Engine and Performance



What is the standard height to mount the engine?
For a propeller to best satisfy particular boating needs, the engine must be attached to the transom at the correct height. A correct conventional installation would generally place the antiventilation plate about even with the boat bottom when the engine propeller shaft is parallel to the boat bottom. Setting the engine lower (deeper in the water) tends to cause excessive spray, increase gearcase drag, reduce underwater clearance, and can adversely affect handling of faster boats. Raising the engine can provide several advantages including reduced lower unit drag thus increased speed, improved handling on faster boats, reduction of steering torque and greater clearance to underwater obstacles. In the past, the negative effects from mounting a stern drive higher than standard was an increase in propeller ventilation, which could cause difficulty in planing, (particularly with heavier loads) and overheating due to more aerated water with less pressure. Most raised installations today are found on high performance boats and these drawbacks are justified by increases in performance. In some cases special high performance drives with low water pickups are used with these installations. However, with Stingray's patented ZP-hull, it's now possible to have all the benefits of higher mounted engines without any of the negative effects or cost for special drives.
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Why do most boats drive from the right side?
In single-engine installations nearly all recreational boat manufacturers place their operator's position on the right-hand side and use right-hand rotation propellers to compensate for the boat roll resulting from propeller torque.
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What is the "trim angle" of the engine?
Trim angle of an outboard or stern drive is the angle between the boat bottom and the propeller shaft formed by moving the engine/stern drive closer to the boat transom, called trimming "in" or "down" or "under." Moving the outboard/stern drive further away from the boat transom is called trimming "out" or "up." When a boat is cruising on plane and the trim is adjusted so that the propeller shaft is parallel to the surface of the water, that is said to be running at "neutral" or "zero" trim. With power trim, this angle is adjusted by a switch located on the control handle.
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What effect does trim have on boat performance?
The trim angle of the outboard/stern drive has a distinct effect on the planing angle of the boat, which, in turn, significantly alters top speed and handling. The engine/drive should be trimmed in for best start-up acceleration and shortest time to plane. The engine/drive would then be trimmed out for peak performance. If trimmed "in" (under) too far, the bow drops and the boat runs too wet. In this condition, top speed drops, fuel economy decreases, the boat may oversteer in one direction or the other ("bow steering"), and steering torque will increase (to the right with a right-hand rotation propeller). Occasionally, extreme trim under can cause a boat to list to the left (with a right-hand propeller).

If trimmed "out" too far, the propeller may lose its hold on the water. Fast vee-bottom boats may start to "walk" from right to left to right, etc. ("chine walking"), steering torque will increase in the opposite direction to that when trimmed in, and getting on plane may be difficult or labored. Porpoising of the boat may also occur.
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How does trim angle affect steering torque?
Trim angle does effect steering torque but with power steering there should be little, if any, noticeable difference in steering load.
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What is power trim?
Trimming can be controlled far more conveniently by power trim, which is standard on all Stingray sterndrive boats. Power trim permits control of the angle of the propeller shaft relative to the boat bottom at the touch of a button. While on plane, the angle of the boat bottom to the water has much to do with maximum top speed, fuel economy, handling, and choppy-water ride. Power trim can pay back dollars in fuel savings or give added thrills and safety with a faster, better-handling boat.
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What is power tilt?
Power tilt is generally used when referring to adjusting the outboard or stern drive up out of the water for trailering or beaching with a switch located on the control handle or sometimes on the transom of the boat.
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What is power steering?
Steering torque is virtually eliminated with power steering. This does for your boat what power steering does for your car.
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Why do I need a tachometer and speedometer?
A tachometer ("tach") measures engine rpm while the speedometer measures boat speed in mph.

An engine is designed to run at wide-open-throttle (WOT), within certain rpm limits. Without a tachometer, the operator has little opportunity to know if the engine is at a dangerously high or low rpm level. Once the correct propeller is selected, the engine will run at wide-open-throttle within the recommended maximum rpm range. Any deviation from this established WOT rpm other than that associated with climatic conditions, elevation, or gross load changes, is an indication of a possible performance problem.
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How does my speedometer work?
As the boat moves forward, water enters through a hole in the leading edge of the drive unit and compresses the air trapped within the connecting hose and the bellows or Bourdon tube in the gauge. This water-to-air pressure, which varies in relation to the boat speed, actuates the needle movement mechanism, indicating the speed of the boat. The accuracy of the speedometer may suffer from a damaged pitot tube, weeds, mud, or debris caught on the pitot tube, a pitot tube that is partially or completely tilted up, or an improper pitot tube installation location.
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What is marine fouling?
Fouling is a kind of unwanted buildup (usually animal/ vegetable derived) occurring on the boat's bottom and lower unit.  Fouling creates additional drag, which reduces boat performance. In fresh water, fouling results from dirt, vegetable matter, algae or slime, chemicals, minerals, and other pollutants. In salt water, barnacles, moss, and other marine growth often produce a dramatic buildup of material quickly. So, it's important to keep the hull as clean as possible in all water conditions to maximize boat performance. Severe cases of bottom fouling can prevent planing by adding too much drag.

