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Ask Nigel – Thrusters, Check

by Nigel Barron

Now is the time of year I write about activities to consider when putting your boat to bed for the winter—things like removing soft goods, getting a dehumidifier, and thinking about fuel stabilization. Lately, customers have emailed about when a good time would be to bring a boat in for some off-season upgrades and one of the most popular inquiries is about bow thrusters.

It used to be that the off-season in boating went from late October until Opening Day on the first weekend in May. But that has become less true for boat yards. Likely a combination of more people boating year-round and fewer recreational boatyards is keeping schedules fairly tight.

I have said to coworkers that that no one has ever complained that their bow thruster worked too well or that they wish they didn’t have one. Estimating a thruster install is straightforward; CSR Marine does around twenty a year. We know how much time it takes to glass in a fiberglass tunnel, and we know how much time the wiring takes. After that, it’s about the specifics of the boat and what sort of access we have for the fiberglass and the wire runs.

But getting one will take time.

For thruster installs, a big factor at the moment is availability of parts. We have rescheduled several boats because we’re finding lead times of 6-8 weeks for some of the components. The backlog on parts is not limited to any specific brand or supplier and covers the entire industry. Airmar, one of the largest transducer manufacturers, predicts a 3- to 4-month backlog for some of their transducers. Sunbrella has shortages of specific fabric colors for dodgers and cushions.

If you are shopping around for a bow thruster, make sure you are looking at a quote for a complete thruster install. When I say complete, I mean ask if the quote is just for a motor and tunnel or if it includes the charging system, batteries, and all associated wiring.

A quick tip in researching thrusters: Look at what the manufacturer specifies for a minimum battery capacity. Pay attention though, because some of the European companies will give a minimum capacity in DIN and not SAE. Side-Power recommends taking the DIN rating and multiplying by 1.9 to get an SAE capacity rating. DC thrusters have specific voltage requirements, and, like all DC motors, are negatively affected by low voltage.

We tend to use exclusively AGM batteries for the thruster installs, because for a bow thruster the batteries usually end up under a bunk. With the price of batteries, it’s an easy shock come bill-paying time if batteries were not on the original quote.

To determine the appropriate thruster for a boat, we look at the overall size and displacement, and any other things such as a lot of windage that might change the effectiveness of a given thruster. All thruster manufacturers have a general size range that they reference.

Again, as no one complains a thruster works too well, look at the size of the tunnel and the size of the motor. For instance, a Side-Power SE-80 thruster and the bigger SE-100 share the same tunnel size. If your boat fits between the two in terms of thruster requirements and it can fit, consider the bigger thruster.

The biggest question is how long will it take?

We like to estimate at least three weeks for a thruster install. It’s obviously not 120 hours of labor, but drying and curing time factors in because of the fiberglass and the fairing of the tunnel, along with the need to paint the tunnel. This makes a thruster an ideal off-season project.

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