mini build help/advice

Airboats with smaller powerplants.
Olf Art
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Re: mini build help/advice

Postby Olf Art » Sun Sep 27, 2015 8:35 pm

mojoe wrote:A 12' fiberglass DD 350 would also be a good starter rig for what you describe. They regularly sell for under $5000, cruise around 25 mph with 3 people or 2 and gear. Will run anything wet. Get good gas mileage and can be very reliable.

Love DD boats, and they don't need to be just a SBC. I've seen DD inline Ford, Chevy, and even Chrysler slant six engines. The trick is to keep them light and to not try to run with the 'big dogs' if they decide to head out cross country. A nice DD will take you anywhere you want to go on the water, and I've never been too proud to park on the bank and walk up to the trees if need be.
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br,lc,LA
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Re: mini build help/advice

Postby br,lc,LA » Sun Sep 27, 2015 10:39 pm

Mm mudmotor
EVT Extreme VTwins was my buddies company where they modded lawnmower/mudmotor/go cart engines
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todd glover
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Re: mini build help/advice

Postby todd glover » Mon Sep 28, 2015 1:48 pm

You don't need 15 ft anything for one person a 6-6.2 bottom x 10 ft out of 80 th built lite by don Davis or John Fenner someone like that with a 670 rotax will do well over 40 mph great on fuel and with frog spit on dry with just a single person 90hp and reliable electric start and if he gets stuck easy to shake losse

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Caddellwelding
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Re: mini build help/advice

Postby Caddellwelding » Mon Sep 28, 2015 8:33 pm

I wish I would of made my boat 2' shorter and might just cut it down too. I run quickslick on my boat and believe it or not it runs a lot better than what I thought it would, on water or dry. I would like to get an actual GPS on it to see if it in fact actually runs as fast as the gps says it does. At 35 on my boat feels like your haulin butt. And after I trimmed up the motor in the back and added 1 degree in the prop its plum scary. I don't feel like it's running 65 by no means cause I've been on my dads at 70 and it was scarier than riding in a juiced up pickle fork jet boat! I think less is more but at the end of the day it's up to you. There is tons of valuable information on the site. Makes building one even more fun!


Sent from Caddell Welding L.L.C

br,lc,LA
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Re: mini build help/advice

Postby br,lc,LA » Mon Sep 28, 2015 8:44 pm

I almost went 13' but we talked it over and kept it 12' and added an additional 6" to my rake and added 1' of running surface to the bottom and 6" overall width.

In short, original sled was 12x7 w/ 5' bottom and 18" rake
New sled is 12x7'-6" w/6' bottom and 2' rake. Engine as you read is a 160-180hp 4cyl turbo Ecotec. Best part is I make 200+/- ft lbs from 1800 out to 5000. I spin a 68" 3bld Whirlwind (original Super Snapper) may try the whisper tip on new boat.
2016 American Airboat's AirRanger pushed by an Airboat Pros 2015 1.4L GM Ecotec... "Nothin' as Fine as Hearing a Turbo Whine"


todd glover
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Re: mini build help/advice

Postby todd glover » Tue Sep 29, 2015 12:48 am

The trick is the width you need 6 ft across the bottom a Jon boat is maybe 3.5 -4 ft my first boat was 6'6 x 10 with a Lycoming 200 and II had a ton of walking room if you make a mini 6 x10 with a 670 rotax it will float in 2 inches of water you need width is super critical more than the extra 2-4 ft in length

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Planeguy
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Re: mini build help/advice

Postby Planeguy » Tue Sep 29, 2015 9:01 am

I just did a search for the Rotax 670. Not a lot of information out there for it but while looking I found the 800 E-TEC snowmobile engine. 147 HP for under 80 pounds plus the reduction drive. I don't know how well it would work on an airboat but that is about a 3rd what an O-320 weighs for about the same power.

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jopete
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Re: mini build help/advice

Postby jopete » Tue Sep 29, 2015 12:41 pm

mine is a PE 150. most folks call them a 220 GPU. it smokes and slings oil, but it usually starts up and gets me there and back. will run dry and will climb thru cypress knees. when i get home i just beat the dents out with a rubber hammer.

the other pic is of my little deckover boat.
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todd glover
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Re: mini build help/advice

Postby todd glover » Tue Sep 29, 2015 1:26 pm

The rotax call ricks rotax in ft Myers the other snowmobile engine won't make the tq a 320 will not the same at all also you need a gear reduction the rotax are built for that but hull width and weight should be primary concern

Robn1020
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Re: mini build help/advice

Postby Robn1020 » Tue Sep 29, 2015 2:06 pm

Guys, thanks so much for the replies and info. Plan is to build with a 583 rotax with a c gearbox and clutch. Still debating on length of boat but plan is aluminum .125 bottom, .100 sides and deck with steelflex on bottom with bottom being 6'.

papajack
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Re: mini build help/advice

Postby papajack » Tue Sep 29, 2015 3:33 pm

Robn1020 wrote:Guys, thanks so much for the replies and info. Plan is to build with a 583 rotax with a c gearbox and clutch. Still debating on length of boat but plan is aluminum .125 bottom, .100 sides and deck with steelflex on bottom with bottom being 6'.

You won't be sorry, mine is fantastic. If you weren't 1000 miles away you could ride my mini and see what you're in for.

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Planeguy
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Re: mini build help/advice

Postby Planeguy » Tue Sep 29, 2015 4:21 pm

todd glover wrote:The rotax call ricks rotax in ft Myers the other snowmobile engine won't make the tq a 320 will not the same at all also you need a gear reduction the rotax are built for that but hull width and weight should be primary concern


I don't understand what you are getting at. No 2-stroke is going to make the torque as a similar powered 4-stroke. The 670 that Rotax Rick builds produces 92 HP at 6350 RPM. If you do the math on that, torque is about 76. By comparison, A Continental C-90 produces 90 HP at 2475 RPM giving you a torque of about 191. I couldn't find a weight for the 670 but it is likely less than half that of the C-90.

I was just looking at power vs weight. My thinking is the weight saving plus the re-drive should make up for lost torque. Maybe the correct question for me to ask so I can gain an understanding is...What 4-stroke would be interchangeable with a 670? (I understand there is no exact swap... if there was I think there would be a lot fewer 2-strokes).

br,lc,LA
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Re: mini build help/advice

Postby br,lc,LA » Tue Sep 29, 2015 4:29 pm

You are comparing an AC motor to a rotax with no gearbox! Gearbox is the Tq difference
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Waterthunder
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Re: mini build help/advice

Postby Waterthunder » Tue Sep 29, 2015 4:30 pm

.125 bottom and .100 sides on a Rotax is kinda mixing up a combo. Adding weight in the hull and taking away torque in the power plant. Here is a awesome performing DD.

Image
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Planeguy
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Re: mini build help/advice

Postby Planeguy » Tue Sep 29, 2015 6:55 pm

Thanks to br,lc,LA I think I finally have the CORRECT question to ask. What is the RPM, HP and/or the torque at the gearbox output shaft (prop shaft) on the 670? Any 2 of those numbers would answer my other questions and give me an accurate comparison.


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