| Dumas prop No. 3115. 2" pitch. Nice
shape although it was a little hard to balance. Balancing instructions
were included. |
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| Note the very long hub and deeper than we
need slot for the drive dog. |
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| I "carefully" ground away the front
hub and drive dog slot. To ensure it was square for good contact with the
tug's drive dog (and so square to the stern tube's bearing) I inserted a
shaft into the prop and lightly spun it against the sander to avoid an
angle on the face of the prop. Wear a dust mask. |
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| I also shortened the hub on the back (prop
nut) side as far as I could without sanding into the tips of the blades.
Here you see the 1/8" nylon pressure tubing I used as a sleeve so
this 3/16" shaft prop would fit the tug's 1/8" shaft. |
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| The balanced and polished prop looks like
this compared to the stock prop. It could use finer polishing on the
surface but I got lazy. Note how the hole looks a little off-center. That
may have been the source of my balancing difficulty. |
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| Finally, I ground a small slot for the drive
dog to engage. Trial and error to make sure they fit together. |
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| This is the mounted prop. It has a nice scale
look compared to the plastic prop. However, for the price of this brass
prop, you can buy a dozen plastic props. Still, this looks NICE! |
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| With 7 cells, you have power to spare. At
full throttle, note the swell at the stern. It is up to the rub rail. With
6 cells you get to "hull speed" in 4 seconds. With 7 cells, you
are there in 3 seconds. Hit reverse, and you will stop in 1/2 boat length
vs. 2 lengths with the stock prop. This prop doesn't cavitate in reverse
like the stock nylon prop does. The quicker response doesn't distract from
its scale appearance. |
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Nice wave pattern. Just enough bow wake to
create a twin set of bubbles behind the tug. More test data to follow.
| Stock Tug |
6 cells |
7 cells |
| Amp Draw - Static Pull |
.50 Amp |
.63 Amp |
| Thrust - Static Pull |
4.0 Ounces |
5.0 Ounces |
|
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TM