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Apr 01, 2016, 12:25 PM
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Build Log

1/32 Scale Build of WWII Woban Class Harbor Tug


I am going to be building a 1/32 scale Woban Class harbor tug. The tug is to used as a rescue tug for my airplanes and a FE hydroplane that I am currently building. Here is the link to the hydro build log: (https://www.rcgroups.com/forums/show....php?t=2603650)

A couple of these tugs were at Pearl Harbor. A brief summary from Wikipedia below:


USS Nokomis (YT-142/YTB-142/YTM-142) was a Woban-class harbor tug built in Bremerton, Wash, and assigned to Pearl Harbor, Hawaii, in 1940. Nokomis was present during the Japanese attack on Pearl Harbor, December 7, 1941. She was the first vessel on scene at the USS Arizona, and was called off by the officers on deck because of the imminent explosion of the battery below deck. It then left and helped beach the USS Nevada, with Hoga (YT-146), and YT-153. The beaching of the Nevada saved Pearl Harbor's mouth from being blocked. After that the USS Nokomis fought fires and dewatered the battleship USS California, for 3 days. This effort made the California salvageable, to be recommissioned again later in the war. Nokomis was also the last vessel to move the surviving YC-699 barge prior to the Japanese attack on Pearl Harbor. Post-war she continued serving Pearl Harbor ships until she was decommissioned in May 1973, and eventually sold for "scrap" to Crowley, in San Francisco. She was renamed Sea Serpent and served many years in the San Francisco Bay as a tug and fire boat. In 1989, after the Loma Prieta earthquake in the SF Bay area, Nokomis and Hoga (which had been serving the City of Oakland as a fireboat) fought fires alongside each other again.

A few pictures attached for reference.
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Apr 01, 2016, 12:37 PM
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...........
Last edited by Tim B.; Oct 23, 2017 at 07:38 PM.
Apr 01, 2016, 12:58 PM
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.

Mark
Apr 01, 2016, 01:03 PM
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.........:
Last edited by Tim B.; Oct 23, 2017 at 07:38 PM.
Apr 01, 2016, 01:28 PM
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The USS Hoga is a Woban Class tug that served along side the Nokomis at Pearl Harbor that is currently a museum ship in Little Rock, Arkansas. I knew it was in Arkansas but I did not know it was in Little Rock. I go there occasionally for work and will have to check it out next time I am there.

Sounds like they are still working on the inside but it is available for viewing from the outside.
Last edited by mmalmsten; Apr 01, 2016 at 08:12 PM.
Apr 01, 2016, 08:08 PM
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I will be building this from my own CAD design of the Nokomis. I came across the Nokomis drawings below when searching the web for free tug plans. I was drawn to the lines of this boat immediately.

At 1/32 scale the boat will be roughly 36 inches long.

There was just enough information in the drawings to get what I think is a fairly accurate representation of the hull, given I only had 4 mid-ship sections to work with from the drawings.

I was able to use the geometry from the Hold & Platform and the Inner Bottom & Hold drawings to determine the beam of the hull along various stations. I was also able to extract the width of the hull at the deck from the Hold & Platform drawing.

The height of of these widths relative to a datum was able to be extracted from the Inboard Profile drawing.

Using the widths and heights at various center line stations allowed me to plot the points in a 2D CAD package allowing me to fit a spline though the points and create multiple hull profiles.

I am almost done with the CAD work for the hull and will start the hull build up soon. In the next couple of days I will post more details of the actual design.

I will definitely have some questions regarding the set up, specifically around the prop, stuffing tube, drive shaft and motor.

I look forward to any input and comments as this build progresses.
Apr 01, 2016, 08:13 PM
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....................
Last edited by Tim B.; Oct 23, 2017 at 07:38 PM.
Apr 02, 2016, 07:13 AM
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This is going to be a very nice looking model.
Apr 02, 2016, 09:20 PM
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Most of my experience in building models is in airplanes and am hoping for some help/insight in picking out the right hardware for this boat. Any guidance or feedback on my choices below are appreciated.

