Port side bowthruster guards

Now that the flanges are finished, I thought it might be a good idea to put some sort of guard on both sides of the tunnels. I toyed with the idea of welding tabs and then bolting in these horizontal bars, but that seemed like excessive work. I decided in the end to just directly weld in these 3/4 inch thick by 2 inch wide flat bars into the tunnels. I calculated that I can slide the propellors in through the center space between the bars and then rotate them to get them on to shafts. This way I can weld, sandblast and paint the tunnels with the bars inplace and then install the units in through the top of the saddle.


The bars are parallel to the keel and the expected final fore and aft trim of the boat. I did this in order to minimize hydrodynamic resistance when the boat is eventually moving through the water. It is 4 inches between the bars – enough room to still stick a sizeable piece of wood through, which isn’t ideal. I am hoping most wood and other debris will be floating and these tunnels should be well underwater. I guess I’m more worried about rope which could get sucked into the blades and tangle up the works. But these bars at 3/4″ thick will definitely take some punishment if I should hit anything.


I was able to talk to someone at Wesmar in the parts department this week. I have ordered all the missing parts for the second unit. They also solved a few mysteries I have been thinking about. There are zinc anodes that go on the end of each shaft! When dryfitting the blades on the shafts, it seemed like the nut screwed on too far and didn’t really seat the propellor onto the keyway and the shaft. The zinc explains that.

They also told me not to use a gasket between the saddle and the steel tunnel, unless the spacing of the center of the propellor was off from the center of the tunnel. The ID of the tunnel is 13 inches and the prop diameter is 12 inches leaving a 1/2 inch gap all around. They recommended just using 3M 5200 series polyurethane marine sealant between the saddle and the tunnel and then bolting it up tight. Same for the connection between the saddle and the unit. I went to McMaster-Carr online and ordered 3/8″ bronze bolts, flat washers, split lock washers and nuts for both units.


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  1. Posted November 4, 2009 at 11:55 pm | Permalink

    wow. Watching the progress is riveting. Oh, sorry.
    Beautiful photos. Good luck!

    • Posted November 5, 2009 at 4:51 am | Permalink

      Thanks for watching and the pun!

  2. Posted November 5, 2009 at 5:29 am | Permalink

    tiny little steps . . . are steps nonetheless. i’ll stop by again one o these days. by the way, i’ve spoken w hank, of livet. cheers

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