Building a boat around 18hp.

Lots of stuff but nothing in particular, I was just being a silly bugger.

Although there was that 12 footer with the 18Hp on it, no steering wheel, damn near killed myself... a few times.

-Tom

 

12 foot 18 hp "boat"? or "IFO"? (identified flying object)...

 

When I was younger, we used to do this sort of thing all the time. I had fun on a Laser knock off with a built up transom and a 8 HP hanging on it's butt. A WOT it became quite unstable, nearly rolling over more then once. I had a hopped up 30 HP (probably more like 45 HP) on a 10' Sear's GameFisher that would scare the crap out of anyone. We shoe horned a small block Chevy into a mid 60's 16' bow rider once. It had about 300 HP and pushed this boat up into the high 60's, but proposed so baddy that we couldn't get her any faster. It had a 3 speed manual trans and a clutch. Put it 3rd gear and dump the clutch. Lots of fun until it augered in off a wave one time.

 

augered in off a wave one time.
anybody hurt?

 

Good one PAR. Okay, they're starting to come back to me now.

Old, small Boston Whaler, centre console, with a 90 or 115 or something ridiculously over powered on the back. Went like a million miles an hour and then suddenly turned 90 degrees. Only drove it once.

-Tom

 

Was it drivable by anyone after once?

 

For awhile had a 33 footer welded aluminum 13 ft beam 6 in draft, with pair of 175 hp Negras on the stern. Scooted pretty good!

 

completely agree with PAR. This 1960 outboard will have quite a bit more than 18hp at the shaft - alot more. So, this may be of interest in your decision regarding the type and size of hull you'd like to build. These outboards also liked to see higher RPM, and were capable of higher HP when they were allowed to rev higher. Reliability might not be as good as new engines, and fuel efficiency was not one of their stengths. Have fun!

 

Nope, the boat was a lose and I imagine it's still sitting upright on the bottom of the Sassafras river. She launched at who knows what speed and came down into a troth, burying the forward 1/2 of the boat. Having about 1,000 pounds of engine/trans and related gear midship didn't let her recover as well as you might think. She quickly swamped and sank like a stone. It was damn fun while it lasted, CG issues constantly troubled her. She swapped ends a few times at speed, tossing crew members over the side and breaking one wrist, but it was to fun to give up.

 

It would be interesting to see the specs, as in cubic capacity etc.

 

Lol...sounds a bit like when I popped the question to my wife...or did you mean 'porpoised' ?
Couldn't have been THAT baddy though since we just marked our 15th.
Still, it's funnier your way.

I like the multi chines in that design of yours better than the RedWing's flat bottom, Paul. Have you got the design worked up or is just a concept ?

When I first got this motor, I put it on the only boat I had at the time that was ready for the water: a freshly glassed but not-yet-painted 'Bolger-esque' 9' punt/box/thing I banged together out of red cedar leftovers from another job. It was to be light and stable for flyfishing and even my 32lb trolling motor was a bit much - even at low speed with my 260lbs and a 4D battery, I couldn't go slow enough to troll a fly.
Hanging the motor on the transom didn't swamp the back end so it must be good to go, right?
First turn at 1/4 throttle and I headed back to the beach. A tiller arm extension could have made it a little more fun in a straight line but I wasn't really that serious about it.
Nothin' like being young and dumb. OK, it was last summer so not young...


Thx for putting up that ad Jimboat. I hadn't seen that one.
Tom, my whaler's 14 with a console and a 40. A 90 would be insane, never mind anything bigger.
Mr E, I think I downloaded a manual from somewhere - I'll see if I can find it over the next couple days.

 

Congratulations on 15th anniversary. Wishing you 100 more happy ones.

I think you have everything you need for a great experiment.
If that 18 can be tweaked to 35 hp, 35 is near to 40.
The Whaler handles the 40 hp and you know what her performance is with it. Try the 18 on the whaler and compare! Just an idea.

 

If you go trolling with your old 18hp bring a gas mask and a spark plug wrench. They were terrrible things at slow speed.

On Boatdesign net we might even be able to track you fishing with Google Earth by looking for a slow moving blue smoke cloud ahead of an oil slick on the water..

 

Just got around to this thread and see that it hits some of my experience. Some here are of the "opinion" that no one can ski behind only 18hp but they are dead wrong. I learned to ski in 1953 with my Aristocraft 12 footer with a Wizard 10 on the transom. Also taught my friends, one of which was at least 200 lbs. Now here is some other info. The Wizard was essentially identical to the Merc 10's which were well known to be underrated so, compared to today's 10 hp, it was certainly more powerful. We also used what was known as "outboard skis" and they were wider than the "inboard skis". We did not use the modern technique of just leaning back and letting the motor do the work or we would have certainly not have gotten up. We pulled back sharply, let the line slack a bit and the boat speed up and so on a few times. Once up the boat was capable of about 25mph per the Airguide speedometer and we could kick off one ski and go single for as long as we liked or the legs held out.

I later added another Wizard 10 on the boat and it did almost 40mph. Pictures of the boat with its then skinny operator with hair are here:
http://www.bluejacketboats.com/scamp galleries.htm
The other boat on the page is my current version "Scamp" at 13' and now powered by a 1980 Evinrude 25. This is essentially the same engine that yobarnacle has and was later sold as a 30hp with the same displacement and a few mods. It runs this boat, which is heavier than the original, at about 31mph with two adults aboard. Since my old boat did 29mph with the Wizard 10 and a Michigan "high speed" wheel, it appears that it was less powerful than the Evinrude 25 which uses a stock prop. The photo shows Scamp with a Merc Mark 20 which is rated at 16hp and essentially the same as the old Hurricane 10's and the later Mark 25. This engine is pristine and I don't run it in salt water which is all we have here.

Now I expect that Frosty will flip when I say that I regularly skied with the Aristocraft and the high pitch speed prop but that will not change history.

Paul's suggestion looks good and appears much like Atkin's Ninigret which would also be a good choice. Atkin wrote me when he was still around that Ninigret would do almost 20 with a 25 hp engine and I expect that he is correct. I would choose either over the flat bottom displacement types suggested for Yobarnacle's use. Current thoughts on how much power is required to drive planing boats is based on a half century of badly designed over weight boats fostered by ready availability of unlimited powerful engines. Look at the photo series of one of my boats at the bottom of this page to see what only 50 hp can do on a decently designed boat.
http://www.bluejacketboats.com/Bluejacket 24 photos.htm

The website has some problems on Mozilla, so use Internet Explorer.