The propeller is the easiest for me to figure out so lets start there and work forward.

Based upon the drawings a scale prop would be 3.5" diameter. I am currently considering the 3 bladed 3.5 prop (picture below) form Harbor Models. From what I can tell this is threaded and will fit on a 3/16" shaft.

The shaft I am considering, also from Harbor Models is the 3/16" shaft and stuffing tube (picture below). From what I can tell the threads on this shaft are compatible with the propeller. It says it comes with a nylon washer and a jam nut. Not sure what this is but it sounds like maybe the propeller is tightened up against it.

Next I would need a coupler to join the shaft to the motor. To select the coupler requires knowing the motor shaft size.

So, moving onto the motor it looks like a good choice, again from Harbor Models would be the 800 Direct Drive Motor w/ Mount (picture below).

The specs. for this motor are:

Top RPM: 5167
Runs on 12 Volts
3 Pole
Maximum amperage draw: 5.28amps
Will efectively propel a 36" deep vee boat with a 2" prop Can also turn props up to 3.5" @ 2500 RPM
Motor mount included.
Overall Length: 4 1/4"
Can Length: 3"
Can Diameter: 2"
Drive Shaft Diameter: 1/4"
Drive Shaft Length: 1/2"

Now knowing the motor shaft I can pick out a coupler that joins the 3/16"driveshaft to the 1/4" motor shaft. This is easy as I just pick the diameters of each shaft to order the coupler. It looks like the only couplers Harbor Models sells are plastic (picture below). I assume there may be better options and would look around more before selecting this one.

Looking forward to any feedback, guidance and suggestions to make sure I am heading down the right path.

Mike
Apr 02, 2016, 11:50 PM
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I bought one of those Harbor Models stuffing boxes and wasn't very impressed with the quality. The idea is that you cut down the tube and the plain end of the shaft to whatever length you need and push-fit the bearings. In reality I had to borrow some green Loctite from work as the bearings were too loose in the tube, and had to cut both ends from the shaft in order to straighten it enough to run well in the bearings.

You are right about the function of the jam nut. Tighten the prop against it, then turn it back an eighth of a turn or so to prevent the prop from spinning off the shaft.

That single-Kardan coupler will do a fine job of connecting motor and prop shafts, but you must make sure the shafts are concentric and not misaligned as it really can only take an angular misalignment. Putting two of them back to back to form a double-Kardan joint will absorb much more misalignment, both angular and parallel.
Apr 03, 2016, 09:40 AM
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One Stop Shopping


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Last edited by Tim B.; Oct 23, 2017 at 07:38 PM.
Apr 03, 2016, 09:43 AM
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Raboesch roller bearing stuffing box


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Last edited by Tim B.; Oct 23, 2017 at 07:38 PM.
Apr 03, 2016, 10:06 AM
r/c ships and workboats
Nice project and the gear you are looking at will work. Would recommend putting a pully or gear set on that motor to increase running time and reduce amp draw on battery/electronics when starting to turn the prop.

( need to get working on mine again since the mold is here)
Apr 04, 2016, 09:39 AM
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Quote:
Originally Posted by keith S
Would recommend putting a pully or gear set on that motor to increase running time and reduce amp draw on battery/electronics when starting to turn the prop.
Thanks Keith. Would I buy this motor and add a gear or pulley or buy a motor same size that comes geared/pulley'd off the shelf?

I looked around and only saw the later. Any insight/guidance is appreciated.

Mike
Apr 04, 2016, 09:51 AM
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Quote:
Originally Posted by Tim B.
Looks like Harbor no longer have Raboesh stuffing boxes, several members here use them as a matter of course, a few bucks more.

He may still have some in stock.
Thanks Tim.

This answers a key question I had, mainly how do you keep water out of the boat.

For the hydroplane I am building the stuffing tub ends above the water line. Even then these boats don't spend nearly as much time on the water as a tug.

So I will be using a Raboesch stuffing box. Looks like the short version of 300-11 should work. These are metric and the propellers I see that are 3.5" diameter are not.

Any suggestions/insight as to what people do here would be appreciated.

Mike


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