Boat Motors - Outboards, Powerheads, Gear Cases & Outdrives

Boat Motors
Boating Know How

Outboards, Sterndrives, and Inboards: Comparison

Outboard motors, also known as OB’s, are the most common motor in the marine industry. The motor is mounted to the boat’s transom and is visible from the steering wheel.  The horsepower range is between 1.5hp to 350 hp. Outboard motors can be 2 stroke or 4 stroke motors.  The 2 stroke motor will have the gas and oil mixed in the gas tank.  The 4-stroke motor will mix the oil inside the motor.  Outboards can have 1 to 4, and 6 cylinders. ... read more

The motor can be started with a pull start cord similar to a lawn mower for the smaller horsepower.   They are often used for fishing and are steered sitting at the back by the transom using a tiller handle attached to the motor. Larger motors have a key start and are steered with a steering wheel at the front - usually used for vessels with more speed used for water sports or for cruising.

Outboard with Key Start and Outboard with tiller handle

Outboards, Sterndrives, and Inboards: Comparison                               Outboards, Sterndrives, and Inboards: Comparison
Outboards, Sterndrives, and Inboards: Comparison
                                   Outboards, Sterndrives, and Inboards: Comparison


motors are also known as I/O’s, which stands for Inboard/Outdrive.  The inboard engine is under the deck at the back of the boat and the outdrive comes out of the transom around the water line.  The inboard and outdrive are connected with a universal joint that allows the outdrive to move, which changes the direction of the boat.  These motors are always key start and steered at the steering wheel.  I/O’s are all 4 stroke motors, with 4, inline 6, V6 or V8 cylinders.  They can be purchased as single propeller or as dual propellers outdrives.  I/O’s are usually higher horsepower engines.  Since the sterndrive engine comes out of the lower transom, it doesn’t get in the way when fishing or trying to pull up to the dock.  The price is usually attractive for a sterndrive and there are boat models that require only sterndrive motors.

Outboards, Sterndrives, and Inboards: Comparison


motors, also known as IB’s, are marinized versions of Chevrolet and Ford automotive engines.  They are placed either in the center of the boat or back at the transom under the deck.  The propeller comes out of the bottom of the hull and is steered with a rudder placed behind the propeller at the back of the boat.  They are often sold in either gasoline or diesel fuel options.

 Inboards are great motors for extreme water sports.  With the propeller underneath the boat, there is less opportunity for someone to get too close to the propeller while in the water or doing water sports

Outboards, Sterndrives, and Inboards: ComparisonOutboards, Sterndrives, and Inboards: Comparison

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4 Stroke Outboard Motors

4-Stroke outboard engine motors: History, Description, Pro's and Con's

By Bill Gius,

If it appears you're seeing more outboard powered boat on the dealership floor these days, you're right. A veritable tsunami wave of change has moved boat builders away from the traditional stern drive power to an outboard motor application.
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In some cases, using the same hull design.

The industry-wide change can be partially attributed to the introduction and development of the four-stroke (4-stroke) outboard. 4-stroke outboards now range in power from 2hp through 350hp (excluding some higher horsepower high performance engines).

Honda brought their 4-strokes to the US in the late 60's, (first Honda 3hp shown) Yamaha in the mid 80's (current 350hp Yamaha cut away shown) and Mercury (current 150hp Mercury shown) in the mid 90's.

4-Stroke outboards have grown in popularity because many of them are more economical, fuel efficient, quieter, ecologically friendly and easier to maintain than stern drives.

But you just don't walk away from a popular and successful design or hull if you're a boat builder.

Here is a stern drive boat with... outboard power.

The Starcraft SCX 210 OB (outboard) could be called a "hybrid" boat. The hull and most of everything above the waterline is still basically a stern drive designed boat; with a 200hp outboard hung on the back. Well, "hung" is a bit of an over simplification. You don't really just "hang" an outboard on the back of a boat that used to have its engine inside the transom. The folks at Starcraft worked with Armstrong and Yamaha to power up this great family bowrider.

According to Peter Barrett, VP Marketing for Starcraft: "We spent many R & D hours with Armstrong getting the boat to balance correctly. We have had a long relationship with Armstrong and they were eager to help us with this project. We're very pleased with the performance considering the overall size of the hull and the depth of the cockpit area."

