Help designing shallow deep police aeroboat

Our USN PBR river boats of the Vietnam rice paddys war would be ideal. Tough as rocks, small, very hard to flip or sink and built for serious police weapons to be used against heavily armed other boats.

 

Yes, with a jet drive, aluminum hull and a 40mm bofors cannon, you could do wonders.

 

Hello everybody

I’m really pleased to see so many people trying to help us. It is very good to see your efforts to achieve what should be the best solution to police shallow deep waters.

I couldn’t know yet which equipment they, at the “Environmental Police” (what is the name of that kind of police in USA?) have from their old hovercraft, so I can’t tell if it will be useful for us or not. The Police Capitan was off town the whole week, so I could not know some basic information, like how many policemen will operate on board, which kind of personal equipments will they carry, etc…

The boat will operate in salt water preventing hunting and illegal fishing as well as policing the integrity of the estuary zone, where many fishes come to reproduce.
Our city is Joinville, located in south Brazil, you may see us at: (http://www.guianet.com.br/externo.php?target=http://www.sc.gov.br/), please see the bay and canals at the extreme north – right click on it to zoom (http://www.mapainterativo.ciasc.gov.br/sc.phtml )

Sorry is not in English.

Thank you
Ricardo

 

Ok Florida guys. Give him the website of your marine police that does the same job.

 

Well, I'd think that the DEP (Department of Environmental Protection) acting through the local marine police along with the US Coast Guard (independent of the other organizations) are responsible. Primary jobs of the US Coast Guard are search and rescue, law enforcement and environmental protection. Regarding your aeroboat, why not a shallow draft aluminum boat with a jet drive?

 

What?

A hovercraft does just fine in 10 inches of water, you must be thinking of
hydrofoils or something else.

As far as "jet boats" go, you need water to jet. What if the bad guys had a airboat or hovercraft and took a short cut across some reeds or sand bars, could you keep up? I think not.

Get you head out of the water, and up into the air fellas.

I think that if you throw enough HP (horse power) into an airboat it will be faster than a hovercraft - a hovercraft will be more efficient with less HP though.

One advantage of an airboat is that it does not have to come up on it's cushion of air and get to "hump speed" like a hovercraft does. Also if you need to sit quietly for long hours, then pounce on people/craft the hovercraft will have to blow the water out of it's air tunnels or bag skirt - taking away the element of suprise.

If I were you Ricardo, I'd find out what the game wardens in Florida use as someone else suggested - good idea.

 

Well, the thing is that we will construct it at the University, and for us working with vacuum bagged composite should be much easier. Nevertheless considering our design students could perform a much better shape doing the boat in a better “to mold” material.
We can construct an aramid (Kevlar) bottom what should guarantee us as a reliable durability when shocking with branches or scratching in sand bottoms.

Ricardo

 

I went to the Florida EPA site and used the search feature for "airboat". I had some hits, but my browser won't allow their slide show.

I found some interesting airboat links.

http://www.boat-ed.com/fl/course/p4-18_fl_info.htm

http://www.marshlandmarine.com/recreation.htm

http://www.americanairboats.com/ab-aps.htm

...........and some more hovercraft info:

http://www.hovercraftusa.com/military.htm

 

Its so beautiful! Well, the hovercraft WILL work well. Just wondering though, if it has its skirt snag, what'll happen?

 

Good question, answer - it depends.

Finger/Segmented skirt:
Each finger is fed air from the air duct/tunnel through round ports. The loop of fabric know as a finger or segment is attached at the top to a frame with a metal clip - like a binder clip. The bottom of the loop which is open to below (the ground/water) is tied with a plastic tie. It's the same kind of tie you can find at any hardware store - white or black, little ribs on it's pointed end, and eyelet catch at the other end. Just loop it throught the loop sewn into the finger, to the harness loop attached to the side/bottom of the hull. The ties are designed to give way and break off before too much damage is done to the durable fabric. Sometimes the finger is ripped off or damaged - it can be easily replace with new clips and ties. It's claimed that you can lose or damage 1/3 of the fingers and still operate the craft. I never seen anyone come close to that, can't imagine the conditions under which this would happen.

Bag skirt:
The bag skirt does not need as much internal ductwork, just feed the bag air and it inflates - air flowing around inside builds up static pressure. Some air is control bled out to feed the plenum, and there are weep holes in the back to let water out. The bag even though it may be sectioned off in chambers can be more prone to serious tears. However the bag skirt is made of heavier material to help compensate. The medium sized hovercraft pictured with the 50 cal. gun is a combination of both skirts, called a "combination skirt".

Note: Hovercraft were used in Vietnam - went thru Sea of Reeds plowing over six foot high shrubs and weeds, and running over Sanpans.

http://www.vietnampix.com/mach2a.htm

 

I've lived with a finger skirt for 15 years, converting to an experimental bag skirt of my own design- hope this works out.

Last nights test inflation, went pretty well.

I should state that the finger and bag skirts of small craft operate at low pressures compared to RIB/inflatable boats. They actually give to the touch and are designed to contour to the surface and deflect to avoid damage and friction.

 

Which is preferable for safety?

 

First off hovercraft have the best safety record of ANY form of transportation ever invented. This is kind of weird considering they have spinning propellers and don't steer worth a darn - and have no brakes.

The low pressure finger skirts are used on small racing craft because of their lean-in ablity. But at the highest of speeds are more prone to "plow-in". Plow-in is when the pressure on the outside front leading edge exceeds in internal skirt pressure. This can result in a colapse of the cushion in the front and an sudden deceleration when coming in contact with the water. This can be scary, but typically all that is hurt is your pride.

The bag skirt is at a higher pressure and less prone to plow-in. However if you hit some thing at speed (like a cresting wave) it can be less forgiving.

The choice of skirt like choice of hull design is not based on safety as much as when, where, and how you intend to operate it.

Most home builts will use a bag skirt because it's easier to build - sometimes a consideration.

The design I am developing functions like a big single finger in the front or may be called a plenum in my case. The sides are bag skirts giving me the stablity I desire. I reworked the ducting so that much of the air flow is directed to the front - which should create an air-curtain making me less prone to plow-in (that's the theory and my hope). It's a spin-off of the Sevtec design but different enough to be considered new in my opinion.

 

For those conditions specified by the thread creator, a finger skirt is better, right?

 

Each skirt type has its strengths and weaknesses, the craft is designed around the skirt system. I am commiting heresy by putting a partial bag on a fingered craft - call me a rebel.

In most situations finger skirts are considered an improvement/superior - that's the short answer.

I wanted the stablity of a bag but not the wave impact/obstical impact liablity. The front of my skirt will act as a low pressure finger (one big one).

Get a room full of hovercraft designers/manufactures together and they will yell at each other touting the virtues of their favorite choice. It's like asking a group of architects what style of architecture is best, or a car buff which is the best car. Everyone has a bias based on their personal needs, hopefully I've been clear about my needs (to avoid river rocks).