Hot Tips on How to Measure Mastbend on Sailing Boat Masts

Measuring the static mast bend successfully on a dinghy mast-Contender

Aim: To determine the relative stiffness of a dinghy Mast as information for the sailmaker/mastmaker/sailor.

First make sure you have all the tools you will require at hand.
Tools required:
– 2 people(makes it easier to measure)
– 10kg weight (tie it to a length of rope approx. 1mtr length)
– 2 support frames (make sure one of them is smaller in section so the measuring stringline fits over it)
– String line or thin line
– Ruler
– Tape measure
– Marker pen or pencil
– Electrical tape masterracksbd(or similar tape in a contrasting color to mast color)
– Paper (or print this sheet and use table at end of page to enter measurements.)

Now we can measure the spar with 10kg, please follow the sequence of following steps:

1. Set up Mast horizontally on 2 supports. One directly under the Mast base, then one under the stay/forestay attachment point.

2. Mark the 25%,50% and 75% points on the mast, to do this divide the distance between the black band length into 3 points (Contender Mast BB length- 5842mm).

The points are then 1460.5mm,2921mm and 4381.5mm.
(Draw these 3 points on the mast so you can see them or use tape marks it is easier to see.)

3. Now set the mast in fore and aft direction on the supports (the mast track will face the floor/ground) and make sure the mast base is held firmly at the bottom support( best if a helper just holds it down or if alone just wedge it under something or weigh it down heavily).And make sure that the top support is directly under the forestay/shroud point.

-Now measure the the distance from the top black band at the aft face of the mast track to the floor or ground and note this on paper or in my grid table.

-Then turn mast 90° (this is for side bend)and measure from top Black band to the floor or ground and note the dimension down on paper or in my grid table.

4. Attach the 10kg weight at the mast top tying it onto the sheave area above the black band.

5. Attach the string line to the aft face of the mast track on the inner(lower) edge of the top black band (tie it on or tape it on). Then lead the line down to the lower Black band, tighten it and attach it so it is on the inner edge of the black band and the projection of the back of the mast track- just tie it onto the gooseneck fitting at the required projection point making sure its in the middle of the mast.

6. Make sure the string line is tight then check it with your eye, sighting along the line making sure it is straight.

7. Now go to the mast top and measure the distance again from the black band to the floor or ground, write it down – this is tip deflection sideways.

8. From the mast top take the 3 offsets – measure from the stringline to the middle of the Mast track and note the measurements (be sure to note top 75%, 50% and bott 25% so the measurements don’t get mixed up).

9. Now turn the Mast again 90° so that the Mast track is underneath this will now be the measurements for fore and aft. From the mast top take the 3 offsets- measure now from stringline to aft face of the mast track and note the measurements.

10. Finally send the measurements to your sailmaker/mastmaker or keep for your info(helpful for comparing different masts)

Mast type_________________________
Spreader Length(measure from tip/stay to side of Mast)___________________
Spreader angle (measure from aft face of mast track to line strung between both spreader tips at center of staywires where they enter the spreader tip) ________________________
Mast diameter at base ______________________

Table of Static mast bend measurements – Using 10kg

Fore and aft
Top 75%=

Top 75%=
25% =

F/a 0kg =
F/a 10kg=
Side 0kg =
Side 10kg =

If you require any help with the measuring details feel free to contact me at

Best regards,
Stuart Brown

Thank you for reading my article.

Helpful tips can be found on my website


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