Page 3 of 3

Budget Bow Thrusters - $1500

Parts List

Coming up with the parts for the bow thrusters took the most time by far.

2 x 60A fuses
1 x 150A fuse
2 x 60” replacement trolling motor shafts
2 x Pontoon mounts
1 x ¼” sheet of starboard
1 x ½ in sheet of starboard
2 x 55lb maxim minn kota trolling motors (digital version is more efficient at lower speeds)
10’ 4AWG marine grade wire (AWG = American wire gauge) to cross the catamarans bridge.
12’ 6AWG
3’ 8AWG marine grade wire
Wire terminators, and extensions
1 1/2’ Longer bolts for pontoon mounts
Ordered two new props $80 each

Electric notes

Crossing the bridge, the bigger the wire the better, motor performance is dependent on the voltage supplied. Initially I didn’t have large enough wire which cut the performance by 40% upgrading the wire size across the bridge kicked it up to around 84%. I used 4AWG. The batteries will need to handle this. I chose to use the existing house bank. I have 2 X 6v Trojan T125’s (235AH total) considering the Peukert factor this will give me 30 min to 50% DOD. This is more than enough time for docking/anchoring, for occasional assistance with tacking and use as an electric dagger board.

Conclusion

This has worked out reasonably well. It gives me the confidence knowing that I can dock single handed under most but the worst conditions. It certainly doesn’t hurt to have a little extra finer control. I would do it again.

Lessons Learned

Location of mounts I’ve mounted the motors off the gunwale in the center, which is probably not the best place for this. As an afterthought if the motors could be mounted so that, when deployed, they are positioned where the twin screws would be i.e. in front of the rudders. This would give the benefit of rudder wash and I assume better steering ability. With these mounted on the bow or stern pointed perpendicular to the waterline, with the main engine running, I think you could swing an aggressive turn.

Using contactors would definitely simplify the installation, fiddling with those tiny controller wires was painstaking work. This will also leave a much neater setup with only two small switches at the helm and you would improve on efficiency having eliminated the controllers. The down side is you will then not have variable control and I’m not sure if this will work yet, still to be tested.

Misc. considerations

The motor manual states that the motor is grounded and that the battery bank used for them should therefore be isolated as it may cause corrosion... I ignored this.
Cutting up the motor obviously voids any warrantee.
The maxim motors are not marine grade. For this reason I stow them, but they won’t last forever. The don’t have zincs and the internal wire is not tinned copper. That said you can pick them up on ebay for a reasonable price.