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The Thrill of High Performance Boating

    There are several good reasons why an increasing number of people are choosing to spend some of their leisure hours participating in high performance boating. For many people the freedom to move over the water at what can seem like a breathtaking speed provides unmatched pleasure. The widely accessible and varying waterways with surface conditions that are as varied as the winds that create them provide a playground broader than that generally available to snowmobiles, trail bikes or off road buggies. There is that informal never ending competition with your neighbor. There s the pitting of your driving skills against the various hurdles provided by mother nature in the form of wind and waves. And yet with this form of entertainment readily available, today's high performance boat package is quite suitable for water skiing or cruising.

    Granted a light high performance boat is not as roomy or does not provide as good a rough water ride as a larger heavier cruiser, but the fuel economy improvement can be spectacular. Consider a 200 HP outboard powering a 50 MPH cruiser as compared to a 75 MPH light, performance boat. Naturally at wide open throttle the engine will use the same amount of fuel on either boat. but since the performance boat's speed is 50% higher so will the fuel economy (MPG) be 50% higher. Now if you back off the performance pack­age to two-thirds, throttle, let's say to 4000 RPM from 6000 RPM, your speed will drop to 50 MPH, but your fuel consumption will be cut to less than half and your fuel economy will now be 2-112 limes that of the cruiser. As both boats are throttled back the economy edge will gradually diminish to the original 50% advantage.

     Performance boat popularity has demanded improvements in propeller and gear case design and these demands have been answered thus providing smoother high speed performance in spite of the steady climb in top speeds. And so with the continuing evolution of more powerful. More efficient outboards and stern drives married to improved, lighter but stronger boat designs, it becomes more important than ever for owners and drivers of hl-performance boats to go through a learning procedure that can make them aware of and perhaps eliminate the surprises from otherwise difficult situations.

    The following information is presented in an effort to walk a new driver through a series of steps that should prepare him for most potential surprise occurrences.

Before You Ever Start the Engine  

     (If you are just putting the boat in the water, don't forget the bilge plug.) Can the gunnel be stepped on? It so, is it slippery glass or wood or is there a rubber, vinyl or some non-slippery step pad? When you step down on the gunnel, how tipsy is the boat? What is the safest way to get in? How would you direct an unsteady person to get in?  Settle into the driver's seat: Is It the bucket type that will give some side support or can you easily slide off? Is there a good place for you to brace your feet? Locate all the instruments, particularly  the tachometer,  trim for engine and jack plate (if installed), speedometer, and  the fuel gauge.

Locate all the controls:

1)     Ignition key location (in control box? on dash?)

2)     Choke if engine has it (on control box? on dash? in key  switch?)

3)     Power Trim (In shift handle? on dash? on steering wheel?)

4)     Shift lever (Is the travel comfortable? Might your knuckles scrape on anything? Can you feel the neutral detent clearly?)

5)     Throttle (Is it combined with the shift lever?) What stops the throttle from full travel in forward and reverse - internal end of travel or hitting against a seat, arm rest or side of boat? Or does the boat have a foot throttle?

6)      Steering Wheel (VERY IMPORTANT - Is it slippery?) How many turns end to end? About three is normal. Grab the wheel firmly with both hands and push and pull on it. Does it seem very strong? It's the only thing you have to hold on to during any accidental or purposefully violent maneuvers. Do you trust it to keep you in the boat?

 Are other accessories visible?

1)  Bilge blower switch (generally not in outboards)

2)  Bilge pump switch

3)  Horn button

4)  Lanyard Stop Switch

    We can't emphasize enough the wisdom of using a lanyard slop switch on Hi-Performance boats or low sided boats. We further suggest that you keep the switch lanyard attached to your life jacket as a re­minder to you and your passengers to wear a U.S. Coast Guard approved life vest when the boat is underway. Should the boat driver lose his balance or be thrown from the driver's position, the chances of anyone being hurt are reduced if the engine imme­diately shuts off. Remember, however, that even with the engine shut off planing boats can take several hundred feet to fall off plane and come to a stop.