Special hull treatments, such as anti-fouling paint, will reduce the rate of bottom fouling. However, because lower units (outboard and stern drive) are made primarily of aluminum, be sure to select an anti-fouling paint having a copper-free, organo-tin base. The BIS Tri Butyl Tin Adipate (TBTA) base paint will not set up a galvanic corrosion "cell" as it is completely compatible with aluminum and avoids any electrolysis problems connected with many other paints. Applied according to instruction, it is very effective in controlling marine fouling.
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How can I protect my engine against corrosion?
The leading cause of corrosion damage is galvanic corrosion, the electrochemical interaction between different metals. It is most hazardous where lower units, both outboard and stern drive, are immersed in salt water, brackish water, and many inland waters with high conductivity caused by pollution.

The corrosion reaction occurs when electrons flow between dissimilar metals connected or grounded through water. In the process, one of the two metals is eaten away. This damaging corrosion can be eliminated by providing a sacrificial metal-zinc or aluminum, which will preferentially corrode to protect the lower unit, or by installing a Quicksilver MerCathode® system to your boat.

Sacrificial anodes are available in several forms. MerCruiser stern drives and most Mercury, Mariner, and Force outboards utilize a trim tab on the antiventilation plate. Stern drives have additional anodes mounted at the outer transom plate. A transom-mounted anode kit is available to provide additional protection, if deemed necessary. The anodes' main purpose is for corrosion protection. By their very nature, they deteriorate rapidly and must, therefore, be constantly inspected and regularly replaced. The engine should not be partially tilted out of the water. If the anode is out of the water, protection for the parts still in the water is lost. Anodes are never to be painted, nor should the area under the anode be painted, as the ground must be maintained. Newer outboards and stern drives will be discontinuing using the trim tab as a sacrificial anode. Anodic protection will be found in other locations.

When a docked boat is plugged in to shore power, destructive galvanic corrosion currents can flow through the important, shock protection, neutral ground wire. A Quicksilver Galvanic Isolator, which is wired in series with the ground wire, blocks the destructive corrosion currents while maintaining the safety function of the neutral ground.
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What type of gasoline is recommended for my sterndrive engine? Should I use gasoline that contains alcohol?
In the USA and Canada, any major brand of unleaded automotive fuel with a posted pump octane rating of 87 minimum is safe for gasoline engines. Premium gasoline (92 octane) is also acceptable. DO NOT use leaded gasoline.

Outside the USA and Canada, use gasoline that has a posted pump octane rating of 90 RON minimum. Premium gasoline (98 RON) is also acceptable. If unleaded gasoline is not available, use a major brand of leaded gasoline.

Reformulated (oxygenated) gasolines are required in certain areas of the USA. The two types of "oxygenates" used in these fuels are alcohol (Ethanol) or ether (MTBE or ETBE). These reformulated gasolines are acceptable for use in your engine. If the gasoline in your area contains either Methanol (methyl alcohol) or Ethanol, you should be aware of certain adverse affects that can occur. See your operation and maintenance manual for details.

In older engines that were designed to run on leaded fuel, use Quicksilver valve lubricant to avoid the possibility of valve seat recession.
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The paint on the top of my sterndrive is dull and seems to have some type of deposit adhering to it. How can I make it look nice again?
The dullness comes from mineral deposits in the water. When the boat is on plane, the top portion of the sterndrive is out of the water. As the water evaporates from the top of the drive, it leaves behind mineral deposits. You can remove them by using a liquid cleaner for bathroom tub and tile, followed by a coat of wax to help protect the surface.
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How does weight distribution affect boat performance?
Weight distribution is extremely important to boat safety as well as performance. Weight can affect a boat's running angle, attitude, performance and ride. For the best top speed with a moderate to fast-planing boat, passenger loading in most cases should be evenly distributed. Each boater should seek out what weight locations best suit his needs. Always remember; weight distribution is not confined strictly to fore and aft locations, but also applies to lateral weight distribution.
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How does altitude affect performance?
Elevation has a very noticeable effect on the wide-open-throttle (WOT) power of an engine. Since air gets thinner as altitude increases, the engine begins to starve for air (oxygen) and horsepower is lost. If the boat has been set up at a lower altitude and then moved to a much higher altitude, there will be a noticeable reduction in power, thus rpm. With Stingray's efficient z-plane running surface, a drop in propeller pitch of 2" to 4" will usually solve most altitude problems. Many boats without z-plane hulls require an outdrive gear ratio change to operate at higher altitudes. However, this fix is only safe at higher altitudes. If the engine is again run at a lower altitude, the gear ratio change must be reversed to prevent excessive engine rpm and excessive torque on drive train parts. Any boat with a high altitude gear ratio has a restricted range of operation compared to one only requiring a different prop when changing altitude.
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How does climate affect performance?
Summer conditions of high temperature, low barometric pressure, and high humidity all combine to reduce engine power as much as 15%. This, in turn, is reflected in decreased boat speeds, (in some cases) as much as three to five miles per hour. Nothing will regain this speed for the boater except the coming of cool, dry weather.

