Net Dynamic Menu by v4.3.0


190 Amp Yanmar kits

240 Amp kit for Yanmar

330 Amp kit for Yanmar

190 Amp Yanmar belt kit

Fast Flow emergency bilge pump- Amazing flow

Inexpencive three step regulator

Marine books by
Scott Fratcher

Fast Flow emergency bilge pumps

ElectroMaax battery chargers

Fast charge rates

Inexpencive universial regulators


How to build a marine wind generator

How to build a yacht wind turbine


How to build a marine trolling generator

By: Scott Fratcher - Marine Engineer/Captain

Today’s fuel prices are forcing many boaties to look for alternative methods of battery charging – ones that don’t use fuel. Scott Fratcher explains how to build your own wind/trolling generator to produce “cost-free” battery charging.

The wind/trolling generator presented here has been the energy producing workhorse of the cruising community for over two decades. It’s compact, has many mounting variations to suit different yacht rigs, and puts out heaps of power.

We regularly see 20 charge amps in 25 knots of wind. Sailing at six knots the trolling generator produces six continuous amps, with a drag load of 15 kg. The wind charger is the quietest I’ve ever heard, and best of all it can be built by any good DIYer in just a couple days.

Four steps to building the generator:

* Finding a motor
* Build a propeller
* Build a trolling attachment
* Put it all together and make power


Finding a motor

The heart of the wind/trolling system is the motor. This is the only component you might actually have to purchase. Because this is a DIY article, we’ll discuss specifications to help you find one of these motors in the scrap bin, or at least know to what to look for at a swap meet.

For years boaties have used old mainframe computer tape drive motors (permanent magnet motors). There are lots of them around, now that computers have moved to hard disks. You can often find them at swap meets, and military surplus stores sometimes have them. You can also search the internet.



We want a permanent magnet motor between 18-48 volts, with an rpm range of 200-600. The higher the voltage the more leeway you have on rpm. The idea is to produce over 14 volts at low rpm (200 or so). For an 18-volt motor to make 12 volts it has to spin at 66 percent of its rated rpm. For a 48-volt motor to produce the same 12 volts, it only has to spin 25 percent of the rated rpm.

To identify a permanent magnet motor, look for the smooth case sides, with bearings at each end. There should be no cooling fans or openings to the windings. The sealed case means the windings also last longer in a marine environment.



When you come across one of these motors, give it a quick “on the spot” test by turning the shaft. If the shaft rotates smoothly and looks to be in good shape, the next step is to cross the output leads. Again spin the shaft and you should feel instant resistance. If you don’t feel the drag it could mean loose or worn brushes, a burned-up armature, the rpm rating may be too high for this application, or it may not actually be a permanent magnet motor.

The second test is to connect an electrical meter to the generator output leads and give the motor a good spin by hand. A quick snap of the wrist should render a short but readable voltage of 10 volts or more.
Note: If you attempt to turn the generator shaft and feel a grinding on the inside of the motor, the magnet may have fallen off the case and stuck to the inside windings. It’s an easy fix to open the case and use some epoxy to replace the magnet. Pay careful attention to the direction the magnet is pointing when you remove it for cleaning and re-gluing.


Building a wooden prop

The prop changes wind flow into torque. Building an efficient wind generator prop can be challenging, but it’s always rewarding. The blade needs three separate qualities. It must:
- spin fast in a good breeze to produce high top amperage
- still produce amperage in light winds
- have enough torque to overcome the starting resistance to begin spinning from a dead stop.

The super quiet prop shown here has been kicking around the cruising world for years and is a good balance between the three aspects of design criteria. And it’s short enough to hang in the rigging.
Once the prop’s completed it must be balanced to prevent vibration when in use. Check balance by laying the center over a knife blade. Slide a small coin along the blade till a perfect balance is achieved. The coin is set into the wood and glued in place.


Rigging the generator

The most common mounting method is a rope harness which hangs the generator in a “triangle” configuration with springy lines. Springy lines keep any noise from being telegraphed back into the hull. Hung in this manner with a good, balanced blade, one can hardly hear the generator spin. The rope harness is attached to the generator motor with the use of big hose clamps and a tail is made from a piece of plywood.

