Help designing shallow deep police aeroboat

[Ricardo Aurelio]

I teach at a Brazilian University and we are making a study group of students to design and to construct a boat for free, that will be used by the environmental police to inhibit the ambient crimes at a bay in our city.
I’ve got a large experience in boat construction, but none in boat design.
Can anybody help me were to go (books, magazines, articles) that could be helpful for our idea?
Thank you very much,

Mares

[kach22i]

I found this list, look at the Boston Whaler listings, seems to be popular in your part of the world.

http://www.coltoncompany.com/shipbldg/ussbldrs/postwwii/government/smallcombatantexports.htm

I've always been interested in how many type of craft are used in the Hong Kong harbor, one of the busiest in the world. Everything from A-Z including hovercraft seems to be made use of.

Don't you need to start with a program that states the function of the craft? How many people on board, crusing range, sea state ablity and so forth?

The more information on your needs you list, the more people can react to and give you suggestions. Have you ruled out inflatables or cross-overs?

[Ricardo Aurelio]

Well

We will have all information about the envoirement police need at the next week, but for sure it will be composite boat.

I'm just trying to gain some knolegments in this matter to be able to offer them some alternatives of idead of boat design.

I'll get the more information I can and then I'll ask for help again.

Thank you very much

Ricardo

[kach22i]

This looks like it might be a useful feature if hooking up to other boats in bumpy waves:

http://www.wing.com/foam_collars.html

I don't know if a catamaran design would give you greater deck suface to operate from, but that's another consideration to think about.

The first stage of my architectural projects was research. The teacher would have students sign up to research certain aspects of the project, then we would compile it in a binder to share.

Having your students research different hull designs, differnt materials and what other police departments are using (and why) will help the whole class out - and give you direction/choices.

Most of all ask the police what they have in mind, and why. A good designer listens to his/her client. Good luck, sounds very exciting.

[mackid068]

What about a RIB? check out nautica RIBs. RIBs have nice, big, soft collars for docking and are fast as you can get without special equipment OR really high costs.

[Ricardo Aurelio]

First of all, thank you again for your interest in helping us.
I agree with you when you say that “a good designer listen to his clients”, we do have to know their needs to be able to satisfy them.
I’d like to share some information about the project later on, if you aloud me.
As regarding catamarans, may be that is a way to go, but I think they need some more deep water to navigate then a “flat bottom” boat, but in other hands it would be more safe when you are considering a “fan” (aero boat). Don’t you think so?

Thank you

Ricardo

[Ricardo Aurelio]

What about a RIB? check out nautica RIBs. RIBs have nice, big, soft collars for docking and are fast as you can get without special equipment OR really high costs.
I know nothing about nautica RIB, I'll look for it. I'll try the terms "nautica Rib" at the Google search engine.

Thak you

Ricardo

[kach22i]

a “fan” (aero boat)
Oh..........you mean a swamp boat or air boat! Darn, I knew there was a hidden meaning in there.

I'm a hovercraft owner can tell you about those. Here in Detroit they had an "aero boat" and used it to go over the ice. I don't think it lasted long as there were hidden deep cracks in the ice, plus transitions (water to ice) were dicey at best.

The city of St. Clair Shore chose a hovercraft, the only time they made the news was when they ran out of gas rescuing the airboat guys and the six-foot waves capsized them.

In Florida both the police and smugglers use aero-boats.

There is something called a convertible, that is to say convertible from Solid-Side-Wall surface effect ship (SES) to amphious operation. This way you get heavy seas operation and can operate over tidal mud flats much like a true hovercraft.

Some good links (see education areas):
http://www.hoverclubofamerica.org/

Here is one that may interest you (Sidewall ACVs & the Convertable Concept):
http://www.hoverclubofamerica.org/HCA_Matl/Library/Library.html



Note: being able to get the bad guys when they are stuck in the mud or their hull is shattered on the rocks is an advantage you should look into. Hovercraft can start from dry land, end up on dry land - some allow for stretchers direct to ambulance van.

