Kobus's Dozer Boat Build

These little boats are very agile, specifically developed to bring logs into the sawmill. I wanted to build a radio controlled one, but since they are very small in real life (only about 5,5m long) at 1/35 scale, it would only be 158mm long and could fit on the palm of my hand.This was the challenge!  Click on the image above for a slide show.

Working the logs. They can turn very sharply and are extremely agile. The pilots know their art and it is a pleasure watching one of them working, reminds me of an English sheepdog.

Typical dozer boat waiting for the day's work.

Typical dozer boat waiting for the day's work.

Typical cockpit of these little boats, they work very hard and take quite a beating.

Copy of some original plans from a local shipyard.

Top view.

During my research I found that some of our club members worked on this idea in the 80s, but the electronics in those days was still too big and clumsy.

A vacuum formed sheet, from a few that Ulrich and Gary King still had. The plastic was hard and brittle with age.
 

First I had to design a drive system that is similar to the full size boat. A dentists' drill was luckily just about the right size.

Some modification required & a prop at the right size & I could start the drive unit.

The electric motor from a park flyer model aircraft and some bits & pieces made up with some gears from a toy gearbox.

A park flyer servo and miniature drone radio control & speed control electronics was added.

Lithium Polymer ultra light batteries & battery charger (the red printed circuit). The coin gives a perspective of scale.

Many attempts and some bad language, until I had a drive unit. The motor on the left drives the yellow gear which drives the propeller via the dentist drills' 90 degree gears. The park flyer servo on the right rotates the double shaft via the white gear so that the whole inner part of the drive rotates for steering and reverse. Very similar to the full size boat.

Added view to display the steering servo & gears.

These boats have a steel 'basket' to protect the prop from the logs & other flotsam. Steel wire bent & soldered & plastic sheet to form the seating ring.

The hull, 158mm long, cut from the heat & vacuum formed sheet & brass 'teeth' to grip the logs are added.

The hull ready to be built up. I made some rough calculations to see how much the stuff I need to put inside can weigh before she will be too low in the water. Not much leeway!

Steel basket fitted.

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These boats get bashed by the logs, so they have a lot of re-enforcement on the hull.

Triangular strips of plastic are heated & bent to follow the hull's curve. Clamps hold them in place until the glue is dry.

Fitting the drive unit in the hull.

Hull ready for spray-painting & the deck to be fitted.

The electronics fitted, deck fitted & non-slip paint finish applied to the deck. Miniature model aircraft on/off switch for the electronics gives an idea of how small the boats is.

The radio receiver & speed controller from the drone electronics had to have a hinge at the back so that I can lift the whole unit up in order to get to the battery!

                                                                    

Toothpick to keep the hinge open so I can get to the battery.

Building the pilot's cabin and engine cover.

Trial fit of the superstructure on the hull. I also did a float test at this stage to see if my weight calculations were good. It floated just right!

Upper section in the spray booth for a coat or two of the yellow paint.

These boats often work at night, so they have strong lights on the cabin roof. I could not find anything at that scale, so I had to make some. A broken electrical switch in my scrap box provided the back parts for the flood lights.

I had some transparent plastic headlight lenses left over from a model car kit. Combined with the copper switch parts, I could make some scale lights.

Lights ready to be fitted.

Now I needed a driver. I found a plastic kit on E-bay of 1/35 WW 2 US army jeep drivers & decided that I could modify the guy at the bottom left to be a dozer boat pilot.

First I had to make a seat, then some orthopedic surgery required by the army guy, but his transformation started taking shape.

Made a steering wheel & got it all lined up & in a natural looking position.

Using a very small brush for his face, eyes & hands, and a bigger brush to change his army uniform to a worker's worn-out denim outfit.

Fitting the pilot & adding some decals kindly donated by a club member who actually worked for this company.

Ready for her sea trials.