5)  Running lights switch

6)  Other instruments

    a. voltmeter or ammeter

    b. hour meter

    c. water pressure gauge

    d. oil pressure gauge (not on outboards)

    e. engine temperature gauge

    f.  engine or stern drive trim indicator gauge


    Now feel around for sharp edges, corners, screws, projecting hardware - anything that could cause injury if you were thrown against it. Do something about what you find, where possible, tape or file to eliminate the hazard. At least be aware of things you can't change. Sit in the passenger's seats. Again, is your rump held in place or can you slide off easily? Do your feet have something to brace against and your hands something to hang on to? (Are there any sharp edges on the fiberglass or trim?) If a passenger is likely to hold onto the seat cushion or back, will it stay secured or is it loosely resting in place? (Later, when you're driving with passengers, remember how insecure you felt in their seats with no steering wheel to grasp. Passengers have one other advantage - you know when you're going to make a turn but they don't.)

For some further peace of mind, let's review an Installation-.

 Is the engine completely bolted in place (all bolt locations utilized)? For engines designed with hand tightened clamp crews, NEVER rely on the clamps only.

 Are the engine steering cables as free of bends as possi­ble? Bends add to steering loads. It is suggested that on boats capable of going over 50 MPH with less than 200 H P (60 MPH with 200 HP or more) dual cable steering be employed and adjusted so that there is a minimum of steering backlash. The more steering backlash that exists, the more difficult it is to control a hi-performance boat.

  At what height is the engine installed?

     If your boat is expected to do 40 MPH or less, the engine should be mounted at the minimum transom height, 20" for a long-shaft engine. If your boat is powered by a 140 HP or better and will do less than 50 MPH maximum, it will prob­ably be best to still leave the engine at a 20" transom height. Lightly loaded boats powered by smaller engines doing between 40 MPH and 50 MPH may benefit slightly by raising the engine up to 1 inch and using a cupped hi-rake propeller.

       If your boat is expected to do 40 MPH or less, the engine should be mounted at the minimum transom height, 20" for a long-shaft engine. If your boat is powered by a 140 HP or better and will do less than 50 MPH maximum, it will prob­ably be best to still leave the engine at a 20" transom height. Lightly loaded boats powered by smaller engines doing between 40 MPH and 50 MPH may benefit slightly by raising the engine up to 1 inch and using a cupped hi-rake propeller.

    As your peak boat speed moves toward 60 MPH, engine height should move up to 22" to 23". This is not just a hi-performance suggestion. Steering torque and boat sta­bility, as well as top speed, will improve as the engine is raised to 23". The only potentially negative result may be some prop "blow out" or "break loose" upon accelerating with a heavy load. It is also becoming important at 23" to use a hi-performance prop possessing a sharp leading edge, crisp cup, and at least 15° of rake.

    At this height your trim tab is no longer effective as a means of altering steering torque. On some gear cases the stan­dard trim tab must be removed to provide blade clearance for Hi-Performance propellers. A flat plate zinc anode, part number C-76214, is available as a replacement to provide continued protection against galvanic corrosion.

     Approaching 70 MPH permits a little more transom height, perhaps 23" to 24". However, at 24" some steering torque pulling to the right (with the common right hand rotation propellers) may occur. Above 70 MPH, 24" to 25" transom height is desirable, but now, at a best speed trimmed-out condition, steering torque may be quite noticeable. And it is becoming important to monitor engine water pressure as some extreme height and trim-out conditions on some boats may cause a damaging reduction in cooling water entering the water Intakes. In fact very serious hi-performance enthusiasts will install a temperature gauge as far downstream in the cooling water ;temperature as possible yet still in the top of the block to avoid being fooled by apparent temporarily high water pressure created by a steam pocket, 140° F (60 °C) is considered the maximum acceptable temperature measured here.

4) Learn what each line in your transom well is and insist that they be tidy to eliminate any chance of kinking or pinching at all steering and tilt positions. You can expect to see:

    a. one or two steering cables

    b. shift cable

    c. throttle cable (looks just like the shift cable)

    d. fuel line (IMPORTANT. See that the primer bulb can easily be seen and grasped.)

    e. Power Trim hydraulic lines

    f. speedometer tubing

    g. electrical engine and power trim harnesses

5)    Check for the location and secure storage of

    a.  a paddle

    b.  a fire extinguisher

    c.  an emergency horn (particularly if one is not perma­nently installed)

    d.  a in throwable life cushion

    e.  the boat registration card (are boat numbers properly mounted?)

    f.   ropes with which to tie up

    g.  a spare strong rope suitable for towing

    h.  spare propeller with thrust hubs and prop nut plus a wrench which fits the prop nut

    i.  a flashlight

    j. a Legal Coast Guard approved life vest for each seat in the boat

    k.  a spare small gas tank (tied doyen)

    I.   the battery - are the battery cables tightened securely? Is it securely fastened down - can't slide or tip? Are the battery terminals covered or protected to prevent accidental electrical shorting,

    m. Where is the fuel tank installed? Aft - best for top speed Bow - best for planing off and rough water.