Another common method is mounting the generator on a pole on the aft deck. I don’t like this system because the noise vibration is “telegraphed” into the hull, so the charger can be heard below decks. Those who use this system claim the wind generator gets more use cause it’s always up and producing electricity.


Trolling attachment

A trolling option uses a small propeller towed behind the yacht (when sailing) that spins the generator. Find an old propeller from a 10-15 hp outboard engine. A 9”x9” prop is ideal for a yacht sailing at six knots. If your yacht sails slower, look for a power prop like a 9” x 7”. If your yacht sails faster, look for a 9” x 10” model.

To build a trolling option we start with a length of stainless shaft (or even a piece of galvanised pipe) – 400 - 600mm. We want a heavy shaft to keep the prop in the water at six knots. Attach the prop to the shaft by welding a 13mm bolt to the shaft and slide the prop over it. The bolt should be long enough so a nut just captures the prop hub. Fill the area between the prop and the bolt with epoxy and we’re just about ready to make free electricity.


Rigging the trolling attachment

The idea is to use a double braid yacht line long enough to have the prop riding firmly inside the second wave behind the yacht. It takes a bit of experimenting to get the right line length. If the line is too short the prop will pull free from the water, snapping back toward the yacht – a bit like an attacking buzz saw. If the line’s too long the prop will climb the back of the wave and won’t deliver optimum charge. A good starting length is 40m of 12 or 13mm sailing braid.

To deploy the trolling prop have the line laid in a big figure eight on deck, with one end attached to the generator and the other onto the prop. Drop the propeller into the water and pay out the line quickly till it goes tight. The idea is to have no drag on the line till it’s completely straight, helping to prevent tangles.

Tip: Typical three-strand line is not suitable for a trolling prop. The line can become “un-spun”, rendering it useless. When it’s right, you should see two amps at three knots, three amps at four knots, five amps at five knots and over six amps at six knots. At about seven knots the prop begins to shoot out of the water scaring the crew. The drag on the boat is about 15kg at full load. Many yachts troll at night to supply power for the running lights, reading lights, radar and any other items that would normally cause the batteries to go dead. During the day the trolling prop is pulled in and the fish lines deployed. To recover the trolling prop, slide a big plastic funnel down the trolling line. The funnel will follow the line till it hits the prop preventing it from spinning and allowing easy retrieval.


Regulating output

Regulating a homemade wind generator can be a little tricky, because it’s a passive system. The wind blows and they make power. When a lot of wind blows they make a lot of power. If we want to shut down the wind generator we can’t disconnect the battery: the drag on the blade would drop to nothing and the wind-generator blade will over spin. Instead, to reduce power output in high winds we use a line connected to the tail and turn the generator away from the wind.

Tip: A tape drive motor needs an inline diode to prevent back spinning. Just about any alternator diode placed in the POSITIVE generator output lead will suffice.


Alternator vs Permanent Magnet Motor

We can also use an old alternator for this project – but it’s a bit trickier and involves rewinding and replacing the inner components.

Alternators and generators both produce electrical power, but the alternator tends to be more efficient because the electrical current is produced by the outside windings while a generator produces the power from the inner windings. Since the outer windings have a greater diameter, they cover more area and thus can produce more power for the same case size. A re-wound alternator also produces your charge voltage at a very low rpm.


Up for a bit of an experiment? How about modifying the alternator?

Like all electricity-producing components, an alternator utilizes two, interlocking magnetic fields. By moving the fields against each other we produce electricity. In most alternators the “field current” provides one of the magnetic fields. That’s no good for a passive charger. We don’t want to waste four amps producing field power – we’d rather have them help charge the battery. So we’re going to replace the field current magnetic field – with permanent magnets.

The steps to modifying a car alternator for use as a wind charge motor are:

  • Pulling the alternator apart
  • Removing the rotor and pressing it apart
  • Removing the rotor windings and replacing them with round speaker magnets
  • Removing the stator and rewinding it with wire about quarter the size, with four times the wraps.

