Fuel Consumption and Fuel Economy

[Seif]

I am about to upgrade from a 36 foot motor boat to a 60 foot. the issue is not only the price of the boat (hence looking for a used boat) but also the associated cost. How can fuel economy be achieved, and how does one calculate fuel cost?

[Mark Johnson]

In our vastly overpopulated (and growing)... as well as rapidly climate changing world, we will soon, be having more and more wars over oil, potable water, and with ocean rise causing lost coastlines... territory!

IF one wants to go with a large "power" boat anyway, AND have extreme energy efficiency, there are a couple of ways...

First off, for the "somewhat" less fuel, at similar or better accommodations...
A 45' power cat would have WAY more room than a 60' monohulled power boat, and if built and kept relatively light, would consume perhaps half as much fuel.

Going even more extreme, at the expense of accommodations... I have seen a LARGE power "proa", where the main hull is light, NARROW, and shaped like a large rowing shell's hull, but still with plenty of room inside.

It had a small outrigger (1/3rd the main hull's size), that kept it stable in spite of the main hull's narrow, round bottomed WL.

Such a vessel would have EXTREME seaworthiness, compared to its monohulled counterparts. It would have a wonderful motion, even at great speed, while sipping a SMALL fraction of the other's fuel. It would also lend itself to a solar array large enough to live in style, 100% self sufficiently!

Power Proa, Belize - ChrisWhiteDesigns' Photos | SmugMug

This vessel might be 1/10th the fuel consumption, for a given speed! If I had the bucks, & wanted to switch to "the dark side", this is what I'd do.

Otherwise, Steve Dashew has the best monohulled power boat out there! Look it up.

[ranger58sb]

Originally Posted by Seif

I am about to upgrade from a 36 foot motor boat to a 60 foot. the issue is not only the price of the boat (hence looking for a used boat) but also the associated cost. How can fuel economy be achieved, and how does one calculate fuel cost?

Several variables: hull form, length, weight, engines, fuel (diesel vs. gas), ideal "cruise" speeds (RPMs), etc... and then futher affected by the real-life load (your own stuff plus current fuel/water/holding tankage), and wind/tide/current (versus direction of travel).

Hum a few bars about the type of boat -- displacement, semi-displacement, planing hull? -- and engines, and it'd be easier for folks to respond. In the meantime, the engine manufacturer will likely have published fuel flow curves at various RPMs.

-Chris

[bob_77903]

[QUOTE=Mark Johnson;1037480]
A 45' power cat would have WAY more room than a 60' monohulled power boat

Could you elaborate on WAY more room. Square footage of each?

[jaxfishgyd]

It's all about hull speed.... Your boat will have a "hull speed" and as long as you stay at that or less, you'll be getting your best economy..
I bought my boat to enjoy and live aboard....
At 8 kts, I'm using 4-5 gph... If I go to 14 kts, then it's gulping 22 gph...
I go down to sailboat speed and I'm using 3gph...

[djmarchand]

Unless you are one of the .1%ers I suspect that your 60' boat will be a displacement speed trawler. It will weigh about 30 tons. That boat will have a "hull speed" (a NA defined term = 1.34* squrt (LWL)) of about 10 kts. It will take 90 hp to drive that boat to hull speed and about half of that to 8 kts.

It will take 5 gph of diesel to make the 90 hp and 2.5 or a bit more to make the 45 hp. So you will get 2 NM/gal at 10 kts and about 3 NM/gal at 8 kts.

These are pretty good rules of thumb for round bottom displacement trawlers. Get a copy of Bebe/Leishman's book, Voyaging Under Power for more info on efficient trawlers.

David

[Ataraxia]

here is the ultimate fuel efficient passagemaker designed by Tad Roberts: The home of Passagemaker for sale at a very good price.

[Cotemar]

Power cats are the way to go if you want to save on fuel and have tons of room.
We charted this Leopard 47 with two Cummins 150hp engines.
Ran on one engine at 2000 rpm doing 9 knots using the autopilot.

[Ataraxia]

Originally Posted by Cotemar

Power cats are the way to go if you want to save on fuel and have tons of room.
We charted this Leopard 47 with two Cummins 150hp engines.
Ran on one engine at 2000 rpm doing 9 knots using the autopilot.

As long as you do not have to pay the mooring fees. Try a mooring in the South of France or Spain and pay double the price.

[twistedtree]

Once you have bought your 60' boat, you can't change the length or weight. At that point there is ONLY ONE variable, and that's how fast you go. Fuel burn will go up exponentially as speed increases. The faster you go, the worse your MPG, and the slower you go the better the MPG. There is no way around it. DJMARCHAND's numbers tell it all. 10 kts takes 90HP, but dropping to 8 kts cuts the required HP (and fuel burn rate) in half, and your MPG will go up accordingly.

[Lexam]

It's a few feet short, but you have to love the mileage! Still trying to convince the wife...

1971 Custom Steel Trawler 54 ft Power Boat For Sale - www.yachtworld.com

[DivingOtter]

Make sure your hull and running gear are clean. Have a diver regularly keep her clean. The hull causes serious drag when growth is present, but the running gear will cause 35 % drag and a higher rpm resulting in more fuel consumption and cavitation. I recently cleaned 10,000 lbs of mussels off a commercial boat that had not been cleaned in 8 years. She consumed a quarter of fuel and gained 4 knots.