Eric's mini

[Eric]

Hey guys, long time reader, never posted on a forum before so be gentle. If this is in the wrong place, please move to appropriate section.

Ok, to the meat and potatoes. I live in the Midwest, near a very shallow river with a hard sand bottom. I currently have a mudmotor, specifically sps 22hp longtail on a 1648 flat bottom jon that works good, as long as I have about 6 or so inches of water. In the winter and heat of the summer, the water is frequently 3-4" deep and 1-2" in a few places. There are a few full size airboats in the area and I think that is the way to go. I love to tinker and have a good DIY background.

My plan is to build a lake buggy single as a starter project. I have the plans but have a few modifications to suit my needs better. I am planning on using the harbor freight 22hp(~100lbs) motor Instead of a 10-13hp (only because its what I already have), Use a direct drive arrow prop (whatever they recommend), raise the sides to 12", and since this will be used as a shallow water boat (no stumps, no dry, only minor beaching on hard sand) reduce as much weight as possible by reducing the hull thickness to about 1/8" and using epoxy and glass to compensate. Using aluminum instead of steel for motor mount and cage, and a lithium ion 12v battery, I think I can have this complete build including 2.5 gallons of gas at about 200lbs. I weigh 200 lbs, so the total weight would be about 400lbs.

I have read countless threads, watched just as many videos, but before I start a project like this I want to have done my due diligence. My goal start is in 4 months (after I take the GRE in june). What is the consensus of the experts?

My concerns
1) I haven't read about many builds using 22ish hp, and the one on youtube I saw was a turd, but the hull was aluminum and looked like it weighed 400lbs on its own
2) my 1648 jon boat(800 lbs including driver) can ride in ~2" of water (@20mph), but my mudmotor prop hops out of the water, so I loose thrust and come off step. Can a 8'x4' airboat like the lake buggy realistically run in 1-2 inches of water almost indefinitely?
3) I am stepping into the unknown here guys (atleast from my perspective), is there anything else I am missing?

thanks in advance,
eric

[aerokirk]

Hi Eric,
Welcome to the site!
I see that the 22hp Predator engine produces it's maximum torque at 2500 rpm which is a good thing for a direct drive prop. When you spec your prop try to get one that works best at that rpm. The maximum rpm of 4000 would be too fast for a direct drive and you would find that you actually loose thrust and gain much noise at that high an rpm. My first airboat was a Jon boat and they can work well for what you're looking to do with yours. Shallow water is an airboat's best friend!

Look forward to reading about your build ... Post pics!

Ted

[Corky]

Hello Eric !! Yes you can run in just a few inches of water but you need to keep the hull light as you've discussed and place all the weight just right...My old mini can do just that{1448 jon/13hp Kohler}..Mine really takes off when the water level gets to around 6 inches or less and I have a good momentum as I head into the shallow water...It took trial and error to get the weight{including me !} just right to travel over any obsticles without getting hung up... I can go places most will never go in the summer unless you have a canoe...Even my new build will never see alot of the areas I travel in that old mini... I think I do it just because I can fish areas that don't normally get flogged...

[Papee]

Welcome to the site! You have it pretty much under control. You will most likely be running a 42 inch prop with that motor. I'm not sure about pitch but they will know at Arrow Props. With that type motor you will be deleting the governor and use the prop to keep your rpms where they need to be. In my experience with the arrow props they work best at 2800 but that could change with chord/blade design. Some props are good to about 3100 rpm, I have a wide chord prop on mine and run it at 3100 rpm max.

1"-2" of water is pretty skinny, your hull will draft about that. My boat will run that skinny water but if you hit a rock or branch on the bottom it will slow you down and maybe knock you off plane. That setup may not have enough power to get you back on plane sitting in that level water. It will no doubt make it over short stretches of skinny water. It does sound like a solid setup for what you want. Good luck with your build, building is as much fun as running these things.

[Eric]

Thanks for the input guys. glad to hear I am at least going in the right direction with this. On a side note, I am planning on using direct drive because of simplicity and $, even the cheapest is $700, as you guys already know. I have toyed around with the idea of making a v belt reduction drive (very common on hovercrafts). What exactly in terms of performance can I expect with a reduc drive: more low end push? more top speed? some of both? Second question, almost every airboat I have seen has the engine mounted pretty high. Why is this? I can only think of negatives like higher center of gravity, but there must be a reason why. Is it just because its would be prohibitively expensive to have a 6' circumference cogged belt? Or does the engine up high it help the performance in some way that I am unaware of? If I am building a reduc drive I could pretty easily mount the engine at or just above the level of the transom and run a belt up to the prop shaft. Thanks in advance again for sharing your wealth of knowledge

[Papee]

The reduction drive is a torque multiplier, how that extra torque is used is decided on your prop design. On a mini airboat you want all of the prop above the transom, this is what determines the height of the engine. A V belt reduction drive would require more than one belt, a belt for every so many HP. I forget what this figure is but it is on here somewhere, either in Buster or Duane Scharbourh's threads.

