Airboat from Hell being considered

[mholt]

A while back, I found an image of an old airboat. The more I looked at it, the more interesting it became. I'd like to prepare plans for it. Maybe build it.

I think it's the prototype of the Tellier airboats. It was built in about 1913.

Of course, I'd make changes. I'd replace the flat, square floats with more boat-like ones. Perhaps with aircraft floats.

Comments?

[mholt]

So you'll know where I'm starting.

[AVari]

I have been considering something similar for some time. The design you are looking at, even with the proposed changes you mention, will not achieve what I think you are trying to do. What are you trying to achieve ?

[mholt]

Why not ask what I want to do before telling me it won't work out?

It's just an interesting idea, and I'd like to see what develops out of it.

[AVari]

The list of air driven water craft built since 1913 is almost endless. I think they eventually evolved into the WIG designs. The attraction of needing to climb out of the water to achieve high speed is still irresistable to most designers. The quest to reduce the planing/wetted surface to the minimum is still thought of as being an inescapable necessity to achieve very high speeds. Lifting clear of the water of course is the ultimate aim. Of course every solution has its problem - and what to do when these craft finally, after a monumental effort, lift out of the water has still to be satisfactorily resolved.
In which direction are you headed ? Or are we merely looking at restoring a vintage craft ? But as with vintage cars - very interesting to a select few but not often considered as a viable means of transportation.

[AVari]

Its been nearly a year now that I posted my deliberately provocative post regarding the flat bottomed, air driven, twin hulled craft being considered by mholt. I was hoping for some reaction by using the terms "still irresistable" and thought of being etc. "
There so far has not been a nibble from any designer seeking to challange my questioning of these two currently held iconic beliefs.
It would appear that designers are still pursuing these two concepts in their efforts to achieve high sppeds.
Has anyone else thought to challenge these two fundemantelly held beliefs requiring to be resolved in our quest for speeds ?

[cthippo]

So what would an alternative look like? A design that moved through the water at very high speed? The problem is that the speed / power curve is in exponential function and so in order to go really fast through the water you need an incredible amount of power. Look at the fastest things that move through the water, torpedoes. The US Mk 48 can travel through the water at 55 knots, but only for about 28 miles and it burns over a ton of fuel doing it. Wiki

The Russians have built a torpedo that can travel at 200+ knots, but accomplishes that speed using a rocket and a supercavitating nose which causes the torpedo to travel in a bubble through the water. It also burns over 2 tons of fuel for a range of only about 7-13 km. Wiki

So, yeah, it can be done, but I think you'll find the tradeoffs aren't worth it.

[AVari]

Lets ignore the torpedo for the moment.
Not having had the benefit (and inevitable limitation of outlook) of a formal marine science education, I am yet to be convinved of the inevitability of the speed/power curve limitation - inevitably referred to by marine designers.
This is just my point. Is such a result always inevitable or is it inevitable because thats just the way we do and build things now ?
I have been looking for someone to seriously look at such a possibility and you are the only one even to have asked what such a design would look like. Most designers dismiss such a possibility without question.
I think I may have the answer and have been looking for a "reputable", "willing" and perhaps more importantly "able" designer to seriously look at this problem without result.
This in spite of the obvious benefits on many levels - humanitarian etc. and perhaps more importantly financial.
No success to date.
Is anyone else out there willing to ponder such a possibility ?

[Submarine Tom]

Build it AVari, build it!!

-Tom

[Frosty]

Ive toyed wit this idea many times, a couple of sheets of alluminium and a handfull of rivets and an olde VW engine with a bit o wood whittled down as a prop.

Perhaps your design in your head is not as minimalist. However I see the theory of a swanp boat slightly different in so much as an air boat is for one thing only and that is flat calm shallow water with weeds in it. Making a double hull or one with floats on it would not get thro weeds at all.

It the flat hull and the air engine that is the 2 main parts of the concept to my opinion.

[cthippo]

The fundamental issue is that water is fairly dense and it doesn't compress much. in order for a boat to move it must push the water out of it's way, which requires a lot of energy. If you get the boat out of the water as in the example of planing hulls, airboats or WIGs then you only have to push air out of the way, which doesn't weigh much.

There gets to be a lot of other factors involved such as surface resistance, wave making, etc etc, but basically until you solve the fundamental problem of how to move water out of your way, you're kind of stuck.

[AVari]

So, just as I thought ..... The problem is to get it, water, out of the way so we can move forward.
Lets see, all we have to figure out now is "how much" water, "how fast" (we know the stuff is fairly easy to move slowly) and in our case also "where" to move it.
Am I right so far ??? guys ?? Help me here.

[Boston]

Cthippo

I would think the fundamental problem was resistance which on a planing hull is often reduced by ventilation, that concept being brought to its extreme by a hovercraft, so of all the possible solutions I would think some degree of ventilation is the most likely solution to gaining speed out of less resistance. Ventilate those pontoons somehow and you will go faster.

cheers

[cthippo]

Originally Posted by AVari

So, just as I thought ..... The problem is to get it, water, out of the way so we can move forward.
Lets see, all we have to figure out now is "how much" water, "how fast" (we know the stuff is fairly easy to move slowly) and in our case also "where" to move it.
Am I right so far ??? guys ?? Help me here.

Water is, I think, A non-Newtonian fluid in that the harder you push on it, the more resistance it has. This is why jumping off a dock into the water is no big deal, but hitting it from 100' up is like hitting concrete.

How much would be the displacement of the boat in question, and how fast would be determined by the speed you were moving through it.

One idea I had thinking about this would be to use a waterjet propulsion system where the intake was at the bow and the nozzle was just forward of the stern. The idea here is that the intake suction would create a "hole" in the water in front of the boat and the exhaust a "hump" behind the boat and so the boat would essentially ride the front of a wave of it's own creation. You would have to move a god-awful amount of water which would require an equal amount of power to have any effect.

Another idea, similar to what Boston is suggesting below, would be to force air out of small holes on the bow which would create a layer of bubbles between the hull and the water it was moving through, though in the end you're still displacing the water.

Originally Posted by Boston

Cthippo

I would think the fundamental problem was resistance which on a planing hull is often reduced by ventilation, that concept being brought to its extreme by a hovercraft, so of all the possible solutions I would think some degree of ventilation is the most likely solution to gaining speed out of less resistance. Ventilate those pontoons somehow and you will go faster.

cheers

I agree, but as I understand the question he's talking about a high speed displacement hull, which I don't think is possible without investing mahoosive amounts of power, but I'd live to be proven wrong.

[Submarine Tom]

Originally Posted by cthippo

The fundamental issue is that water is fairly dense and it doesn't compress much. in order for a boat to move it must push the water out of it's way, which requires a lot of energy. If you get the boat out of the water as in the example of planing hulls, airboats or WIGs then you only have to push air out of the way, which doesn't weigh much.

Water has a density of 1 and does not compress. Air is 800 times less dense than water and does compress.

80 cubic feet of air weighs about 6 pounds vs water where 80 cubic feet weighs about 5000 pounds.

cthippo, what is that ridiculous little picture by your name?

-Tom