I read an interesting quote in this newsgroup: "If you have to worry
about fuel perhaps you should own a bigger boat".

OK, well, that is probably good advice but I would still like to own
and operate a (decent sized) boat. There must be a size of boat where
fuel is only a moderate or at least an acceptable issue.

For example, I think we can agree that smaller 14' - 16' boats are
quite fuel efficient (compare to the 20+') and I am assuming that most
of these owners do not have to worry very much about how much they
will need to dig in their wallets at the end of a typical weekend.
At the other end, I seems to hear and read that essentially 25'+ boats
are fuel gulping monsters (0.5 to 1.5 GPM).

So I guess my question is: at what point (size of boat) does this
transition occurs. Yes, I know the usual "it depends" will come up but
I am just trying to get a sense of what is good, what is not. For
example, could I expect an 18' boat to behave (fuel) more like a
16' or more like a 24'. How about a 19'? a 20', etc? Surely there
must be some sort of arbitrary cutoff point.

Or is it simply a linear incline that is 16' 17 18 19.... you
get the picture. I am getting the sense that fuel consumption, when
it comes to boating, follows more an exponential curve. So I am
trying ot find the point where there is a good "ratio" between size
and fuel consumption i.e. I would like to have the biggest boat
possible that I can afford to operate without freaking out about fuel.
Right now, I am thinking 18' to 22' range but I am not sure if these
are also fuel-gulping monsters.

Cheers! Andre

You will find a more direct realtionship between speed and fuel consumption
than
LOA and fuel consumption.

In fact, larger boats (like trawlers) more often run in displacement mode than
on plane, while those 16-20 footers running on plane will burn more. There are
many examples of boat over 40 feet than can achieve fuel economies of 4-5 nmpg,
but unless you put up a sail or find some unusual exception, it simply won't
get any better than that.

A larger boat usually opens up the option for a diesel engine, and that will
save you some fuel in most cases. The engine itself is quite a bit more
expensive than a gasoline substitute, so those old homilies you hear about
never being able to save enough fuel to offset the cost of a diesel are
generally true. (You may save in the end because the diesel could run 2-3 times
longer than the gas without replacement or rebuild, and resale will be better.)

For smaller boats, the two most fuel efficient speeds are dead idle, followed
by the point where the boat first gets over the bow wave to achieve plane. It
might be accurate to say that many planing hull boaters use twice the fuel they
need (on a nmpg basis) to achieve planing mode by adding that additional
500-1000 rpm to increase speeds beyond that point.

As far as "if you have to worry about the cost of fuel, you can't afford to
boat", there is some truth to that. Even if you're getting
0.5 nmpg and fuel costs $2.50 a gallon, many boaters would find that expenses
for repairs, moorage, maintenance, and insurance (and possbily a boat payment
as well) will be more significant than the cost of fuel.

I'll throw this into the inevitable list of messages that's sure to follow:
Every boat that takes an outboard motor will have a max suggested
horsepower. You may not need that. Try and find a dealer who seems to care
about what he sells, and find out how much horsepower your chosen boat needs
to simply be safe, taking various factors into account. If you don't feel
you're getting an intelligent response from the dealer, call the boat's
manufacturer.

Above all, the boat needs to be able to manhandle the kind of turbulence
you're likely to face on a bad day. Get you home safe, in other words. To be
fuel efficient and comfortable, it needs to be able to plane and still have
a bit of reserve left while carrying a load (people, gear) you feel will be
typical. For instance, my 14' yacht has a recommended max of 25 hp, if I
recall correctly. I'm sure the main factor is the weight of the motor. But,
I have a 15 hp motor and with rare exceptions which don't impact safety, I
never feel I'm missing anything.

What's your intended usage? Our Bayliner 1950 Cuddy (about 3200 lbs with 4
people and ski equipment, fuel, etc.) Burns about 15 gallons per day with
it's little 120 hp 2.1 liter 4 cylinder Volvo engine, but that's because we
tube and ski. At about 2 bucks a gallon for premium unleaded gasoline, that
equals about $30 per day. If we were to cruise all day on a longer lake, we
might use 30 gallons, because we wouldn't be stopping as often. If we just
tooled around the lake at moderate speeds, stopping often to explore coves,
fish, etc, we might use 10 gallons in a full day. I'd say that our's is a
best-case scenario as far as fuel usage is concerned with this size boat.

