Mast Rake Calculator

Mast rake is the angle the mast makes from vertical, measured forward or aft. Most sailboat masts rake slightly aft to improve helm balance and upwind performance.

Why mast rake matters:

• Aft rake moves the center of effort (CE) aft, increasing weather helm
• Forward rake moves CE forward, reducing weather helm and eventually producing lee helm
• Proper rake gives balanced, neutral-to-slight-weather helm: the ideal for safety and performance

The direction is worth getting straight, because it is easy to reason backwards. The centre of effort is where the sails’ driving force effectively acts; the centre of lateral resistance is where the keel or centreboard resists sideways motion. Rake the mast aft and you move the CE behind the CLR, so the wind pushes the back of the boat away and the bow swings up into the wind. That is weather helm. Rake forward and the CE moves ahead of the CLR, so the bow gets pushed away from the wind instead, which is lee helm and much less safe: a boat with lee helm bears away when you let go of the tiller instead of stopping.

Measuring mast rake: Hang a weight on a string (plumb bob) from the masthead. Measure the horizontal distance from where the string falls to the base of the mast. Rake = arctan(horizontal offset / mast height).

Typical rake values:

• Most fractional rig sloops: 1–3° aft
• Performance dinghies (Laser, 420): up to 5° aft for upwind, less for downwind
• Cat-rigged boats: often 3–5° aft
• Forward rake: unusual, and the cure for stubborn weather helm

Adjusting rake: Change the length of the forestay (in unstayed masts) or backstay tension (in stayed masts). Moving the mast step forward or aft also affects rake.

Helm balance check: ideal is 3–5° of rudder angle to hold a straight course upwind, felt as a gentle pull on the tiller. Let go and the boat should round slowly up into the wind and stop. If it holds course indefinitely or bears away instead, the CE is too far forward and the mast wants more aft rake. If you are fighting the tiller with 10° or more of rudder, the CE is too far aft: rake forward, or flatten and depower the mainsail, which does the same job faster in a gust.

Two things confuse this measurement. Weather helm grows sharply with heel angle, so a boat that feels balanced upright can be a handful at 25°, and the fix there is usually a reef rather than rigging. And rudder drag rises with the square of the angle, so excess weather helm is not merely tiring, it is slow.