Giant Holes in Boat!

February 5, 2017  Hours spent building to date:  3,369

Spent most of the week cutting big holes in the bow of the boat for installation of a Vetus 25 bow thruster.  Bow thrusters were pretty much confined to luxury yachts when I started sailing, but new technology has made them accessible to almost any cruiser. For a boat such as Tardis with a substantial deckhouse, single engine and not much boat in the water, a bow thruster is a tremendous tool.  Basically it’s just a small propeller in a tunnel that runs through the bow driven by a powerful electric motor up in the boat.  So even when the boat is stopped with no steerage way, blowing around in the wind, the thruster can still move the bow into a dock or around a corner.

I installed one on Memsahib, and it was a lifesaver.  Memsahib had a long, shallow keel, barndoor rudder and basically no reverse.  So her turning radius was 40 yards.  126 dockings, 146 locks and countless tight turns on the Great Loop would have been nerve-racking without the thruster.  I know her turning radius was 40 yards because the Travelift pit at Norwalk Cove Marina is exactly 40 yards wide and the yard foreman told me, “When we turn the leaky tiki around in here, we clear the side by about an inch.”

Still, putting a thruster in is hard, tricky work.  The tunnel is only about 4 1/2 inches across, but it goes into the bow where the hull is sharply angled both down toward the keel and in toward the bow.  So the hole becomes a strange-looking conic section about five inches across and eight inches high, bulging on one side.

(I started this post at 28-9.  But after the next score I stopped, since the Atlanta defense was looking a little tired, and New England could tie with the right combination of points.  Then at 28-20, I woke up Molly and said, “They have a chance and plenty of time.”  The great Tom Brady and his bunch of elderly and rag-bag receivers have done it again.  Now back to bow thrusters.)

The key to pulling this off is to make a pattern exactly the size of the tunnel, and use small holes and positioning dowels, then increasingly larger holes and dowels to make absolutely sure the tunnel is in the right spot, square and level before even thinking about a saw.  Until the first saw cut, you can recover pretty easily.  Afterward would be a terrible patch job.  This installation was made a lot easier because I was able to use a reciprocating, plunge-type saw for the final cuts that didn’t even exist when I put the thruster in Memsahib.

Other work this week included gluing up all the cabinet doors and fixing the one that was too narrow by cutting off the stiles right at the rails, plowing out a new groove in the rails with the dado cutter, and replacing the stiles with new ones of correct length using cherry culled from the scrap pile.

Small dowel through the tunnel template.  This makes it east to cut to length, check for level and square and mark holes for larger dowel to come.

Small dowel run through the tunnel template. This makes it easy to cut to length, check for level and square and mark holes for larger dowel to come.

Large dowel all the way through -- level and square to the centerline.

Large dowel all the way through — level and square to the centerline.

Large dowel comes through the boat -- exactly where I wanted it.  But since it's a small hole, I could have adjusted from this point easily if there was a problem.

Large dowel comes through the boat — exactly where I wanted it. But since it’s still a small hole, I could have adjusted from this point easily if there was a problem.

Marking jig exactly the size of the tunnel.

Marking jig exactly the size of the tunnel centered using the big dowel.

Roughly marked out using a batten to extend the line from the jib to the boat.

Hole roughly marked out using a batten to extend the line from the jig to the boat.

Holes drilled parallel to the waterline, starting with 1/8-inch, then quarter then 3/8.  Held back from the line for a tight fit.

Holes drilled parallel to the waterline, starting with 1/8-inch, then quarter then 3/8. Held back from the line for a tight fit.

Hole after cutting with plunge saw.  Too small and rough, but will gradually be brought to a tight fit with the tube using a drum sander.

Hole after cutting with plunge saw. Too small and rough, but will gradually be brought to a tight fit with the tube using a drum sander.

Starboard side in.

Starboard side in.  Since the hole was cut overly small to avoid a cutting error, it took about an hour of sanding to get to a tight fit. 

Holes for the port side can be marked from the inside using the tube as a guide and a batten to extend the shape to the side of the boat.

Holes for the port side can be marked from the inside using the tube as a guide and a batten to extend the shape to the side of the boat.

Thruster tube in.  Decent fit.

Thruster tunnel in. Decent fit.

The giant holes -- port one hasn't been smoothed and fitted yet.

The giant holes — port one hasn’t been smoothed and fitted yet.

Thruster dry-fit on bench.  The thruster is offset so the prop ends up on the centerline and the weight is centered over the tube.

Thruster dry-fit on bench. The thruster is offset so the prop ends up on the centerline and the weight is centered over the tube.

Propeller fits well.

Propeller fits well and spins freely.

This is the tailpiece held into the shaft with goop and bolts.  The prop shaft runs through a small hole in the tailpiece up to the thruster motor.

This is the tailpiece held into the shaft with goop and bolts. The drive shaft runs through a small hole in the tailpiece up to the thruster motor.

Tube and thruster lower flange tacked into the boat with epoxy.  Lots more glass work to come.

Tube and thruster lower flange tacked into the boat with epoxy. Lots more glass work to come.

Cabinet doors ready for finishing.

Cabinet doors ready for finishing.

Head door

Head door

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One comment on “Giant Holes in Boat!

  1. PAT HARRIS
    February 6, 2017 at 9:50 am #

    AMAZING PROCESS AND CUTTING.
    You could be a brain surgeon.
    I’m impressed.

    Like

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