Motor Sailing with an Electric Motor and Generator

Electric motors boast many advantages over diesel motors. They are quiet, clean, and virtually maintenance free! They run when you need them to and stand idly by when you don't. When sailing along with speed, the spinning propeller actually generates electricity for you to recharge your battery banks.

The one advantage that a diesel motor has over an electric is range. There is nothing quit as energy dense as fossil fuel on a yacht. A small volume of liquid will power your yacht for hours and miles without a single complaint. If you run low on this magical wonder juice, all you need to do is pull up to a fuel dock and pour some more into your fuel tank! This is a quick process that takes only minutes to complete. 

Electric motors carry their energy source inside of batteries which will gladly give up their power, but seem to resist accepting power in return. When a fuel tank is empty, all you need to do is pour more fuel in! When a battery is empty, you will need to force power back into it with considerable effort, a process that can take many hours to complete. 

If you plan on motoring fast and far for long periods of time, a fossil fuel motor would be your best choice. If you plan on using your motor for short spurts of power, followed by days of sailing, an electric motor might be a better fit for you.  

Electricity stored in batteries is odorless and clean. It doesn't need to be run through filters or polishers to keep it clean, instead it simply sits waiting for you to call on it. 

Now, what if you find that an electric motor would be your dream power source in your yacht, but you do plan on the occasional motoring. You could solve this dilemma with a simple compromise. A generator will grant you the ease of fossil fuels and the convenience of electric propulsion. The generator powers your battery charger which feeds the battery bank and motor. 

Now, your range and speed will be decided based on your charging capabilities. Your generator will only provide as much power as the charger can put out. If you have a 5 amp charger, then you will only be able to motor along at 5 amps with the range of your fuel supply. If you are wondering, 5 amps is hardly moving and you might be better off to just drift with the tide! 

If you have more charging capability, say 25 amps, you would then be able to motor along at 25 amps (which is still slow, but you would be moving at around 3 knots) for as long as your fuel supply lasts. 

As you can see, the more charging you can produce, the more speed you can motor with. While you may feel limited by your charger, this should not be a concern. 

For example, say you have 15 amps of charging capability, which will motor you along at around 2 knots. You want to go 5 knots and are drawing 60 amps, you can simply throttle up to 60 amps and know that you are drawing 15 amps from the charger and 45 amps from the batteries. This will let you motor along for a few hours at this speed before you will need to slow down and run at a speed governed by the generator and charger. 

This might seem like it is limiting, but if you need to motor 20 miles, 5 knots will get you there in 4 hours. Once you are there, you can let the generator continue to run and recharge the battery banks once you have arrived with speed and ease. 

Generators give you a portable charging solution, adding greatly extended range to your electric propulsion setup. When coupled with solar panels as well, you will find that you will be able to motor along well enough to grant you the peace and tranquility you wanted every time you need that short burst of power. 

Motorsailing

Sailing and motoring are often viewed as two different and mutually exclusive aspects of boating. The truth is, sometimes, they can work together beautifully! 

The idea behind sailing is that the wind will rush through your sails at an appropriate angle, allowing your sails to generate lift and pull your yacht through the water. The idea behind motoring is that the rotational energy from the motor will be transmitted to a propeller used to push your yacht through the water. 

On days with plenty of wind, sailing can exist as the sole method of powering your vessel. On days with no wind, there is no way for the sails to power you and the trusty motor will provide mechanical propulsion to keep you moving. But what about days where the wind is a little light?  

If there doesn't seem to be enough wind to power your yacht, you could always supplement your speed with a bit of throttle from the motor. The idea is simple, as your motor pushes your yacht through the water, it will also push you through the air and create apparent wind over your vessel. This apparent wind can then be used to power your sails and provide a nice balance of power, between sails and motor, working synergistically to motorsail you along at a comfortable speed. 

While motorsailing might sound like the solution to low wind days, there are a few important factors that need to be present for it to work well: 

There needs to be some wind present. 

The true wind can't be coming from directly ahead or directly behind you. 

If there is no wind at all, meaning you are completely becalmed, then motorsailing will be futile. As you move in any direction, the apparent wind will always be coming from directly ahead and the sails will luff just like if you were caught in irons. Having the sails up might make you feel like you are motorsailing, but the energy wasted on making the sails flap and slat is going to be robbed from your potential forward speed. 

