Unless you’re extremely familiar with a specific boat’s hull, it can be difficult to know whether or not your outboard motor is mounted at the right level. Most boat owners have dealt with this problem at one point or another, but it’s surprisingly difficult to find good information to solve it.
We got some input from the experts to create this quick guide to checking your outboard’s height. It’s never a perfect science, but there are some very simple ways to put you on the right track.
P.S. – Prop slip can be a major factor here, definitely take a look at our guide to identifying and solving prop slip with your outboard.
Symptoms of an Outboard Mounted Too Low – The Short Answer
An outboard that is mounted too low will limit your boat’s optimal operation. You can often tell that an outboard is too low if you are experiencing sluggish speeds, poor handling, excessive spray, porpoising, or even water pushing up into the cowling.
That’s a very brief, basic accounting of symptoms, but you’ll usually find at least one of these symptoms if your motor is too low. The problem is that none of those symptoms are by themselves precise indicators. We need a little more detail to better find the right outboard height.
How to Know if Your Outboard is Mounted Too Low – A Detailed Guide
Outboard height is tricky, mostly because every hull is different and the same is true of every individual outboard. Optimal mounting positions can vary from boat to boat and it’s not always easy to luck into correct placement with guesswork alone.
Fortunately, there is usually one reliable indicator to tell whether or not your motor is close to the correct mounting height. This indicator is your anti-cavitation plate and its position in relation to your hull.
Anti-cavitation plates can be found on most outboards. They are the flat plates located on almost every outboard’s lower unit. They are a big help to proper boat operation, but they need to be in the right position in order to do their job.
Basically, you want to make sure that your anti-cavitation plate is skiing on the surface of the water when your boat is on-plane at operating speed. The most important factor in making sure this happens is actually where this anti-cavitation plate is located in relation to the bottom of your hull.
Here’s how to make sure that your outboard is at the correct height by using your anti-cavitation plate as a guide:
- Find a straight edge that is around 8′ to 10′ long. A long 2×4 is perfect for the job.
- Trim your outboard down and into the proper position.
- Place your straight edge lengthwise against the underside of your hull, allowing 2′ or 3′ to hang off the back toward your outboard.
- Check the position of the anti-cavitation plate in relation to the straight edge. The bottom of the plate should be at or above the top of the straight edge.
That’s the quick and easy way to get yourself on track to finding the right outboard mounting height.
Since the goal of your anti-cavitation plate is to prevent surface air from being sucked into your prop, it is designed to be at a certain height. An anti-cavitation plate in the correct position will barely skid on the surface, helping to create a steady flow of water to the prop without the introduction of air. The angle of your hull and the trim of your motor should line up to put the plate in a level position.
List of Common Issues Caused By an Outboard Mounted Too Low
- Inability to achieve top-end speed: A lack of top-end speed can be an obvious indicator, but is hard to discern. It is difficult to determine whether or not you are able to run at your highest potential speed unless you are very familiar with your boat and previously had an outboard mounted at the appropriate height.
- Poor handling: This is another obvious indicator. It’s usually fairly easy to tell whether or not your boat is handling properly. A number of factors can contribute to poor handling, but a low outboard will almost always cause less-than-ideal handling.
- Excessive spray: If your outboard is kicking up an inordinate amount of water, it’s often a tell-tale sign that it’s mounted too low. Some spray is always ok, but it should be smooth. A simple eye test will typically be all it takes to know if you’re in good shape here.
- Porpoising: “Porpoising” occurs when the bow of your boat starts to bounce up and down as you run at a normal speed. This is caused be a handful of factors, but a low-mounted motor is often one of the most common.
- Water pushing up into the outboard cowling: If your motor is so bogged down that you see water making its way into the motor’s cowling during normal operation, your outboard almost certainly needs to be raised.
After reading through this quick guide, you should have a pretty good idea of whether or not not you have your outboard mounted at the correct height. I’ve always found the anti-cavitation plate method to be very reliable in getting me very close to the perfect spot.
If you did conclude that your motor is too low, you should be able to do a quick measurement to get to that perfect spot. Moving up one or two holes on your mounting bracket will do the trick in most situations. If you find that your motor is too low and you’re out of holes on your bracket, it may be time to call in the professionals to handle a bigger job.
Outboard height is one of those things that doesn’t seem like a big deal until you realize what you’ve been missing. There’s a great feel to things when everything is perfectly lined up and your hull/motor work together seamlessly. You’ll know it when it happens, so make sure to test in the water the work you’ve done on land.
Now that you’ve got everything set in the right place, go get on the water! And let us know if this guide improved your boating or if you have any additional tips to offer!