You may miss many advantages if your boat is not getting on a plane. There are some easy ways to troubleshoot the issue if you know what causes a boat not to plane. Here’s why a boat struggles to get on a plane or won’t plane at all.
A boat won’t plane out either due to a bad propeller, improper motor placement on the transom, wrong trim position, uneven weight distribution in the boat, low engine performance. However, there could be many other reasons, but primarily those elements will cause a boat not to plane.
Mechanically either a bad spark plug, misfiring inside the cylinder, a bad fuel filter/pump, a bad carburetor will decrease the engine’s performance, making you unable to push the engine to its optimal limits. That makes your boat struggles to get on a plane or won’t plane at all.
Don’t worry much about those technical terms. We explained all of them in a detailed way in this post below. Non-technically either an improper motor height, wrong trim position, more weight at the stern (uneven weight distribution in the boat), a bad propeller (spun hub or any) will not plane a boat.
Without further ado, let’s see in a detailed way what causes a boat not to plane and how to tackle those issues.
What Causes A Boat Not To Plane?
A Bad Or Damaged Propeller Will Not Plane A Boat
A propeller plays a crucial role in your boat, and it’s one job to spin and move your boat forward. But the same propeller can cause your boat not to reach max speeds or decrease your engine performance, which causes your boat not to plane.
- A damaged or dinged, or chipped propeller will reduce the boat speed drastically due to the water that is not sliding on the dinged propeller smoothly, directly decreasing the speed. Your boat may take a long time to reach top speeds (cruise speed). It also struggles to get on a plane.
- So, visually you can tell whether your propeller is damaged or not. If it is chipped off by 10-15% or more or has dents on it, replace your boat propeller.
- A spun propeller hub will not plane your boat. A spun propeller means that the prop hub has spun inside the propeller. Once the hub spins inside of the propeller, the propeller will spin freely (slowly) and not along with the hub.
- In other words, Spun hub usually pulls good to a certain point, and the motor acts as it goes out of gear, the rpm’s skyrocket, but the boat does nothing. AKA “Prop slippage.”
- The rubber hub of the propeller is a fortified ring made of durable rubber, which is inserted between the prop shaft and propeller’s inner hub. So, if this rubber hub is detached (damaged), the propeller’s movement to the propeller cannot be transmitted, and the blades, in turn, cannot respond or turn along with the prop shaft.
Too Much Pitch
- If your prop has too much pitch (For example, a prop with a 20-inch pitch would move 20 inches in the water with each complete rotation), the engine will have a lousy “holeshot” — the ability to jump up on a plane quickly — and will lug (or drag).
- In other words, your boat takes longer to get on a plane than it used to with a propeller with too much pitch.
- A lower-pitch prop is like a low gear in a car—you’ll accelerate quickly, but top speed will suffer, and the boat will struggle to get on a plane. The best play is a trade-off between these extremes, a prop size that puts the engine in the sweet spot of its RPM range for everyday use.
So check the propeller condition if you are not getting the boat on the plane. But just don’t automatically assume that propeller is causing the issue. The engine could be down on power for some reason, or there could be an issue with the hydraulic trim system that does not allow the outdrive or outboard to trim all the way down.
Related post – How often to replace a boat propeller? Check this article to know some of the main bad boat propeller symptoms to look for while replacing a propeller on your boat.
Improper Motor Placement On The Transom Will Not Plane A Boat
There are some severe disadvantages to raising the boat motor. With the propeller closer to the water surface, it’s more likely to ventilate and slip-on acceleration, making it harder for the boat to get on a plane.
But if the motor is mounted too low, the anti-ventilation (cavitation) plate will drag in the water when the boat is on a plane and can cause excessive spray around the motor and transom. So, keep it in the sweet spot, not too high or not too low.
Some of the recommended measurements (motor heights)
- With the boat sitting on the trailer, trim the engine, so the cavitation (anti-ventilation) plate or the engine is parallel or even with the boat’s pad (boat’s rear flat center planning surface), use a straight edge.
- Take the prop off and, using a straight edge, measure the distance from the boat’s pad to the centerline of the prop shaft. It should be 3.5 inches, not less than 3.25″, or not more than 3.75″.
- When you trim the engine down, the lower unit should tuck in towards the hull. The cavitation plate and prop shaft are angled down about 10 or more degrees. Look at your trim gauge and see if it is working and shows trimmed down.
So, check the placement of the engine on the transom and determine whether it is in the sweet spot or not.
A Bad Trim Position Will Not Plane A Boat
If you are not trimming well enough, it’s hard to get your boat on a plane because the improper trim position will not lift the boat up while accelerating. Your trim position plays a crucial role in planning your boat.
- Initially, it would be best if you started with the trim position all the way down; it will give you a quicker “holeshot.” As the bow rises and once it drops down, then you need to raise (trim up) the outboard slowly until your boat feels like just moving on the water’s surface.
