Understanding Mast Rake

Correcting the mast rake on Paikea

You may be asking what exactly is Mast Rake and why is it important. Mast rake is the angle at which the mast leans aft from the vertical position. The picture below shows the rake in a Gunboat 68. The angle of the Gunboat mast from the red vertical line to its aft position is referred to as the mast rake.

The rig is designed to be in a position where the boat will be correctly balanced and easy to sail. When you move your mast rake you move the whole sail plan either forward or aft. Rake is determined by forestay (or headstay) length. When you lengthen the forestay you lay the mast further aft creating my rake. When you shorten the forestay you stand the mast more upright and reduce the rake. How much rake a boat needs to generate the right amount of weather helm is a function of hydrodynamics (hull form, keel shape, and placement).

Every yacht should be designed with an optimum position in which the mast should be placed. This information may be available in the boat specifications and, if you can find this information, you should always try to tune to these numbers. However, as in our case, we have modified the boat and the position of the forestay attachment point (you can see our posts on our forestay attachment here) is now higher than it used to be. This means that our forestay is now longer than it should be and as a consequence our rake is too far aft.

Rake refers to the amount the mast is leaning fore or aft and it will affect the performance of your boat.

Gunboat 68 mast rake

We’re playing with our forestay in this episode.

When we replaced our front beam over 2 years ago, we changed the geometry a little. The issue was we couldn’t find a scrap piece of carbon mast big enough to span the width of Paikea. We came up with a solution to use two smaller pieces connected to a central longeron/bowsprit piece. We also angled the entire arrangement upwards a fraction to lift the front section away from the water.

The bows Catana42s slope down towards the water and we wanted to lift the trampoline and beam higher up. The issue we then had was that our forestay was now a fraction too long for the new setup. The longer forestay meant that our mast leaned backward more than it did before. In other words, we now had too must mast rake.

In order to fix the problem we had to buy a new forestay or shorten the existing one to fit. As we are running our upgrades on a budget and it seemed wasteful to throw away a perfectly good stay that was relatively new, we decided to shorten what we had. It did prove a bit tricky to find someone in the Caribbean who was capable and willing to take on the swaging job for us. We ended up finding a great rigging shop called FKG in Sint Maarten and finally got the mast rake where we wanted it.

If you want to see more on making our carbon front beam and longeron check out this episode on Making our carbon front beam and longeron