Edit: Sevtec is one make of amphious hovercraft which I read about having rough sea capability. While in Alaska they claimed to of survived 15 foot (5 meter) high wave swales. Below is one of their stories, but not the one I read before.

http://members.aol.com/sevtec/sev/AK.html

PS: This looks like a really informative Airboat site:
http://www.canadianairboats.com/faq.html

[Ricardo Aurelio]

I guess they need a boat capable to navigate in at least 10 in deep water.
They already have a "fan" engine that was isntalled in an old Hovercraft that didn't last much in our waters.

Ricardo

[kach22i]

I guess they need a boat capable to navigate in at least 10 in deep water.
They already have a "fan" engine that was isntalled in an old Hovercraft that didn't last much in our waters.

Ricardo
Please find out for me what kind of hovercraft (factory or homemade), pictures would help.

I know salt water (and brine water) is very tough on boats/hovercraft - finishes,electronics and rubbery parts (like fuel lines or skirts).

I operate in fresh water, once a Florida guy saw my 1989 Scat II HP and said it looked brand new compared to the ones in Florida operating in the glades.

I'm trying on an experimental skirt on my craft, couple more weeks and I hope to be done.

[mackid068]

Factory-made works well. Navigate at least at 10 kts or in 10 foot deep water?

[kach22i]

Factory-made works well. Navigate at least at 10 kts or in 10 foot deep water?
I think Ricardo meant that the craft needs to be able to navigate in water which is only 10 inches deep.

Also I need to tell Ricardo that RIB's are inflatables, but he must of figured that out if he went through with that Google search.

Please remember that English may not be Ricardo's first or primary language. Looks to be real English and not Americanized English.

The engine of the old hovercraft may not be powerful enough for a standad sized airboat. Also the intergral fan which many single engined hovercraft use is set up to produce static pressure for lift as well as velocity for thrust - and needs a duct. An Airboat just needs a big propeller for thrust, which will be more efficent (and quiet) for that application.

Go to that Canadian airboat website I gave already, there are design tables to see if you re-use the parts you have. You may not be able to do what your first impluse is.

Hovercraft do kick up a lot of spray, this may of lead to premature wear if they did not wash down the craft after each and every use. Salt is an unrelenting and unforgiving corrosive.

[mackid068]

Woah, 10 inches. Hovercraft would be a no-no in water that shallow (it wouldn't be fun to have to repair) Oh, my mistake, whoops...Airboat is still the best bet.

[cyclops]

Sounds like a job for a surplus US Air Force A10 Warthog and it's 30mm Gatling gun. One firing round pass would elimanate ALL crimes on the water in a 20 mile area. Force is only elimanated by a more powerfull force. Allright that is a bit of over kill. Any small milatary jet of the nearest Air Force with cannon fire would do. Would the local politicans allow the killing of criminals in a crime?

[gonzo]

What area in Brazil is it going to operate in? What are the powerplants available?

[cyclops]

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.

[mackid068]

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

[Ricardo Aurelio]

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

[cyclops]

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

[mackid068]

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?

[kach22i]

Woah, 10 inches. Hovercraft would be a no-no in water that shallow (it wouldn't be fun to have to repair) Oh, my mistake, whoops...Airboat is still the best bet.
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.

[Ricardo Aurelio]

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?

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

[kach22i]

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
New Coast Guard vessel to replace the former hover craft in Saginaw Bay, Michigan.

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

http://www.hovercraftusa.com/military.htm
(Marine Assault with 50 .Cal Mounted)
http://www.hovercraftusa.com/wmt.jpg

[mackid068]

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

[kach22i]

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

http://www.vietnampix.com/bilder/mach2a.jpg

[kach22i]

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

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.

[mackid068]

Which is preferable for safety?

[kach22i]

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.:p

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.

[mackid068]

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

[kach22i]

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).;)

[kach22i]

I found this, Jerry said it better than I was able to.

From: Jerry
To: HoverLovers@yahoogroups.com
Sent: Sunday, June 19, 2005 10:49 PM
Subject: Re: [HoverLovers] FINGER VERSES BAG SKIRTS (mike)

The bag/finger skirt offers a compromise between the two. Less stable than a standard bag skirt, but more stable then a standard finger skirt. Easier maintenance as I believe, the fingers are replaced rather than the skirt, so the bag get little wear on it.

