Hobbies And Interests
Things You'll Need
Instructions
Making the Water Tunnel
Find the tunnel center-line on the hull. You will make a tunnel through the hull that acts as a channel for the water pushed into and through the tunnel as the thruster spins. The tunnel position should be forward and low with at least 6 inches between the waterline and the tunnel's top.
Drill a 1/4-inch pilot hole at the tunnel center line on the underside of the hull. Allow 2-1/2 to 3 inches of clearance near the bulkheads to remove the hydraulic motor assembly, which requires removal from time to time for servicing and maintenance.
Insert a 1/4-inch diameter steel rod into the hole. Push the rod through the hole until it makes contact with the opposite side of the hull. Level the rod that aligns it to the boat's fore and aft at right angles.
Mark the location where the rod makes contact on the opposite side of the hull. Drill another pilot hole at this location from inside the yacht with the 1/4-inch drill bit.
Measure the outer diameter of the tube. Add 1/8-inch to the diameter size when preparing to cut the hole for the tube insertion. The additional space allows room for the epoxy adhesive you will apply to the tube. Mark the location for the holes to be cut to the appropriate size by creating a "scribe line."
Connect the hole saw attachment to the drill and bore the hole within the scribe line, leaving a 1/8-inch space.
Mix the epoxy with micro-balloons, applying it to the tunnel and along the inner walls of the hole to seal the core material.
Clamp the tunnel in place within the hull to the position where it will be permanently mounted. Confirm that the tunnel is level. You want the tunnel at a 90-degree angle to the boat's center-line.
Mix a combination of the epoxy with silica micro-balloons and cabosil thixotropic agent. It should be the consistency of heavy paste. Apply it to the joints where the tube connects with both sides of the hull -- inside and out.
Draw a line around the excess tube to denote where you will make your next cuts to the hull. Your cuts will be on each side of the tunnel so that it will fit flush against the hull. Make your cuts with a carbide blade hand saw. Allow the epoxy to dry overnight.
Sand away any excess epoxy and clean the work surface before you begin work again.
Apply a liberal amount of fiberglass epoxy, saturating several sheets of woven roving -- heavy-duty fiberglass cloth. Apply 10 to 12 layers of roving, extending 10 inches onto the hull at the site of the tunnel. Apply the same amount of layers 6 inches within the tunnel from the opening. Be sure to apply roving to both sides of the hull.
Sand the exterior joints that connect the tunnel with the epoxy mixture with the cabosil thixotropic mixture made the previous day.
Fitting the Saddle
Prepare the bow thruster by taking apart its assembly. Unfasten the prop nuts and zincs located at the prop shafts to remove the propellers.
Unscrew the 12 1/4- by-20-inch hexagonal cap screws located at the top edge of the gearbox. Remove the 3/8-inch nuts at the ends of the edge as well. This will allow you to remove the thruster saddle. Use the saddle to outline its large center hole into the tunnel.
Measure the location where you want to mount the thruster onto the tunnel, leaving a 2 1/2- to 3-inch clearance for the hydraulic motor assembly removal as noted earlier.
Cut a hole where you outlined the area for the saddle on the tunnel. Place the long end of the saddle through the large hole, clamping it to the tunnel.
Drill four holes into each side of the saddle. Secure each drilled hole with a carriage bolt and nut before drilling the next. Remove the saddle. Square the holes so they will allow the proper fit for the carriage bolts. The saddle should be centered and aligned with the tunnel to prevent the props from rubbing against the tunnel.
Installing the Bow Thruster
Sand the tunnel once again, removing the shine from the epoxy resin. Wipe away the dust with a solvent and rag.
Fit the saddle onto the tunnel, bolting it back into place to full torque. Use 35 foot-pounds of torque on the 3/8-inch bolts and 25 foot-pounds for the 5/16-inch fasteners. Check to see that the saddle is still properly aligned and the prop will be able to turn. If so, disassemble the saddle.
Apply a polysulfide sealant to both the surface of the saddle and the tunnel. Reassemble the saddle back in place on the tunnel. Remove any excess sealant from the 3/8-inch carriage bolts as you screw them through the top of the saddle. You want a clean thread for the placement of the nut. Cover the assembly and let it cure for 24 hours.
Insert the O-ring in the saddle positioned in its center. Carefully place the gearbox into the hole of the saddle.
Start each of the 1/4-inch fasteners. Place a 3/8-inch nut and washer on each carriage bolt at the gearbox within the saddle. Tighten each bolt, evenly torquing each twice. Re-install the props and zincs onto the prop shafts, securing them with Locktiteòon the threads and torquing them to 50 foot-pounds with a plumber's basin wrench for the appropriate amount of pressure.