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Marsh Hawk Airboat

January 21, 2009



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Marsh Hawk

Marsh Hawk Radio Control Airboat

Completed Summer 1990

 
 

Airfield Models (http://www.airfieldmodels.com/)Prototype Specifications and Equipment

Length: 50"
Width 22"
Engine: O.S. 1.08
Displacement 9-1/4 lbs
Servos (2): Rudders and Throttle
 
 

About Marsh Hawk

I thought a boat would be fun, but I didn't want to mess around with a "proper" boat and all the support equipment necessary.  I knew it wasn't something I would want to continue with, so something simple, yet fun was in order.  I also have an interest in float planes, so a retrieval craft for aircraft that are dead in the water would be nice to have as well.

Given these requirements an airboat or "swamp buggy" as they're sometimes known seemed to be perfect.  It could be built to use an engine that I'm already familiar with, requires no special running hardware and is very simple in its operation.  The only equipment that I would need would be a radio that uses an FCC designated ground frequency.

Over a period of several years I sketched a variety of airboat designs.  These ran the gamut from Everglades type swamp buggies to twin sponson boats with welded steel or aluminum rods that would connect the sponsons to an engine/radio pod.  I wanted something that would be different from any other airboat I had seen.  The final result was the Marsh Hawk which was completed in 1990.

 
 

Construction

The Marsh Hawk was built almost entirely from 1/8" veneer plywood.   It was incredibly inexpensive to build.  In fact, the entire project cost around $125.00, over half of that being the finishing materials.  This is the first boat I ever built.  I knew nothing about them other than they are supposed to float on the water.

I had some data on buoyancy and formulas for determining how much volume was necessary to support a given weight.  I neglected to use any of this information and lucked out in spite of myself.

Marsh Hawk Hull PartsWhen I started on this project, I did not have a saw large enough to cut down the plywood so I drove around town talking to cabinet makers to find out how much they would charge to cut a few parts for me.  I couldn't believe some of the quotes I received.

I happened to stop into one shop, Mayo Cabinet Works in Gainesville, Florida that was owned by a very nice gentleman who said "Do you know how to use a band saw?  There it is."  and set me loose in his shop.  He did not charge me a dime even though he had to stop what he was doing to come over and show me where the power switch was.

I spent an entire afternoon in his shop cutting out hull formers and the planking.  He only asked that if I ever become famous that I give him credit for helping me with the project.  I doubt I will ever be famous, but he does deserve a lot of credit for being a genuinely nice and helpful person.

A few months later I was building a cabinet to store my wood in and had him cut the pieces for me.  I did pay for that work.  I needed one more short length of 2 x 2 to complete the project and he gave me the piece.  When I started driving screws into it, they were being twisted in half.

He broke out laughing when I came back to his shop before I ever said a word.  He knew he had given me a rock-hard piece of oak.   Jokers... got to love 'em.  Anyway, he's a nice guy and if you ever need cabinets made or any other wood work, talk to him first.

After I had all the pieces I needed, I built the boat in about a month of spare time.   It was completely covered with fiberglass cloth and then sprayed with automotive primer.  My friend, Barney, who has done auto refinishing for years taught me how to use my Badger touch-up gun properly and everything I needed to know to put on a great spray finish from prep through the last coat of paint.  The finish turned out better than I hoped for.

Before the finish, coats, however, I placed the primered hull in a swimming pool to check it for leaks.  I was a little concerned about the fact that it sank about 2/3 into the water leaving only the very top of the hull was above water.  The boat is a tunnel-hull design, so my hope was that as the boat gathered speed it would skim the water as it was designed to do.  This is exactly what happened.

 
 

Running

On the first day of test runs I took it out the engine kept dying and I assumed it was because water-spray was going into the carburetor.  I added a plate about 1/2" in front of the carburetor and the problem was resolved.  The boat ran well.  However, the streamlined engine pod support resisted efforts to turn.

Torque also has a large affect on the boat.  It turns much more sharply in left turns than in right turns (or maybe it is the other way around I do not remember).   The next version will have an all flying rudders (no fixed fins).  At speed, the boat spends more time in the air than on the water.  It looks like it is flying about an inch above the surface.

The most unfortunate thing is that I never managed to get a photo of Marsh Hawk running at full throttle.  Nobody who saw it run knew how to use the camera and they were all afraid to run her.  I begged, pleaded, offered cash... but nothing worked.  The next photo is Marsh Hawk at about 1/2 - 2/3 throttle.

Marsh Hawk skimming the lake

The next time I took the boat out there were some guys out with their racing boats.  One of them had a radar gun and clocked my boat at 59+ mph in a straight run.  They commented that I had built a very good hull.  Then they asked me to get my boat out of the water because they wanted to race.

 
 

The Present

When I entered the Army, the movers packed the model in such a manner that it was bulging the sides of the box.

Both rudder assemblies were completely destroyed, the engine pod was cracked and the joint where the pod support entered the hull was cracked.  There were also miscellaneous dings, dents and cracks all over the hull.  When I went to make a claim, the Army told me they would pay me $10.  When I returned from Hawaii three years later, the Marsh Hawk was damaged even further.

Marsh Hawk has been sitting in a corner patiently waiting for me to do something with it.  I am not sure if I will ever repair it.  I may update the drawings to revise a few things and build another.  It sure was a fun model while it lasted though.

Marsh Hawk II - Twin Turbine Powered Airboat.In the mean time, I have made a few sketches of a twin turbine model named Marsh Hawk II.

I am not sure how turbines react when they suck water in, but if you have a couple spares lying around that you would like to donate to the experiment, I will let you know what I find out. Cool people give me turbine engines.

 
 

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Copyright 2002 Paul K. Johnson