Accompanying this weather-induced loss of power is a second, but more subtle, loss. At rigging time in early spring, the engine was equipped with a propeller that allowed the engine to turn within its recommended rpm range at full throttle. With the coming of the summer weather and the consequent drop in available horsepower, this propeller's lower rpm will result in further loss of horsepower and an additional decrease in boat speed.   This secondary loss, however, can be somewhat regained by switching to a lower-pitch propeller that allows the engine to again run at the recommended rpm.

For boaters to realize optimum engine performance under changing weather conditions, it is essential that the engine be propped to allow it to operate at or near the top end of the recommended maximum rpm range at wide-open-throttle with a normal boat load.
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Can I use any synthetic engine oil after the break in period?
Any engine oil can be used as long as it meets the specifications listed in the engine manufacturer's manual.
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Are there any special recommendations for caring for a boat that is used in salt water besides flushing the engine?
In addition to flushing your engine after your boat has been exposed to salt water: clean, wash, and dry all exposed metal parts and coat them with a preservative such as WD40. This will prolong the life of the exposed metal parts.
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Will a hydrofoil help the performance of my boat?
Stingray does not offer hydrofoils as an option, therefore we do not have any first hand knowledge of their operation. Hydrofoils may help the performance of a boat especially at low speeds. Your dealer should be able to give you pros and cons about hydrofoil performance and installation.
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Where is the drain plug located on the Bravo sterndrives?
The drain plug for the Bravo sterndrives is located behind the propeller. To drain the oil, remove the propeller and then remove the drain plug.
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At idle speed, my boat lists from left to right, and eventually goes in a circle. Watching the wake from the back of the boat, the churning water rolls from the left to the right. At higher speeds, the boat tracks perfectly straight. Is this normal, or can something be done to minimize it?
What you are referring to is low speed bow steer, and it is common on all single engine boats at idle speeds. Below are some suggestions that may help.

  • First, you will never be able to troll or run your boat at low speeds without someone steering the boat. The faster the boat goes, the better the straight line tracking will be.
  • Running trim at different angles will have an effect. Trim to high will usually increase the tendency for the boat to wander back and forth.
  • Where the load is in the boat will have an effect.
  • Try faster trolling speeds (if the fish will allow).
  • Try putting a trim tab behind the prop in the bottom of the cavitation plate where your boat now has a round flat plate. This can help in some cases. Motors with power steering do not come with a trim tab. This tab helps reduce steering torque on non power steering motors. Adding this tab will effectively increase your rudder area.
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I have a boat with a MerCruiser engine. Is it normal for one exhaust manifold to run very warm while the other runs cool to the touch?
MerCruiser says that this is normal. Their response is:

Water coming out of the thermostat housing is not divided equally between the starboard and port side. Water takes the path of least resistance, and most will go out one side. The other side does get water, but not the same amount. Hence, one manifold (or exhaust elbow) will be cooler because of more water flow than the other side with less water flow. This should be more noticeable at lower speeds. At higher speeds, more water is flowing and both manifolds get closer in temp to the touch.

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My speedometer or speedometer hose is leaking water. What can I do?
Over time, the rubber hose can start leaking from vibration or soften from the pressure of the hose. We have not found a screw clamp that will work because the hose is small and the screw clamp tends to pinch the hose on the side, causing it to leak. The best solution is to remove an inch of the hose to get a fresh end, install two small tie wraps, and pull them tight without the hose connected. Pulling the tie wraps down BEFORE installing the hose allows for a tighter connection once the hose is installed. Then push the hose back onto the Speedo barb, the hose connector or the barb on the transom plate bringing water from the pick up in the lower unit. This will usually cure any high speed-leaking problem.

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My trim gauge is not on the first mark when the drive unit is in the full down position. How can I adjust it?
If your trim gauge is moving when you trim your motor, but the needle does not stop on the bottom mark of the trim gauge (at full down), the sending unit may need to be adjusted. A sending unit, which controls the trim gauge, is located on the gimbal housing between the lower unit and the transom. The trim sender is on the starboard side of the gimbal housing where the lower unit pivots in the gimbal housing.

To adjust your trim gauge, loosen the two screws on the sender just enough to rotate it by hand. The sender requires very little movement to affect the trim gauge position. To adjust the gauge properly, the boat needs to be on a trailer or lift so the drive will clear any obstructions when you cycle from full up to full down position. The motor should be OFF, the drive in the full down position, and the ignition switch in the on position. Slowly rotate the sending unit until the trim gauge is on the bottom line of the trim gauge (not below it), and retighten the switch. Recycle the trim full up to full down and recheck the gauge for the correct needle position. If it is not correct, reset the sender and retest it.

These instructions are for MerCruiser Alpha and Bravo drive units. DO NOT try to adjust the trim limit switch. See your Stingray dealer should any trim limit adjustments be needed. This switch controls how far the trim will move without using the tilt button and protects the drive from side load damage from excessive trim under power.

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Can I use ethanol fuel in my boat?

Information added Sep 12 2006

The document below was originally published in Mercury Messenger magazine.

Mercury Marine's View of Ethanol




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