Is the fuel tank vented? (facilitates filling, eliminates trapped air) Is the fuel tank storage area ventilated? (greatly decreases chance for explosive gas vapor/air mixture buildup)

Starting the Engine

Wear a good quality lifejacket regardless of how well you swim. Have a friend accompany you in a second boat. Your owner's guide covers starting thoroughly, but as an abbreviated review, follow the prescribed starting procedures including:

1)     Operate bilge blower for 5 minutes, if boat is so equipped.

2)     Prime the fuel system with the primer bulb.

3)     Advance the neutral warm-up lever, or the throttle in the neutral warm-up position slightly.

4)     Hold the choke 'on' (outboard only) Listen for the click the engine. It can be reassuring if you aren't sure about your battery.

5)     Crank the engine with the choke" on' until it fires off. When it starts, release the choke, but be prepared on a really cold engine to hit the choke briefly if the engine sounds like it is starting to die from lack of fuel.

Boating Off Plane

With a high performance boat you need a high-pitch prop which puts a much higher load on the engine when you shift into gear. Therefore, the engine must beset up with a higher neutral idle RPM than required for a low-pitch prop installation, With any prop, the in-gear idle RPM should be from 500 RPM to 700 RPM, but neutral RPM may be 800 RPM to 1000 RPM when using a high pitch prop.

It's wise to always shift into gear with a quick motion so as not to grind the clutch teeth. Never shift when any passengers aren't yet seated. Practice a little. Watch out that you don't move the lever so far as to open the throttle when you aren't Intending to. Idle away into at least three or four feet of water. Before you accelerate to on-plane. let's look into backing up. Drop the engine into reverse and as you begin move, look at the build up of water on the transom. How much reverse throttle can you apply before you are concerned about any water coming into the boat? Most new boats have self draining transom wells which will hold out considerable water. However, routing holes for all the lines in the transom at the sides of the well are often not sealed and water may come in through such holes. Check this again whenever you have passengers in the back seat as the boat will sit lower in the water. Also, don't forget the adverse effect of waves washing over your transom when backing into them. While backing, frequently look at the transom so that you are aware of the situation.

You might idle forward a bit to feel out how the boat responds. While coasting forward check how quickly it stops when applying reverse thrust. Get to know how much reverse thrust you can generate to break your forward motion. It's safer (and drier) to learn about maximum reverse thrust while coasting forward -and that is when you need it - rather than when accelerating backwards. Remember, the boat will not slow up as fast when filled with pas­sengers or heavy gear as when It's light. In addition a well trimmed out engine provides less braking.

Does the boat hunt around a bit when you try to idle forward in a straight line? This is common and is generally dealt with by learning how to steer by making small, early corrections. Don't let the boat gain any turning momentum.

OK, Let's Get On Plane

    First, choose a relatively calm day for your first run (and leave any passengers on the dock).

   Second, If your boat is not equipped with a windshield, which does slow a fast boat some, it's advisable to wear goggles, tight-tilting sun­glasses. or in some way protect your eyes from the high-velocity air impact that may contain an occasional bug.

Third, St he water deep enough to plane off? You may need up to a foot more water to plane off in than you need to simply idle around in. Trim the engine to full down (in or under). Does the trim indicator read correctly? Notice the kicked-under attitude of the engine. Now trim out to the maximum where the trim will automatically shut off. Notice the position of the trim indicator needle and the kicked-out attitude of the engine. These are the extreme limits you should operate in while planing, but in practice you will probably need much less than maximum trim-out. To first get on plane try it trimmed full down. This should make for the quickest planing, but when you are on plane you will probably feel some definite steering torque pulling to the right. The boat may also want to bow steer which can cause an unintentional turning. The boat is probably riding too flat.

So you will want to trim out to a position where the engine is about vertical, a rather medium trim position. On most boats this will provide nice handling and good top speed. When planing off, give the engine enough throttle to get on plane quickly. To linger in the "mush' condition can be unnecessar­ily hard on the engine and certainly makes big waves that generally annoy others. Steer back and forth a little to get the feel of the steering torque. Later, try planing off at more of a mid-trim position. Pay attention to varying steering torques so that should an emer­gency arise you will know how much effort will be required to miss something in the water. Also note how the bow comes up higher during planing off at a more trimmed-out condition. Generally, prop break loose will be a little more severe as trim-out is increased.