Old car alternators are easily obtained, as are old car speaker magnets. So the only tricky bit is rewinding of the stator – and we’ll come to that in a minute. First – the inner rotor. Once you’ve pulled the alternator apart, the rotor must be pressed open and the windings removed. We want to replace the wire with round speaker magnets (old car speakers are perfect). These round magnets have holes in the centre and we want to slide them over the rotor shaft. The idea is to make a stack of these round magnets that fill the space inside the rotor. They must be stacked like-pole-to-like-pole (usually about four will do) so the stack will try to push itself apart during assembly.


Re-winding the stator

The number of winding wraps in the stator is what produces the voltage per RPM. We want a low RPM range of about 200-400, but typical alternators start producing real current at around 1500rpm. That means we need about three or four times as many windings pushed into the stator. How do we do this? Start by examining the stator carefully. You’ll see it’s really three separate windings that combine at the diodes to become one charge source. Remove the old copper wire and insulating paper. You should now have a clean stator to begin the project.

Locate some new winding wire about a quarter the diameter of the original windings. To form the wire to fit the stator many techs use a block of wood ground by trial and error to the perfect shape to fit the stator gaps. The plastic insulating material is simply Mylar paper bought from a bookstore, and the restraining pieces that hold the wire into the stator grooves are round wood dowels. When you have laid the wire into the stator soak it all in varnish and hang to dry.

If this phase of the project sounds too finicky, the stator can be purchased separately, or a local alternator shop can rewind the stator for your project.

Note-How to build a wind/trolling generator is continually updated with new information. If you built a generator send me an email and let me know how it went. Send photos and I'll post them on this site to help others.

Anybody have a good design for converting an alternator to a PM generator? Something past the experiment phase? I would love to post the plans here.


Ask a Marine Mechanic Online

We have partnered with JustAnswer so that you can get an answer ASAP.


Call now to book a 2010 vacation in the South Pacific


How to build a marine wind charter

Click on the plans above to download the high quality version of these original plans


Basic Fast Flow Emergency Bilge Pump Kit

$599USD plus shipping


Fast flow pump installed.

Always ready - Alwasy pumping

Pump arrives in parts for easy install. No need to remove the prop shaft

Prop shaft bilge pump installed and ready for use

Impeller blades split in two for easy install and come in various sized to meet every boat's needs

Pump is ready for installation.

This is a safe boat with the Fast Flow propeller driven bilge pump

Example of a propeller driven Fast Flow bilge pump in operation

Fast Flow emergency bilge pump in position ready to save the day


Basic Fast Flow Emergency Bilge Pump Kit

$599USD plus shipping


Order your books by Scott Fratcher here


Metal boat repair and maintenance. A must read for any steel boat owner.

Print: $31.10

Download: $12.00


How to repair a steel boat without sandblasting. Special report.

Download: $4.00


In order to get a good job as a marine engineer we need a marine engineer licence, commonly called a Certificate of Competency

Print: $39.49

Download: $29.50

How to get a job on a mega yacht as a marine engineer? It can be done without a licence.

Download: $4.00


50 money making ideas run from a boat

Print: $39.90

Download: $39.90

Make money with boats? You bet! It's done every day, but most people won't tell us how they did it. This book is a tell all to give the layman the tools needed to start their own onboard cruising business.

How to make money with boats has become an instant classic selling around the world making dreams come true. If your planning a cruise, or your know somone who is this is the perfect book.

Print: $39.90

Download: $39.90


Print: $21.37

Download: $9.00


How to buy boats cheap? Dozens of tricks used by adventurers around the world every day. This book is a must read for anybody ready to purchase a boat.


Print: $29.96

Download: $9.00

The race was a heartbreaker, but eventually Earthrace took the round the world speedboat record. This book is the log and blog of the 2007 race where Earthrace set dozens of fastest ocean record crossings.


Download: $12.00

Earthrace in color. The same book as above, but in vivid color to bring all the race moments right to the reader.


Print: $14.97

Download: $9.00

Anchor King is a narrative book of short stories of the Sausalito California waterfront in the late 1980's. Anchor King contains the award winning short story "Sex Toys?"

Print: $115.47

Download: $5.00

Tjalk Operator's Manual is an example of how to build a yacht manual. Over 300 pages showing how to drive a twin engine, single rudder vessel and much more.


Click here to purchase

"Earthrace-First time around"
by Scott Fratcher

Download Now for just $9.00






   © Team Yachtwork 2007