[Eric]

Most of the light hovercraft up to about 30hp used a single belt. I have the blueprints for a universal hovercraft uh16s that calls for a subaru engine. The reduc drive on that uses 3 maybe 4 belts. If i was designing my own for 22hp, i would probably use a double belt design just for redundancy. I imagine a double would reduce slippage but increase losses from friction so performance wise it might be awash, just more reliable

[Papee]

Hover crafts typically have a shorter prop, I would not use any hovercraft related specs for figures for an airboat. There is a lot of slippage in a vbelt reduction. You only see them on lower HP situations. Most redrives for airboats use a cogged belt because of the slippage and the tension you have to put on a vbelt to keep it from slipping. They do work in the lower HP motors though.

[Eric]

Thanks for the heads up. It makes sense though. There is more friction on an airboat hull and subsequently drivetrain than a hover.

[Corky]

I've seen some airboats that have the engine low...It would definitely be more stable down low...The factors down low include enough air movement to cool the engine...And not low enough to cause problems if you get water in the boat or swamp the whole rig...Maintenence might be another factor it's just easier to work up higher..

[Andrew82]

Hi Eric,
I have been reading all the comments on your build and I know it was a few months back. I was wandering how it all worked out? I have a little 10ft flat bottom I just purchased and have actually been looking at the same engine and prop set up. I was wondering if you had any advice for a first timer on how this project worked out and maybe some do's and don't.
Thanks in advance for any help.
Andrew

[yamahaulerG1]

Hi Andrew A 10ft boat will work but with such a small surface area is hard to get on plane a 12-14ft jon boat work better with the same motors because they draft less water and also more stable a standard 10ft is usually very unstable with a heavy motor up high I had one and the motor was 65lbs full of gas/oil with the prop on and it made the boat unstable I wouldn't have wanted to take it fishing in deep water. But in a field of shallow water it was like a go cart u didn't want to stop riding

[Eric]

Hey Andrew, I ended up getting into anesthesia school so I have 0 extra money or time right now (or for the next 3 years). I did finalize my build based on alot of input and youtube videos. Essentially the #1 thing that experienced people say is that minis dont like extra weight so i obsessed on keeping weight down.

I decided that the 22hp mini I was going to build either wouldnt run dry ground or would be a VERY poor performer when out of the water (plus i dont have much need to). So with that in mind, my plan was to build a single seater lake buggy 4x8 and make it a "deckover" but it would be solid foam building up 4x8 sheets of 2" extruded polystyrene to a thickness of 8". Use a hot wire to cut the front profile, epoxy it all together, then glass it in. This would provide a hull that weighs about 40 lbs and would be strong enough to repel the occasional czech hedgehog submerged just under the water. Another benefit, in kansas, it would be an unsinkable hull even if punctured so it adds an extra element of safety when it is cold and nasty outside. Building with epoxy and glass is a huge topic and i am only an advanced novice but would be happy to answer more indepth questions about the hull design

Second, the harbor freight 22hp engine is almost crap. It wont run 1 week old gas, it has no alternator, and compared to the Briggs 23hp, it weighs about 35lbs more. Also, there will be random crap inside the motor that needs to be fixed for it to even run right from the factory, for example the vacuum line that runs the fuel pump was totally kinked. If you like tinkering with small engines (i dont) go for it because it will need it. and lastly if you ever decide to mod the engine, the harbor freight has virtually 0 aftermarket parts while the briggs can be taken out to 35hp

The build list would look something like this

foam hull 40lbs
briggs 23hp with oil 83lbs
reduction unit 15lbs
prop and hub 5lbs??
lithium ion 12 volt battery 5lbs
cage and rigging using 1/2 conduit 25lbs
3 gal gas tank full 21lbs
misc. fuel line, battery cable, etc.. 5lbs


So the realistic boat weight would be about 200 lbs. depending on how you cut the front and how the weight is balanced, would only draft 1.6 inches without rider, and 3 inches with rider (I weigh 200 lbs). There is a lake buggy build on here by Gg Kustomz. He has a few youtube vids of his boat and it appears to run really good. my best estimate is that his boat weighs about 270lbs, rider looks to be about 165lbs and has a 13hp engine. This build cuts weight and adds hp.

Keep us posted on how your build goes!