The true wind needs to be coming from any direction other than directly ahead or directly behind you. If the wind is from directly ahead, motor sailing will only increase the amount of apparent wind coming directly at the vessel and you will actually suffer in speed because of air drag. If the wind is directly behind you, as you move forward, the apparent wind will become even less. 

Having the wind off to an angle, just like if you were sailing, is the trick. The apparent wind will always move forward as you motor sail, making it appear that you are on a close reach, no matter where the wind is coming from. As you begin to move forward, simply trim your sails to the apparent wind and you will see your speed go up a little bit as the sails begin to help provide a bit of forward power as well. 

We were once becalmed in a naval firing range testing area (while not in use, obviously) and had no chance of getting out of there. It was getting late and we wanted to anchor somewhere for the night, but anchoring was prohibited there as well! We motored along at 2 knots for a while until a slight zephyr came over us. We raised the mainsail and staysail and found that our speed increased to 3.5 knots! I then cut the power from our electric motor and our speed dropped down to 0.3 knots.  

As you can see, the sails alone provided almost no speed in the light breeze, but with the apparent wind from the motor, we were able to scoot along at an appreciable speed for having no worthy wind around us. 

One last scenario where motorsailing can pay huge dividends is when pinching. If you are sailing along and there isn't really enough breeze to make the keel as effective as it could be, a touch of throttle will mend all these ailments.  

As you sail, the wind is actually pushing your yacht to leeward but the keel offers some resistance to this motion. As you move forward through the water, the water passing over the keel provides lift, just like the sails do, and pulls your yacht to windward. This cancels out the leeward slip and allows your yacht to move to windward. 

This system only works if you have enough speed of water passing over your keel. As you move slower, the keel is less effective as a hydrofoil and you begin to slip to leeward. If you are trying to pinch, then you will begin to loose speed and will slip to leeward. Obviously, if you are pinching, it is because there is something to leeward that you are trying to avoid and slipping further to leeward would be deleterious to your navigational plan. Eventually, you will be forced to tack and sail away from this obstacle, only to tack back and clear the obstruction. All of this takes time, and if you are trying to get someplace as quickly as possible, this could be viewed as time wasted.

The alternative in this situation would be to motorsail just a bit as you pinch. The propeller will give you the speed you need to maintain the functionality of the keel as a hydrofoil while the sails pinch with the close apparent wind. Once you round your mark, you can then turn off the motor and fall to leeward as you resume sailing on a normal and relaxed pace. 

We have used this trick multiple times, when tacking would cost us around an hour of additional sailing time. This has saved us hours in our arrival and meant the difference between reaching our anchorage with sunlight versus having to anchor in unprotected waters for a night because we didn't make it in time. 

Engine Choices

On older and smaller sailboats, a popular motor choice is the gasoline outboard. These motors offer the ease of replacement of any outboard, but suffer from the fire risk of carrying gasoline onboard. A common argument for these motors arrangements is that you will already be carrying gasoline for your dinghy outboard, now you can power both with the same tank!

Gasoline is a very dangerous substance on a boat. The liquid is highly flammable and the fumes are explosive! A small problem can easily become a life threatening explosion that will engulf the boat in flames.

Gasoline inboards complicate this problem further by bringing the entire unit inside an enclosed area where fumes can collect and await detonation.

Modern boat builders have recognized the risks involved with gasoline, and have since moved over to diesel motors. Diesel fuel is flammable, but not explosive and there is no fear of the fumes blowing your boat up.

While much less dangerous, there is still a safer option yet: electric. Electric motors require no fossil fuels at all, and therefore pose no risk of fires or explosions from fuel leaks. Instead, electric motors are powered by massive battery banks that feed them the needed amps to keep the propeller spinning.

As with everything, there are pros and cons of each.

Gasoline outboards are very inexpensive and if they die, they are the easiest to replace. Their fuel is a hazard, but it is usually kept in a red plastic tank in the cockpit. If the tank starts to deteriorate, it can be easily replaced. All of the fuel and fumes is kept out of the cabin, so there is much less risk of an accidental explosion.

Gasoline inboards are inexpensive to buy, but costly to replace and repair. They also bring gasoline and all of its hazards inside the boat where deadly explosions could occur. Gasoline engines are also not that efficient and will struggle to push a sailboat at hull speed for days on end without any rest.

