Smoke on the Water: Tuning your Boat for Maximum Performance

9/19/2006 by

Copyright:© 2006 Horizon Hobby, Inc.

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One of the cool things about driving an RC car or truck is the ability to modify the setup to change the handling and performance of the vehicle. That’s great, but you can’t do anything like that with a boat, right? Wrong! You can drastically change the performance and handling of your boat a number of different ways. Whether you’re dealing with the V-hull design of the ShockWave, the catamaran hull of the ThunderCat, or the all-out performance design of the Miss LLumar unlimited hydro, you can definitely improve the performance of your particular boat.

Prop Angle

Common sense tells you that when you push down on the bow of your boat, the stern will raise up. This is what your prop essentially does while it’s spinning and churning as it’s propelling your boat on the water. Along with forcing your boat forward, the angle at which the prop is mounted will force the nose of the boat to come out of the water. By changing the angle, you can control how long it takes for your boat to plane out and how smooth the ride will be. Generally speaking, if you are traveling in choppy waters, your boat will generally have a more stable ride when you trim the prop down. In smoother water, you may find that your boat doesn’t bring enough of the nose out of the water at speed, which will hurt your top speed due to the increased drag on the bottom of the hull. Or the opposite can be true. If the nose comes out of the water very easily or the boat begins to porpoise, then your prop may be trimmed up too high. When trying to get the smoothest and most efficient ride for your boat, it will help to think in terms of angles. Your boat is actually riding on the prop when it’s being propelled across the water, so in reality, when you’re changing how the prop is trimmed, you’re in effect raising or lowering the bow. When you have more of an angle between the prop and transom, your boat will ride more on the transom and bring the bow out of the water. This is referred to as up-trim. When you run with your prop flatter with less of an angle, your boat will generally run flatter with more of the nose in the water. This would be an example of down-trim.

On some boats, both the prop height and prop angle can be altered to change the attitude of the boat as it skims over the surface of the water.

On boats such as the Miss Llumar and Miss Elam, you’ll need to add washers between the hull and the prop mount to change the height and angle. It’s slightly more complicated but works well all the same. Just remember to use stainless steel or brass washers though, otherwise you may run into rusting issues.

Trim Tabs

Trim tabs can have a dramatic affect on the handling of you boat. Bending the tabs down will help keep the bow down, while bending them up will allow the bow to come out of the water.

In addition to the angle of the prop, trim tabs can have a dramatic effect on the overall handling and performance of your boat. Trim tabs are simple little devices that are attached to the back of your boat. These aluminum tabs can be adjusted up or down to change where they meet the water. By changing the angle of deflection, you can keep the nose in the water better. The trim tabs also stabilize the ride of the boat as it glides across the surface of the water. The trim tabs can actually make it possible for you to run your prop at a slightly greater angle, which may yield some performance gain as well. When making adjustments with your trim tabs, bend the tabs in the direction that you wish the nose of the boat to go. For example, if you want the nose to sit higher at speed, bending the trim tabs up will help accomplish this. Bending the tabs down will help keep the nose of your boat in the water better. While you can achieve similar results using the trim tabs that you might get by changing the angle of the prop, changing the angle of the prop and the thrust angle will have a more pronounced affect on your boat’s performance. Think of the trim tabs when you want to fine-tune your boat, but use the prop angle for larger and more dramatic changes. The only exception, of course, is in the event that your boat features a fixed drive system; the trim tabs then are the only way that the attitude of the hull at plane can be altered.

Turning Fin:

This turning fin on the Miss Llumar helps the boat carve through corners. Make sure you keep the leading edge straight and sharp for optimum performance.

