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!

Honeymoon Cruise: Day 9

Today was a roller coaster of a day! We had fun, panicked for a while, and then relaxed later on.

Today's plan was to drive to Ocean City and spend some time swimming in the ocean and walking along the boardwalk. Then a 25 knot wind blowing through the anchorage threw a monkey wrench into our plan. Maddie really wanted to go to Ocean City and we had decided that we would leave tomorrow morning, so today was the only day that we could go. To calm my concerns about Wisdom dragging anchor and drifting away, I let out some more chain, giving us plenty of scope to hold us still. 

We were anchored in 8 feet of water with 60 feet of chain out. Our bow roller sits 6 feet up, so our effective depth for calculations is 14 feet, giving us a scope of 4.3. The bottom in this creek is soft mud, which our Bruce anchor digs into like a champ! We have held fine for the past few days with very strong tidal reversals, but I was still concerned that we might drag anchor with the strong winds while we were away; so I let out 40 feet more of chain, changing our scope to 7.1. The snubber was tied and the anchor was very well set in the mud.

The creek is very protected! 25 knots of wind produced no wave action, but the wind resistance on the boat kept the chain taught. I felt ok leaving the boat for the day during these conditions because I knew that the anchor was well set with plenty of scope and a well tied snubber. 

We drove to Ocean City and experienced the typical touristy attractions: walked on the boardwalk, ate some boardwalk fries, played mini golf, and then we got a phone call that changed everything!

The Coast Guard called my cell phone to alert me that my boat was adrift and had been towed to the floating pier of a Campbell's Boatyard. Maddie and I quickly got in the car and drove the one hour drive back to Oxford. The Coast Guard agent didn't have any additional information but we did let him know that we would be there to recover the boat as soon as possible.

Maddie and I began wondering how the pets were doing? Morty, our corgi, and Sammy, our parrot, were locked inside the sailboat while we were away. Maddie Googled Campbells Boatyard and the result that we saw terrified us! I pulled up the sailboats satellite tracker on my cell phone but the last reported position was where we anchored it. According to this, the boat had not moved, but the last ping from the boat was a few hours old, so we figured it hasn't updated yet and the boat must actually be far away from where we left it; otherwise, why would the Coast Guard have called us?

Somehow, we had drifted from the small creek by Oxford, out the creek and down the river! We were very glad to hear that the boat had been recovered but were wondering what kind of damage the boat must have sustained while banging into the pilings that line the creek we were anchored in.

Maddie and I stopped worrying about what might have happened to the boat and instead began devising a plan of how we would get the boat back. We were thinking Maddie could wait at my grandmothers house I row to the boat and sail it back, or my grandmother drive us to the boat and we both sail it back, or set sail from there and return to Fells Point in the morning. Many options filled the air in the car until Maddie cut though the confusion with: "I'm tired and need to get a shower, lets go to your grandmothers house first and decide a plan once we are feeling refreshed." This was a good plan, no amount of talking would get Wisdom back into the creek and she is currently tied up to a pier, not drifting through the river as a navigational hazard and lost to us.

We got back to my grandmothers house and I ran to the shore to see if by some miracle the boat was still anchored where we left her, and there she was! She was still anchored in the same place, not tied up to a floating pier, and not far from the creek! How could this be?

I looked at the marina next to our sailboat and noticed that they had a floating pier with a sailboat of similar size tied up to it, so I rowed over to talk to the marina manager and let him know that the boat he has tied up is not mine and they should contact the real owner to let him know what had happened. 

Turns out Campbell's Boatyard has multiple locations, and this was one of them, it even had a floating pier! The marina was closed but I got talking with a friendly sail boater who was tied up on the floating pier. They started telling me how my sailboat "dragged anchor for 200 feet, but hasn't moved in a while". I told them that I had 100 feet of chain out, and when the tide changed, my boat simply swung to its new position. I soon realized that this guy has probably never anchored and that I was wasting time. 

When I put all the information together, I figured out what had actually happened today:

• The people who called were the people tied up to the floating pier at Campbell's Boatyard. Not that my boat was now tied up to the floating pier at Campbell's Boatyard, this was an error in communication on their part while relaying information to the Coast Guard.
• The 100 foot scope was a bit excessive, but when the tide changed, the boat swung and drifted 200 feet. 100 feet from where it was resting to be over the anchor, and another 100 feet to its new position.
• The boat never dragged anchor, the anchor had never moved. They must think that dropping anchor is like parking a car, it stays exactly where you put it and will never swing or drift.

