Fuel consumption: sail/motor. are you serious?!

[Anton Tokar]

Hey all!
I just for a minute considered getting a motorboat instead of a sailboat as my first boat (for liveaboard).
and I asked to chat with GPT to give me a fuel consumption comparison.
And I cannot believe my eyes,
how could a boat eat 30-100 liters an hour???
just impossible.
what would be my budget for motoring 24 somewhere???

[Statistical]

Why would you ask ChatGPT for anything. The numbers are almost certainly wrong and comparing apples to oranges picked randomly and just thrown together.

Still generally speaking most motor yachts are fast. Fast boats require a lot of fuel. Big boats require a lot of fuel. Big fast boats require a crazy amount of fuel. Keep in mind drag for displacement hulls (or planing hulls below planing speed) increases by the cube of velocity. Going twice as fast doesn't require 2x the power it requires 2^3 = 8x the power. 8x the power means 8x the fuel.

Planing hulls get more efficient at high speed so they break that cube rule but since they are high speed more efficient or not they still use quite a lot of fuel. The downside also is that planing hulls are rather inefficient at low speeds.

If you want a motorboat that is big & slow and thus lower fuel consumptions look into trawlers. 40" trawler going 7 knots will use about 2 gallons an hour and half that at 5 knots. That is just a rough estimate there are countless variations but it puts you in the ballpark. There is a forum dedicated to them:
https://www.trawlerforum.com/forums/

[Don C L]

I must be missing something; I don't see the 100 l/hr in the info.

And is this for diesel or gas?

And did you mean motoring for 24 hours?

[pcmm]

like all boats, what you burn depends on the type of boat, the engines, the driver, etc. one of my friend just brought a new to them 40ft twind diesel Searay home and to get from Long Island Sound to Troy, NY they burned 185 gallons of Diesel...That's more Diesel than I used to go from Whitby Ontario to Sandy hook, NJ AND BACK!!!

[Danm1]

Also pretty much meaningless without speed/distance data. 2 liters an hour at five knots and 10 liters per hour at 25 knots are not that different getting from point A to point B.

[capn_billl]

motorboats suck fuel. No question.

My Searay used 200 gallons US to go 250 miles.

[MicHughV]

Some time ago, I got a twin engined fishing boat...twin 150 Yamaha's....

I was stunned...nay...shocked at the fuel consumption...

At cruise (3,500 rpm)....about 13 gallons per hour....wide open (5,500 rpm)...about 45 gallons per hour..

about 50 l/hr cruise...170 l/hr wide open.....in metric.....

[kayakerChuck]

My 27' Tiara open got one mile to the gallon at a cruise speed of about 18 knots. Top speed was about 30 knots, fuel consumption at 30 knots- about 4 gallons/mile, or 120 gallons/hour.

[HankOnthewater]

How long is a piece of string?
I have been on powerboats where 80 lt per hour was deemed fuel efficient.......
For a sailing boat I use the (my) rule: 1 lt for 1 NM.

When going 2/3 to 3/4 of hull speed, you will use similar to the rule. When going close to hull speed..... a lot more (ie triple, quadriple the rule, or even worse than that)
Skinny, light weight boats use a little less, tubby heavy boats a little more.
A smaller boat ie 33 ft (10 mt) uses less, a larger boat (>15 mt) a little more.

Then of course the following have an influence:
- fair bottom
- clean bottom
- correct pitching and size of the prop
- is the engine HP more or less matched to the displacement of the boat?
- overloading a hull will increase fuel consumption
- headwinds or going against the current has a large effect on fuel consumption, as does a short steep chop
- motorsailing will decrease the consumption, and you can (in most cases) sail closer to the wind...... but if the sails are really baggy, maybe invest in new sails first, as motorsailing to windward is not really that effective with baggy sails.

My 16 mt 22 ton boat uses 4.3 lt per hour, doing 5.5 knots. That is in fairly flat seas, clean bottom. That is for me the most economical.

[Adelie]

A 45’ trawler going about 6kt will get about 2nm/gal.
A 50’ sailboat motoring at about 6kt will get about 8-10nm/gal.
Both diesels.
The trawler will probably have somewhat more living room than the sailboat.

Being dependent on wind for propulsion sailboats tend to be optimized for low drag at the expense of living volume.

[HeinSdL]

Two observations
1. My 44' X with a regular yanmar consumes 3.3 liters per hour at 70% power or close to 7 knots. That number combined with the hour meter is back up for the fuel gauge.
2. What's this trust in ChatGPT these days? 6-8 liters per hour, what a COMPLETE nonsense. No doubt it will be 'further enhanced' but it should be clear that this technology will further diminish the need to have a brain ourselves (and to feed said brain with real knowledge) and the need for communities such as this. No criticism on anyone here, but... be careful. Not even speaking yet of the fuel (pun!) which will be poured on the culture wars/polarization/etc, happy times ahead.

[Apollo19.5]

I always prefer nm/L at cruise when comparing boats. I have stink boats and a yacht. Tinnie is 3nm/L (4.5m Honda 50hp), Centre console is 1.2nm/L (6m Yamaha 115hp), Yacht is 2.1nm/L (14m VP55hp). WOT nearly halves this on all of them

[MicHughV]

Never gave fuel consumption much thought until I got my fishing boat which is equipped with a fuel flow meter, it can read mpg, gallons per hour, etc, etc.
At first I thought there must be something wrong with the gauges, but there was none

But, I consider myself fortunate. At our marina are fishing boats equipped with quad V8 outboard engines......300-350 hp each, which must have a prodigious fuel appetite.

Add to this, marina fuel, which is typically the non-blended variety, and also comes at a premium.....around $6/gal.

A short fishing trip can set me back $300 in fuel costs......it takes $900 to fill the fuel tank...

I think I'll go cry in my beer...

[CaptTom]

Originally Posted by Anton Tokar

I just for a minute considered getting a motorboat instead of a sailboat as my first boat (for liveaboard).

That was a very reasonable thought. Many people find that a power boat is far more comfortable than a sail boat for long-term living aboard.

But like all things, the answer is "it depends."

If you're going long-distance cruising, sail wins hand-down. Not only in fuel costs, but endurance. By that I mean it's hard for a small boat to carry enough fuel to cross oceans, so the ability to sail really becomes important. Power boats with a lot of living space are generally less comfortable in any kind of rough seas.

If you're going to be sitting at a marina, you'll find the living space in a big, tall, boxy power boat much more comfortable. After a while some people find sailboat interiors like living in a tube. Everything is smaller and squeezed into odd shapes. Many have small port lights, making the interior dark and isolating. Lots of cockpit and deck space detract from interior living space.

The compromise is a so-called trawler style boat. Efficient and seaworthy hull, but slower than a go-fast power boat. Large, comfortable interior with lots of light. Full galley, head(s) with separate shower, full or queen berth, all the comforts of home.

Of course, I may be biased

[Cargile]

Originally Posted by pcmm

like all boats, what you burn depends on the type of boat, the engines, the driver, etc. one of my friend just brought a new to them 40ft twind diesel Searay home and to get from Long Island Sound to Troy, NY they burned 185 gallons of Diesel...That's more Diesel than I used to go from Whitby Ontario to Sandy hook, NJ AND BACK!!!

As someone already stated, "comparing apples and oranges". Panache is something the Searay has that yours does not. In this instance you get what you pay for.