Logic behind fuel efficiency?

[TrentePieds]

Here is a nice little 50-footer for you to learn about fast powerboats. Sisterships come up for sale now and then in Scowegia, as these boats are becoming obsolete.

https://www.youtube.com/watch?v=YsFvxLTDdaQ

About 20 tons displacement, 1,200 HP, 40 knots, fuel tankage about 350 gallons, range about 200 NM.

The physics of high speed power boats are such that all high-speed designs and their performance at high speed tends to be much of a muchness. You may deduce from that, that fuel burn for any 20 ton fifty-footer at 40 knots tends to be 2 gallons per nautical mile.

Your comment about not worrying about diesel being $6/gall (which it is here) if you've spent $3M on the boat is well taken. Why would you worry about it costing $2.5K to run 200NM? Which in flat water you could do every five hours. But the replies you've had,i.e. that it's all about range, are really much more apposite. If you would have 2K NM range out of this boat you'd obviously have to carry ten times the tankage, i.e 3,500 gallons. That would increase her loaded displacement by about 12 tons. Do you think you could still drive her up on the plane and do 40 knots?

As I said above, high-speed power boats are flat-water boats. High speed is not really attainable with safety in open water, but you'll come to appreciate that intuitively once you've been aboard a boat doing 40 knots in a one foot slop :-).

As for "knifing through 30 foot swells" - dream on! And don't believe everything you hear!

Back to Skeene's Elements of Yacht Design :-)!

TP

[Cadence]

Originally Posted by TrentePieds

Here is a nice little 50-footer for you to learn about fast powerboats. Sisterships come up for sale now and then in Scowegia, as these boats are becoming obsolete.

About 20 tons displacement, 1,200 HP, 40 knots, fuel tankage about 350 gallons, range about 200 NM.

The physics of high speed power boats are such that all high-speed designs and their performance at high speed tends to be much of a muchness. You may deduce from that, that fuel burn for any 20 ton fifty-footer at 40 knots tends to be 2 gallons per nautical mile.

Your comment about not worrying about diesel being $6/gall (which it is here) if you've spent $3M on the boat is well taken. Why would you worry about it costing $2.5K to run 200NM? Which in flat water you could do every five hours. But the replies you've had,i.e. that it's all about range, are really much more apposite. If you would have 2K NM range out of this boat you'd obviously have to carry ten times the tankage, i.e 3,500 gallons. That would increase her loaded displacement by about 12 tons. Do you think you could still drive her up on the plane and do 40 knots?

As I said above, high-speed power boats are flat-water boats. High speed is not really attainable with safety in open water, but you'll come to appreciate that intuitively once you've been aboard a boat doing 40 knots in a one foot slop :-).

As for "knifing through 30 foot swells" - dream on! And don't believe everything you hear!

Back to Skeene's Elements of Yacht Design :-)!

TP

I hadn't heard scowegian in years. My father would use it.