Tritoon Airboat

[Gbenz]

Long one, please remain seated during this entire event.

Most Airboats in Fl are shallow water boats made to run on the ground when needed with both aircraft & auto v8 gas engines 160 to 750hp+. Avg size abt 13 to 14ft by 7 to 8ft wide. Speeds are generally 30 to 40mph & few over 50mph.

We've looked at the pontoon kits & thimk one somewhere can be properly modified to accept a 250-300hp v8 Navistar or Gm diesel with low rpm, high tq & wide blade prop(quiet). These engines with proper gearbox will produce 12-1500lb of tq & weigh in prop box & all abt 1250lbs. Prop cage abt 300 more.

Engine mounts can be fabricated easily which mount on 2-2.5in fore-aft tbar runners. 4-6 are usually used instead of the 2 needed for extra strength.

The air propeller needs to be as close to the water as is feasable for lengthwise stability. The entire power package & prop needs tobe as near the transum as possible for deck roominess.

A small outboard motor mtd where it usually is will be maintained because of braking & backing needs. Center console is desired with air rudders(3) interconnected with outboard steering.

The center tube needs tobe 18 or 20ft & outboard tubes 8 or 10ft. Looking at 19in tubes & 4000lbs capacity should be close to what we're looking for.

The tubes full length will not be easy to maneuver with the standard 2 rudders is why we add another & shorten the outside tubes. With 8 or even 8.6ft across the transum & abt 3 or 3.5 at the front bow should have lotsa room.

Use all metal & lockdry with no wood or carpet on this one.
May need a center tube with greater diameter than those at the outside for handling but is it workable?

Must be sure this boat will plane & the tubes must be rigid via xing them together. No ocean for this one but tubes need tobe deep v right?

All replies either pro/con or otherwise appreciated.

Thanx, Gben

Oh yes, 4-5 people & 3 blade air prop is 84 or 86inch.

[Gbenz]

An error has occured in my above post.

Instead of saying 12-1500lbs tq it should say 10-1200lbs tq & 12-1500lbs of thrust at standard temp.

Have you guys found something bad wrong with my above proposal that you're not saying?

Too much weight aft? OK we'll put the 100gal fuel tank at a bow station. We could also us a troller instead of a regular outboard. The center console could be mtd at a station just ahead of the boat to stay well clear of the prop blast. Is there such a thing as a conical shaped pontoon?

Yes there are a few diesel airboats with USCG, Canada & other places in the north country. They are faster on the ice & snow than in the water & are built very tough todo so.

We did want(x2) a 450hp Allison C20 turboprop with Hamilton reverseable prop & all but at 35k$$$$ my comptroller ruled it out. Lycoming T53 too but comsumption jumps from 28 to 60gph.

Tell us what is what Guys when you can.

Thanx, Gben

[kach22i]

Look at this:
http://www.russianboat.com/



Lots of power means big propeller, or smaller ones either in tandum or side by side.

How fast that propeller spins determines the noise and the rotational moment. You may want to consider something in a duct if just for safety reasons.

You may get some help here:
http://www.hoverclubofamerica.org/fo...hp?showforum=8

Or look at this stuff:
http://hovercentre.com/

http://www.canadianairboats.com/faq.html

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

NOTE:
You don't want that bow to plow in, the wave will fly over you and into the propeller, perhaps a hydoplane configuration of two front sponsons and a flat tail would be best.

I favor a pusher, not the front mounted tractor shown below.

[kach22i]

It could be pretty big.





Here you go, not bad for $200.

http://www2.towerhobbies.com/cgi-bin...1p?&I=LXMPH6**

[Gbenz]

Thanx Kach22i,

You've went far beyond the call & we appreciate it from the Russian radial to an aircraft that lands on air to the lawn mower that needs no wheels! And not tobe outdone a mult million effort right here where we were driving sunday pm wondering what Atlas was at our port. Don't you just love the Inet?

I spent a good bit of time over at the Hovercraft Club site & saw many of your contributions there & will go back & pick up where I left off.

Now an Airboat as I know it with a Cat bottom would really be the way togo but most all Airboats are flat bottoms. If it could only be done in abt 18ft with pontoons. I do know that speed is costly so I'll need to stay around 25 grand if possible.

I've worked aircraft sheet metal but fiber & resins is out of my reach I believe.

From what I've seen the larger pontoons seem tobe hard to push & so for this reason we want to stay as short as is possible & still have room for 4-5 to move around. Speed would certainly be nice coming home from down the St Johns river many miles.

One reason we want to use the pickup truck diesels is not only our good experience with them but the ability to use power programs to jump the power up if needed in some cases 50 percent.

Counter rotating props with gearboxes are fairly reasonable & can jump power upto 30 percent. The outboard motor if powerful enough & tuned with the airpower could really mean that speed could be an option.