"Our goal, first and foremost was to duplicate the rear seating comfort and utility that we had in the SCX I/O series. We did so by keeping the same design as the I/O, moving away from a traditional space killing splash well and converting the engine area into a generous storage area. Key features such as the flip up sundeck, large rear facing stern seating combined with a big usable stern swim and ski platform would all be lost without the use of a bracket on this outboard model. This stern swim platform really makes this boat a fresh water or salt water tow sports animal!".

The SCX210 OB we drove was equipped with Yamaha's newest 200hp 4-stroke outboard. It features an inline, 4-cylinder, 2.8L, 16 valve, DOHC engine that delivers a very thin profile for single or dual engine application. According to Yamaha: "this new four-cylinder, four-stroke F200 is the lightest 200-hp four stroke on the market and can easily replace lower horsepower or larger V6 outboards and thereby increase the performance of mid-sized boats." As you can see in some of these photos, the outboard installation not only gives the boat a lot of useful deck room but the location of the installation perfectly balances the boat in the water. It's not bow high or sitting squat in the water.

The SCX210 OB has a custom wakeboard tower and you know, so do a lot of boats these days. Even pontoon boats have wakeboard towers; that doesn't necessarily make them good wakeboard boats. The SCX is a decent wakeboard boat. It's not an inboard tournament boat; it's a very nice bowrider that puts up a good wake. We ran it at 18mph, 28mph and 40 mph; wakeboard, tubing, slalom and barefoot speeds. WOT speed was 42.3mph.

You have to pay attention to trim and speed but you can create a nice wakeboard wake that will give you good air. At slalom speeds the wake flattens down enough for recreational skiing but at barefoot speeds the turbulence off the prop is very rough. The 2,500 pound boat puts a nice hole in the water so it also gives a pretty health wake for barefooting. Depending on how crazy you want to get for tubing, it will deliver a lot of fun behind the boat.

The stern drive design also give the boat tremendous stability. We attacked some wakes from a couple large cruisers and it cut the wakes beautifully without delivering a violent shudder to the passengers.

This boat clearly exemplifies the transition from stern drive power to outboard power. It's done well while expanding and extending the life of an exceptional hull design.

For more info on the Starcraft line of boats and to find your nearest Starcraft dealer click on: // For more information on Yamaha Outboards check out: // For more information on Armstrong Transom Brackets click to: //

Bill Gius is a three-plus decade marine industry veteran with extensive, hands-on accessory, boat and engine experience. Bill has been working with for six years to help manufacturers and dealers use iboats' online marketing, advertising and lead generation services. Bill can be reached at 800-869-1686 x199 or
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Product Spotlight | Mercury 150 4-Stroke Nuts & Bolts

Article written by Bill Gius

If you have a fiberglass or aluminum outboard powered boat, you don't want to feel vibration from your engine at any RPM range. ... read more The more horses you hang on the back of the boat, the more your outboard weighs. The more weight that teeters on a hinge, so it can be trimmed and be tilted, the more engineering that has to go into the design of every component of the engine's transom bracket. At around 455 pounds, the new Merc 150 is "light" for its horsepower. Between you and me, 455 pounds isn't what I'd call "light". I'm not sure how many of my close personal friends and myself it would take to lift 455 pounds but the 150 is lighter than comparable Suzuki, Yamaha or Honda's by 19-23 pounds.

Inside the engine is a very violent place. All those explosions cause the pistons to move along pretty quickly. And they have to come back to get banged on again; and again and again. No matter how good the engineering and manufacturing of the actual engine part of the outboard, there will be some vibration that will escape the block and try to get transmitted to the parts of the outboard that hold it to the back of your boat. The drive train, from the power head all the way to the propeller tips, also generate some vibration. Engineers work to attenuate (reduce) as much of that vibration all along the system but all those gears meshing together also add to the opportunity for vibration. Modern engines and drives are designed tremendously better than the same horsepower engine from just 15 years ago. Four stroke engines have further advantages in reducing vibration and noise because of the inherent design in an engine that has four instead of two combustion "cycles".

