Slippers

[schoonertack]

Any thoughts on easy pushing displacement powerboats? Seems all the good old stuff does so much better than popular powering formulas would indicate, Three and four horespower a ton is quick and ready, but I know of several old ladies that go on 1 and 1/2 per ton and better, fuel prices are climbing again, so what do you guys think?

[Meerkat]

Sails ;)

[mmd]

Are you looking for a discussion on a particular type/size of powerboat, or just powerboats in general?

[paladin]

Stick with long full displacement hulls and don't try to go faster than 1.34 times the square root of the waterline length................big slow turning prop and engine...

[Tom Lathrop]

I expect you are referring to the discussion by Weston Farmer in "From My Old Boatshop". Very interesting look at what can be done. One thing to keep in mind is that these boats had very high length to beam ratios. He said that you needed to have your hair parted in the middle when driving some of them since they were so tippy.

His redesign of the "Coyote" saves most of the advantages in a boat with reasonable stability. There seems to be no secret as to how they got their performance on the very low power available to them at the time. You have to be willing to put up with their crankyness in handling and lack of stability to get the high speed/power numbers that they gave though.

Paladin, It's possible to go a lot better than the 1.34 X WL^1/2 in a properly done (for this purpose) monohull without planing. That old saw is a detriment to inovative thinking and should best be forgotten except for heavy boats of about the "normal" length/beam ratio of 3.

[ 11-06-2002, 05:18 PM: Message edited by: Tom Lathrop ]

[ahp]

For what ever it is worth, in large sizes even one hp per ton seems to work. It did on what I went to sea in, a 10,000 ton Victory ship and a 20,000 tom seaplane tender.

[schoonertack]

Yes a good line of thought open ended discussion. I know , and have done it, that a big set of twins ready to snarl at the turn of a key counts for lots of points over a beer. I now have some time flexability, and I don't want to run home, or run to the fuel dock. I wan't to keep my lines in the water, or around the next point, over to you.

[john welsford]

How big do you want, Thomas Firth Jones has a couple of nice 20 ft or so launches in his earlier book, I have a 15 ton 44 footer designed to have a range of around 4000 miles on 300 gallons ( my personal boat, we are just beginning the build now) and I've done a lot of study on this one.
The secrets are in long slim boats light for their length but heavy for their waterplane which tends to give a low wetter area for the displacement, a large slow turning prop with two or three high aspect ratio blades, low windage and an efficient motor.
I hate to say it, but on the latter the most fuel efficient motors around are the modern turbocharged medium speed motors, but I find them hard to live with and would hate to have to fix it so I have a Gardner 3LW and will be cruising at 900 rpm on just under 1/2 gal an hour ( 7 knots)
Fuel efficiency in small boats has been a lost cause for quite a few years but there is interest enough for a very few of us to be doing some research and experimentation.
One very very effective solution is the power catamaran , a local designer here does really well with a line of development in very deep narrow hulls of 16/1 beam length and better, a 45 ft 10 ton passenger ferry will run at 25 knots on a pair of 60 hp diesels and leaves hardly any wake ( a real consideration in many places)

JohnW

Originally posted by schoonertack:
Any thoughts on easy pushing displacement powerboats? Seems all the good old stuff does so much better than popular powering formulas would indicate, Three and four horespower a ton is quick and ready, but I know of several old ladies that go on 1 and 1/2 per ton and better, fuel prices are climbing again, so what do you guys think?

[ahp]

You might reseach back a 100 years ago and see what the steam yachts had for power. I seem to remember that a 100 ft LOA yacht would typically have about 100 hp. I can't tell you about displacement, but these were rather slender, easily driven hulls that were intended to go about 8-9 knots.

"Fast Commuters" were another story. Where I went to college we had the engine for Horace Dodge's fast commuter in a glass case, a quadruple expansion engine which delivered 1000 hp.

[schoonertack]

John Welsford I like where you are going with your boat, displacement length 240 apr? The size is nice to. You have, what two horespower a ton displacement? Length/beam 4/1? Did you select a prizmatic coeff. around .54? Schooner