     If you are using the increasingly popular non-through-hub-­exhaust style props (chopper or cleaver), you may need considerably more throttle and RPM to push up on plane, because the prop must digest all of the exhaust which at low accelerating speeds is easily drawn into the low pressure side of the temporarily heavily loaded blades. Do not hesitate, if necessary, to let the engine RPM climb to 5500 RPM, 6000 RPM or even 6500 RPM for the short duration of planing off. Once up on plane, the prop blades will shed the exhaust bubble and will appear to shift into a more solid bite. You can feel the engine speed jump down a few hundred RPM. The boat will shoat forward slightly. (If this occurs more than once, it's due to the blades not shaking their bubble at the same time.) Once on plane you can expedite this occurrence by a brief backing off on the throttle. If this type prop is run deep enough in the water, If the boat load is light, and if you accelerate on plane at pail throttle, it may not break loose at all.

    Conventional through-hub-exhaust props may also break loose but usually not as severely. This is the result of a high engine setting allowing the prop to pull in surface air. The higher the installation, the more important it is to keep the prop blade leading edges sharp, the tips thin and sharp, and the cup totally concave with a crisp corner or trailing edge.

     Now that you're on plane, get used to the boat at 30 MPH to 40 MPH. Trim in and out fully to experience the changing steering torque. Feel it shift from pulling to the right when kicked under to pulling to the left when kicked out unless your engine is mounted quite high (this reaction would reverse were the engine equipped with a left-hand rotation propeller). Maneuver around at the trim extremes so that you can learn at a relatively safe speed how badly your boat will want to bow steer and potentially spin out when trimmed under, or to porpoise, blowout the prop or chine walk when trimmed too far out. When circling around, slide over your own wake to experience your boat's ability to handle wakes. Take your own wake at a medium speed turn to check out the boat's tendency to bounce and hook a chine, particularly with tri-hull or cathedral type bottoms or the newer tunnel Vee bottoms.

JERK TEST (no reference to driver intended)

    This test must be performed with no passengers as their weight will influence the results. Initially at a speed of 35 MPH trim your engine out as far as you might ever expect to run. If your boat is equipped with a power transom lift, lower your engine to the extreme down position. This engine setting usually provides the greatest likeli­hood of chine walking. Now feel out which direction your boat wants to turn when going straight ahead. A low minimum tran­som height should cause torque to the left. A higher minimum transom height should cause torque to the right. With your hand at the top of the wheel jerk the wheel 180° (In 1 /2 second or less) in the direction the torque wants to go and hold it with no reduction in throttle. This manipulation is what a driver might be expected to do if suddenly confronted with an object dead ahead. The boat may rock over and back a few times (chine walk) but should quickly dampen out If the boat does calm down quickly increase your speed by about 5 MPH and repeat the test. As you test at higher speeds sooner or later you will probably discover that you cannot hold the 1/2 wheel turn, while main­taining your throttle setting without feeling excessively uncomfortable in your boat. You have now discovered at what speed you can make an emergency turn safely. Trimming the engine under or raising the engine will probably raise your safe emer­gency turn speed a little. However, you and anyone allowed to drive your boat should be aware of this handling characteristic. With tunnel vee boats or flat bottom boats with an inadequate steering fin, the boat will begin to merely crab but not change direction appreciably.

    With V-bottom boats factors that can raise your safe handling speed are a tighter steering system or eliminating steering backlash, going to stiffer, mounts, or redistributing your boat load, usually forward a little. Now if you are ready for WOT (wide open throttle) and the wind and waves are light, trim the engine to a medium position, get a good grip on the wheel, and increase the throttle so long as you feel secure. The boat will rise higher out of the water and in many cases, particularly with V-bottoms, require continual small steering correc­tions to hold it level and in a straight line, as it wants to fall sideways off the narrow aft portion of the bottom that remains in the water, off, n referred to as becoming 'squirrelly.' The steering torque will probably be harder to the right. As your experience dictates and provided everything feels under control, hit the trim out button briefly. Typically the bow will come up a little and the boat speed will increase a hair. However, watch for a little steering torque change, and the handling may get a little more "squirrelly.' You're on your own now as to how much trim out you want to try. Usually your ability to handle the' squirreliness" will determine how far out you want to go. In other cases the top speed will start to decline while the steering torque and rooster tail will still be climbing.

