Measuring for a Spinnaker or Code Sail

Measuring for a spinnaker or Code sail is relatively straightforward. Only a few key measurements are needed to determine the correct sail size.

Down Wind Measurement Guide

You'll need a long tape measure that can be attached to your spinnaker halyard and hoisted to full height.

As always, don't forget to attach a downhaul line so the halyard can be retrieved safely.

Measuring "Spinnaker I" and Maximum Luff Length

Start by hoisting the tape measure to the point where the spinnaker halyard exits the mast.

Lock the halyard in place and measure down to deck level. If your mast is mounted on the cabin top, measure to the side deck.

Next, leave the tape hoisted and bring the lower end of the tape measure to the point where the tack of the sail will be attached. For traditional Symmetrical Spinnakers this is not required.

This may be:

• An anchor roller fitting
• A bow fitting
• A bowsprit

The resulting measurement is your maximum luff length.

Measuring the J Dimension

After lowering the tape, measure the horizontal distance from the tack attachment point to the front of the mast. This measurement is known as the spinnaker "J" dimension.

For boats using a symmetrical spinnaker, this measurement is typically the same as the spinnaker pole length.

Measuring the C Dimension

With the tape still attached at the tack point, measure aft to the location of the spinnaker sheet block. This distance is known as the "C" measurement and helps determine the sail's sheeting geometry.

Measuring for Code C Sail

The correct luff length for a Code C depends on how the sail will be set.

Deck-Mounted vs. Bowsprit-Mounted

If the sail will be flown from the foredeck inside the pulpit, the tack must sit above and clear of the pulpit. This usually requires a slightly shorter luff.

If the sail will be flown from a bowsprit, the luff can be longer because the tack is positioned farther forward.

Estimating Luff Length

As a general guideline:

• A deck-set Code C often has a luff length close to the mast height above deck.
• A bowsprit-mounted Code C typically adds the bowsprit length to that measurement.

The Most Accurate Method

The best way to determine luff length is to hoist a tape measure on the spinnaker halyard and measure directly to the future tack position.

From that measurement, subtract:

• The height of the furling drum
• The height of the top swivel
• Allowance for stretch under load

Note if you are purchasing the furler from us, we will have these dimensions.

In most cases, this total deduction is approximately 24 inches(60 cm).

For example, if the maximum measured luff length is 42.25 feet the finished sail luff would typically be around 40.25 feet.