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Bow & Stern Thrusters


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When deciding on the type of installation for a boat’s new Bow or Stern Thruster, some crucial factors have to be taken into consideration. Firstly, do you have room to do the installation. The tunnel and motor dimensions have to be considered and carefully worked into the installation design. Factors such as the height of the tunnel in relation to the vessel’s waterline are very important as a miscalculation will result in the Thruster not operating to it’s maximum potential or even not functioning at all.

The space required inside the boat is also important. We always try to find a position to fit the unit and the ancillary equipment where we are creating the minimum amount of disturbance to surrounding structures but also in a position where it can be properly checked and maintained. Running cables to and from the Motor is also a factor we need to consider.

Thruster tunnels are made in various sizes to accommodate different thrusters. For vessels up to 50’ in length, the common sizes are 135mm, 150mm & 185mm diameter. Tunnels are cut into the hull & bonded using GRP structures. Once fitted, the area becomes very strong…..much stronger than the surrounding hull as the two halves of the hull are now supporting each other via the tube. The Drawings in Fig 1 show the dimensions to consider when choosing and installing the thruster. Stern thruster installations are a little less position dependant, but must still be correctly installed to work properly.

Fig 1.

Once the tube is fitted, we will create a faring on the exterior of the hiull as seen in Fig 2.. By creating this faring, the disturbance to the water flow over the hull is vastly reduced, and any effect of the the bow thruster on the boat’s performance through the water is reduced to a bare minimum. With planing hulls, the bow thruster assembly will be out of the water in most cases when at planing speed.

When selecting the size of thruster required, it’s always a good idea to go up, rather than down in size where possible. A more powerful unit will take far less time to move the boat than a slightly under powered one. 1 -2 seconds should be all that is required to assist in most berthing or manoeuvring operations. If the motor has to be operated for long periods to move the bow or stern, then it’s probably too small for the boat or hull type. As a benchmark, the VETUS BOW55, a 55kgf thruster is a good unit for the 30 - 40’ yacht .  Added extras like remote control units can be installed as retrofit items. These make life easier and safer still by enabling the crew to control the boat both from the helm and the deck or pontoon.

Fig 2.

12 and 24 volt DC Thrusters can be fitted in different ways, but they all need to be powered by a battery. All thruster units require a massive amount of current to operate. For example, the BOW55 model mentioned above will draw up to 400 amps when operating. This means you need a large, powerful battery installed and a quick and effective charging system  in place to ensure the motor is able to deliver full power every time when you need it. There are 2 basic options for fitting. The links below describe each in basic detail and give an approximate idea of installation costs of each.

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