inboard VS I/O ski boats and fuel economy

tfret

Petty Officer 1st Class
Joined
Sep 6, 2006
Messages
396
All other things being equal, such as boat length, engine size, driving and use, etc. which gets better fuel economy a full inboard or stern drive? Or are they roughly equal? Specifically I'm refering to ski boats and run abouts in the 19' range.
 

trejac

Petty Officer 3rd Class
Joined
Jan 31, 2009
Messages
89
Re: inboard VS I/O ski boats and fuel economy

Here are the things that I believe matter to fuel economy
Size of motor
Weight of boat
Prop
Final gear ratio

All things being equal I would think the draft on the inboard might cause alittle more gas usage, just a thought! No scientific evidence to prove.

Last year I had a 4.3 Carbed in an I/O. This year I have a 5.7 Black Scorpion Fuel injected. Last year?s boat was 18; this year?s boat 22'. It appears this year?s boat is getting better mileage. Fuel injected more efficeint than carbed.
 

zopperman

Lieutenant Commander
Joined
Jun 22, 2011
Messages
1,551
Re: inboard VS I/O ski boats and fuel economy

Diesel inboard? Gasoline I/o?? also something to consider...
 

haulnazz15

Captain
Joined
Mar 9, 2009
Messages
3,720
Re: inboard VS I/O ski boats and fuel economy

The stern drive will get better fuel economy simply due to the ability to trim the boat up out of the water. The OP said all else being equal, so the only real variables are weight placement (engine mid-ship vs stern) and trim. The trim is what gets you the fuel economy. In the long run, the fuel savings is rather miniscule, so I wouldn't make that the determining factor in which boat to choose. The ability to trim also allows you to make rough water conditions more pleasant.
 

H20Rat

Vice Admiral
Joined
Mar 8, 2009
Messages
5,199
Re: inboard VS I/O ski boats and fuel economy

Diesel inboard? Gasoline I/o?? also something to consider...

not many inboard diesel ski boats! Actually, i'm fairly sure there are none....


Technically, the inboard is more efficient, but... Ski boat hulls are much 'wetter' than a typical I/O, and the prop/gearing on a ski boat is much lower, they need to do about 38 mph tops for a dedicated ski boat. All things considered, if you take two typical off the shelf bowriders, one I/O, one inboard, same engine, the I/O will get better mpg's.
 

NSBCraig

Lieutenant Commander
Joined
Aug 21, 2007
Messages
1,907
Re: inboard VS I/O ski boats and fuel economy

A question- you said ski and runabouts. What are you really looking for? cause a ski boat, a wake boat and a run about are actually different things. Sure it gets confusing because everybody claims their boat does that.

An inboard ski boat or wake boat are going to be better in every way when used for the purpose they were designed. An in/out runabout is going to more fuel efficient when "running about".
 
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