Pick The Horsepower
To start, choosing the amount of horsepower (hp) helps you also pick the size of motor. It’s based on the size of your boat and it’s loaded weight. The reason for this, is horsepower affects the stability of your boat.
Let’s look at two examples. First, if you use a too powerful outboard on a small board it can cause unbalanced movements. This added power will also put pressure and stress on the transom, leading to damage. Second, using an under powered outboard on a larger vessel will burn out the motor. Due to the amount of drag and huge demand to move the boat.
So, how do you choose the proper horsepower? It’s easy, on most boats (built after 1973), there is a capacity label. You can find it located in the stern, often in the cockpit of the boat. It’s either from the coast guard or the National Marine Manufacturers Association. The label shows the largest amount of horsepower plus the total weight limit. Below is a general example of what this label should look like.
Example Capacity Plate
Keep in mind, this is the max horsepower the boat can handle. You should consider where and how you want to use your boat. If you plan to navigate shallow rivers or calm lakes you don’t need a high horsepower outboard motor.
For most boats rated at 40 max hp and lower, an 8-20 hp outboard motors is ideal. This size will deliver plenty of power to propel the boat. Plus this size range offers better fuel efficiency, lower prices, and easier handling. Below are explanations of typical outboard motor horsepower ranges.
2 to 3.5hp
The most planet friendly option for both small and large outboards is a 4-stroke outboard. It suits boaters who own canoes, dinghy, inflatables, or small sailboats. A light and portable 1-cylinder model may suffice. Although expect to only have forward gears and a speed limit of around 16 kilometers per hour.
4 to 6hp
An outboard in this range are one-cylinder, but more robust and include reverse gears. This range can reach speeds of up to 30 kilometers per hour. They are best suited for a larger canoe, dinghy, or inflatable sized around 10 feet (3.05 m), and weighing 100 kg plus.
8 to 20hp
Outboards in this range are still small, except they have two cylinders that deliver faster speeds. This range is suitable medium size (14+ feet) fiberglass or aluminum boats, or sailboats. These outboards tend to vibrate less, include electronic starters and other tech.
20hp and beyond
This range is for the large boat category which handles sea and swells. Inshore boats might get away with 20 hp but for high speed activities (water skiing) 75 to 90hp engines are best. Choose a four or even six-cylinder outboard motor. Next, if you own a larger sport boat that travels offshore, consider an outboard with at least 400hp.
Measure Transom Height To Determine Shaft Length
Figuring out the shaft length to choose for your new outboard is as easy as measuring transom height. The reason for using this measurement is to ensure the shaft length matches it. Doing so, will put the propeller right below the boat. Allowing the propeller to pull water from underneath and push it out behind the boat.
To measure the transom height, measure from the center on for transom (rear of the boat). Take the center measurement from the top to the bottom of the hull.
Rest assured, if the motor you choose has a shaft that’s one-inch off measurement, it isn’t a big deal. But if its five inches off, it could create a stabilization problem when in motion.
Choose A Fuel Type
There are three main types of fuel choices for portable outboard motors. Including gasoline, propane (LPG) and electricity. Although the latter, is an only a small motor solution.
Gas-powered outboard engines have been the standard fuel for decades. This fuel type is the least expensive and puts less strain on the engine valve seats. It’s straightforward to use and maintain, even when you’re at sea. But it’s messy to transport and gives off dirty exhaust.
Recently, most boaters are moving from “Two-stroke” gasoline engines to Four-stroke models. They’re doing this to help reduce exhaust emissions. Despite the added weight, a four-stroke engine offers other benefits as well. They’re quieter, less thirsty, and don’t need to mix up large quantities of oil and gas. That said, they also are more complicated and expensive to service.
Using pressurized LPG is much like a gas motor, except for a different carburation setup. This fuel is cleaner and more efficient than gasoline. As well, it won’t gum up or degrade components inside the engine. Since it’s pressurized the motor is easier to start up, there’s no risk of flooding the engine like with gas. Another bonus of propane is the ease of transporting. It’s much easier it is to travel with small LPG canisters, instead of hauling liquid gas.
