Budget Bow Thrusters - $1500

    The problem

    When I bought my catamaran its reverse was not functional, nor was the electric start. Unfortunately neither was my budget, in fact it hasn’t been the same since I got her. Propulsion was provided by an unreliable, single, two stroke outboard giving her about the same turning radius of a big rig. With me scrambling back and forth to start the motor every time she died, the heavenly twins being a center cockpit, this gave me some decent exercise. I learnt a few things in the scramble, one, plan several steps ahead coming into an anchorage, two, keep that handbrake “anchor” handy and how to flip a tit with the anchor tied to one of the bows.

    Although it was fun, I decided to come up with a solution if I’m to be single handed in a breeze. Problem is I needed something soon and on a budget. After having looked at numerous options; twin diesel engines, twin hydraulic screws, steerablesillette leg, electric propulsion, bow thrusters etc. I think I finally found a budget solution for the docking and windage woes which will solve the problem until I get a diesel in.

    The Solution

    Well, of course, bow thrusters are the perfect solution, but they are not cheap and installing them on a sail boat is major surgery, not to mention the price tag. My custom solution is not the prettiest solution, granted, as with my installation there will be visible motor mounts, but it can be installed without major surgery and amateur DC electrical knowledge. They can be installed off the stern in various configurations but my current steering configuration didn’t allow for this. Two, 55lb (0.8HP), trolling motors with the controls mounted at the helm. These can be purchased relatively cheaply because they are mass produced. Total cost was $1500 for all parts which is pretty damn good considering two vetus 55lb thrusters will set you back $3750 before parts and installation, and we all know how much twin screws cost, weather it’s hydraulic or twin diesels, we are looking at well over $10K. In fairness those Vetus thrusters would probably perform better. You could probably do better than this if you hunted around for a bargain on the motors. Once I found all the parts, installation and testing took three days.

    Installation

    Installing the bow thrusters on the boat was pretty easy. This being a sail boat there where considerations on placement of the budget bow thrusters, see the next page for details.

    Pontoon mounts, Cut some starboard ½” and ¼” strips. One ¼” overlapping the gunwale. Longer bolts where needed. Still need to drill out and epoxy the cored deck. I chose to use pontoon mount because of the boats layout. You may well be able to use the standard mounts.

    Pontoon mount bracket

    The controller will need to be as close to the battery and motor as possible to reduce the amount of wire needed as the size of wire needed to handle the amperage draw is large and pricey. Dismantle the head and cut the pot (speed control) wires. Unplug the motor wires.

    Trolling motor speed pot

    The stock shafts where to short for my boat so I ordered longer ones. Cut the original shafts off and chiseled out the remaining carbon fiber shaft. Painstaking work because you need to take care not to damage the threads or wires. Was advised by the manufacturer to heat up the casing to loosen the locktight and they would screw out but the carbon shaft simply caught alight. So much chisel work was needed. These composite shafts are really tough!

    Trolling motor shaft

    Extended the wires using 8AWG wire cause you have a longer shaft and need to reach the plug socket. Drilled two 1 1/8” holes to install the plugs.

    Trolling motor plug

    Mount each controller in line with the batteries and where the motor plug is to be placed. This is to keep the wire run as short as possible and consequently lessen the voltage drop or size of wire needed.

    Install big 150A main fuse and two 60A fuses next to each controller.

    Fuse for trolling motor controler

    Ran some small controller wires from the controllers to helm and soldered them where the pot wires where cut on both the controller and pot.

    Mounted the speed controls in original casings and use old shafts as mounting poles. This gives me two variable speed controls at the helm.

    Testing

    Speed : 1.5 knots with both motors full forward (might have picked up a bit more speed but I was short on space. This speed was reached in two boat lengths.

    Turning : 90 degree turn done in 14 seconds. Without using rudders or the main engine.

    The initial test was disappointing, the amperage draw is only 84 and is, according to the manufacturer meant to run at 100, 50 amps each, which is 0.67HP each, as opposed to the published 0.8hp. According to prop calculations 100amps should push her at 2.9 knots and 84 amps at 2.7 knots, so 1.5 is disappointing. Which leads me to believe these, stock, wheedles props aren’t as efficient as they could be. According to the manufacturer they are designed for around 4 knots. I have ordered some larger 3 blade props which claim additional power. I’ll post an update when they arrive. Turning ability however is reasonably good in calm. I tested this without the use of the rudder or outboard and was able to navigate the tight marina single handed with ease. She did turn on her axis. I noticed afterward I forgot to pull the main prop out the water but I doubt this slowed it down much.

    Parts List

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

    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.