mast bend instruction

How to measure your mast bend

To build fast sails it is important for the sailmaker to know how a mast bends. There are different ways depending on the boat class how to determine the mast deflection.

Here we explain how it is easiest for most catamaran sailors to measure their masts in the rigged state.

You need a

stay wire, 8.5m long (varies by boat), 2.5mm diameter
a PT-1 Loose tension gauge
thin rope around 9m long
tape measure
pen to mark the mast

Step 1: Prepare the boat and mark the mast

The boat has to be put on its side with the mast set, support the mast on the main fitting. Make a note of spreader angles and diamond tension.

We recommend a default setting of 55mm spreader angle and 27 LG diamond tension.

We need the mast bending curve along the length of luff of the sail from upper gooseneck fitting to the top of the mast.

Mark the mast down from the top hook at

1/8
1/4
1/2
3/4
1 = complete luff lenght

Record the height of the spreaders.

Step 2: Attach and tension the wire

Lock the rotation in the center in line with the middle of the boat or the boom. We are interested to know the mast bend with 0 degrees rotation.

Take the ring from your sail and shackle the wire on to it.

Hook it on the mast and the other end to the boom in the same position the clew of your sail would be
Spannen Sie das Drahtseil mit der Großschot.

Apply tension with the mainsheet.

Step 3: Tension to Loose Gauge 19

Connect the loose gauge to the wire 1m up from the boom.

Apply more tension on the mainsheet until you have 19 on the loose gauge.

Be careful that the loose gauge is reading correctly.

Step 4: Attach the measuring string

Now attach the string line to the mast from below the mast hook to the gooseneck on the trailing edge of the mast.

Step 5: Measure the deflection (LG 19 and 20)

Measure the offsets at each location marked on the mast (trailing edge to the rope)

Repeat the measurements with a tension of 20 on the loose gauge.

Enter your mast bend values online

Enter the bend values measured on your mast here. You will then automatically receive an e-mail with a personal analysis of your mast (stiffness, top behaviour and load characteristic) including a comparison chart.

1. Contact details

Name (first and last name) *

E-mail *

2. Mast & setup

Boat class *

Sail number (optional)

Mast manufacturer

Mast serial number

Year built

Mast length total, without mast foot (mm) *

Diamond tension (LG, min. 29)

Spreader length (mm)

Spreader position, height from bottom (mm)

Spreader angle (mm, default 55)

Measurements Loos Gauge 19 (~125 kg tension) — deflection in mm, enter from BOTTOM (3/4) to TOP (1/8):

3/4 (bottom) *

1/2 (middle) *

1/4 *

1/8 (top) *

Measurements Loos Gauge 20 (~135 kg tension) — same positions, also from BOTTOM (3/4) to TOP (1/8):