Comparing fuel consumption of twin and single engines.

[tom52]

1) Is it reasonable to assume that twin 150HP shaft driven engines at 3000rpm will produce the same speed as a single 300HP engine at 3000rpm on identical hulls? Or are their significantly different losses from friction etc between engine revs and push at the props for single and twin set ups ?

2) If I look at the power performance curve of a 300HP engine and read off the l/hr at 3000rpm and compare it with the l/hr (times 2) of a 150 HP engine at 3000rpm am I comparing like with like ?

 

[rustybarge]

1) Is it reasonable to assume that twin 150HP shaft driven engines at 3000rpm will produce the same speed as a single 300HP engine at 3000rpm on identical hulls? Or are their significantly different losses from friction etc between engine revs and push at the props for single and twin set ups ?

2) If I look at the power performance curve of a 300HP engine and read off the l/hr at 3000rpm and compare it with the l/hr (times 2) of a 150 HP engine at 3000rpm am I comparing like with like ?

Twins don't quite use double the fuel, but it's not far off.

Compare the new leanburn 300 hp Suzuki which uses 6 g/ hr at 4000 rev cruise, with a single 150 hp which will burn 4.5 gals hour at 4000 rev.

So twin 150's will use about 8 gals/ hr.....?( maybe 20% or more)
Twice the drag.
Twice the combustion heat loss.
Twice mechanical losses.
Twice the maintenance.

I'm considering the same dilema as you, here's my new boat that I need to buy outboards for:

View attachment 32240

 

[omega2]

We have twin 180's a mate has a single 400, not a lot of difference in fuel or speed at the end of the day. Sometimes we think maybe a big single? but then we revert to always got one as a back up. You pays your money and takes your choice. As stated twice the everything plus the weight, and if one packs up the other keeps you on your way but progress is funereal.

 

[[2068]]

... progress is funereal.

8kts is better than 0.5kts drifting sideways

 

[omega2]

8kts is better than 0.5kts drifting sideways

every time!! but most boats have anchors.??

 

[rosssavage]

Having had an engine failure at sea, twin every time. If I hadn't had two engines it was a lifeboat tow (serious mechanical failure, no chance of repair at sea). As it was, drop the speed and divert to nearest suitable marina. Peasy.