Spreader Bar Length Calculator

I’m sure you’ve witnessed this scenario on any chartered fishing trip where they believe they know more than the laws of physics. A giant six-foot long bar goes flying into the water, filled to the brim with a dozen large bird teasers. As the vessel crests a wave, the entire contraption fold like an overfilled beach umbrella. Hooks intertwine, the spread disintegrates and the fish flee in terror. This wasn’t bad luck. This was simple math. The fish were never the issue; rather, it was the math involved based off the rigging.

Spreader bars is kind of a give and take. On one side, you’d like some width for a good visual profile and to get your teasers well away from prop wash. But on the other, you need enough stiffness so they don’t slap against the hull when boat rolls. With the above calculator, you can plug-in your specific set of conditions and let someone else do the math. That way you’re not guessing at drag estimates and coefficients; you’re forced to think through actual constraints of your rigging instead of choosing by how something might look cool in shop.

How to Pick the Right Spreader Bar

First thing: What are you targeting? Mahi will come up to the bait and respond better to moderate speeds and bright colors. The area covered isn’t so much that it creates too much drag. Five to seven drops on a bar in the twenty-four to thirty-inch range is typicaly sufficient.

Conversely, tuna swim fast and deeper. They want more of a display in front of them. Often this mean a wide bar that is thirty-six to forty-eight inches. This gives them multiple options all at one time. For those of us fishing for billfish, we’re basically constructing a distraction factory. Marlin and sailfish is curious critters. They’ll check out big commotion from afar, and those bars can grow as long as sixty inches.

As important as the bar’s length is what it’s made from. You can get away with light fiberglass if you’re using small lures on calm water, but put a heavy bird on there at high speed and it will buckle. Bars made from titanium or some sort of mixed material (hybrid) has more spring resistance and can take heavier loads before bending permanently. The bar is like the suspension system that holds your lures in place. You want it to be rigid enough to stand up to the wake and current. It should of be flexible enough to absorb shock, but not too much.

The variable least considered by most folks, until it’s too late, is sea state. A long bar turns the boat’s roll into a lever action. This increase the force on the outside wings, forcing them to either smack against the hull or transom. The fish spook from your line. As you’ll see in the reference tables, a shorter bar is always recommended in rough water. Why? There’s a tradeoff here. You sacrifice some spread width for stability but maintain a tighter setup with less movement of the center of mass from the tow point.

Another common mistake is amount of space between the drop-backs. When a fish bites, or they turn around, all those teasers gets fouled up on top of each other if they’re too closely spaced. Leave enough room that each drop back can wiggle free from the others. About one and a half times length of the lure in between hooks is a good rule of thumb. That way it’s a clean presentation with each teaser swinging its own tail. The calculator will do that check for you and let you know if spacing is too close for the lure size you’ve chosen.

The speed is the difference. The velocity squared equals drag. In other words, if you bump up the number of knots by one increment, it exponentially increases the tension on your clips and tow lines. What might have been a perfect run on a bar at six knots will be a nightmare at nine knots pulling as hard as it does on the same count of teasers. That’s why some bars is so rigid and small while others are so wide and flexible. On high-speed trolling like yellowfin or wahoo, you’re sacrificing visual spread for mechanical strength.

Finally it’s all about having the proper set up. It is not necessarily about having the most lures or the longest string, but about what will last in the conditions and put a good lookin’ face on the bait for the fish. You need to find the magic number of what you can have out there without losing any form and yet still make enough commotion to draw strikes. When everything swims free and your bar runs true, then it gets good. Then it’s time to go fishing.