Diesel inboards are work horses! They will keep banging along as long as they have oil and fuel. They are expensive to purchase, expensive to replace, and expensive to maintain, but they will power you along without complaints or rest! This is one of the key selling points of a diesel inboard in a sailboat. If you cross an ocean and have no wind the entire time, a diesel motor will be able to power you along the entire way without complaining. While they are an invaluable tool to those who have them, they are also a smelly companion in your cabin. That classic "boat smell" is a combination of the toilet hoses and diesel motor. It isn't always very strong, but it is always present.

Electric motors are the last of these options. They will never explode because they have no fuel, but they will also never push you across an ocean without complaints. As they power you along, they will draw on your batteries. More range means more batteries which means more weight, which means more power to push you along. It is an endless cycle that will never get you very far. Electric motors should be seen as "short term" power options. Say you need to motor into a marina berth, or out of the way of a cargo ship, this is where the electric motor will shine. It will power you along on short distances without problem, but it will run out of electricity long before you make it across the ocean.

Electric motors are best for those who plan to sail. In the situation where there is no wind while crossing an ocean, you would be forced to sit there as you wait for wind to come (which it will eventually do). Cost is another variable. All electric motors achieve the same end result, and the different brands available offer a huge spread in prices. We went with one of the cheaper options by Electric Yachts and it has been a blessing! It always runs when we need it and it didn't break the bank to purchase or install. There are other brands that are many times more expensive, but they too achieve the same goal.

The choice about which motor is a personal one. If you can't really afford anything, a cheap used outboard will be your friend. If you are a power boat disguised as a sailboat, a diesel will be your best friend. And if you want to sail, an electric motor will be your best friend.

How bad will my prop walk be?

Now that you know what propeller walk is, and what makes its effects worse, it is time to figure out how your own boat will respond.

There are generalities, such as Right Hand propellers will walk to port when in reverse and Left Hand propellers will walk to starboard when in reverse. It is easy to know which propeller you have by looking at the hub. Stamped on the hub of the propeller will be LH for Left Hand or RH for Right Hand.

This propeller is Left hand, which means it will walk to starboard when in reverse. Great! This is easy to tell on a boat that is out of the water with a propeller that is high and dry. What if your boat is sitting in the slip with the propeller under water and below the hull? How will you read if your propeller is RH or LH? You don't have to!

Instead of worrying about which handed propeller you have and then trying to remember RH to port under reverse or LH to starboard under reverse, simply observe the way your prop wash moves around your yacht. This will give you a real world understanding of how your vessel will behave. 

All the factors that relate to prop walk will be tied together and prominently displayed for you in one easy test. All you need to do is tie the boat up in a slip on a calm day with still water and put it in reverse under hard throttle. 

As you know, hard throttle will lead to faster propeller speed which will cause prop walk. This along with prop angulation, enclosures, hull and keel type, will compound to display how the entire system will behave in the real world and not just in the theoretical realm.

With the boat properly tied and placed in reverse under hard throttle, look at the water around your yacht and note where the prop wash is coming out. In the most idealistic situation, all the prop wash would rush out from under the bow of the boat. This would indicate that all the thrust from the propeller is being directed forward and the boat will move astern in a straight line with no prop walk.

If you see the prop wash coming up on one side of the hull, then you know you will have prop walk away from the side you see the prop wash rising up on. This is because the thrust is being directed towards one side of the boat, and the boat will move away from the direction of thrust causing it to walk towards the side without the thrust and notable prop wash.

How severe your prop walk will be is directly, related to where the prop wash is appearing in relation to the boat. If the prop wash is appearing near the bow of the boat, the prop walk will not be that severe. If the prop wash is appearing near the stern (or near the propeller) then you know the prop walk will be more severe. Worst case scenario, the thrust and prop wash will appear all on one side of the hull and directly next to the propeller. This would indicate that all the thrust is being projected laterally from the propeller, creating a boat that will reliably move forward and sideways. 

While it would be ideal to have a boat that can comfortably pull in and back out of a slip, knowing how to use your prop walk will help you maneuver your yacht in close quarters without the sheer panic of a boat that is moving the wrong way when you didn't expect it to. Once you know how your boat will respond when placed in reverse, you can properly predict and plan out your approach and exit from a berth without causing an entertaining show for all the bystanders who are waiting to grab a line and pull you into the slip to end your embarrassment.

