Is your mast straight? Is it really straight? A straight mast is the most important part of your boat tuning and setup. You shouldn't start anything else until your mast is completely straight. Only then should you move on to tuning your mast diamonds, forestay, pre-bend, and rake.
Because the thistle mast is so bendy, it is extremely susceptible to getting small bends and curves over time. The locations vary, but there is typically a large single bend the length of the mast composed of a few smaller bends, often near the middle and lower spreaders.
First, you will want to evaluate the straightness of the mast with no diamond interaction. Sighting the mast by eye alone can be difficult. Not only does the ambient angle of the lighting affect how the bend/straightness appears, but it is very difficult to determine where in fact a bend is along the length of the mast.
To take the guesswork out of the process, take the main halyard down the mast and attach it to the gooseneck and cleat the halyard taught with a knot in place of the halyard ball. Then tie a spare piece of line tightly around the mast, pulling the halyard into the mast track. Do the same with a piece of line at the top of the mast, as the shiv is often offset to the side of the mast track once load is applied. Make sure the halyard is centered in the track at both ends.
Disengage all diamond wires and sight the halyard along the length of the mast. Note where the halyard is not in the middle of the track. If the halyard is within the mast track, the mast shouldn’t need to be straightened off the boat. While doing this sighting, ensure the halyard is held perfectly centerline by the keeper lines at the top and bottom.
If the halyard doesn’t fall within the mast track, it needs to be straightened. Keep the same setup, but remove the mast from the boat and put it in between two chairs or picnic table benches with the ends setting on pads. Move the supports in so only the section of the mast with a bend is between them.
At the apex of the bends sit or push down on the mast - you must apply the force slowly and steadily - NEVER BOUNCE THE MAST. Depending on the bend it may take your full weight for several minutes to work a bend out. If you think your boom bend under vang load is gross looking, this will be another level of discomfort. Keep working the mast, until you are within tolerance.
Once the mast is straight, engage the top diamonds. Pin the halyard along the length of the top diamond section and check for straightness along that length. Adjust the diamond tensions side to side ¼ turn at a time until the section is straight. It helps to be in the ballpark of your desired diamond tension while doing this, but the right number isn't necessary. Being on the light side of diamond tension is better. Disengage the top diamonds and do the middle diamonds, then the lower diamonds using the same process. Do each section individually as each section interacts with the next.
Once all the individual sections are straight, attach all the diamonds and check straightness again. Often, it will be slightly out of straightness. Adjust the diamonds to get it perfect. Then, check your numbers for the diamonds so the average of each side to side meets the tuning guide. If the difference is greater than 1 ½ to 2, the mast may need to be straightened again or the process begun from the beginning to get it within tolerance.
At this point you should have a straight mast. Time to move on to the diamond tensions and the rest of setting your rig up.
If you have questions about this process, find Brad Russell or Mike Ingham in the parking lot at St. Pete for MWE or send us an email at bradarussell@gmail.com or mike.ingham@northsails.com.
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