Fuel Consumption - The Theory!

[oldgit]

Re: Leisurely Fuel Consumption?

Stern drives.

A boat change a while ago.Went from a Princess 33 with outdrives to a Broom 37 hull with Perkins M130 Hp on shafts.
The difference in fuel consumption , bearing in mind the HP on both boats was virtually identical, almost impossible to detect at displacement speeds and not vastly different at 12 -15 knots either.

 

[Momac]

I have outdrives and cruise with a shaft drive slightly bigger boat and the fuel use difference is nothing to get excited about.

 

[CLB]

Re: Leisurely Fuel Consumption?

A planing hull will not be at its most efficient at 12-15 knots. Take two similar planing hulled boats, one with stern drives and one on shafts, and get them cruising at 20 or more knots and you will see a significant difference. Lets take a boat around 37ft, as this is where you will find some crossover. A shaft drive boat at speed, probably a little over 1mpg, maybe 1.2ish. A sterndrive boat at the same speed, probably nearer 2mpg.

Anyway, that is neither here nor there for the OP. I was just looking for clarification ref the Bavaria comment so that the OP didn't take sterndrive consumption at speed to be what he may likely achieve in a shaft drive boat.

 

[BruceK]

Re: Leisurely Fuel Consumption?

mmm. I was always under the impression stern drives were more fuel efficient than shafts. Oh well. Every day a school day

 

[lionelz]

Re: Leisurely Fuel Consumption?

Bear in mind the only thing about fuel is that the cost is controllable, it is not likely to be your biggest cost. Mooring fees followed by maintainance will probably get that gold star.

A tank of fuel is usually good for 250miles ish on a planning boat and on the size you are looking at I guess the tank is. Say 700l.

Short trips. 2 tanks a season ? £1500 ? I don’t want to dismiss it, just bear in mind it is not really the prime cost.

Absolutely agree with this statement when I first purchased my boat I was worried about the fuel consumption but unless you are going to a 1000 hours a year it not even an issue, your mooring fees will probably be the most expensive thing

 

[NBs]

Re: Leisurely Fuel Consumption?

Those figures are good, and pretty much what I would expect, but you will get even better MPG at real displacement speeds. This boat will be pushing water at 9.3 knots, and I would expect to see well over 2mpg, possibly 3 at full displacement. .

Hi,

You are right, about 1kn off the pace and consumption 1/2 less drive 8 kn.

NBs

 

[oldgit]

Re: Leisurely Fuel Consumption?

mmm. I was always under the impression stern drives were more fuel efficient than shafts. Oh well. Every day a school day

and.................
if you are moored like most of us in a marina /boatyard or upriver mooring, it could be some distance to where you can actually exceed 6 knots or so to enjoy the advantages of *utdrives.
The end of the speed limit on the Merdeway is probably 6 miles or so from the moorings.
2 hours of any day out will spent at displacement, whatever drive .
Is there not some sort of limit in the Solent ?