“How to…Drive a Fast Boat Safely” In competitive angling, having a fast boat to reach the honey hole first is an advantage, or is it really? What happens if someone has the money to afford all the bells and whistles but is not capable in safely handling a speeding projectile? – BoatTEST.com
In competitive angling, having a fast boat to reach the honey hole first is an advantage, or is it really? What happens if someone has the money to afford all the bells and whistles but is not capable in safely handling a speeding projectile?
On the water, the sensation of speed is enhanced. For most people, 50 mph (80km/h) in a boat feels like 70 or 80 on the road. Those who have run triple digits on the water know that there’s more to operating a boat than slamming the throttles forward and hanging on. Attention needs to be paid to the boat’s trim, over-revving the engines when running in waves and, of course, the conditions. Following are the details that require attention travelling across the water at high speeds.
Before slipping into the bolster or high-backed bucket seat of any performance boat, a driver needs to know what kind of hull bottom design is beneath him. Traditional offshore performance boats have Deep-V bottoms with at least twenty degrees of dead rise at the transom. To run fast in calm water, they require lots of positive trim and are actually happier running in some chop. Bass boats have similar designs with shallower dead rise, a keel pad and a broad bow flare that help create lift. But that perform best and most safely in smooth water.
Stepped V-bottoms literally have steps designed into the running surface that generate lift and require less positive drive trim. These boats run flatter and faster on the same power compared to a conventional V-bottom. Catamarans are air-entrapment designs with two hulls connected by a flat deck in between. They are designed to run on top of the water and are the fastest of the three designs power for power.
A boat that is designed to run 60 mph (97km/h) or faster should have hydraulic steering. It provides more precise control by using pressure in the system’s hoses to move the drives or outboards when the steering wheel is turned. Conventional cable systems lack the precision or durability to hold up in performance applications. For running in offshore conditions, heavyduty trim tabs such as Mercury Racing K-planes or similar units from Livorsi Marine with position indicators at the helm are a must. For the boat’s interior, the captain and a companion travel in stand-up bolsters with dropout bottoms or high-backed bucket seats in sit-down boats.
Trim tabs or after planes are a pair of flat, movable surfaces that extend aft from the boat bottom; one on each side of center. Each surface is individually adjustable up or down and, on the more sophisticated installations, by a remote control switch. These “trim tabs” are not to be confused with the small adjustable fin located on the gear housing just above and behind the propeller and used to help offset steering torque. It is also called a “trim tab”.
After planes offer another method of trimming your boat in addition to power trim. When a boat’s running attitude exceeds five degrees, it is beginning to run increasingly less efficiently. Therefore, stern-heavy boats that need to run at a slow plane (20 to 25 mph) will be greatly aided by after planes both in the efficiency and comfort departments.
Other benefits of after planes are faster planing, control of list or boat roll, and additional fuel savings made possible by allowing the boat to run at a lower engine RPM while remaining in an efficient planing attitude.
On any performance boat, the captain should know what neutral or level trim is. With the boat on the trailer, use a level to find neutral for the drives and tabs, if equipped. This will vary from boat to boat because of transom angle. Have someone at the helm raise or lower the drives until a level pressed against the bottom of the anti-cavitation plates on the drives zeroes out.
Do the same by aligning the tabs with the running surface. Note the position on the trim indicators for the drives and tabs. Remember that trim tabs can be lowered to keep more of the boat in the water in rough conditions or to level loads, but unlike drives, the boat won’t go faster if the tabs are raised past neutral. Once they lose contact with the water, they make no difference.
A cavitation plate (anti-ventilation plate) is a permanent horizontal plate on the vertical shaft of the outboard right above the propeller. It sits just at the water level when the boat is up on plane, that is flush with the bottom of the boat, for a planing designed hull.
It prevents ‘cavitation’ of the propeller - prevents air from the surface of the water being picked up by the action of the propeller. Cavitation drastically reduces a prop’s effectiveness and efficiency. It basically pushes air rather than just water. Over-revving can also result.
