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Mini-Airboat build project. I'm a Disaster brigade Volunteer

Hello Guys,

I am very new to this forum so Please be kind. I am from Manila, Philippines :)

My intended usage is :
1. for recreation
2. for food distribution and rescue during floods that regularly occur now in the Philippines.

I have no need for speed, 30KPH ( 19MPH) is perfectly okay with me.
I also know the complexity of designing an airboat from scratch so I will minimize the engineering to the absolute minimum and instead buy everything off the shelf if possible.

1. Basically I want my airboat to be about 12-14 feet long (Standard close/Open Van length in the Philippines, for easier transport)
2. i must be able run it at 30kph . 25KPH would be okay 20KPH would be the minimum top speed I would want.
3. I plan to purchase the propeller in the USA
4. I plan to purchase a brand new 155cc Fi Yamaha motorcycle automatic scooter rated at 15.5HP
5. or a brand new Kawasaki NS200 cc Fi motorcycle 6 speed motorcycle rated at 25HP depending on the advice I generate from this forum
6. I have access to a machine shop and a mechanical designer for fabrication
7. I plan to ask a professional boat builder to make me a fiberglass Flat boat or buy standard plastic double wall boats here in the Philippines
8. I have estimated the total boat weight to be more or less 300-400 kilos or 660-880 pounds
9. I will probably load the airboat up to 1000 pounds more during flood food distribution and rescue
10. If people here would recommend aluminum to be much better, I know of somebody who can built a flat boat made of aluminum
11. For rescue operations after a strong typhoon, water would be relatively calm but a lot of garbage or debris would be floating in the water that is why an airboat would be very practical.
12. Must requirement is an Fuel injected engine. Because it will probably be use very sparingly and my experience with carbureted engines is that they become very hard starting if you don't use it for more than a month

I do not want to use a second hand 4 cylinder engine because I am not a skillful mechanic and a brand new 4 cylinder engine in the Philippines is very hard to source or is very expensive probably costing at least 10,000$. A brand new small displacement mtorcycle in the Philippines cost about US$2,000 which is acceptable for me.

Can anybody give me rules of thumbs of an airboat? how much HP do I need, to achieve 30kph given a certain boat weight . Any other tips on how I should start will be extremely useful and appreciated. :)

Thank you very much. :)

A 12-14 foot boat is not a mini. Mini's are more like 8-10 feet with 1 seat and would be pretty useless for rescue operations as payload is 0. You need to be thinking about how to make at least 150 Hp at a prop RPM of 2800 or less for that size and load, that's bare minimum and you will want more.

If you are limited to 25 Hp, you should think about a mud motor drive for your purposes.
Oh, Thank you Slidin Gator for your insights. I was hoping to have a small boat that does not have a propeller underwater. As I said lots of debris during a disaster. I would prefer a propulsion system above water. operating on land is not really necessary for my needs. :)
Unfortunately, the Laws of Physics do not flex even a little bit where our
intentions and/or desires are concerned, even when our cause is a noble one.

As a general rule of thumb, you might figure that one horsepower will propel between say 4 and 6 lbs. In the later instance, the boat would operate acceptably in the water without a large load, whereas in the former instance it would operate acceptably out of the water or with a large load. As you can see, what you were hoping to do, has no chance.

If you [Search] this sight for Rescue type boats you will find that while they are about 140% bigger than what you propose, they are powered by between 300 and 500 percent more than even the minimum that Gator eluded to. The "air screw" we employ doing what we do is among the most inefficient means of propulsion in existence. This is largely due to the massive amount of "slip or cavitation" involved with moving air. Water born propellers suffer from the same affliction but are FAR more efficient because water is considerably more 'solid' than air.

If the suggested mud motor isn't workable for you, the only other thing I can think of would be an outboard motor with a 'jet drive' type of lower unit on it. Naturally, constructing a workable debris guard could be a challenge, but should remain within the realm of doable if you are persistent.

Best of luck to you. Being in hurricane alley so to speak, we appreciate what you are wanting to do and why.
Thank you, Slidin Gator and Deano for your insights. I might have to redo my size, weight and maximum speed requirements and see if this are acceptable. I really would like to have a airboat, unlike in the US where there are probably tens of thousands of airboat, its very rare in my country or even non-existent so the fact that i have one is some sort of a novelty factor. :)