A bag skirt has better stability and less sensitive to balance and weight shift, although it does effect it, but not like a finger skirt. Bags are easier to make and less expensive. The ride isn't as smooth as a finger skirt. Repairs between a bag and finger skirt are a matter of opinion. Fingers are just replaced. A bag has to be patched, but in the field, a hole punch and a few wire ties make a very quick repair and get you back on cushion and moving again. The bag will wear faster on rough surfaces so mainly used for water use.

Finger skirts conform to terrain better. Offer a smoother ride and wear better on rough surfaces. But "generally" require higher hp engines as all the lift air goes into the fingers and exits under the craft. So a high reving single engine with about 1/3 to 1/4 of the air into the plenum to feed the skirts, or a separate engine (i.e. Air Commander) but they use I think, a 20 hp 2 cycle for lift where a similar size bag skirted craft would use 8 hp or less for lift.

The bag/finger combo is usually much harder for the home builder to make. That's why we don't see many of them on recreational craft.

As Michael said, if the primary use is water, go with a bag. If it's a 50/50 water-land craft, or more land than water, a finger skirt would work better for you. It's all a matter of what you want the craft to do and what it's primary use is or will be.

Jerry

[mackid068]

Combinations work well. Bag/finger may be best.

[kach22i]

FYI:
Big hovercraft event in southern Ohio this weekend, just south of Columbus in Chillicothe.

http://www.hoverclubofamerica.org/

[Ricardo Aurelio]

Well,

I have 25 years of experience constructing composite “one off” sail multihulls, but I must confess I do not have any know how about finger skirt.
There is one thing that I’d like you to figure out: we have to think about a tough boat, but it must be light too otherwise we wont be able to navigate in shallow deep waters.
I’ll ask you to excuse me but couldn’t talk to the one that will define all the boat parameters (such as number of passengers) so by now I can only speculate about that boat.

Thank you very much

Ricardo Aurelio

[mackid068]

Steel or aluminium are both very strong materials and, overall, are pretty light.

[kach22i]

Aluminium I think is lighter and cheaper in most applications than exotics like Carbon Fiber/Kevlar which needs to be baked in an autoclave to reach full strength.

If cost was no object then I would still have to look at the corrisive affects of salt water on Carbon Fiber/Kevlar.

How does Aluminium do in salt water? What spec/quality do you need to purchase? What kind of paint if any to protect it?

This is way out of my area of speculation but I'm interested in learning all I can.

Go for it.

[mackid068]

Honestly, I have no idea about marine quality metals nor about paints. All I really know is that they are used in many vessels and were used for PBR (Patrol Boat, River) or "pibbers" (riverine patrol craft, nice and strong) in Vietnam. These vessels, along with many other metal-watercraft have been proven extremely sucessful, in addition to being stronger than fiberglass.

[Ricardo Aurelio]

Well, I finally got all the information about the boat our local Environment Police need. I was wrong thinking their needs should be shallow deep boat. They already have a hovercraft and a small powerboat for that purpose.
It must be an offshore boat capable of carrying 6 policeman plus some extra loads as prisoners and arrested merchandise.
The boat should have a small stem platform or deck to aloud the police to easily enter into other boats.
I believe a central piloting “house” should be a good idea.
Do you have any suggestion?
Thank you for your help.

Ricardo Aurelio

[mackid068]

Probably a rigid hull inflatable. Look at protector boats. (Protectorboats.com) Or, perhaps, Maritime Skiff (Not a RIB though) maritimeskiff.com

[kach22i]

1. I gave a link which listed "Boston Whaler" and similar boats used in police work all over the world - please look at it again. The Boston might be exactly what you are looking for. They have a good website too.

2. They still have a hovercraft! Happy days, I love hearing that. Any chance of getting additional information on it, it's spec's, how it's used and pictures?

[Ricardo Aurelio]

Thank you all for your help.
I'll let you know the "work" development.

Ricardo Aurélio

[Sean Herron]

Hello...

That was funny and to the point - always good to cut the mustard... :)

SH.

[kach22i]

always good to cut the mustard

I'm not that fond of mustard, a little more garnish is welcomed. :cool:

[mackid068]

Rigid hull inflatables are perfect.