Many high-performance boaters are aware of a phenomenon that limits their top speed below what would otherwise be pos¬sible with the available horsepower. This phenomenon is com¬monly called “gearcase blow-out,” “propeller blowout,” or just “blow-out.”
Following is an explanation of why blowout occurs and how to correct it.
Since low pressure is the cause of cavitation, anything that fur¬ther
reduces the pressure on any side of the torpedo will hasten cavitation. Trimming the unit out will cause lower pressure on the underside of the torpedo, around the skeg; but an even more insidious culprit is the effect of a surfacing propeller pulling the aft end of the torpedo to the right with a right-hand rotation propeller. This causes lower pressure on the left side because of the angle at which the gearcase is forced to run through the water. This is commonly called the “crab” angle. The typical combination of a surfacing right-hand propeller and trimming out for best speed creates an extra-low pressure pocket on the lower left side of the torpedo.
However, cavitation itself does not cause the “blow-out.” Blow-out occurs when the very low pressure cavitation bubbles eventually reach back to the aft end of the torpedo in sufficient quantity to suddenly pull in, or connect up with the engine exhaust gases. The cavitation and exhaust gas linkup is more prevalent with a non-through-hub exhaust propeller.
Once the connection is made, the exhaust follows the cavitation bubbles forward and floods out over the lowpressure side of the gearcase (the left side with a right-hand rotation propeller) and feeds back into the propeller blades, causing a sudden and drastic reduction of lift or thrust generated by the low-pressure side of the propeller blades. This partial unloading of the propeller creates four sudden reactions:
The bow-lifting effect of the rake diminishes, causing the bow to drop.
The hard-steering torque to the right is suddenly reduced, causing the boat to veer slightly to the left.
The reduced load on the propeller allows the engine to rev up by 200 to 300 RPM.
The wetter boat bottom and reduced propeller efficiency cause the boat to go slower by perhaps a couple of miles per hour.
How to correct blow-out
With the latest gearcase designs, blow-out should not be a problem below 80 mph.
However, if the problem exists, contact your dealer. A special gearcase is available for many outboards and some stern drives that should cure the problem. The special gearcase has an extended torpedo nose, more rudder area, improved high-speed cooling water intakes, and a cupped skeg, which greatly reduces “crabbing” and steering pull to the right.
Other than running with excessive trim-out, the most significant cause of the blow-out is a torpedo that has been buffed in a way that rolls off the trailing edge of the torpedo.
Some gearcases eliminate this problem by casting the torpedo in a slightly conical shape, leaving a slight raised sharp edge just ahead of the trailing edge of the torpedo. This patented feature, which can vary from .005” to .050” in height, retards the connection of exhaust to torpedo cavitation by creating a higher pressure fence much like the diffuser ring or flare on the aft end of a through-hub exhaust propeller, which deters the exhaust from being drawn forward into the low-pressure side of the propeller blades. Within the range given, the higher the bump, the higher the speed protection, but with slight additional drag.
On the plane
A go-fast designed for all-around performance will plane off easily in most cases. Use enough power to get the bow to drop quickly to maintain good forward visibility. Some older designs propped exclusively for top end required the driver to nail the throttles and wait for props to catch after over-spinning initially.
On some boats with high bow rise, losing forward visibility can be a problem. Make sure the way is clear ahead and get the bow down quickly.
Especially in a performance boat, the captain is responsible for keeping the least comfortable passenger as content as possible. That means keeping the boat riding level fore to aft and laterally. For virtually all designs, the approach is the same when running into head seas. Start with the drives and tabs trimmed down with the tabs at neutral or slightly below to extend the length of the boat’s running surface. To pick up speed, trim out the drives a little at a time so that the boat is still riding level and skimming across the waves cleanly.
Running with the waves is a little more challenging because using too much negative trim will cause the bow to stuff into the back of the lead wave and excessive positive trim will cause the stern to “trip” off a wave and throw the bow skyward. This often results in the bow slapping down, which, depending on the impact, will hurt passengers or eject them. To run safely in following seas, use enough positive drive and tab trim to run slightly bow up. If the bow starts hopping, the trim is too high and needs to be tucked in
a little. If the bow plows through the water and pulls to one side or the other a little more positive trim is required.
