Whether you’re a seasoned motor yacht skipper or are looking to make the jump from diesel to wind power, you might be wondering what type, if any, engine you’ll need to compliment your sails when the force of mother nature isn’t up to the job.
In short it is prudent to have an engine fitted to any sailing vessels over about 6 foot in length, largely as a safety measure to ensure you’ve got better control over your boat in a congested marina. Smaller boats such as dinghies aren’t considered large enough to do any major damage and can easily be controlled by paddles when necessary.
What Kind of Engines do Sailboats Have?
As with motor boats the simplest and least intrusive way of powering a sailing boat is to use an outboard motor, clamped to the transom.
Even though a dinghy isn’t really large enough to worry about powered assistance; there is always the option to use a small electric outboard, or ‘trolling’ motor when navigating around a harbour. Indeed some people choose to use lightweight electric outboards to give them power assistance on larger vessels such as skiffs up to about 30 foot in length.
If you do opt to go down the electrical route, bear in mind that the classic foibles around electric motors, and more importantly the batteries that power them, will likely rear their ugly head. In essence, such small motors need to be run at full power to move a sailing yacht at a reasonable speed. And as you might expect, a typical battery bank won’t sustain greater horsepower for any great length of time.
Nonetheless, for short journeys (ie in and out of harbour) at low speed, in calm conditions, you might be okay relying on an electric outboard.
The other great advantage of using a lightweight electric outboard is of course that it doesn’t have to be a permanent fixture (and eyesore) on your transom; you can simply stash it below deck and grab it as and when needed.
Despite the advantages of electric motors, diesel engines remain the most popular power plant of choice among sailing boat owners, simply because they’re so reliable and have a power to weight ratio that can’t be beaten.
Whilst diesel outboards are an option, personally I don’t think they fit the sailing boat aesthetic terribly well, thus inboard diesels are a much better option, especially on vessels over 25 foot where the engine is to be a permanent fixture.
For many years the sailing boat inboard diesel market was dominated by one particular model the ‘Atomic 4’ made by the now defunct Universal Motor Company. Westerbeke continue to make and supply spare parts for these engines, which can come in very handy given the abundance of boats fitted with Atomic 4s on the second hand market.
In the wake of the success of the Atomic 4 many other manufacturers have gone on to achieve popularity over the last 40 years, and now models by Yanmar, Westerbeke, Kubota and John Deere are commonplace aboard new sailing vessels.
For simplicity’s sake sailing boat inboard engines are typically installed near amidships with a straight propeller shaft. More complex arrangements such as V-Drives tend to be reserved for motor yachts, where such configurations offer significant operational advantages.
As far as how much fuel is typically carried, depending on how thirsty your engine is a 30 gallon tank for a 30 foot yacht is a good baseline. Bear in mind that while this gives you a bit more flexibility to keep moving when you’re travelling greater distances over a period of days or weeks, it isn’t a substitute for being under sail.
It’s also a really good idea to keep a couple of jerry cans full of diesel in addition to your primary tank. This will get you out of trouble should you realise you’ve been a bit too reliant on your engine for any reason and need to be able to limp back to shore!
If you want the benefits of an electric drive but without the drawbacks of batteries, then diesel-electric propulsion is a good choice.
If you’re not familiar with what this means, it’s quite simply the use of an inboard diesel engine (generator) to generate the electricity required to charge the batteries that drive the electric drive motor or motors. Very often you’ll make use of the generator for other auxiliary system such as air conditioning as well, so having a generator aboard is useful beyond powering the drive system.
One of the most obvious benefits to a hybrid system besides the fact that batteries can be charged as you go, is if you choose to use azimuthing ‘pod’ thrusters that give you superior maneuverability in the confined space of a marina.
How do I Calculate the Right Size Engine for my Sailboat?
You’ll find there are a number of different calculations you can use to determine what size engine you should fit to your boat, from how fuel efficient you want to be, to whether you plan to use the vessel at speed (not so likely when using your engine to navigate safely in a marina).
