By ED OLDHAM

Halibut season is scheduled to open April 10 and if you haven’t done it already, now is the time to get your boat ready.

Personally, I’ve been working hard on mine, and this column will address one of the most important factors — the motor’s propeller.

Proper propeller selection is essential for the longevity of your motor, the single most expensive component of most boats. Furthermore, with the rising gas prices, you’ll want your motor to perform as economically as possible.

Over the past couple of weeks, I have been toying around with changing the prop on my boat. Like a lot of anglers, I bought mine used and assumed it was fine the way it was, but lately I’ve had some questions.

Here’s my scenario, your’s may be different but the basics are still the same. I have a 2001 Arima 21-foot Searanger with a skip tower with a Yamaha Vmax 150 motor. The prop that came with it is a three-blade, 13 and three-quarter by 17.

First some prop basics. The 13 and three-quarter refers to the diameter in inches and the 17 is the pitch of the blades. Pitch is the theoretical distance the prop will travel forward with one revolution, not taking into account the slippage.

To determine if you have the correct prop, you need to find out from your engine’s owner’s manual what the rpms should be at wide open throttle. For my motor, that is 4,500 to 5,500 rpm. With the prop I have on, with my standard load out of the boat, my engine would turn 5,800 rpm, about 300 to high.

I also have a fuel-flow meter on my boat so I can insure that I’m being as fuel frugal as I can. With the boat’s current configuration, the best I can get is 2.68 miles per gallon. But with a little adjusting, I’m sure I can get it over 3 mpg.

The rule of thumb is that if you go up in pitch by two inches, you’ll reduce your engine rpm by 200 to 300. This would be perfect for my situation, because it should get the motor down to that 5,500 rpm at wide open throttle.

My concern was the motor would always turn at 5,800 rpm with differing loads, so my first choice was a three blade, 13- and three-quarter by 21 prop. This way if the pitch was too high, then the rpm would fail to reach 5,500 and it did. It only got up to 5,200 rpm.

So the rule of thumb applied in this case, I went up four inches in pitch and my rpm decreased by 600 rpm. My next prop is going to be a 14 by 19 and my rpm should be perfect.

Some other things to consider are the number of blades and the material the prop is made of.

Three or four blades? Three blades will give you more top-end speed whereas four blades, in the same diameter and pitch, will not. But it will give you faster acceleration, which is great if you are towing a skier.

Aluminum or stainless steel? This is really about personal preference. Aluminum will flex more and it will absorb a hit better than steel. This is the main reason I choose to go with the aluminum. There are a lot of logs out in the sound and I would rather have a bent prop than a broken one.

Tuning up the boat early will make this season a more enjoyable one on the water.