Harnessing Hydropower for Efficient Cruising

Explore the benefits of hydrogenerators with seasoned sailor Joe Drago as he shares his personal insights on this innovative power solution for cruising vessels. Learn how these devices harness the kinetic energy of water to provide reliable electricity, offering an efficient alternative energy source. Dive into Joe's personal experiences and discover if a hydrogenerator is the right upgrade for your cruising adventures!

Hydrogenerators for Cruising Sailors
By Joe Drago

In the world of cruising boats there has always been the search for more efficient on-board electrical equipment and the search for the most efficient ways to power it. Solar has been the standard for a long time now and probably will not be replaced any time soon, but solar does require the sun to be shining. While on passage, most boats consume significantly more power than while at anchor (chart plotter, radar, auto-pilot, etc) and the solutions are pretty cut and dry. You need a large battery bank to make it easily through the night and cloudy days and a large solar array along with possibly a wind generator or you may be running the engine for an hour or two per day to keep up. I was struggling with power options as I have a ketch rig and limited room for solar. I really did not want a wind generator on my mizzen mast so I was looking for other options. I noticed many of the around the world racers were using a hydrogenerator along with modest solar arrays to power their non-stop journey around the globe. It seemed like a super simple idea and if the units were working for them they may be worth looking into. The new iterations of hydrogenerators have come a long way and are certainly worth some thought for the right applications. Let’s start getting into it.

What is a Hydrogenerator?

A hydrogenerator is typically an impeller that looks like a propeller that is attached to or somehow turns what is something more or less like an alternator. The impeller is lowered into the water or towed behind the boat and as the water flows past the impeller it spins the “alternator” and therefore generates electricity. The faster it spins the more electricity is produced. It is a super simple concept that can work incredibly well. There have been many different designs out there over the years from the log type that you would tow behind the boat like an old speed log to the modern designs that look like a slimmed down version of an outboard engines lower unit. They work incredibly well, but you do need to be moving to make power. As with anything on a boat everything is a compromise!

Who will benefit the most?

Since you have to be moving to generate power, hydrogenerators are best suited for the long distance cruiser and may not be as beneficial for a coastal cruiser. For the coastal cruiser the money spent on a hydrogenerator may be better off spent on additional solar instead. If you are mostly day hopping with the occasional overnight or spending very long periods of time in one location then it may not be the best option for your boat. On the other hand, if you are spending multiple days offshore fairly frequently then it may be something to consider. Something else to think about is the faster your boat sails the more power you generate. So the longer your waterline the more you will benefit. Most do not really start producing much power until you are sailing over 4 knots. So if you are sailing on average 5 or 6 knots or faster it may be worth looking into. Boats averaging 4.5 or 5 knots on passage may or may not find the cost benefit ratio worth-while. 

Let’s look at some numbers and my personal experience

I personally have a Watt and Sea Cruising 300 model hydrogenerator. I have had my unit for almost two years of full time sailing on my Cape Dory 45, Resolution and it has been a game changer for us. I mentioned earlier we do not have much room for a large solar array and this has supplemented our power incredibly well. We do A LOT of passage making as we are a sailing and hiking/climbing expedition business, and we also do offshore sail training so our boat is on the move often. I find we do not generate much meaningful power at 4 knots or below, but power production increases exponentially as we increase speed.

This unit along with some other manufacturers has an app you can use to see its power production in real time and at about 5 knots of boat speed we are making about 6-7 amps of power (roughly what a wind generator produces in 15  knots of wind or about a 125 watt solar panel in full sun). At 8 knots we are making about 18 amps and we have had some days making over 20 amps when we are pushing the boat hard.

We used to arrive in port with our batteries running low and motoring during the passage even if we did not need to just to charge things up. Now we arrive to an anchorage with full batteries and our solar just keeps up with our use on anchor. We have also significantly reduced our fuel consumption and wear and tear on the engine (idling diesel engines for long periods with little load is not great for them). On our unit there is the option for different size impellers for faster or slower boats. I have been using the 240 mm diameter one which is the middle size. The larger 280mm size would increase our power output a bit more at slower speeds. I was hesitant to purchase the larger size at first thinking well, that is more drag, but after a lot of testing I do not notice any difference in speed at all with the hydrogenerator in the water or out. Granted we are on a relatively heavy full keel boat that is hard to slow down once she is moving along.

For the offshore sailor these units have dramatically changed life on board and I am starting to see more and more out there in the wild as of late. It is certainly a very viable option for the right application. 

Pros 

• Takes up very little real estate on board
• Almost completely silent
• Relatively easy to install and extremely easy if you have a Hydrovane self steering vane already. They make special mounts to mount it directly to that instead of your transom.
• Almost zero maintenance 
• Generates power 24 hours a day, rain or shine, as long as the boat is moving
• Can generate an impressive amount of electricity when you’re sailing fast

Cons

• Only works when you are moving
• Tends to catch Sargassum and other seaweed as well as lobster pots
• Juice may not be worth the squeeze for smaller boats with shorter waterlines
• Relatively expensive up-front cost, but you do end up with fuel savings and reduced engine wear and tear over time. 

So for the vessel covering a lot of miles each year I hope this was some food for thought. Solar is still the best bang for your buck, but in higher latitudes, at night, or just some cloudy day sailing it’s hard to beat the constant power input from a hydrogenerator. I love mine and it’s up there with one of the best upgrades I have made to my boat, Resolution. 

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