Anytime waves are parallel or quartering to a boat, the captain’s trimming skills will be put to the test. If a boat is running parallel to the waves, lower the tab on the opposite side of the boat to level the ride and set the drives at neutral. With waves hitting the boat from the aft quarter on either side, take the same approach. Use the tabs to level the boat and trim out the drives incrementally. If the boat doesn’t have tabs, use the drives to level the boat.
Performance boats were never meant to be turned like personal watercraft or ski boats, but people still seem to want to try it. With a nonstepped V-bottom, before turning, either trim down the drives or pull back on the throttle to reduce the speed and set the boat in the water. Hold the steering wheel in a constant position to complete the arc and maintain consistent throttle to keep the boat on plane.
Drivers of some stepped hulls get in trouble when turning a stepped hull because they use the same approach as turning a non-stepped hull. Never apply negative trim to a stepped hull prior to turning. This forces the bow down too far. It will dig in and the stern will snap around, causing the boat to spin out or “swap ends.” When turning a stepped hull, leave the drive trim where it’s set, raise the tabs (if so equipped) and make the turn with the same steady hold on the steering wheel and the same consistent throttle pressure. Be ready to correct the wheel against the turn if the boat feels like the rear end wants to kick out.
Keep a lookout
Hitting another boat, a piling, or some obstruction can ruin your whole day. When going fast, you should know the waters you are in and stay safely in deep water. Keep any eye out forward and left and right for other boats. Move away from them and don’t play chicken.
Walk on the wild side
The key to running any performance boat is that small things make a big difference. A positive tap on the trim buttons could be all that is required to “free up” a boat to run those big speed numbers. It can also be the difference between being in control and causing a disconcerting handling problem. How a captain responds to these scenarios is crucial.
When running at speeds above 80 mph (129km/h), he can’t just yank back on the throttles and hope the boat settles. If a boat starts chine-walking, pull back on the throttles a little or trim down the tabs slightly to stop the oscillation. An experienced pilot can “drive out” of a chine walk without slowing down, but that’s a move best left to veterans. The easiest way to stop a boat from porpoising is to trim down or apply a little more throttle because the boat is searching for more speed.
When observing from behind a boat, the propeller turns clock¬wise when underway with a normal righthand propeller. As water resists the clockwise rotating propeller, it causes the boat to roll slightly in the opposite direction (counter clockwise) or down on the left (port) side and up on the right (starboard) side. To offset this slight imbalance, the driver’s seat is placed on the starboard side. Boats differ signifi¬cantly in the degree of their reaction to prop torque.
Don’t drive fast in low light conditions. No matter how good you think you are, don’t drive fast. Every year, people are killed driving into unseen breakwaters, pilings, boats, barges, and even islands. Each year, driving fast in low light conditions claims scores of deaths. (The same precautions apply when encountering fog – Ed.)
Fast boats are fun but in the wrong hands they can be dangerous. Unfortunately, it seems that the people with the least amount of experience are often drawn to race boats like moths to a light. By definition, these are people who like the thrill of living dangerously.
If you are one of those people, just remember that over about 350 people are killed in the USA each year in boating accidents and speeding. Out of control boats are the biggest single cause of death.
Never drink and drive a boat! It sounds obvious, but all too many people do it. If you are going to break this cardinal rule, at least don’t drive fast.
For years, our advice to boaters who see Cigarette-type high performance boats speeding along is to always head behind them. Chances are they don’t see you, and behind them is the safest place to be.
*This article is edited and re-printed with permission from The BoatTEST. com
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Most bass boats have a V-hull design with shallower dead rise, a keel pad and a broad bow flare that help create lift
Indicators that show the position of the drive and trim tabs are critical on any highperformance boat
When a performance boat is trimmed too high in following seas, it will stand up on end and then stuff the bow severely on re-entry
Basic hull designs
Hydraulic steering provides more precise control and should be installed on any fast boat
A cavitation plate prevents air from the surface of the water being picked up by the action of the propeller