Prop Walk

While sailboats rely on the wind to propel them through the water, they also have some similarities with power boats, the propeller. A sailboat powered by a propeller will handle very differently as compared to the way it will handle under sail.

First, all the power is hidden from sight. When sailing, you can easily see how each of your sails is behaving. Is it full? Is something blocking it? Is something impairing it's ability to work? Is one sail overpowering the other? With a propeller, all of these factors still come into play, but they occur under your hull and hidden from view.

Propellers are composed of blades which are arranged to push water in a certain direction, and they do this very well. They come in all sorts of shapes and styles, purpose built and designed to perform their best at the given task.

While all propellers are purposefully designed for their selected task, one thing they all have in common is they all work best in forward. Propellers are usually used to drive a vessel forward for many miles, and only used in reverse for short periods of time while maneuvering. This means that your propeller is designed to move you forward with ease while sacrificing reverse performance, making close quarters maneuvering all the more interesting. 

One of the most "interesting" thing about propeller powered vessels in reverse is a phenomenon called propeller walk, or prop walk for short. When you put a sailboat in forward, it will move forward; but when you put it in reverse, you will move sideways! To a beginner, this might seem like evil magic that has cursed the boat as he tries to enter his slip. The curse that has come over his boat as he tries to maneuver is called prop walk, and it can work against you or be used in your favor once you figure out what is going on.

In the simplest of explanations, prop walk is the lateral result of the propellers rotation. In forward, the water is being thrust over the rudder, giving you forward motion and steerage. A slight and unconscious adjustment of the helm will cancel out any of these effects, making it feel like it doesn't happen in forward, but it does. You typically put the boat in forward and head off to a distant destination, so any wavering from your course due to prop walk goes unnoticed. When you put the boat in reverse, you tend to be very close to your destination, so any lateral wavering is greatly noticed and not appreciated.

The reason it feels more pronounced in reverse is the rudder has no effect on steering at slow speeds, so the lateral movement from the propeller goes unchecked. As you begin to waver from your course, you frantically turn the wheel trying to correct your course, but to no avail! Tempers rise as the boat seems to have a mind of its own.

To help you understand why your boat is doing what it is doing, lets look at what causes prop walk in the first place.

Prop walk is amplified by:

• Deeper location of the propeller
• Enclosures near the propeller
• Angle of the propeller shaft
• Speed that the propeller is rotating
• Hull shape and keel style

Deeper water will amplify prop walk because deeper water will provide more propulsive force, conversely, shallow water will provide less propulsive force. The lower blades of the propeller will provide more thrust from the propeller, while the upper blades will provide less. This difference in thrust will produce a bias which results in a lateral component to the propeller spinning. If the propeller is in very shallow water, prop walk is reduced because the entire propeller is not producing much thrust. In deeper water, the propeller will produce significantly more thrust and this difference in thrust from the upper blades to the lower blades will be amplified, resulting in more noticeable prop walk. 

The water around the propeller will also play a huge role in the amount of prop walk. A propeller that is exposed to clean and clear water will show fewer signs of prop walk when compared to a propeller that is quite restricted. A propeller inside an aperture will produce more prop walk because of the apertures tendency to cause water to shoot laterally from the aperture. The top of the aperture will shoot a weaker jet of water because it is in shallower water while the bottom of the aperture will shoot a much stronger jet of water because it is in deeper water. The same propeller will have significantly more prop walk when placed inside an aperture as compared to one that has nothing around it.   

You can see the different angles of the blades on these angled shafts. The blade in the background is nearly vertical while the blade in the foreground is quite aggressive. The propellers on this boat are set in opposite rotational directions to help cancel out any prop walk.

An angled propeller shaft will cause more prop walk simply because it will have an adverse effect on the angle of the propeller blades. If the propeller shaft is set on an angle, one side of the propeller will have blades that are significantly less effect, as they will be nearly vertical and with negligible thrust and nearly horizontal on the other side with significant amounts of thrust. At low speeds, the vertical blade will have no effect and the horizontal blade will push laterally, unopposed by the vertical blade on the other side; causing a lateral push which will cause prop walk. A horizontal shaft with no angulation will reduce this problem, as the propeller will be set straight with the blades on both sides of the propeller working at similar levels of effectiveness.

