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MastTuner for Android

From the Finger Lakes Marina RNYC - Across the lake and a little north of the yacht club

My 1975 Lancer 28 has a deck stepped mast which I have raised and lowered twice a year for the last 7 years. That process, and the rig I use, is the stuff of a different article but I did want to tell you about a great new tool for checking the mast once it's up.

After I raise the mast I have to tune it. In the past, if I could find a glass smooth day, I would hang a plumb bob from my mainsheet halyard, and measure where it touched the boom. That gave me a general idea of how the mast was standing. Unfortunately, getting on and off the boat would send the plumb bob ducking and weaving for several minutes, and my weight on the boat was enough to throw things off, so my measurements were always “in the neighborhood”.

This year was different. The company I work for makes applications for Android cell phones and iPhones. One of our applications, Johnson Visual Level, uses a superimposed level line on the camera's view finder. Although it’s useful for leveling pictures, TV sets, etc., I thought, with some minor adjustments, it might also work for my mast.

My coworkers, Ben Kalb and Andy Zickler, liked the idea enough to make some changes to the original program.

In Johnson Visual Level, the green lines stay level and plumb no matter how the camera is tilted. What I needed was a line that stayed parallel to the screen, but told me how much I was tilting the phone. I wanted to face the mast fore and aft, and see if it stood straight but I also wanted to view it from the side, and measure the rake.

(NOTE: This should be done on a day with no wind, with the boat perfectly horizontal. Move things around if you have to, to balance the boat).

You have to look closely to see the green horizontal and vertical lines in this picture. The small black box in the center of the screen is showing the degrees of tilt.

With MastTuner running on my Droid, and viewing the boat from the bow or stern, I hold the horizontal line at 0, and align the vertical line with the mast.

Notice the glass smooth water. Picking a windless day to do this will really help. Besides, with no wind what else are you going to do?


If you look closely, you can see that the top of the mast looks a bit warped. The side stays are keeping the mast straight up to the spreaders but from there the mast bends slightly to port. My port and starboard shrouds are not set correctly. I verified this by standing at the base of the mast and sighting up.

Now for the disclaimer: Although MastTuner helped me identify the bend in the mast, rigging work is best done by a professional rigger. Improperly tensioned shrouds and stays can lead to all kinds of expensive problems including mast and deck hardware failures. If you do decide to do your own work, educate yourself, buy the right tools (at a minimum buy a Loos gauge), and get advice from a pro.

With MastTuner, I was also able to check the rake of my mast.

In amongst this forest of masts is my Lancer 28. By aligning the green line with the top of the mast, and holding the degrees readout at 0°, I was able to clearly see the amount of rake.

If I had a mark on the boom, I could compare where the vertical line crosses the boom, and know how far fore or aft to adjust the mast.

Instead, I can get the exact readout in degrees, and use that as my guide. Fortunately, MastTuner makes this easy.




To measure the angle of the mast, I tilt the phone so that the green line lays along the mast. The readout displays the angle in degrees. If you prefer, the configuration menu will give you the option of displaying the readout in inches/foot, millimeters/meter, or percent.

(2.6° is a bit steep for the sailing I do so I will adjust the rake of the mast to 1.5°).

MastTuner is a simple application for a quick check of your mast. It helped me find a couple of problems with my mast, and will help me tune my standing rigging when I set the mast again next Spring.

MastTuner is a free Android application. Use your Android phone to search the Marketplace for MastTuner, or scan this code with any barcode scanning application.

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