Friday, July 12, 2013

Bow-thruster project underway!

As a rule, I don't care much for holes in boats. Much less an 8" diameter hole that goes clear through the bow. But, this is a necessary step in getting the bow-thrusters installed in SeaClearly. Not, by any means, the first step.

First, the questions of:
Side-Power SE100

  • Which bow-thrusters?
  • How much thrust?
  • Where can they fit?
  • Where can all of the components fit? (Batteries, chargers, motors, controls, etc)
  • Are we crazy?
  • What are we going to lose in the process? Storage? Water tank?

The specifications for the thrusters have a lot of parameters. Just a few key considerations are listed here.

  • The tunnel needs to be at located at least one-half the tunnel diameter below the working waterline. One full diameter is better. But it needs to be one diameter above the bottom also.
  • The length of the tunnel needs to be between 2 and 4 times the diameter. Never more than 6 times the diameter.
  • It needs to be as far forward as possible but still meet all of the criteria above. 

It originally looked like the optimal placement would be right through our forward water tank. Not ideal. Much more work, lost water storage, undoing plumbing. Not good.

After a lot of investigation and evaluation, we came up with a plan that works much better. We could move back just a bit and miss the water tank. This would put it through some underutilized lockers, and leave a large portion intact. The batteries can fit adjacent to the current house battery bank and even be switched to parallel with them in an emergency. The charger we are adding can be used as a backup for the existing batteries. We are feeling pretty good about it.

Thorough tenting with
 zipper door to forward cabin
Completely taped

So, we committed. First step was actually clearing out all of the stuff from the forward cabin. The next step involved tenting and taping so that the unavoidable dust could be contained.

New hatch in the center.

Then Bill, our installer, came out and we talked through  the process. I was pretty nervous and kept asking how to make sure we had the right spot. Finally he says 'Well, eventually, we have to make a hole'. I laughed at myself and away we went.

Bill cut a new hatch through the top of the berth and moved some plumbing out of the way. He marked the best spot on the inside of the hull for tunnel
placement, leaving enough room to work the fiberglass and mechanicals. Then, he stuck a drill bit through our boat.

Next, came a bigger hole. Two inches. Then, move to the other side. Another two inch hole. And then a pipe stuck all the way through as the starting point for the really big holes. Bill leveled up the pipe, decided to move the center up, enlarged the holes, raised the pipe up about an inch and wedged it in place. Level, straight.

Two inch pipe through. Tunnel on the ground.
Starboard inside, water tank forward.

So now, the really scary part. An 8" hole is bad enough but there is not one flat spot on a sailboat hull. So, the hole isn't round. It is some ridiculous convoluted shape that needs to be transferred to the hull. Fortunately, they have done this before. They have a cool tool - a jig, of sorts - that they slide over the two inch pipe. This allows them to spin a marker around the pipe and draw the appropriate shape onto the curved hull surface. Pretty frickin' neat. The result is a very odd shape that will accept a perfectly round fiberglass tube. Twenty minutes with a Sawsall and we have big holes in our boat.


That is as far as we got today. More later!


  1. Very interesting. I think Bill is a runner, everything will be fine. :)

    1. Yes, Bill has the right body type for a boat carpenter. Thin, wiry, fits into small spaces:)

  2. Fascinating. It actually seems like a good location. Did you measure the thickness of the fiberglass outside of the core at that spot?

    1. Hi Thierry, Glass is 5/16 on each side of the core.

  3. I just realized you drilled through my beer locker!

    1. The fiberglass tube will act as a chiller circulating water around the locker!

  4. OK, Duane, The suspense is killing me. No update for more than a week! Is it done yet?

  5. Sorry:) Working on a new post.

  6. Thank you for this great tutorial! Thought I might share this website I came accross which I found very useful: