Wind of Charge

Our yacht's navigation lights, instruments and other appliances draw power from the battery bank comprising two 110Ah batteries. This means we could (in theory) run, say, a light with a power of 12W - corresponding to a current of 1A - for 220h, or 9 days. On longer passages, this obviously means that we must have ways to charge the batteries - and/or keep our electricity consumption to a minimum. On the latter front, we have replaced internal lights, as well as the tricolour - a masthead navigation light used while sailing - with efficient LEDs. For charging, Auriga came equipped with the engine alternator and a dated wind generator (Rutland 913) - a favoured option for offshore sailing providing almost unlimited clean energy. Unfortunately, the old wind generator suffered irreparable damage following two ocean crossings and 12 years in the scorching Spanish heat - the bearing which allowed it to turn following the wind direction seized. A replacement was needed.

Our new wind generator 

Reviewing all the available options would take quite some time. One feature, however, they all have in common - high cost (like most yacht toys, really). Long story short, we decided to "test" an unbranded turbine supplied by Renytek, which, while conspicuously resembling the Air X/Airbreeze turbines (a closer inspection suggests most parts would be interchangeable), costs about 6 (six!) times less. Like its legitimate siblings, it clamps around a 48mm pole. This posed a slight problem, as the old Rutland mounts inside a smaller pole with an outer diameter of 45mm. Even after removing the seized and corroded remains from the inside, a sleeve was needed to make up for the difference in diameter. A quick run to the local stainless workshop provided us with a suitable section of pipe - the inner diameter was just over 44.5mm, while the outer was closer to 50mm - not a problem for the generator that mounts with a rubber spacer, as a quick test confirmed.

A sleeve making all the difference

 The tube was cut lengthwise along the weld seam (thanks to Martin for the tip) and slipped over the top of our generator mast easily (I used a Dremel with a high speed cutting disk and the boat's vice - both extremely useful). The cut is necessary to allow the tube to compress - this way the clamping action is transferred from the generator base all the way to the innermost mast tube.

Sleeve - side view

Sleeve - top view

Pre-assambly checks - generator casting and rubber spacer

Next, I prepared a three-strand cable with a suitable current rating (the generator can output 300W - or 25A at 12V) and ran it partly inside, partly outside the pole, and down through the deck.

Final assembly followed, involving a synchronized pole-dancing performance by Igor and Matt, a dropped nut, a run to the chandlery, a G-clamp and finally a lot of torquing. Below decks, the output of the generator is converted into usable battery charging current by a regulator. While the supplied unit lacks the bells and whistles, it looks well-built, with a massive heatsink presumable dissipating excess heat from the dump resistors. Looks very much like something we would build in the lab - easy connections via screw terminals, sticky labels, and some symbols illegible by anyone but the builders.

Insides of the regulator

Regulator mounted on the mains/charger board

The regulator fitted nicely on the dedicated electrics board on the front of the battery box. It is connected in parrallel to the mains charger - may the strongest win. A single charging cable runs to the master switch (now residing above the chart table) - this way we can charge the batteries together or individually.

Unfortunately, the winds in the marina were too light to test the turbine. I even went through the effort of removing the rotor to check for any unwanted friction - it turned out that the the felt resistance comes from the magnetisation of the stator core. I couldn't help noticing that many smaller generators spin happily in those light winds, unlike the higher-rated models similar to ours. It remains to be seen if this will prove to be an issue - we will report on the charging performance as soon as we have had an opportunity to test it properly.