Hello all I'm wanting to build a airboat strictly for goose hunting and have no idea what size I will need. I will explain the conditions I will use it in.

The first few months will all be open water max run is 2 miles up river then in novemeber to January the lakes freeze up so mainly this boat will be used on ice. I need something powerfull enough to go from water and beable to get up on the ice. I just need something big enough to haul me and my dog and gear. I will never use this to run on dry land or even just mud. I don't want something I can turn on a dime with either.

Questions:

What size motor?
Will a wide john boat hull work with ribs? I could weld a flat bottom on if this is an no. Can also weld pontoons on the side to widen it.

Any other tips would be great!! Wanting to keep the price down as much as I can!

Thanks!

Colton

Welcome to the site.
Lif you can do the mods to a Jon boat I assume you have the capabilities to start fresh. I would not build a bull that was less than 14ft unless it was a single person ride boat. A longer hull allows you to spread out the weight more.

I would go with an aluminum hull, with all .125 materials, five foot bottom and 20" gunnels. I'm partial to the 084 and have been running the same motor for almost ten years with little problems. If you're going to be running with a lot of extra weight a reduction drive would be necessary. A reduction drive is a good choice any way if it is in your budget. The prop and reduction drive is most likely your biggest cost of the build at about half the cost of the whole build.

I found a rotax 377 on craigslist would this push me across the ice?? Would I need a reduction for that motor?

Sorry for for my ignorance just un educated on airboats....

Any rotax or two cycle for that matter would need a reduction drive because they make their power at rpms above the capabilities of a prop. Props can only be spun at about 3100 or less depending on the prop. Those 2 cycles make power around 6-7000 rpm.

Welcome to the site. Im with papee on this one. If you can do the mods I would just build from scratch welding using .125 aluminum since you plan to run on ice. Yes the 377 should push a boat at a decent rate. I think they produce around 35 hp. And yes you will need a reduction drive for that engine to get the hp out of the engine but keep your prop down to....well safe prop speed. Good luck on the adventure your about to embark on lol.

Steve

Okay thanks so far! Im not partial to that engine just saw it. Ill be honest Im wanting to find a motor in the 3-800$ range and can not afford any reduction drives. (Assuming im looking at the right ones that run about 1000$ dollars??) I also looked at the harbor freight predator 23 V-twin its RPM's are 4000 so I guess that is still spinning to fast. Any motors you guys can think of that I could run direct??

Thank you!!

Colton

The pretatir will get you sliding. Not fast but itll get you going. You can mount a prop direct drive on that and use the prop as a governor to slow the engine. The 084 engine will spin well over its rated 3600 rpm but when you put a prop on it itll slow the rpms down to 2800-3000. A good prob to experiment with would be the ultra prop in my opinion. You can get different pitch blocks and trim the blades until you find your sweet spot.

So just because the engine says it is 4000 does not mean my prop would spin at 4000 directly? As long as it could push me the dog and decoys across the ice I would be stoked.

I know ice is a lot slicker then water. But ive never run my boat on ice with me being in florida. If thst engine is rated at 23 hp at 4000 youll probably only get about 15-18 hp at 2800-3000 rpm. So just keep that in mind. You might want to look into tge 4a032 engine. I know papee ran one for a while

Oh and that motor will spin up to 4000 with a small enough prop on it but I would not do that. As im not sure of any prop that will hold together at those rpms.

http://www.competitionaircraft.com/recommendations.html


take a look at the recommended prop for a 20 hp briggs engine. I would say if your not after speed I would go with a shorter prop with a lot of pitch. Just my opinion though.

Ok I have also emailed a few prop manufactures about motor and prop questions. I'm just wanting to confirm I could slide on ice with a small motor directly attached to the right prop I will look through pappe's posts and try to find his build on that motor you suggested

Hi; Perhaps I can provide a bit of info and possibly some new thoughts. I used airboats in fall/winter/spring in Ontario Canada (lots of enthusiasm and little money). re propellors more diameter = more thrust and less speed. Think helicopter rotor. The fun comes in balancing power to rpm to thrust. Use 600 mph for prop tip speed and match diameter to max engine rpm. Set pitch to allow full throttle at max operating rpm. We used 8hp brigs with good speed on ice, no go on snow, real slow in the water. A VW 1600 cc direct drive worked well accross all conditions. Use a coating on the bottom to help sliding on sticky snow and to help wipe the bottom clean when coming from water onto ice with snow cover. If not then ice will freeze to the bottom (even plastic) and you will get to remove it before the boat will move. Remember if it breaks, at best you will have a long hard trek home, so use good reliable bits. Great fun. We made our boats from plywood and they worked well.

Mike

Pm sent thanks!

One thing to keep in mind, a small power plant like that may not get you from water to ice. They just don't have enough thrust to get you over the hump.

I agree with lahti on the slick bottom ... not sure if you get much snow where you are or just ice, but snow on top of ice will definitely slow you down considerable and require more HP. I'm now running snow on my Bray fiberglass hull and I will definitely need to get Quick Slick on asap as it does stick whenever you stop. I'm running the 4a084 with a redrive and whirlwind prop.