Thrusters and Manoeuverability

After the first year of boating with Tropical Horizons we started to make a list of projects that we would like to accomplish in order to make the most out of the boat. For the most part, we knew that we would be sailing shorthanded with just Karen and I handling the boat. With this in mind, the first item on our list was the installation of a bow thruster.

I researched many different types and brands of thrusters and came to the conclusion that there are essentially 3 different types of thrusters available. First of all for the purpose of this post, what is a thruster and why are they needed? Ok many of the old salts who will be reading this will say, that a truly competent captain doesn’t need a thruster of any kind to help manoeuver their boat. I would agree that yes, given time and patience you can for the most part maneuver any boat into just about any location without the aid of thrusters, but sometimes it’s nice to have a helping hand. Thrusters are auxiliary mechanical systems that are used to displace water in such a way as to aide in the maneuvering of a boat. Typically thrusters are located at either the bow or stern of a vessel.

So let’s understand why we felt we would install thrusters on our boat. In short, if we can reduce our stress while docking the boat, we will enjoy it more. Docking is a stressful exercise, wind and current can sometimes work with you or against you. The deck hand does not always know just how the boat is behaving simply because they are not at the helm. Finally, when you have a relatively flat bottom boat with no real keel to speak of, small rudders and smallish props with limited torque from the engines, and add to that a large surface area that is presented to the wind, you have a recipe for high stress docking. Let’s face it we are out here to enjoy ourselves and not get stressed out.

The hunt for thrusters begins.

I discovered that there are only three systems out there available for a boat in the 41 foot range. These systems include the following:

-external pods
-tunnel thrusters
-water jet thrusters

Pod Thrusters:

Pod Thruster

Pod thrusters are external pods that are installed on the hull via a through hull fitting and mounting bolts. These units tend to be more expensive when simply looking at the cost of the drive unit; however, when the cost of installation is factored in, they are a competitive option to Tunnel Thrusters. The main advantage with the Pod Thrusters is that interior modifications to the boat are minimal.

Tunnel Thrusters:

Tunnel Thruster

The most common that you will find out there are the tunnel thrusters. As a retrofit option, these systems require that a large hole be cut into the bow of the boat with a fiberglass tunnel that is glassed in place and faired to the hull to produce the least amount of drag possible. The drive unit is located inside the hull and the props are located in the tunnel. These can be either hydraulically or electrically driven. The installation of this type of system is generally complex and requires space within the boat to house the drive unit. For larger yachts you will find hydraulically driven units which offer more torque and can run for longer periods of time.

Water Jet Thrusters:

Water Jet Thrusters are much like a jet boat, where through hull openings are connected to a series of pipes that deliver water from a high pressure pump in order to force the bow or stern in a given direction. These systems are not very common and can be quite complex in design. The one advantage I can see with this type of system is the amount of space needed for the thrust ports and the ability to run the pump off of the main engines thus eliminating the need for an extra battery bank.

After weighing the pros and cons of each different type of thruster available, we opted to go for the Pod Thrusters. The Yacht Thruster product seemed to fit our requirements and budget. We obtained a quote for our size and displacement of boat and a 24 VDC system was recommended. I figured if we were going to do this why not go for the complete maneuverability of both bow and stern thrusters? I’m glad I did that, as this arrangement would prove useful at crowded fuel docks, and when running on a single engine, which would happen in the near future.

I ordered the new thrusters and delivered them to MacDonald Turkey Point Marina for installation over the winter months. I also took the opportunity to have the technicians at the marina clean up the electrical at the helm, sort out the navigation light issues and install a hot water heater. When spring came around I found out that I had a burned out starter motor on an engine and that the thrusters worked well to bring the boat into its slip. I was excited to see all of the work that had been done over the winter; after all, they had 7 months to work on the boat. There were some disappointments with regards to the battery installation, which I cleaned up this past year and they also did not bother painting the pod units which caused some corrosion issues but all in all the installation was a solid 7 on a scale of 1 – 10.

What I really liked about the external pod system was that there was very little space needed inside the boat for the installation. A tunnel thruster would have required the complete tear down of the forward cabin and rebuilding of the cabinetry after the fact. This would also make servicing the unit almost impossible.

The thrusters did work out well, however the fuses that are used in the system are very different from common marine fuses that can be found here in North America. I still need to find the fuses in order to have a spare on hand. The dual joystick controller at the helm is great and is easy to use. I have to admit I am glad to have both bow and stern thrusters as well, there have been many times where I was in a tight spot and being able to spin the boat around its own axis without any drifting was helpful. I don’t find that the pods really add any significant drag on the hull and really the effect on fuel consumption is not noticeable. We did have some issues with galvanic corrosion which was a direct result of stray currents from the neighbors’ extension cords that were just sitting in the water as well as other poor grounding issues around the marina. We also learned that the fact that the marine technicians did not paint the units after installation also added to this issue. To address the corrosion issues, I decided the sand down the housings and encapsulate the pods in epoxy before painting with antifouling paint. Upon haul out, there was no noticeable corrosion. This was an easy fix and should extend the life of the units for many years to come.

Bow Pod Thruster encapsulated and painted.

Stern Pod Thruster encapsulated and painted.

All considered, I am happy with the installation and performance of these thrusters. There are a few things that I have learned however, and a few improvements I have yet to make. That list is as follows:

1- Make sure all aluminum parts are well isolated and protected. A little paint goes a long way here, but do make sure your paint is approved for use on aluminum. Copper based paints will destroy the housings. Because our units where damaged by stray marina currents, I encapsulated all of the metal on the pods in epoxy first.

2- Size the battery bank appropriately. These units do draw a great deal of power in short bursts, so don’t use deep cycle batteries, use starting batteries for this application. Calculate your power based on the 5 minute bursts that these are designed to work at. The battery charger will not be able to supply the thruster with the power needed to run if your battery charge drops too low. The units that we have on board require 350 Amps when both running. We need as a minimum 1400 MCA (marine cranking amps) for our system. The marina only installed a bank that had 800 MCA capacity and this has proven to be too little in some circumstances. You also want to make sure that the thruster battery bank is separate from the start and house banks. In our installation this was simple as the thruster bank was 24VDC and the other banks are 12VDC. This is an improvement that I am currently working on.

3- Size the in-line fuses on the charger appropriately and use the proper type, again the marina used a fast blow fuse that was far lower than the capacity of the charger. This costly mistake killed our first battery bank.

4- During your routine daily checks, make sure the charger is charging the batteries and is not in a fault state. There is no remote panel on the charger that is provided with the system. I have made a suggestion to the manufacturer that this would be a nice feature to include on future systems. I will most likely try to integrate a NMEA 2000 battery monitor and interface it with my GPS/Plotter/Sounder units.

Am I happy with the bow and stern thrusters?  Yes, the addition of these units has made our boating experiences much more enjoyable.  If anyone is considering adding thrusters to their boat, I would strongly suggest that you install both bow and stern.  The additional cost is not prohibitive and the added manoeuvrability is well worth the investment.