I built the mast shown here for the "Notion", a 34' steel sloop. The mast is unconventional in that it is octagon shaped (eight sided). It stood on the boat for almost 18 years before it was sold, still on it, as far as I know.

Materials Used in Sailboat Mast Building

Cold rolled steel, pickled in oil, is used for the main column and usually between 16 and 14 gauge in thickness. Cold rolled material is readily available, uniform in thickness, and has a surface which is near ready for paint since it has no mill scale. Most other parts of the mast are fabricated from A36 Hot Rolled Steel. This is the same steel used for hull construction.

Paint coating for sailboat mast building should be a good quality primer and finish coat, be sure to follow the manufacturers recommendations. Interior halyards are not recommended. The entry and exit holes for interior halyards usually develop maintenance problems. The holes invite water and weather on the interior causing corrosion problems. Exterior halyards don't have these problems because the mast is sealed with weld and you do not need paint on the inside.

Electrical wiring is installed in accordance with "The Standards and Recommended Practices for Small Craft by the ABYC (American Boat and Yacht Council, Inc.)

I have broken the components of a steel mast into the following categories:
PICK ANY OF THE LINKS BELOW FOR MORE DETAILS

• Mast Column Details

• Mast Head Details

• Spreader Details

• Cabin or Trunk Penetration Details

• Mast Step Details

• Tang & Tang Adapter Details

• Referring to the drawing, start the fabrication with a 10' foot section of half mast and tack weld a 7.5' transverse center divider to it. When tacking these two pieces together, be sure there are no twists or other distortions. Any twist in this first section will carry through the entire length of the mast.

• Next, tack weld a 5' starter section to the first 10' section.

• Next, attach another 10' center divider. The center divider will hang over the original half mast section by 7.5'. Support this overlapping center divider temporally. You now have a section of mast which looks like the drawing below.

• Before proceeding to the next step be sure this initial fabrication is free of twist or curves by carefully sighting down its length with your eye. Your eye is the discriminating instrument that maintains a straight, twist free finished mast.

• Follow this procedure of staggering transverse center dividers and mast sections until the designed mast height is reached. Note that no seams will ever align with each other.

• At this point, consider the installation of the electrical conduit and wiring. The conduit can be fastened to the interior mast wall by clips fabricated for this purpose.

• Before welding the mast continuously by stagger welding, add the mast head and mast step hardware to hold the mast shape at its ends.

• Continuously weld the mast - see notes below.

• Add the other hardware to complete.

Care must be taken to avoid distortion when continuously welding any part on the mast by using a staggered welding sequence - especially the mast column.

Good penetration is necessary along the weld seam joining the half sections together while forming the mast column.

Do not continuously weld until the entire mast column has been tack welded together, using small tacks 1" apart, along with the mast head and mast step components.

When continuously welding the mast column, use a staggered weld sequence. Starting at the bottom of the mast weld a two inch long weld bead, skip a space approximately 18", then do another 2" weld bead - skip again and do the last 2" weld bead. Then change to the other side of the mast, do the same welds, just opposite the first set of three weld beads. Follow this sequence until the top of the mast is reached.

The mast now has 2" welds 18" apart from the bottom to top, on both sides. This is done by staggering the weld beads all the way up the mast.

After the mast has cooled return to the original side, near the bottom. Pick a spot between the first set of welds and do another three weld sequence. Move the opposite side and do the same.

After the second run is done, repeat until the mast column is completely welded. It is important to let the mast cool between runs of welding.

Provided the mast was straight before continuously welding, the finished mast will be a straight.

So, there you have it ... sailboat mast building!