Some valuable lessons were learned today:

• Always leave the satellite tracker on, sending a signal, and plugged in. If the boat ever does break loose and drift away, you will be able to find it in the bay based on the updated position reporting.
• Don't panic about things that are far away or out of your control. Worrying about what might have happened to the boat was pointless. If it did happen, worrying about it won't undo the damage. If it didn't happen, worrying about is pointless. In other words, don't worry and just deal with it as it happens.

The day did end on a very positive note, all our pets were fine and we had a good time in Ocean City. We said goodbye to my grandmother because we were going to be leaving very early in the morning with the ebbing tide. For now, we will rest easy knowing that everything turned out ok in the end.

Honeymoon Cruise: Day 8

The morning started off with a long and heavy downpour, the skies were gray and we were still in a very lazy mood.

I looked outside the companionway and saw no desire in leaving the boat. The rain was falling straight down with no presence of wind, so I decided I would set up some rain collection devices. 

I positioned the staysail in a way that it covered the majority of the foredeck and drained into a bucket placed at its lowest corner. I also raised the boom with the topping lift and set another bucket under the gooseneck to catch any rain that drained off the main. All of these measures proved rather ineffective. The main produced 1/4 of a bucket and the staysail produced nearly 1/4 of a bucket. My plan was to do some laundry today with the rain water I collected, but I couldn't collect enough rain to make the endeavor worthwhile. Just like everything else, laundry got pushed back to a later date when we had more water and more desire. 

Watching all the rain fall on the deck and dribble through the toe rail makes me wish I could collect the rainwater from the deck! The deck offers a lot of surface area which is collecting and then disposing of a lot of fresh water. If I could set up a system that would collect this water, we could supplement our water needs while cruising and avoid the necessary trips to shore to re-water the boat. I know that the deck collects a lot more than just water, bird poop, salt, and regular dirt seem to accumulate on the deck when we are sailing. If the deck were our water collector, I would be much more motivated to keep it spotless, and a quick scrub at the beginning of a rain storm would clean the deck, allowing any crud to be washed off before the tanks were allowed to be filled. While I didn't get much done, my mind did begin devising new projects and plans!

Once the rain passed, we went to shore and made our way to a local movie theater where we got to see "Finding Dory". This was surely a highlight of our day! Maddie and I both remember watching "Finding Nemo" as small children, so seeing the story continue all those years later was a very entertaining moment.

After that, we enjoyed some locally made ice cream and sat by the shore watching the tide flow in. Our day passed as slowly as the water rose before us. 

Later that afternoon, we ventured over to St. Michael's to get dinner at "Aweful Arthurs", which despite the name, was very wonderful! Fresh seafood and gluten free options on the menu made Maddie and me quite delighted! While we had a boat stocked with foods for the trip, we enjoyed eating at unique places that have the local flavors cooked into the meals.

The day was drawing to an end and we made our way back to the boat for another nights rest.

Electric Motoring

When you decide you want to crank up your electric motor to reach a destination, there are some important steps to follow.

First, you should understand how to read the display from the electric motor.

The display is organized into two columns. The left column shows: Battery voltage (V), Engine power production (KW), Time remaining at current draw rate (HR). The right column shows: Motor consumption in Amps (A), Battery charge remaining (%), and Propeller RPM (R/M).

In this example, the battery has 47.97 volts DC, the motor is drawing 121 amps, producing 5.82 KW, 88% battery remaining, making the propeller spin at 1121 RPM, and has a remaining run time of 1.2 hours.

The reason this is important is if you are trying to motor somewhere, this information will be very important in determining if you will make it or not. A good chart plotter with navigational functions can provide you with an ETA to your destination. The ETA is your Estimated Time of Arrival. If your ETA is longer than your remaining battery run time (lower left corner), you are not going to make it at your current speed. 

At higher speeds, you will have less run time because the engine will be drawing more amps to move your vessel. Slower speeds will provide more run time, but it will also take you longer to get anywhere. On Wisdom, we can travel at full throttle (7.5 knots) for 24 minutes. This will give us a range of 3 nautical miles. At 2 knots, we consume around 10 amps and have a run time of around 20 hours, giving us a range of 40 nautical miles.

As you can see, moving slower will give you more range, but it will also take you forever to get there. This is why I use the ETA readout on the chart plotter in combination with the remaining run time in the lower left corner to find a speed that will get us to our destination with at least an hour of run time remaining. This extra hour will provide us with some buffer to changes in weather or currents, and avoid a complete discharge of our engine battery bank (which would destroy the batteries).