Mini Air Boat Question/Info needed

**fresh water hunter** · 03-28-2016, 05:06 PM

check out airboatpros chucks ecotec builds he did a 300 hp all aluminum 4 cylinder turbo engine on a little boat sweet amount of blades depend on length and hp tq you have to turn them plus pitch fist you have to get a motor and weather direct drive or redrive that will give you a prop size prop legnth will tell you how wide the top of your hull needs to be

**Papee** · 03-28-2016, 05:20 PM

I agree, the direction you are going the ecotech setup would be a good fit. You wouldn't really need the turbo if you wanted to save some cash.

**Rollbar** · 03-28-2016, 05:30 PM

OK thanks for the info etc, I'll google it/chuck/ecotec builds.

Thanks again,
Jim

**Rollbar** · 03-28-2016, 07:37 PM

Originally Posted by fresh water hunter

check out airboatpros chucks ecotec builds he did a 300 hp all aluminum 4 cylinder turbo engine on a little boat sweet amount of blades depend on length and hp tq you have to turn them plus pitch fist you have to get a motor and weather direct drive or redrive that will give you a prop size prop legnth will tell you how wide the top of your hull needs to be

Very Nice !!!!!! HP/Torque, but, it's computer driven motor and I'm looking at old school/easier to fix when stranded. Don't have to mess w/PC's, CPS/TPS etc, so I'm thinking a regular motor if the Rotax doesn't work out.
Great info though-Thank you again, Jim

**Rollbar** · 04-30-2016, 04:56 PM

Question(s) on the 4a084.

1. On the 4a084 engine that is a 20HP, can it be bumped up to a higher HP? Or should a reduction drive be used/work better since it is 20HP? If so, what would be gained by using a reduction drive with the 084 engine (see pics below from Duane)?
2. Would the 4a084 push a 12'x7' Hard Chime well with two people (400lbs + fuel + boat weight) or should I build smaller (10'/11'x6'6" Hard Chime)?
3. When running a Mini (12'x7' hard chime or 10'/11'x6'6" depending on responses), and having a two person in-line seating arraignment, is it better to have the driver in the front seat? My thinking is yes, and my thought is if I go out by myself it will plane faster but what do I know (I originally wanted to sit in the back and wife up front and have her lower in the boat etc,,,).

Thanks,
Jim

P.S. I know I asked some of these questions, but that was in consideration in using a Rotax 65hp engine. I'm back to the drawing board.

**Corky** · 04-30-2016, 07:31 PM

The military rating was a little different than a normal rating{high altitude,worst case senario}..At sea level its closer to 40-45 hp...I'm a hotrodder through and through but the 084 does'nt appear to take radical mods too well...In our application some mods will make the already marginal heat dissipation go over the top and run hotter than you'd want it to...Actually ,running a redrive where the RPMs are sustained up close to the limit seems to make the engine run hotter than a direct drive from the info gathered on this site...

Placing the weight is'nt as you'd expect in an airboat..Too much weight up front actually hinders performance and easy planing ability...General rule is the boat should balance out at close to 3/4 the distance to the transom...Example, a 15ft boat would balance out at the 5ft mark forward of the transom...Keep in mind this is a general guideline...Length and shape of the hull as well as engine HP all affect the balancing...Only way to get it dead on is trial and error after the build is complete...IMO for a mini you want the seating inline a side-by-side seating arrangment will block too much air...My old mini had the operator's seat up front with a steering wheel for years...It never got on plane until I moved the seat back to the guidelines I've posted...

**Rollbar** · 05-01-2016, 02:03 PM

Thank you very much Corky.

I found this on the net and some good info from Canada.

These engines produce 45hp and will spin a 54"x24 - 58"x28 prop direct drive producing around 200 - 210 pounds trust at about 3200prm static stripped of all the un-needed stuff.
They do not need any thrust bearing modification since the center bearing is a thrust bearing. They weigh about 125lbs stripped.

I am putting a redrive on mine with a 68" Ivo ground adjustable prop. It should produce around 240 - 250 pounds trust static. I know a guy who put a 72" 3 blade Ivo and got 260 pounds thrust, but at 4200rpm.
These engines are made to run at 3600rpm constant in the generators they were used on. 4000rpm for a few minutes for talk off should be no problem. They are very reliable.

My wish is these great little engines would put out 80hp reliably, however the heads limit modifcations to a minimum because they cannot disapate heat enough for radical modifications.
Shaving the heads 10 thousand is pretty much max. 36mm carb, dual carbs or EFI and exhaust is about it for mods. I will using an a recommended SU HS4 carb because it is a constant velocity carb which adjusts mixture with altitude.

I was reading one forum where I guy tested several mods with no sugnificant gains. He noted the best performance was with the stock intake.

**Rollbar** · 05-01-2016, 03:29 PM

P.S. I just bought a 4a084-4engine off eBay for $600.00-FREE shipping.

The lady called and asked how did I want it shipped, I said it was listed as free shipping. She said no, no, no, no, no. I said pull up your ad, she said ok.

Ok so I'm back to the mini dept.

Thank you all for the help,
Jim