Seems to me that numerous variables beyond boat length come into play here-
such as the weight of the boat, how much weight you will carry, what speeds
you normally cruise and for how long, what type/size of engine (4/6/8 cyl,
gas, diesel, 2 or 4 stroke, etc), whether it's a planing hull or a
displacement hull, etc.

Our 1950 Bayliner says that it's 18.5 ft on the title, but Bayliner states
19.5 feet in their literature. With a tape measure, I get 19 feet not
counting the outdrive leg. So, depending on who you're talking to, they
might call this boat an 18, 19, or even 20 foot boat. It certainly outweighs
most 18 foot boats.

As we've discovered for ourselves, the maintenance costs on the boat have
been more expensive than the fuel we've burned. Carb rebuild, U-Joints,
trailer service, plugs/wires, oil changes, prop service, this fuse and that
pump- you get the picture. Next boat I buy will be a more expensive, quality
built boat that will hopefully minimize my ongoing repair and maintenance
expenses, which are much more arbitrary and more expensive than fuel.

Bottom line- boats burn lots of fuel- no way around it. The more weight you
move through the water, the more fuel you will burn. Other variables also
factor in, such as hull type, smooth/rough water, ambient temperature,
(cooler weather = better fuel economy, to a point), altitude (closer to sea
level = better fuel economy) etc. If fuel is a primary concern, get a little
12' fishing boat with a small 4 stroke outboard, or a larger vessel with a
fuel efficient diesel engine.



"Melandre" wrote in message
...
I read an interesting quote in this newsgroup: "If you have to worry
about fuel perhaps you should own a bigger boat".

OK, well, that is probably good advice but I would still like to own
and operate a (decent sized) boat. There must be a size of boat where
fuel is only a moderate or at least an acceptable issue.

For example, I think we can agree that smaller 14' - 16' boats are
quite fuel efficient (compare to the 20+') and I am assuming that most
of these owners do not have to worry very much about how much they
will need to dig in their wallets at the end of a typical weekend.
At the other end, I seems to hear and read that essentially 25'+ boats
are fuel gulping monsters (0.5 to 1.5 GPM).

So I guess my question is: at what point (size of boat) does this
transition occurs. Yes, I know the usual "it depends" will come up but
I am just trying to get a sense of what is good, what is not. For
example, could I expect an 18' boat to behave (fuel) more like a
16' or more like a 24'. How about a 19'? a 20', etc? Surely there
must be some sort of arbitrary cutoff point.

Or is it simply a linear incline that is 16' 17 18 19.... you
get the picture. I am getting the sense that fuel consumption, when
it comes to boating, follows more an exponential curve. So I am
trying ot find the point where there is a good "ratio" between size
and fuel consumption i.e. I would like to have the biggest boat
possible that I can afford to operate without freaking out about fuel.
Right now, I am thinking 18' to 22' range but I am not sure if these
are also fuel-gulping monsters.

Cheers! Andre

On Friday 13 August 2004 3:08 pm in rec.boats Melandre wrote:

For example, I think we can agree that smaller 14' - 16' boats are
quite fuel efficient (compare to the 20+') and I am assuming that most
of these owners do not have to worry very much about how much they
will need to dig in their wallets at the end of a typical weekend.
At the other end, I seems to hear and read that essentially 25'+ boats
are fuel gulping monsters (0.5 to 1.5 GPM).

There are several factors involved here.
Firstly - all petrol (gasoline) engines guzzle more fuel than diesels.
Second - Planing hulls require enormous power and thus fuel.
Third, displacement speeds are proportional to the square root
of waterline lenth. Typical displacement speed is 1.3*len(feet)^2

As a typical data point, a 60 foot trawler with 2 x 650 HP CATs
will use about 10 gal/hour at 10 knots in displacement
mode or 40 gal/hour at 20 knots WOT. An 80 footer will actually
use rather less fuel for the same engines and speed.
This is a helluva lot less than small high speed planing boats.

Bigger and slower uses less fuel.
Planing is expensive at any speed.

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On Friday 13 August 2004 6:59 pm in rec.boats Chris Newport wrote:

Third, displacement speeds are proportional to the square root
of waterline lenth. Typical displacement speed is 1.3*len(feet)^2

Ooops - before anyone else notices the branefart :-
Displacement speeds are proportional to the square root of
waterline lenth.
Typical displacement speed in knots is 1.3*sqrt(len) where len is in feet.


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