Clearly the need to travel at speed like a motor vessel isn’t necessary with a sailing boat, but you’ll still need enough power to get you out of trouble should you find yourself in challenging conditions.
Without digging too deeply into the naval architecture behind this, a good rule of thumb is to choose an engine that will allow you to cruise at maximum hull speed plus a little bit more to cope with challenging conditions. In other words with the displacement hull of a sailing boat there is, for all intents and purposes, a limit to how fast the boat will travel. Whilst going faster than this limit (hull speed) is certainly possible, it requires a great deal of power to do so, which is both expensive and impractical.
So choosing an engine that provides 30% power than is required to reach ‘hull speed’ will ensure that you reach the maximum speed possible, even in rough conditions.
Hull speed is determined by the following formula:
HS = 1.34 x √LWL
(Hull Speed = 1.34 x the square root of the length of the vessel at the waterline)
So for example a 25’ yacht with a LWL of 20’
1.34 x √20 = 5.9 knots
I know what you’re thinking, where does the 1.34 figure come from? Well this is a constant relating to the wavelength of the waves generated by the displacement hull. Don’t worry too much about it, just know that it works!
Knowing the hull speed of your boat means you can determine roughly what the best engine will be for your sailing boat. For instance if you’re looking to replace your existing engine with something more powerful, knowing how close it currently gets to hull speed will give you some idea of how much bigger you need to go to actually achieve it.
As for determining a suitable engine from scratch, there are many factors to consider, but the oft quoted rule of thumb is 4hp per ton of displacement. Again see which engines are able to deliver this, and then see if you can cross reference with your hull speed estimate, as well as taking into account what manufacturers of boats of a similar size and design fit to their vessels.
How Much Does it Cost to Retrofit an Engine to a Sailboat?
Whether you haven’t got an engine in your sailboat at present, or you don’t think the one you have is correctly sized, you might be interested to know how much it might cost to get one fitted.
For an inboard engine between 6 and 80 kW, you’re looking at somewhere between $4000 and $10000 purchase cost, while a boatyard will probably charge you between $3000 and $5000 for the privilege of installing it for you.
Of course there are more variables involved in this than I could possibly mention here, but this at least gives you a rough idea of what you can expect to pay.
Is it Safe to Sail Without an Engine?
Many of us cut our teeth in the sailing world commanding dinghies and small boats, none of which are fitted with engines. So the process of coming alongside and docking in a sailboat using only the power of the wind shouldn’t really be a daunting experience for most sailers, yet most would baulk at the thought of doing so in a larger, heavier vessel.
In short, it is safe to sail without the force of several artificial horses ready and waiting should you need them, but only if you’ve got the confidence to do so. It’s important not to simply assume that your experience of handling a smaller vessel will carry over when in command of a much larger one. The increased inertia of a bigger boat in particular can catch you off guard if you’re not careful!
Above all the most important consideration is to think several steps further ahead when under sail, simply because you can’t course correct with the same speed as you can with an engine. If you currently rely on your engine a lot at present but are toying with the idea of taking a more pure ‘sails only’ approach, then a good place to start is practice docking without the engine, or at least gradually tapering down your reliance on it.
The other thing to watch out for is whether legislation in your locale demands that you have some form of engine for backup purposes. Indeed some locations such as the Chesapeake and Delaware canals are legally off limits to non motorised vessels, so in such places, even with your sails up, you must be under engine power at the same time.
Advantages of Not Having an Engine
Whilst having an engine takes a lot of the stress (and arguably skill) out of sailing, it isn’t all good news, and there are a few drawbacks to having an engine in your sailboat:
- The cost of the engine, both in the initial outlay and maintenance is significant. You’re looking at several hundred dollars a year just to keep the thing running, serviced and winterized
- The cost of fuel also needs to be factored in. Yes sails need to be replaced and repaired too, but fuel is by far a bigger consumable
- Because your engine likely doubles as a generator to aid with the running of other systems, you’re likely reliant on those systems as well, whether it’s your fridge or air con. Adopting a pure sail only approach might make you want to think twice about having the expense of other systems to worry about too.