The downside of propane is having to make room onboard to many canisters. Bear in mind, a small 16oz (604.79 g) canister offers about two hours of running time at half throttle. The other issue is that propane the lack of visual indicators to show fuel levels. So you have to keep an extra canister for range emergencies, which is annoying.
As I mentioned, electric motors aren’t powerful for use on anything but small boats. This is because this “fuel type” needs external batteries for power. Often the heavier the battery the more power it provides. Adding tons of batteries weighs down your boat, so electric outboards tend to be under 6 hp.
The benefits of electric powered motors are plentiful though. This type will deliver instant power, emit no exhaust, and easy to start. Yet for range, it depends on if you choose lithium powered motors or lead-acid. Lithium deliver 4-5 hours of range at half throttle, whereas lead-acid is much less time.
Another consideration for electric outboard motors is shaft length. It’s often longer than gas fuel types, to ensure the prop doesn’t cavitate because of the instant power.
Select Electric Start
Ever driven classic tiller-style outboards? If so, you may have experienced a recoil starter. The classic recoil-start engines could be difficult to turn over. Today, using a recoil-start engine is even easier. Thanks to auto-decompression, which bleeds off cylinder pressure to reduce pulling force.
Still, pulling a recoil in windy or rainy conditions isn’t fun. For a quick and easy start, some portable outboard motors feature electric start. Using a push of a button, (imagine a BBQ starter) to ignite the fuel is as simple as it gets. Wouldn’t you want instant start up when your boat is drifting toward some rocks? I know I would.
Consider High-Power Thrust
For owners of heavier boats like pontoon or large aluminum boats, pick a motor with high-trust. Powerful thrust helps the boat get up to speed quicker and increases maneuverability. Which further aids in moving your boat easier in high wind and current. Or trying to back up away from the dock. Nothing is worse than not having enough thrust to navigate a heavy boat. It’s also a good feature if you like fishing using the trolling method.
Pick Adjustable Controls
An ideal tiller handle should be long for ease of reach. It should also be able to provide one-hand operation. In your palm you should be able to control throttling, steering, shifting, and tilting.
Tilting your motor is important for avoiding damage to the propeller. For example, as you pull your boat out of the water at a boat launch. Another reason is if you need to navigate shallow waters, tilting up until you reach deeper water. When it’s time to tilt the motor, the right tiller will provide a simple motion of push and snap in any angle.
For boaters who need a little extra help, high-end and larger outboards come with power tilt. Keep in mind, never engage power tilt when the prop is running, it can cause serious damage.
Another premium feature is power trim to raise and lower the height of the propeller when in motion. This option is awesome for navigating different water depths.
Understand Electronic Fuel Injection (EFI)
Fuel injection systems are a complex topic, so here are the basics of why you want an EFI system. First what is it? Electronic fuel injection (EFI) replaces the need for the carburetor which mixes fuel. Instead, it injects fuel direct into the engine’s cylinder using electronic controls. EFI results in no need for fuel priming, fast starting, low emissions and great fuel mileage. The added fuel efficiency is great if you plan for a lower horsepower (hp) engine on a higher rated boat. You also get superior throttle control is the coldest conditions.
Another bonus for EFI is its temperature and elevation compensating. This means if you live in mountain or colder states the EFI engine has no performance reduction.
The caveats for EFI is higher initial price, its heavier and specialized maintenance.
In Summary: Portable Outboard Motor Guide
By now you can see, there are many factors to consider before buying a portable outboard motor. Pay attention to your location, size of boat and intended use. Try to pick a model that promotes ease of use and versatility in any waterway.
Choose a 2-stroke or 4-stroke model if you love to do your own maintenance and prefer simple motors. Or upgrade to EFI outboard motor for clean emissions and reliable use in any climate.
Thanks again for letting Outdoors Informed help with your research. We do it so you spend less time indoors and more enjoying a great day on the water.