All outboard engineers understand how vibration travels too. The Merc engineers and marketing folks thought about that and came up with a pretty neat name for their engine mounting system. They call it the "Focused Engine Mount" system. Merc could have used an engine mounting system and transom bracket from one of their other outboards. Those designs have held up to dozens of years of real world use on hundreds of thousands of engines and well over 300 horsepower outboards. They've worked just fine. But this is a totally new design all around.
Hidden in the midsection of the engine (the part below the engine block and above the gearcase) is this focused mount system. They're mounted to attenuate the focused forces and vibration of the engine at the key load points. The mounts are also kept from the effects of heat and any dripped oils that could damage or change the characteristics of the rubber in the mounts. The composition of the rubber and how it's fastened to the mounts allows the rubber to be compressed at different rates. At lower RPM's where you're apt to feel more true engine vibration, the rubber is "softer", because it's not as compressed. At higher RPM's when you're up and running it's more compressed and more firm to better hold the engine in line with the boat (that keeps it from wobbling back and forth and helps keep you going straight).

All that is attached to the engine side of the transom bracket which incorporates the trim and tilt hydraulic pump and ram.

On some transom brackets the hydraulic pump is mounted outside the bracket. On the 150, it's inside the bracket, protecting it better and making for a more compact system. Even though this engine weighs in at 455 pounds, it uses a single hydraulic ram for trim and tilt. Some other engine use two shorter rams for the trim and a single longer cylinder for tilt. Again, this makes for a more compact and yes, less costly system.

In this and the two previous articles we've taken a good, introductory look at the new engine. Mercury hasn't told me the pricing yet but it's now available and they have suggested it's going to be more competitive than other makes. That will be important but durability, performance and fuel economy will also play into the engine's total cost. Four stroke's suck less fuel than two cycle engines; they don't have the power curve of a two stroke and durability is an argument I don't want to start but this engine is worthy of consideration when you're shopping for pontoon, fishing or cruising power.

Bill Gius is a three-plus decade marine industry veteran with extensive, hands-on accessory, boat and engine experience. Bill has been working with for six years to help manufacturers and dealers use iboats' online marketing, advertising and lead generation services. Bill can be reached at 800-869-1686 x199 or
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How to Flush Your Outboard Engine
A video presentation on how to properly flush out your outboard engine. Presented by BoatUS. ... read more

Video Transcript

Hi, I’m Pat Piper, editor of BoatUS Trailering Magazine. As a trailer boater, you probably have an outboard. And having an outboard means it’s going to be in sand, or it’s going to be in dirt, or it’s going to be in seaweed, or it’s going to deal with salt water.

All of those are reasons you need to flush the engine. And that’s what we are going to do today. And best news of all, it is easy to do.

You’re going to need muffs which actually fit over the water intake of the outboard. Muffs are really easy to use. And as you can see here, there’s a hose attachment. This one has a side attachment. Some variations of a muff will actually have it at this end. Whatever works for the outboard, is going to work for you. That’s the important thing.

Obviously you need a hose, a water source and you are going to need the keys to the engine, because we are going to be running the engine on land.

We now have the hose attached to the muffs and we’re now going to put them on. You’ll see here, there is a water intake valve. This muff is going to cover this side. And the other muff is going to cover the other side. Now, here’s how you do it. It’s pretty easy, we’ll just slide it right on.

Now, let’s stop right here. You see that this is facing this way. Why you might ask. Let’s try it this way and put it on. It will fit, but look what we’re hitting. And what if this would ever get into gear? That’s why we’re going to put it on this way. It’s safe, and it works better.

Some people will actually coat the inside with some water to get a better seal. That’s your call. Now we’re going to turn on the water.

Okay, the water is running right now. Now you’ll notice there is a lot of water going on here. It’s because the engine isn’t turned on yet and the water pump isn’t engaged. That’s going to happen in just a minute. One thing we want to make sure of, is that the engine is in neutral. So I’m going to go up and keep the throttle control lever. I’m going to turn on engine, and we’re going to flush this outboard.

We are up and we are running. Here’s what you’re looking for. Water is going through the engine. The water pump is working beautifully. And it is coming out, just like when you are out there waterskiing or fishing.

The engine is in neutral and we’re going to let it run for 5 minutes. Let it get up to operating temperature and let everything flush through. Fresh water that is. And then we will shut it down, and then we are almost done.

Engine has been shut down. The water has been shut down. Take off the muffs and we’re good to go.

This outboard has been flushed. It’s happy. We’re all happy.

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