The Three Star River Tow Boat
Mark IV

By Michael Ross

Introduction:
A number of years ago Jim Smith, a long time member of the club, obtained a set of plans for "The Battling Polo Tug." He built his first one of these boats from those plans, and was able to determine that the boat required a few changes. His suggestions included increasing the width of the hull for added stability, and to increase the draft of the hull.
Back in 2001 I was able to obtain a copy of these plans, along with the article that Mr. Smith had written to explain the changes that he suggested. The original plans were not very good, and trying to incorporate Mr. Smith's suggestions on the fly was a little more work than I really wanted to do. So I sat down at my trusty computer, and dusted off an old copy of AutoCAD, and generated a new set of plans that incorporated Mr. Smith's suggested changes.
In the beginning we all just referred to these boats as “Polo Tugs” but the Edina Model Yacht Club elected to change the name of these boats to “The 3 Star River Tow Boat”, or as I often call them The 3S RTB’s.
At the present time (to the best of my knowledge) the club has not established any specifications, or standards for motors, propellers, batteries, drive shafts, stuffing boxes or any other hardware. All these things are left up to the builder, and to available materials. The materials called out are only suggestions, and can be replaced with whatever materials the builder may have available to them.

Note of Caution: Many of the dimensions on the drawings are dependent on using the suggested materials. If the builder chooses to use materials other than what is suggested on the drawings, care should be taken to adjust the dimensions appropriately. For example if 1/8 thick Balsa is used where 1/16 Bass is suggested, the dimensions of all adjoining objects may need to be adjusted for the extra material thickness.

The original plans for “The Battling RC “Polo Tug” Event - Regulation Design For Special Events in RC - “Work Boats”“ As designed by Joe E. Brown of Western Rivers Work Boats, and William Zumwalt of Sink’um & Float’us Salvage Co. As adapted by The St. Louis Admirals RC Model Boat Club.
There are a number of dimensioning errors in these original plans, and so many of the dimensions just do not add up right. So I created the layout for the Mark I, in order to correct these dimensioning errors.

While based on the original “Polo Tug” designs, the Mk. II incorporates the changes that Mr. Smith has suggested. Including his design for the “Rudder Cross”.

Is based on Mr. Smiths suggestions for the original “Polo Tug”, while incorporating a number of my own ideas, and is inspired by one of the boats actually built by Mr. Smith.
Where the Mk. I, and the Mk. II incorporate the original “fast-back” cabin design. The Mk. III is based more on an typical River Tow Boat design, that we might see around here.

Note:Printed copies for the complete set of plans for the Mk. III might still be available

I have incorporated a number of design changes that I hope will improve the operation of the boat. I have included a few suggestions from other people who have also built the Mk. III. The Mk. III called for the Rudders to be fabricated from Brass. This caused some problems for people who did not have access to metal working tools. Those who wish to, can still use 3/16 Thk. Brass as called for in the Mk. III plans.
The Mk. I - III are designed to use a smaller motor, such as the Graupner 400, or the Pitman that Mr. Smith is using.
A number of us have learned that a 550 size motor is just a little too big. Short of glueing the motor can to the bottom of the hull, a 550 requires the propeller shaft to be mounted at an angle of approximately five to ten degrees. At higher speeds this has caused the propeller to push the stern of the boat up, causing the bow to be submerged.
So I have increased the draft by a half inch, to allow for a 550 size motor to be used, while maintaining a more horizontal drive shaft.
The increase in the draft, also allows for wider rudders, which should provide better handling. I have also decreased the attack angle of the bow. It has been my observation that the bow angle was just too shallow.
I have made some slight modifications to the design of the Main Cabin. Now the builder has a choice in building options.

1.) The Mk. IVA. Building the cabin assemblies so that the entire cabin structure is removed to gain access to the interior.

2.) The Mk. IVB. Attach the walls of the Main Cabin to the deck, and then gain access to the interior by removing the cabin roof(s). I have added a couple of ‘cat walks’ out to the Bow Knees. No special reason. I just think that they look better that way. These ‘cat-walks’ are optional, and can be left off if you choose.
In any event, the Bow Knees are now shorter (as measured from the deck) then they were in the Mk. III. Though they are longer in over all length than before. The changes to the bow, allow the Knees to be extended further below the water line, which should make pushing other boats (should be read as assisting stranded boats) easier.
The shorter Knees, along with the old bow angle made it too easy to ride up over some boats when attempting to push them.

The Three Star River Tow Boat Mark IV Introduction
The Three Star River Tow Boat Mark IV Plans