Dissko · 04 June 2020, 09:01

Quote:

Originally Posted by Obsidian

For example a Yamaha...

150HP @4000RPM will draw 23 litres per hour
175HP @4000RPM 26 lph
200HP @4000RPM 36 lph (32 @3500 maybe better comparison)

Figures from: https://www.boat-fuel-economy.com/ya...umption-liters

Ah, thanks. So it`s a bit up from 175 to 200 then. And way more than my 115hp(on a smaller boat).

Dissko · 04 June 2020, 09:02

Quote:

Originally Posted by 36valley

Can't comment on the difference, but my XS650 with a Suzuki 150 does 1.2nm to the litre cruising at around 25 knots.

Thanks. Re fuel consumption the 150 or 175 would be the smart choice.

Obsidian · 04 June 2020, 09:08

Also bear in mind engine weight, I believe my RIB will perform better if I drop from a 150 to a 135 in part because there is a big difference in kiloage.

Dissko · 04 June 2020, 09:45

Quote:

Originally Posted by Obsidian

Also bear in mind engine weight, I believe my RIB will perform better if I drop from a 150 to a 135 in part because there is a big difference in kiloage.

Good point. Some would maybe say it would be underpowered. I got some comments here in that direction when i was about to get a Tornado 585 with 115hp.

Obsidian · 04 June 2020, 09:55

Quote:

Originally Posted by Dissko

a Tornado 585 with 115hp.

Sounds perfect to me!

It all depends what you want from your boat of course. I use mine for teaching, safety/camera work and family cruising so speed is not my #1 concern.

Fender · 04 June 2020, 10:36

Quote:

Originally Posted by Dissko

I know it`s depending on how you drive, but anyway. Thanks!

Plus you might find economy hit adversely on a smaller engine working hard compared to a larger unit - you get into some seas or extra bodies onboard then potentially the bigger boat / engine comes into it own

Maximus · 04 June 2020, 22:21

All salient points above....you'll find the running costs difference between the engine sizes and RIBs your talking about will be pretty negligable overall.

The fuel economy will be affected a lot more on ...Driving style (Heavy on the Throttle)....Loading ...and Sea conditions than a few Horse Power and a little extra Length.
As Fender says a larger Unit will be working less hard...and just because you have potential perforce on Tap...doesn't mean you will be useing it most of the time.
For me...Go Big as you need ..can

Last Tango · 05 June 2020, 08:20

I went from a 130hp Honda to a 150Hp Merc on my 6.5mtr.

Fuel economy slightly better over the season (0.85 ltr/ml), both acceleration and top end better. Gave the boat a lot more sparkle but the real significant difference was how much quieter the engine is. 25Kn @ 3.5k..(19" Tempest +).

willbank · 06 June 2020, 07:41

Quote:

Originally Posted by 36valley

Can't comment on the difference, but my XS650 with a Suzuki 150 does 1.2nm to the litre cruising at around 25 knots.

Can second that - my XS650 with Merc 150hp would do best 1.2 litres/nm and I could average 1 litre/nm reliably even when doing short, fast 35+ knot trips & harbour pootling.