Updated: Nov 11
“Rooster Tail” is a jet stream of water that shoots into the air behind a boat. It’s created when the propeller tilts back and shoots an amazing display of water resembling an outstretched rooster’s tail. Although impressive, high rooster tails can indicate that the boat is over-trimmed or that the bow is dropping and the boat is losing performance.
“Prop Slip” is the difference between the theoretical and actual forward speed of a boat based on the angle of the blades. The propeller naturally “slips” and doesn't travel the full distance in one revolution. Propeller slip is not a steady factor and is constantly changing. It accounts for efficiency loss due to weight, drag, hydrodynamics, and aerodynamics. But it’s not an absolute determining factor, typically there is a range of preferred slip percentages to find your optimal propeller based on your boat, motor, set-up, and performance objectives.
“On the Drain Plug” is a saying that the boat is flying well, just almost none of the hull dragging or the boat is riding just on the drain plug. Boaters are reminded to pull the drain plug as a boat leaves a ramp to avoid spreading unwanted plants or animals to other water bodies. It is also illegal in some places to have your drain plug installed with your boat trailered on public roads.
“When in Doubt, Trim it Out” means to raise the bow of a boat slightly. Trim is the running angle of the boat in the water. When you adjust the outboard’s trim, you can raise or lower the bow. When finding the optimal trim, you can improve the boat's performance and fuel economy, too much (blowover) or too little (hook) might cause a catastrophic wreck.
“Prop It” often refers to trying different propellers to see how they perform. The propeller's size and type are put on the boat, and the boat is test-run at wide-open throttle. The propeller's pitch and size can cause the boat to be over-propped or under-propped. Over-propped means the engine cannot achieve its max-rated RPM. Under-propped means the engine reaches max RPM too easily, so the boat doesn't go as fast as expected.
“Setback” in outboard boating is the distance between the transom plus jack plate to the trailing edge of the running surface of the hull. The more setbacks, the more leverage the motor has on the boat. It adds weight to the rear of the boat changing the center of gravity (CG), which can help raise the bow and allow the motor to run in cleaner water. too far back, you may need to trim under for maximum speed and the boat might hook easier due to the steering leverage being moved further back from the boat's designed turning point.
“Air Entrapment” in outboard boating provides a boat with more lift and reduces hydrodynamic friction from the water. Since water is about 800 times denser than air, drag forces are greater, slowing the boat as it moves through the water. Air entrapment can be improved with the right propeller for different outboard applications. These propellers can improve performance on air-entrapment tunnel hulls, multistep, monohull, and V-bottom designs. Yet, too much air entrapment can also cause split-second blow-outs or worse a blowover.
“Number of Blades” on a boat propeller can affect its speed, efficiency, and grip. 3-blade propellers are generally more efficient and have better top speed. However, 4-blade and 5-blade propellers have more blade area, which can provide better hole shot and handling at speed but the added drag can decrease speeds. However, the additional blades can also provide more lift and water displacement. 4-blade and 5-blade propellers can get you on the plane faster and at a lower RPM. 5-blade propellers require more power to swing and work best on the newer more powerful 4-stroke outboards 300 HP or greater.
"Gear Ratio" with a 1.75 the engine driveshaft needs to turn 1.75 times to turn the prop shaft just one complete revolution (e.g. 1.75:1). A 1.62 ratio the engine turns 1.62 times for every revolution of the prop shaft, (e.g. 1.62:1). Drags racers prefer 2:1, which is simply two revolutions of the driveshaft vs one for the prop shaft. A higher ratio = more engine vs. prop shaft rpm's. Top-end racing applications such as Super Speedmaster (SSM) lower units are closer to 1:1.
