Solving Boat Performance Issues
By: Mark Romanack
A boat that performs well is a beautiful thing. Those that don’t perform well can usually be corrected with some simple steps such as experimenting with weight distribution or prop selection issues.
Having been in the fishing and marine business my whole life, one of the most common things I notice about fishing boats is they often don’t run up to their performance potential. In part, this problem occurs because in an effort to keep a “boat/motor/trailer” price package reasonable, dealers often equip boats with less than desirable outboard motors. A boat that is underpowered is almost certainly going to experience a host of performance issues.
In general, it’s always best to equip a boat with an outboard that is at or near the maximum horsepower rating. For example, a boat rated for a 90 horsepower engine, should be equipped with a 75-90 horsepower outboard. Anything less is likely going to lead to serious performance issues.
While not putting a big enough outboard on a boat can certainly lead to performance issues, there are lots of other things that can cause a perfectly good fishing boat to run well… like crap! The good news is that most boat performance issues can be corrected if you have the know how.
Probably the most common boat performance issue is a boat that bounces up and down in the water. Commonly called porpoising, when a boat has porpoise issues, the bow of the boat lifts too much and then can’t sustain that bow lift, causing the boat to ride in the water like a school of porpoise breaking the surface and then submerging. In most cases, a boat that is experiencing porpoise issues has a weight distribution issue. Too much weight in the front or back of the boat can and often does cause a boat to porpoise. In extreme cases, the problem can make it impossible to keep the boat on plane.
Moving weight around in the boat to strive for the best ride can be accomplished by using sand bags. Once you figure out where weight needs to be added and where it needs to be removed, a boat that porpoises badly can normally be corrected by permanently re-distributing weight inside the boat. This often requires moving batteries to different locations in the boat.
It is important to understand that bow lift is controlled by how much engine trim is applied. If the engine is trimmed too high, the bow will start bouncing creating the porpoise effect. Simply, using the outboard trim switch to trim the engine down slightly will solve the problem in some cases. The trim switch is located on the control box if you have a console boat or on the handle of the outboard if you own a tiller boat model.
Getting a boat to perform correctly requires an understanding of how to properly trim an outboard motor. On console models, the trim switch is located on the control box handle. On tiller boats such as this image, the trim switch is on the outboard motor handle. Trimming the engine up or down slightly makes a huge difference in how a boat performs.
In other cases, the “trim sensitivity” of the boat is so touchy, even the slightest adjustment causes the boat to porpoise or to run way too flat.
In this case, one of the easiest ways to tackle the problem of a porpoising boat is to experiment with different prop sizes and pitches. A prop that is not spinning at or near the manufacturers maximum RPM level is likely going to cause the boat to experience performance issues, including the problem of porpoising.
The first step in propping a boat is to determine what the maximum RPM level the manufacturer of the outboard recommends. Most dealers will allow their customers to experiment with different props, under the “you break it and you bought it” policy. Ideally, the engine RPM level at wide open throttle should be within 100 or 200 RPM’s of maximum. It’s simply amazing how much difference a prop can make and no two boats react the same to different brands, sizes and pitch props.
When a boat is performing properly, the prop will be spinning at or very near the outboard motor manufacturers maximum limit. For example if the manufacturer recommends the engine to run at 6000 RPM under full throttle, the best prop is going to be the one that comes within 100 RPM’s of this standard.
Most boat owners use an aluminum prop on their outboard motor. The problem with aluminum props is they flex a great deal under power and are often a poor choice in regards to gaining maximum performance from a hull.
Stainless steel props are more expensive, but because steel is more rigid than aluminum the prop doesn’t flex as much and generates more lift and thrust which in turn causes the boat to enjoy more speed and more mid-range RPM control over the hull.
I recommend stainless steel props on all boats that have an outboard motor of 90 horses or greater.
SUMMING IT UP
In most cases, a boat that isn’t running great can be corrected. Making sure your boat is not under-powered is an important first step in achieving good to excellent boat performance. Experimenting with weight distribution within the hull and trying different props will correct the vast majority of boat performance issues. Using a stainless prop instead of an aluminum prop is yet another easy way to improve boat performance.
If after taking these steps the boat is still experiencing issues, chances are an after market product such as trim tabs are going to be necessary. I view trim tabs as a last resort as they are generally expensive and the average angler is not going to be able to install them correctly. Thankfully, most boat issues can be corrected without going to this final step.