More Later & thanx agn,

Gben

[kach22i]

You may be interested in this type of hull bottom.

Sea Coaster SES

http://www.defense-aerospace.com/cgi...Y&modele=jdc_1

The patented SeaCoaster catamaran design features cavities in the bottom of each hull into which air is blown providing lift to the vessel, reducing resistance, and thus allowing higher speeds to be obtained.

http://www.seacoaster.com/


http://www.seacoaster.com/Article/index.htm


A while ago I posted or someone posted a large airboat with stepped sponson hull built in 1917 or so. It was a brown sepia photo, plus there are drawings posted on the Internet. I will try to find them for you, the term "catamaran" stimulated my brain and I just pictured it.

[kach22i]

Not the one I was looking for, but interesting - from a great/fun site.

http://www.lib.berkeley.edu/news_eve...aritime/9.html

[kach22i]

Before throwing out your basic tri-hull concept, perhaps looking at more designs (even fantasy ones) will help.

http://www.multiaxis.com/3d%20laser%...%20gallery.htm


Weird Cat.
http://www.kkg.at/de/127/

[kach22i]

One design to look at might be the wing-boat design/thread.

http://boatdesign.net/forums/showthr...light=Michigan


Oh and I found those old photos/drawings too.

http://boatdesign.net/forums/showthread.php?t=

http://users.telenet.be/thomasweynan...-aviation.html


http://mars.ark.com/~mdf/N_miscd.html


Another to look at;
The Bug (Elcoplane):
http://boatdesign.net/forums/showthr...light=michigan

[Gbenz]

Thanx Kach,

Some rather wild stuff but still need something diy that we know how todo from a reasonable kit form assembly.

I will try to contact the U Fab factory people to see if they know how to float what we need to carry in the locations specified. I can guess from now on abt what the length & diameter of the pontoons need tobe but once paid for we cannot doit agn. We need at least some iotta of assurance before our little $$$ are lost.

As far as placement of the power package upon the platform we have several airboat manufacturers capable of doing this. But they tell us also they have no common knowledge nor experience concerning any pontoon airboat.

Of course I'm staying the course abt pontoon sense it appears tobe easiest & less costly for what we need. Would still like to hear if itis ok to use a larger diameter center than the two outside pontoons.

Right now before the fact we can dictate to both the capacity & performance of our finished product. But after the fact it will then dictate to us while I spend days & nights out there with sandbag ballast trying to determine ifit allows myownself togo along.

At this time it appears that when all is said & done there will be much more said than done.

Many people have a certain inherent resistance to things that are a lot different, even a little different. This one single fact even when paying for assistance has met me all my life & may indeed follow me to the boneyard. However, I happen tobe one of those to expect nothing in order to avoid the fate of failure.

Anyone see what happened to the Crown Princess & the hard port turn in the Atlantic? I know already that most likely smoking cigarettes caused it!

Later, if not sooner. Still have 100 or so in the Gallery to see yet.

Thanx Gben

[kach22i]

Originally Posted by Gbenz

Would still like to hear if itis ok to use a larger diameter center than the two outside pontoons.

Every Trimaran I've seen pictures of has had a center pontoon/hull/sponson which runs full length and extends at the bow well in advance of the side pontoons.

The side pontoons are really just skegs which under most conditions may give extra buoyancy used to stablize the craft at extreen sideway angles. Maybe that's just one type of trimaran, or a really bad observation on my part, I'm no expert.

You may want too look/post in other sections of this board.

Like here (Multihulls):
http://boatdesign.net/forums/forumdisplay.php?f=31

In anycase, I'd also ask the airboat guys to rig the entire engine and propeller assembly on adjustable rails so you can get the center of gravity and thrust just right. I'm sure there is a way to engineer the exact power assembly location, but with any prototype/experiment you may not get it right the first time. One can only hope to get it close enough when you are charting new waters of technology. Of course if you had unlimited resources and computer modeling resources for fluid dynamic animation it could be a different story.

[Gbenz]

Thanx Kach,

Just as you say the heavy tbar stringers used to secure the engine mounts in airboats generally multi hole for the purpose of moving the engine fore or aft if need be.

Just as info Playcraft Boats at St Cloud fl claims to hold the speed record for Tritoons at 81mph. The pic showed the boat completely clear of the water at that speed except for the two 300hp outboards. Looked like abt 22 or 24 length but was not stated. We could be almost happy with one half of all that.

I've read someplace where it gave displacement per pound of weight & cannot go back toit. Does anyone have this info. With this I can at least do a little on my own beany for the very basic faults.

Foils really got our crazy heads fumbeled if not spun but this would have tobe very minute scale that would function among the pontoons for later plaything. May have all 3 tubes built for ob's just in case. Will need to stay 102in or less width for highway travel(sorry it took all this time to say it).

Will be in touch with U Fab in Canada 1st of wk.

Thanx agn Kach,

Gben