aegir-ran

The anchor roller passes through the bow sprit. While steel tubes were used to prevent the bolts for the roller bracket from digging into the wood of the bow sprit, the bracket has still shifted causing the roller to dig into the bow sprit platform. I designed a brace and used SendCutSend to manufacture it out of 316 steel.

The bracket is bolted to the bow sprit with lag bolts behind the axial of the roller (outlined in red).

The bow thruster has been installed. To make the job easier, the equipment was installed from the bottom up, beginning with a bilge pump and the electronics. The electronics comprise of a Victron SmartShunt 1000 Amp Battery Monitor, a Victron DC-DC Orion-Tr Charger (which connects the lithium batteries that are under the V-berth to the house battery bank in the engine room), a Blue Sea Systems 7713 ML-RBS Remote Battery Switch (that can be used to remotely disconnect the bow thruster from the battery bank), and breakers/fuses. The electronics were mounted on a board to make it easier to service in the future. Note also two selves were fiberglassed in, a small shelf for the bilge pump and a larger shelf (at the bottom of the photo) that will be used to support the thruster motor. On the left of the photo is a support that will be used to support a third shelf for the batteries.

The transmission for the bow thruster was installed in the tube and a priming paint was applied.

A support for the bow thruster’s motor was fabricated from fiberglassed marine plywood. The stainless brackets were designed in Fusion 360 CAD software and were fabricated by SendCutSend.

A custom battery pan was also manufactured by SendCutSend.

Finally, a shelf for the batteries was glassed in, the bow thruster’s motor was installed and the batteries (two Battle Born 100Ah 12V LiFePO4 Deep Cycle Batteries) were installed.

The fiberglass tube for the bow thruster was installed. Under the V-berth, tie lines were dropped and pilot holes were drilled on the port and starboard side of the hull.

Using a string and two points on the keel, I confirmed the pilot holes were centered, then a jig was passed through the two pilot holes. The jig comprised of a steel rod that was sharpened to a point on one end and bent twice such that the point was a distance from the axis of the rod that was the radius of the fiberglass tube. Note the two red chalk marks that were used to confirm the pilot holes were centered (made by tying a piece of chalk to the end of a string that was taped to the leading edge of the hull). The jig was then used to scribe the hull.

A saber saw with a diamond blade was used to cut out the oval that was scribed.

Note the hull is 1-1/4″ thick where the holes were cut.

The tube fit the holes that were cut perfectly.

Before glassing the tube in, the hull was ground down past the gel coat.

Once glassed in, the excess tube was cut off, leaving enough of the tube protruding to create the leading hydrodynamic edge.

After glassing in the outside of the tube, the leading edge was flared to improve hydrodynamics. Cabosil (collodial silica), a very hard material, was used to flare the leading edge.

Low density (fairing) filler was used to smooth the installation.

Finally, the inside was fiberglassed.

The entire project took two weeks.

In preparation for installing a bow thruster during the next haul-out, I need to estimate the needed capacity. The box thruster must be capable of countering wind. The force applied by the wind onto the boat is determined by the factors including the wind speed, angle of wind attack, and lateral wind draft area of the boat. The wind pressure is given by the formula:

P = 1/2 × ρ × V² (lbf/sq.ft), where:

ρ (rho) represents the specific mass of air = 0.0752 lb/ft²

V is the velocity of the air in ft/s, where 1 knot = 1.688 ft/s

The wind-draft of the boat can be determined by multiplying the wind pressure by the wind draft area. The wind draft area is determined by the shape and the dimensions of the of the boat (its windage) and the wind angle, and the greatest wind-draft is created if the wind is at 90 degrees to the boat. An efficiency reduction factor is generally applied to account for windage, and a value of 0.75 is frequently used. To calculate the required torque to rotate a boat, we need to know the wind pressure and the length of the boat.

The Aegir-Ran has a LOD = 36 ft and the freeboard is about 3 ft, giving wind draft of 36 x 3 = 108 sq ft. Adding the cabin, hard dodger, and the sail pack adds perhaps 50 sq ft, which is why the efficiency reduction factor is often used. I will assume the lateral draft is 200 sq ft and I will not use an efficiency factor. Assuming we want to counteract a wind force of 25 knots, the wind pressure is:

P = 1/2 × (0.0752 lb/ft²) × [25 knots x 1.688 ft/(s x knot)] = 1.59 lbf/sq.ft

To counteract this wind pressure, we sill need the following amount of torque:

T = 1.59 lbf/sq.ft x 200 sq/ft x 36 ft/2 = 5,724 ft.lbs.

The thrust-force required is the torque divided divided by the distance from the bow thruster to the pivot point. In our case, we will assume we want to pivot about the stern, do the distance is essentially the LWL = 33 ft:

F = 5,724 ft.lbs. / 33 ft. = 173 lbf.

I have decided to install a 12 V Ventus bow thruster. Examining the specifications of the models, it seems the BOW7512D is the best model with a maximum thrust of 180 lbf.

A Garmin inReach GPSMAP 86i has been activated. The “safety” plan was selected, which is the least expensive subscription. The plan allows unlimited SOS messages, ten text messages/month, and unlimited check-in messages. The check-in messages are sent to selected e-mail addresses, the Facebook page, and the Instagram page.

The check-in also updates the MapShare page.