Knowing that a horizontal prop shaft is ideal, why don't more boats use this style? Because the engine needs to be mounted at the other end of a straight propeller shaft. Deep keeled sailboats can mount the engine low in the bilge and have the propeller located aft of them on a horizontal shaft, but all other boats with a straight shaft will need to angle the system to allow the engine to be mounted at a higher position than the propeller. The only way around this is to use a sail drive which we will talk about later.

Speed of the propeller has a huge impact on prop walk. At slow rotational speeds, prop walk is not as apparent because there is less turbulence created by the spinning propeller. There is also less thrust produced, so any difference in thrusts will be less notable and therefore less apparent to your maneuvering. A slow moving propeller will gradually move the boat in a set direction without causing much in the way of secondary effects. A fast moving propeller will generate a greater amount of thrust and a whole host of secondary effects, most notably, prop walk. 

Hull and keel shape will be the final component in the generation of prop walk. A shallow bilge sailboat with a thin fin keel will have much less prop walk when compared to a deep bilged full keel sailboat. The shallow bilge sailboat will not interact with water coming off of the propeller as much. Whatever water from the propeller that does reach the shallow bilge will have much less thrust, meaning that the water interacting with the underside of the boat will be much less powerful. Since the thrust form the propeller will have less effect on the hull, less prop walk will be noticed, allowing the sailboat to reverse more predictably. 

A deep bilge hull will interact with deeper water where more thrust is present and the effects of prop walk will be more prominent. Deep bilge hulls tend to have full or long keels, which will actually separate the thrust from a center line propeller. This means that thrust from the ascending blades with their greater thrust will be pushed down one side of the hull and the descending blades with their weaker thrust will be pushed down the other side of the hull. This stark difference of great thrust on one side and little thrust on the other side will result in significant prop walk!

Source: http://www.x-yachts.com/range/xp/xp-50/#PhotoSwipe1471987985724

To tie all these individual factors together, the ideal propeller situation for minimal prop walk would be:

• Shallow bilge
• Shallow propeller
• Low RPM
• Propeller free and clear of all obstructions
• Propeller mounted horizontally with no angulation

Source: https://upload.wikimedia.org/wikipedia/commons/f/f3/Saildrive-First-40.7.JPG

If you have a shallow bilge, how can you mount the propeller with no angulation? The sail drive! A sail drive will mount the propeller free and clear of any obstruction with no angulation. This is one of the reasons sail drives are so popular on sailboats, they provide a clear and unobstructed propeller mounting location where the engine can be located higher than the propeller with no angulation issues.

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The ideal set up for the worst possible prop walk would be:

• Deep bilge
• Full keel with the propeller set in an aperture
• High RPM
• Propeller mounted close to the rudder post
• Propeller mounted on a steep shaft angle

This setup would yield a boat that would move forward and sideways! 

If you have significant prop walk, running your engine at lower RPMs would help alleviate the issues. If you find yourself wishing to back into a slip, try using light bursts of low throttle. This low throttle will keep prop walk to a minimum while moving the boat astern. Once you pick up a bit of speed (which will be light since you are not giving it much throttle), put the motor back into neutral, allowing it to drift backwards without any influence from the propeller. This will allow you to drift backwards in a predictable manner without suffering from the lateral thrust of prop walk. Learning how to use prop walk to your advantage may be a better solution. 

Prop walk will reliably push your stern in the same direction. Right Hand propellers will push your stern to port, Left Hand propellers will push your stern to starboard. If you have significant prop walk, you can use it as a stern thruster. If you find yourself on a pier or sea wall and need to get off of it, applying hard throttle will actually push your stern off the pier (if you are set up to prop walk away from the structure) like a stern thruster, but without all the complexity or added maintenance of an actual thruster.

Once you know which way your boat will walk, and how strong the prop walk is, it is important to note one additional feature of this phenomenon. Prop walk will do the opposite if your boat is moving forward with speed. This means that if you have a LH propeller and walk to starboard when you put it in reverse from a standstill, you will actually rotate the stern to port if you put it in hard reverse while moving forward with speed. 

Not all boats do this, so be sure to test it out in open waters so that this little feature doesn't catch you off guard during close quarters maneuvering. This phenomenon is caused by the confused water rushing past the propeller as the propeller is spinning fiercely in the opposite direction. The disturbed flow will cause the boat to pivot in the opposite rotation from the norm when not moving forward.

Before you begin cursing your boat for making you look like a landlubber who "tried to park his boat" when you attempted to back into your slip, figure out which way it wants to walk and learn how to use it to your advantage!