Unlimited Hydroplanes are by far some of the fastest and most unique boats you will ever see, be it in scale or 1:1 form. Hydros have been designed with one thing in mind: going fast while turning in one direction. Full-scale hydros are designed in an LTO-configuration, or Left Turn Only. RC hydroplanes are a little different, set up in an RTO, or Right Turn Only, pattern. The reason is to accommodate the torque that is placed on the hull by the rotation. With this in mind, unlimited hydroplanes feature what’s known as a “Turning Fin” mounted to the right sponson. This helps the boat get traction in a corner faster and prevents inertia from making the boat flip over. While there aren’t any real adjustments that can be made to the turning fin, you can’t completely neglect it either. Extremely rough waters can exert tremendous stress on the turning fin, which could possibly bend or tweak it so it’s not at the proper angle. Inspect it occasionally to make sure there isn’t any damage to the leading edge. If you keep the turning fin straight and sharp, it will travel through the water with less resistance and help your boat reach a higher overall top speed.

Prop Height

Looking at the rear of a Pro Boat Shockwave, the number of tuning options is actually quite amazing. From changing the prop height, angle, trim tabs and stabilizers, there’s more adjustability than most people realize.

On some boats, you can change not only the prop angle but also the prop height. Boats with this adjustment have a slotted prop mount that will allow you to raise or lower the height of the prop. This, in turn, will change how much of the boat is in the water as it races across the surface. Raising the prop will raise the boat more out of the water on a plane. Lowering the prop will place more of the boat in the water. You may think that running the prop as high as possible would be ideal, but there is a potential problem with this theory. If the prop is too high, you may encounter a problem called cavitation. Cavitation can best be described as the sudden formation and collapse of low-pressure bubbles that cause a loss of forward drive from the prop if it comes into contact with one of these bubbles. This can be caused if the prop is at too great of an angle or if the prop is too high; this can even be caused by an out-of-round prop or the wake behind the boat. If you notice your boat losing forward drive and it suffers from a “herkey-jerkey” sort of motion while accelerating or when the boat should be at speed, you’ll need to lower the prop or reduce the angle.


While the setup tips that have been mentioned above are available as adjustments, there’s another feature you should check out before you even purchase your boat. Many hull configurations have a series of lines cut or molded into them. These lines, called strakes, direct water around and under the hull. They also provide assistance when turning, as the trailing edge of the strake will help the hull “bite” better when turning. This will provide a more locked-in feeling and help the boat carve through the water better. It’s similar to comparing an ice skater with dull skates to one with freshly sharpened blades; the skater with the sharper skates will be able to turn better and bite into the ice better. You really can’t do anything to the strakes that are in the hull to make them bite better or improve performance, which is why this is something you need to look at before you buy a boat. The larger or deeper the strakes, the better they will cut into the water and more effective they will be.

Here are two great examples of Strakes on the underside of a boat. Strakes help provide stability in a straight line and improve turning rates as well.

Let’s Give You Some Props!

The number one rule of boating should be to always make sure your prop is sharp, undamaged, and balanced properly. A prop with cracks or damage to the edges can hurt performance in a number of different ways.

The condition of your prop can dramatically affect the overall performance of your boat in the water. A prop that is out of round, unbalanced, chipped or damaged can cause a variety of turning problems. As the prop spins, it actually sends out a series of harmonics. These frequencies can cause air pockets around your prop, causing your boat to cavitate. Additionally, a damaged, chipped, or dull prop will not be as efficient as a new or sharpened prop. A less than ideal prop could cause your boat to not get up on plane properly, hesitate, porpoise, or just run poorly. You can never replace your prop too soon, but you can wait too long to replace it and then run into problems. If and when you decide to replace your prop, make sure you use one that is the right size and pitch. If the new prop is too small, your boat will accelerate quickly but top speed will be affected. Too large of a prop will cause your engine or motor to lug out of the hole and take longer to get up to top speed. An oversized prop can also prevent your boat from getting up on plane properly as well. Like many other things in life, it’s a balancing act.

Boating can be a fun, fast, and refreshing way to enjoy radio controlled hobbies. Like many things in the hobby, you can tweak your boat to maximize its performance and overall handling. It’s important to remember that you should only make one change at a time; this way you get a better feel for what that specific change did for your performance. Now go out there and have some fun on the water.