   With tunnel Vees or pure tunnel boats because there is consid­erable trapped air under the boat, the driver should keep this style of hull running flatter. In high speed boat jargon these hulls are "less forgiving" if a sudden gust of wind is encountered at high speed. Many high performance boaters are aware of a phenomenon that limits their top speed below what would otherwise be possible with the available horsepower. This phenomenon is commonly called "gear case blowout" or just "blowout". Following is an expla­nation of why blowout occurs and how to correct it.

    To be practical the torpedo of a non-racing gear case must be of a diameter and length just sufficient to house the shafts.. gears. bearings, shift mechanism and a few other related parts. Hydro­dynamics designers can only hope to make the exterior shape of the gear housing the best they can (within their design constraints) to deter cavitation from occurring at the torpedo nose or any sur­face interruptions such as a lubricant filler hole Inevitably a speed is increased cavitation will occur. Since low pressure is the cause of cavitation anything that further reduces the pressure on any side of the torpedo will hasten cavitation. Trimming the unit out will cause lower pressures 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 which the gear case is forced to run through the water. This is commonly called the "crab' angle (see Figure 2 below).


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 in itself does not cause the "blowout'. Blowout 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 gasses. The cavitation and exhaust gas link-up is more prevalent with a non-prop jet exhaust propeller.

Once the connection is made, the exhaust is pulled forward and floods out over the low pressure side of the gear case (the left side with a right hand rotation propeller) and feeds back into the prop blades causing a sudden and drastic reduction of In or thrust generated by the low pressure side of the propeller blades. This radial unloading of the propeller creates four sudden reactions:

(1)     The bow lifting effect of the rake diminishes causing the bow to drop.

(2)     The hard steering torque to the right is suddenly reduced causing the boat to veer slightly to the left.

(3)     The reduced load on the propeller allows the engine to rev up by 200 RPM to 300 RPM.

(4)     The wetter boat bottom and reduced propeller efficiency cause the boat to go slower by perhaps a couple of miles per hour

 Recently several outboard manufacturers are marketing spe­cial gear cases with longer, more streamlined torpedo noses. This helps by adding more rudder area thus reducing the "crab angle" and provides a larger, more gentle nose radius which reduces nose cavitation. This change has usually increased speed by up to 3 MPH in the 90 MPH range. Some of the gear cases also include 'cupped skegs. i.e. casting or bending the trailing edge of the skeg to the right to help steer the unit back out of its crabbed position (assuming a right hand rotation propeller). This not only noticeably raises blowout speed but greatly reduces steering torque. Addition­ally skeg sizes have cable, increase with higher engine installations to help reduce the crab angle "gremlin". Other than running with excessive trim out one of the most significant causes of blowout is a torpedo that has been buffed in a way that rolls off the trailing edge of the torpedo. (See Figure 1 above) The latest Mercury /Mariner answer to this problem is casting the torpedo in a slightly conical shape leaving a slight raised sharp edge just ahead of the trailing edge of the torpedo. The 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 Quicksilver prop jet propeller which deters the exhaust from being drawn forward into the low pressure side of the prop blades. Within the range given the higher the bump the higher the speed protection but with slight additional drag.

Should you experience blowout, contact our Service Depart­ment at Fond on Lac, WI for a recommended solution. One of the more important specific tasks to perform at or near WOT is a sudden chop of the throttle. If you are trimmed out a bit  with relatively high engine installation, the steering torque is prob­ably very noticeable to the right. When you chop the throttle it will reverse and briefly go hard to the left If you are not expecting it, the wheel could spin out of your hand and put you in an unexpected, hard left turn. It would be wise to work up from half throttle at this maneuver. In addition, it your boat is a bow rider, check it out with some additional, people simulating weight in the bow. Its a good idea to discover your rig's degree of maneuverability at W OT (as it is at all speeds) because it may be very limited. It your boat is very fast and the steering effort is annoying (with one hand on the throttle) you may consider installing a foot throttle. Many experienced hl-performance boaters insist on a foot throttle.

    When you ultimately find yourself boating I n a 10-20 MPH wind, you should explore the effect of the wind. Depending upon the degree of deck flare in your bow, a bow wind lifts the bow, necessi­tating less trim. Running into the wind with too much trim has been the cause of many hi-performance boats blowing over. Side winds tend to blow very fast, V-bottom boats off to the side - off that delicate balance that you're trying to hold. Tail winds generally are no trouble. On some very sensitive boats a tail wind lets the boat run so flat that it loses speed.

