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“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

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.

Know neu­tral

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.

Fol­low­ing seas

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.

Quar­ter­ing seas

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.

Turn smart

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.

Rolling over

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.

Most im­por­tant

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.)

Safety first

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

The BoatTEST.com team is a group of highly trained pro­fes­sion­als, all of whom have years of ex­pe­ri­ence in their re­spec­tive fields. These in­clude writ­ers, ed­i­tors, on-cam­era boat­ing ex­perts, field tech­ni­cians, cam­era­men, video ed­i­tors, pro­duc­ers, and mu­si­cians... all com­ing to­gether to make the fi­nal con­tent you see here on BoatTEST.com. We hope you en­joy their work as much as we en­joy work­ing with them.

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

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