"Throw a Blade" is a term used in boating to describe when a propeller blade breaks off while the propeller is spinning. The blade may fly off at some speed, hence the term "throw". If a blade is thrown, it can feel like you've lost a transmission. The boat will slow down and vibrate pretty badly and will stay that way through your throttle range. You will also lose handling, it may feel like you've blown up your powerhead. Yes, it's dangerous, also check your prop before running for imperfections and tiny cracks that can lead to big breaks.
"Can you Swing It?" refers to a propeller with too high a pitch that can cause a boat to have slower acceleration and lower top speeds. A propeller with too high a pitch can also cause the engine to "lug" or not reach the bottom of the recommended WOT RPM range. This can put stress on the engine and gearcase components. A propeller with too high a pitch can also cause lower-horsepower engines to bog down. This can wear down internal engine parts that aren't built to withstand that kind of stress.
"Blow Over" is when a tunnel hull, catamaran, or hydroplane race boat suddenly goes airborne and flips. Blowovers are common for hydroplanes because the hull is designed to generate lift to skim over the water. A blowover can occur when something unbalances the forces that keep a boat on the water; such as a sudden gust of wind, a reduction in downforce, propeller angle, and rough water conditions. When this happens, the front end of the boat lifts too far and the control surfaces can't counteract the sudden increase in lift. The boat can quickly fly into the air and backflip. Blowovers are more rare among deep vee-bottom hulls.
"Blow Out" occurs when the ratio of air to water around the propeller is so high that the propeller is no longer grabbing water. Instead, the propeller is trying to propel itself through air or a relative vacuum. Blowout can be caused by the prop running too high, vent holes being too large and allowing too much air to the prop, trimming up too far or cornering, or exhaust gases in a low-pressure area at high speeds. Blowout can also be caused by a rapid change in water pressure along the blades of a propeller. This can cause the water to boil, creating thousands of tiny air bubbles, and cavitation, that burst on the surface of a propeller blade and side of the gearcase.
"Porpoising" is the repetitive motion that causes a boat's bow to bounce up and down out of the water. It occurs when a boat won't trim properly. The boat bounces, alternating between diving and lifting as it compensates for the trim problem. To stop porpoising, you can try to trim down or speed up. You can also try to add more or shift weight further forward. Another common cure could be to find the correct prop, pitch, and or engine height combined with the right trim settings at speed.
"Chine Walking" is a chain reaction that occurs when a boat is running at high speed, usually 65 mph or higher. The boat falls off to one side and then flops back to the other. This is because the boat is trying to run on a very little hull. Chine walking is caused by a boat's roll balance instability, engine torque, rotation of the prop, and the hull lifting out of the water as speeds increase. Chine walking is more likely to happen with deep-V and "padded" bottom boats and can be exacerbated when trimmed.
"Over Trimmed" in boating means that the trim tabs are too low, forcing the bow down. This can cause the boat to veer suddenly, especially at high speeds. "Over-trimmed" in a high-performance outboard boat usually means the motor is kicked out too far, making the boat unstable. The boat may skate around with reduced steering capacity and the bow may lift and drop in a phenomenon known as "porpoising" or even "blowing over", which are terms we cover here as well. Trimming up too much can also make it harder to get on the plane and reduce top-end speed.
"On the Pad" is the flat and/or bottom running surface of a V-bottom boat. When a boat is trimmed up, the pad is the part of the boat that is in contact with the water. At high speeds, the boat rides on the pad, with little or no hull in the water. The pad allows for a more efficient planing surface, which increases the boat's top speed when optimal flying "On the Pad!
“Prop Walk” is the tendency of a propeller to push a boat's stern sideways. It affects most single-engine vessels. For example, a single right-handed fixed propeller will tend to push the stern of a vessel to starboard when going forward and to port when going in reverse. Prop walk is also known as the paddlewheel effect.
"Standing It on Its Tail" in boating can refer to getting water out of a boat. For example, if a boat is full of water and the bilge won't drain, you can try standing it on its tail to get most of the water out. High performance boaters do this while running the boat, or maybe by accident getting the bow way too high in the air.