An Introduction to Rigging, pt. 1: Spread and span

When I was in high school I went to a coxswain clinic where Mike Vespoli taught us the basics of rigging and talked about how to measure each variable, what it meant, where to measure from, why it was important, etc. That’s what I’m going to post in this series so that you can get a basic idea of what rigging entails beyond just taking the riggers on and off your boat.

So, why is rigging important? Its main objective is to accommodate all the different bodies in the boat so that when they row, regardless of their size, the oar still moves in the same general arc through the water. The more similar the oar’s trajectory, the more efficient the boat will be.

Here’s what this series will go over:

Part 1 || Spread and span, with videos included that show how to measure them

Part 2 || Oar length and inboard

Part 3 || Pitch, with videos included on how to measure it in your boat

Part 4 || Rigger height and work through

Part 5 || How to rig and de-rig a boat

Part 6 || The tools you nee to rig a boat

Going back to physics, when you row you’re using leverage in a lot of different places. One of the reasons why tall people are appreciated in this sport over their vertically challenged counterparts is because the longer you are, the farther you can reach, and the more leverage you can get on the oar to power it through the water and move the boat. Leverage in rigging comes from spread (in sweeping) and span (in sculling), as well as from the inboard and length of the oar, which I’ll talk more about in Part 2.

Spread

A fulcrum is the point about which a lever is supported and pivots. A lever produces force on one end (the load) while pressure is applied on the other (effort).  So, when effort is exerted on one end, the lever pivots about the fulcrum to produce a load on the other end. Thinking in terms of an oar, you create leverage by pushing off the foot stretchers, pushing with your legs, pulling with your upper body (to an extent), and driving the oar through the water. The pressure you put on the handle allows it to rotate around the oarlock and move the blade through the water. The “load” is the pressure you feel against the blade from the water. You are moving the load as the oar goes through the water.

So, how does that relate to spread? And what is spread? Spread is the distance from the middle line of your boat to the pin of the oarlock. If you increase the spread it will make the boat feel lighter but your rowing will be less efficient because the fulcrum will be farther from where you’re exerting your effort.

The best analogy I can think of is to think of it like you’re holding a broom strick when you’re sweeping up something on the floor. If you could balance the broom on your hand, the point where your hand sits on the handle when it’s perfectly level would be the fulcrum. Keeping your hands there is where your sweeping will be the most efficient. If you move your hands one way or the other (towards the top of bottom of the handle), the broom will feel lighter and maybe easier to move, but you’re movement isn’t nearly as efficient because you’re not generating enough effort to move the load on the other end. Make sense? Kinda, sorta?

The spread of your boat will be determined by the experience level of your crew, how skilled they are, the size of the boat, etc. It is adjusted by moving the pin either closer or farther away from the boat. If you look at the this picture of an oarlock and rigger, you can see that the oarlock is in a slot that allows it to move back and forth when the bolts are loosened.

Typically, the spread is somewhere between 80-88ish centimeters. To take it’s measurement using a standard tape measure, this is what you do:

Measure from one gunnel to the other and find the middle of that measurement. If it’s 10 centimeters, the middle would be five. Simply divide by two.

Move the tape measure so that the number you just determined, the middle (5, in this case), is sitting on the gunnel. The end of the tape measure should be hanging out over the center of the boat.

Extend the tape measure out towards the oarlock’s pin and measure. That measurement, from the center of the boat to the pin, is your spread.

Mathematically it’d look something like this:

[(Distance from G1 to G2)/2] + (Distance from G2 to pin) = spread

…where G1 = one side of the boat and G2 = the other side, the side that the rigger is on.

Here’s a quick video demonstrating how to measure spread. Remember, spread only applies to sweep boats, not quads, doubles, or singles.

Span

The difference between sculling and sweep rowing is that instead of one fulcrum, there are two. The spread then goes from being from the center of the boat to the pin to being from the starboard pin to the port pin. Similarly to in sweep rowing how moving the pin farther from the boat decreases the efficiency of your stroke, the same is true with sculling. The average distance between pins is usually something like 157-160ish centimeters and is adjusted in the same way (moving the oarlock closer or farther from the boat by loosening and moving the pin).

Measuring the span is fairly simple, but after thinking about it for a second I realized that the “simple” way I was thinking of was wrong. This is something that Dr. Davenport touches on in the video below, which I was actually internally very excited about (“yay, my thinking is on the right track!”). I was thinking that all you’d have to do would be to take your tape measure and measure from one pin to another – very “keep it simple, stupid”. However, that only tells you the distance the two pins are apart – it doesn’t tell you their distance from the center of the boat. They could be 160cm apart, but the starboard oar could be two centimeters further from the center than the port oar, which can mess you up when you get out on the water. So, as Dr. Davenport suggests, to get your span, first determine the spread (distance from the center of the boat to the pin) for each oarlock and then add the two together.

Mathematically it’d look like this:

{[(Distance from G1 to G2)/2] + (Distance from G1 to pin)} + {[(Distance from G1 to G2)/2] + (Distance from G2 to pin)} = span.

And here’s another video showing how it’s done.

Next week: Oar length, inboard, and blade profile