Slot Affect Sailing

The effect of sails in combination is not simply additive. Two sails can be twice as effective as one sail or less than twice as effective. The combination of jib and mainsail in a Bermuda sloop is very common because these two sails form a particularly beneficial symbiosis. The governing aerodynamics of this happy union goes by the name of the slot effect, about which much—too much—has been written over the years. By now the warning bells should already have rung in your head: as soon as the word 'aerodynamics' is mentioned, you should anticipate conflicting claims and arguments over the physics of the slot effect. As always, I will banish detailed explanations, and also a brief summary of the common misconceptions, to the appendix. It is appropriate here, nevertheless, to at least state the cause and effect of 'the slot' because it is an important part of sloop performance.

Airplane designers know all about the slot effect. The flaps on an aircraft wing, both at the front and the back, are control surfaces that permit the pilot to change the way that air flows over the wing. Staggered wings on an old biplane also influence each other. Way back in the 1930s Prandtl was able to write that 'the total induced drag of a biplane is smaller than that of a monoplane of the same span and of the same lift.'

More on the Slot Effect Arvel Gentry continues his discussion of jib-mainsail interaction By Arvel Gentry SAIL Magazine, August 1973 Last month we first studied the air flow around the main alone; then we added a jib, and this gave us a good picture of how the jib affects the mainsail. This month we will do just the opposite.

• Older tracks equipped with slides, a slot with slugs, or a slot with a boltrope, are all friction factors that affect halyard loading. With the older, more friction-bound hoist pathways, the halyard endures less peak loading because much of the energy transfer results in direct pressure from the sail to the spar, thanks to friction in the track.
• Here (Vancouver Canada) the ferry departures are referred to as “sailings”. When the weather is particularly windy, sailings are cancelled so people cannot get from Victoria to Vancouver by car.
• A stack pack adds windage that can detrimentally affect sailing performance. For many leisure sailors and cruisers, this is not a major concern. Lazy jacks are not intended to replace the topping lift as support for the boom. Never loosen the topping lift to the point that the lazy jacks bear the boom's weight.
• Palace is a modular building added in the Seat of Power DLC, it affects and boosts buildings built within the street range of the palace, which depends on the number of wings built. The palace contains five different departments, each of them has a certain passive effect, which can be amplified by obtaining prestige levels. You can also choose one out of five policies to be active within each.

* Symmetric spinnakers can be difficult to use and are hard work because they are flown only when the boat is running downwind and must be doused for other points of sail. The spinnaker of fig. 4.12 is symmetric (note the spinnaker pole that separates the mast from the spinnaker weather-side clew). There are also asymmetric spinnakers that can be deployed to windward. For downwind sailing there are also genoa foresails ('jennies'), which are large jib sails, and the so-called gennakers, which are genoa-spinnaker hybrids.

Slot Affect Sailing Fishing

Apparent wind velocity

Apparent wind velocity

Main

Figure 4.13. The slot effect is well known to airplane designers but has been understood in the context of sailing only within the last 40 years. On a windward point of sail, the jib influences, and is influenced by, the mainsail. The jib redirects the wind flow so that mainsail drag is reduced. The mainsail increases the jib's lift.

This fact may seem surprising, and certainly to someone schooled only in the Newtonian momentum flux ideas: the frontal area of biplane wings is greater than that of a single monoplane wing, so shouldn't the drag be greater? Well, no—that's aerodynamics for you. Explanations later. The important point is that drag is reduced, and the same thing applies to sails.

Jib and mainsail combine in the same way as the staggered wings of a biplane. When beating to weather, the combination is a very efficient sail plan. The typical orientation of jib and mainsail, and of apparent wind and heading directions, is shown in figure 4.13. The jib redirects wind on the lee side of the mainsail (jib and main form a 'slot' for the air passing between) so as to reduce mainsail drag. Another effect, surprising and perhaps counterintuitive, is that the mainsail influences jib performance. How can this be, given that the mainsail is mostly downwind of the jib? All explanation deferred.

All that the practical helmsman needs to know is that the mainsail's presence makes the jib a more effective fore-and-aft sail. If the jib has a mainsail behind it, the jib provides more lift than it would in isolation. When racing on a close haul, the helmsman 'shifts through the gears': he

Figure 4.14. Aerodynamics in action. The airplane wing provides vertical lift; the boats' triangular mainsails provide horizontal lift, whereas the foresails provide drag for downwind movement. What this picture does not reveal is the physics that applies underwater. Thanks to Simona Manca for this image.

Figure 4.14. Aerodynamics in action. The airplane wing provides vertical lift; the boats' triangular mainsails provide horizontal lift, whereas the foresails provide drag for downwind movement. What this picture does not reveal is the physics that applies underwater. Thanks to Simona Manca for this image.

repeatedly trims the jib and main as his yacht picks up speed. The jib is adjusted first because it influences how the mainsail should be trimmed, due to the slot effect.

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Trying to decide which time slot is right for you:

• Morning charters in the summer are usually hot! pack a towel for a swim. In other months they typically begin with cooler temps and a mild to moderate breeze. By the end of the sail, you can expect warmer temps and usually a very light breeze. If you are new to boating or concerned about the conditions this is probably your best choice.
• Afternoon trips typically begin with higher temps, particularly noticeable at the dock, but with a stronger breeze that makes it feel great once on the water. If you are a sailor and looking for the best sailing conditions, this is probably your best choice.
• Sunset trips typically combine the best parts of morning and afternoon trips. They typically begin with lots of breeze and higher temps followed by calming conditions and lowering temps as the evening progresses.

What to Bring:​

• Sunscreen (no spray on type please), Camera, Hat, Snacks, Beverages including alcohol are welcome. Bottled water and ice are provided for you. No RED wine, please.

​Rain:

• In the summer, the forecast almost always calls for a chance of rain. It's UNLIKELY that this will affect your trip due to our proximity to the coast.
• The Captain will contact you if weather is a concern. We want you to enjoy your time aboard.

What to wear:

• ​It's HOT in the summer. Dress for it. In the winter, dress in layers. Feel free to bring additional layers aboard. We have plenty of room to stow them.
  
• Please, no heels or marking soles. You'll likely see the Captain in flip flops.​

Kids and age limits:

• We've had ages from 2 months to 1068 months (that's 89 years old in case you were wondering) aboard. All are welcome, but if your child is used to going to bed at 7pm and you book a sunset sail that ends at 9pm, don't be surprised if they are grumpy. We board directly over the stern and it's one step up into the cockpit. It's by far the easiest sailing charter to board in the area.

Seasickness:

• We've never had a seasick guest on one of our 3 hour charters.

Gratuity:

• ​If you feel like you received above average service, it is customary to tip the Captain and crew.

What time do trips start:

• Trips are adjusted for sunrise/sunset throughout the year. Our online booking calendar reflects these adjustments

Is the boat in the pictures the boat we will be on?

• Yes, and it HAS A TOILET!​​

Cancellations:

Slot Affect Sailing Games

• If you must cancel or reschedule your trip, please notify us at least 7 days in advance. ​Reservations made within 7 days of the trip cannot be canceled.​ Deposits for Special Excursions are non-refundable unless canceled by the Captain.
• Your Captain reserves the right to alter, cancel, or reschedule your trip should the weather adversely affect the enjoyment or safety of your trip. Thankfully, this is extremely rare.

Food:

Slot Affect Sailing Charter

1. While you are welcome to bring food aboard, we do recommend simple and easy to eat items since our time will be spent sailing and elaborate meals often mean we must stop the boat or take time away from your experience to eat.