    There is one maneuver left that could cause trouble, particu­larly with a fast, stern-heavy performance boat. When coming off plane there will be a following wave that inn some cases can roll right over the transom, even into the boat. Turn around and watch for It, and it appears necessary, give the engine a little throttle just as the wave arrives. This situation can become much worse with two or three people sitting in the stern of the boat. In  generally as you add passengers or weight of some kind. there are some things to be aware of.

    Generally they are added toward the rear of the boat where seats are commonly found. This will make planing off more difficult and prop blowout more severe. However, once on plane, things are generally a little better since with more weight, the boat sits lower in the water. The boat should be more stable in rough water, in turns, and at maximum speed. Of course, it will be somewhat slower and you don't want to drive around as sporty as you might when out alone, as a courtesy to your passengers. If your passenger load is toward the front as in a bow-rider design, planing should not be very difficult. However, top speed will be off more noticeably.

Special Multiple Engine Considerations On V-Bottom Boats

    An engine mounted off center on a V-bottom boat will normally be operating behind an angling surface. This depresses the water flow coming off the boat bottom lower on one side of the gear case strut (the side toward the center of the boat) than the other. Since the cooling water intakes are usually located in the strut, this phe­nomenon can cause air to be sucked in through the top holes of the center facing intakes if the engines are raised much above the basic 20" or 25" transom height. This problem has led boaters to plug the upper holes on the inside intake. This can be done by purchasing a pre-partially plugged plastic water screen or applying an epoxy body putty. In some cases, on very fast multiple engine boats with very high transom settings, the inside intakes will be totally plugged and the outside intakes will have their upper holes plugged. This may keep air out but adequate cooling may now depend on high boat speed to ram enough water into the few remaining intake holes.

    Another more obvious problem in picking up adequate cooling water can occur in turns where the engine on the outside of a turn with a boat that leans well into the turn can have its intakes mo­mentarily lifted above the available water line. If this becomes a serious problem, plugging upper holes can again be helpful.

    The most recently discovered cooling problem with multi­engine boats has to do with the center most strokes which typically are located about a loot off of the boat centerline. The vast majority of the hulls in the 30' range normally equipped with twin engines terminate these strakes from 5' to 10' ahead of the transom. If these strakes are not terminated smoothly, (perhaps a 12" transition) they can cause surface air to be sucked into the low pressure created behind the stake and at speeds generally over 50 MPH cause low. extremely irregular water pressure on any engine whose water intakes lie in the path of these air bubbles. Fixes include fairing out the strakes with body putty, moving the engines further out (and up), changing to a special high performance, low level water intake gear case and plumbing in transom mounted auxiliary water pick­ups. Again, water pressures or water temperature gauges are ex­tremely beneficial and could save you a big repair bill.

If your dual engine boat is very fast and may encounter rough water. you may desire switching one of your right hand rotation gear case for a left hand rotation unit Fast dual engine boats with both props turning in the same direction have been known to have their sterns walked around in a hurry when coming off of a wave. Counter rotation is also helpful in holding down steering torque. The majority of dual engine enthusiasts turn their props outward although many feel any difference in handling is not measurable. What about TOE IN - PARALLEL -TOE OUT. We have never seen any evidence to suggest that gear cases should run anything but parallel. However, to achieve this condition on boats with surfac­ing, counter-rotating propellers, a little toe out (assuming props turning outward) may be necessary when the boat is at nestle have the engines ultimately run parallel when up to speed. This is due to steering system springiness and steering torque resulting from the "paddle wheel effect" of a surfaced propeller.

Words of Wisdom

    We recognize that a boater at the helm of his magnificent sport boat has a tendency to feel like he's "King of the Waterways," However, it sport-boating is to avoid being legislated out of exist­ence, a lot of common sense and concern for others on the water must be observed. Any conscientious and courteous sport-boat driver will not mix speed with swimmers, skiers, fishermen, sail­boats, etc. Since you can obviously get there very quickly, go where it's totally safe and your noise and wake won't be bothersome to others. One more comment must be made regarding high speed oper­ation of faster hi-performance boats. Many, if not most, high-speed boats require from their driver a high level of concentration and quick responses. Between holding the boat on its point or pad and watching the water ahead for any traffic, stray wakes, or debris coming at you at perhaps over 100 feet-per-second, a smart driver isn't going to give up any of his driving abilities by dulling them with liquor or drugs.

source: Mercury Marine circa early 1980's

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