- In other words, if you see the wakes near the bow starts to go away, that tells you are riding back on the pad, a proper plane. Generally, your sweet spot will be around when your motor is perpendicular to the hull. The same applies to a boat with trim tabs.
There is one caveat: if you trim your engine too high, you will see a ventilating and porpoising effect.
Ventilating Effect. It occurs if the propeller is closer to the surface, not completely submerged inside the water. It’s more likely to ventilate and slip-on acceleration, and it can absorb air instead of water, which overheats the engine quickly. And it also decreases the speed. So, you don’t want to trim too high.
Porpoising Effect is lowering and raising the hull continuously due to a bad trim position. It occurs due to a bit high trim position, indicating you to trim the engine down a little.
Finally, after the holeshot, you should trim the engine up until you see the porpoising effect. Being in that sweet spot (perpendicular to the boat hull) implies more mileage, less fuel consumption, and good speed.
Check this helpful video on trim position to make a boat both plane and maneuver well on the water.
Uneven Weight Distribution In The Boat Will Not Make It Plane
The weight distribution in the hull also plays a crucial role. Too much weight in the stern will cause the stern to squat and be sluggish getting up on the plane. Having all the batteries in the back of the boat, the anchor, full Livewell, etc. All these small things will increase the stern weight.
A ton of weight in the back of the boat and even more water in the hull can prevent you from planing out. So try to avoid more weight at the back and rather distribute it evenly on the boat.
Low Engine Performance Will Not Plane A Boat
If you check all the above things and still your boat is not planning, then most probably, the issues lie in the motor. It can be causing your boat not to plane by not giving your engine ample performance.
Either due to a bad spark plug, misfiring inside the cylinder, a bad fuel filter/pump, a bad carburetor will decrease the engine’s performance, making you unable to push the engine to its optimal limits. That makes your boat not to plane or takes too long.
- Misfiring in the cylinder can cause a comparable loss of power. For example, if one cylinder misfires in a four-cylinder engine, your boat will lose around 20% – 25% of its power.
- From the spark plugs to the ignition coils, many different things can cause an engine to misfire. The most common causes of misfires are worn, improperly installed, bad spark plugs, malfunctioning ignition coils, faulty spark plug wires, and vacuum leaks.
- A compression check can indicate that the piston rings are working properly and that the cylinders are in good condition. The test measures how much pressure is built up by the motion of the piston inside the cylinder, given in pounds per square inch (PSI).
- It is a reading of an engine’s ability to compress the fuel and air charge in the cylinder (with a piston). 120 PSI would be considered very good (probably above factory specs), and 90, in fact, 80, would be acceptable.
The compression test is simple, principally, but the many different types of outboards can add numerous complexities. The following steps are only general guidance.
Your engine may require different steps depending on factors such as whether it’s a 2 or 4 stroke, has fuel injection, has computers onboard, is hand-cranked, or has a starter motor, and how its ignition can be disabled.
These variations and other issues will bear on your ability to do this yourself. So, unless you know how to do it yourself properly, please don’t risk it by doing it yourself (source).
Fuel Related Problems
- Fuel-related problems are another important thing to check whether your fuel filter is working properly or not and even the fuel pump is working or not.
- Fuel pump, Fuel filter, Injectors. These three vital components work together to ensure fuel flows smoothly from the fuel tank to your engine.
- If the engine isn’t getting enough gas, it will sputter at high speeds. It could be a clogged fuel filter, clogged fuel lines, or problems with the fuel pump.
It can also decrease the engine’s performance. Under heavy loads, a bad fuel pump may randomly cause the engine to hesitate, surge, or sputter. That hesitate, surge, or sputter tends to be more prominent when accelerating. A bad fuel pump will starve the engine of the extra fuel needed when quickly accelerating.
A bad fuel injector also reduces the engine’s performance. Even an unvented fuel tank will create a suction that will not allow fuel to flow to the motor properly. So you need to check all the fuel-related things as well.
Related post – How often to replace a boat fuel filter? Check this article to know some of the main bad boat fuel filter symptoms to look for while replacing a fuel filter on your boat.
The Key Takeaways From The Post
Inability to achieve top-end speed. A lack of top-end speed can be an obvious indicator, but it 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.
One among them is planning. If your boat is unable to plane, there is something that starving your boat to reach high speeds, making it unable to plane. Either due to a bad propeller, improper motor height, wrong trim position, uneven weight distribution in the boat, low engine performance.
If you are trimming properly, start diagnosing the issue with the propeller and its hub checking, motor placement, and later the compression test and fuel-related issues.
Still, if you are unable to plane your boat, you need to look at whether the trims are working or not, and you better go near the mechanic in your area for more insights.