Minimum HP for antique hydroplane??

[paulfromyork]

I’ve seen a lot of hydroplanes in the photo section. What kinda’ HP do you need at the minimum. They look like FUN.

[garry-in-michigan]

They are classed by engine size. Class M (midget) is 7.5 cubic inches. Mainly for lighter weight people. they put out 7 to 10 HP, The record in the 1940s was 42 MPH. Class A is 15 cubic inches. Speeds in the 50s. B class in 350CC – speeds in the high 50s – C class – 500 cc – 31 cubic inches, Speeds in the 60s.

Antique C class is popular. most running PR Johnsons or Modified Evinrude Speeditwins. The Japanese Yamato is a more modern racer and gives a good boat ride. For REALLY antiques – The Elto high speed Speedster was a nice hotrod of the late 1920s. The Elto Quad was also a head turner in it’s day. The first four cylinder outboard that started the horse power race that was brought to a halt by the "Great Recession" of the early ’30s . . . 😀

[chinewalker]

Yep, all depends on the boat you’re running. Would never put a D class engine on a J/M class boat, or vice versa.

[jw-in-dixie]

Not a hydro, this is a one-off home-built (1951) vee-bottom 8′ runabout made from two sheets of 1/4" marine plywood. Very stable and responsive on the turns.

Initial motor was a 1940 five-horse LT10 Johnson because that’s all I had. Lucked up on a Mercury KG7 Super Hurricane shortly thereafter, and ran it for fifty years, logging more than 7000 miles. Got a Merc 200 (22 HP) powerhead, put it on a KE7 tower with the original KG7 lower unit and have been running it since.

Lots of fun, cheap to build. I’m waiting for a cool morning to hit the water again, at 84. 😀

[paulfromyork]

Are there sources for plans for this V-bottom beast?

[Tom]

I built a similar boat called the Blue Streak when I was in high school. I got it to plane with a Zephyr and a skinnier me. Plans are free at:

http://www.svensons.com/boat/?p=Runabou … /blustreak

The picture shows someone sitting upright in the boat. That guy would have to be shorter than 5 feet to do that. But even kneeling, it was a lot of fun. I didn’t have a steering wheel in it, too many different motors that would have to be adapted, and none had a remote throttle. Most fun was a ’29 Evinrude Fastwin. Stupidest was a MK-20.

T

[cajuncook1]

quote jw in dixie:

Not a hydro, this is a one-off home-built (1951) vee-bottom 8′ runabout made from two sheets of 1/4″ marine plywood. Very stable and responsive on the turns.

Initial motor was a 1940 five-horse LT10 Johnson because that’s all I had. Lucked up on a Mercury KG7 Super Hurricane shortly thereafter, and ran it for fifty years, logging more than 7000 miles. Got a Merc 200 (22 HP) powerhead, put it on a KE7 tower with the original KG7 lower unit and have been running it since.

Lots of fun, cheap to build. I’m waiting for a cool morning to hit the water again, at 84. 😀

JW in Dixie,

You may be 84, but that picture in 2008 of you in your hydroplane has the spirit and grin of a teenage kid!! That pictures always puts a grin on my face!!

Cheers,

Cajun

[paulfromyork]

So please pardon what I don’t know. What’s the approximate HP of a 4 cylinder two stroker? I’m thinking somewhere around 10HP? I know, I know. It depends. Displacement and stroke and more. I guess with a hydroplane, more is better, until the boat sinks stern first. That would be too much motor.

[wedgie]

An Evinrude Zephyr has four cylinders that puts out 5.4 hp . I believe it is the smallest 4 cyl outboard made.

http://www.oddjobmotors.com/ihatezephyrs.htm

[2fast4me]

Evinrude Lightfour, bout 9.7 HP, not so light though. Well Light is relative I think 67 Lbs. Mine gives a nice ride on my 12 ft AlumaCraft. Best Wishes.

2Fast4Me

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