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RDM / SDM compatibility throughout the range (except Raceboard and Formula Blades) is, as far as I know, unique to Loftsails.

Here I’ll outline the differences in performance each type delivers relative to rider weights, ability and conditions.

(By the way, the sail in the picture above is rigged on an SDM mast … )

First some background for those unaware of the differences:


Standard Diameter Masts
 (SDMs) are mostly around 48-mm. wide (internal) at the base and the lower tube that will fit various lengths of mast extension (dependent on how fast they taper towards the top section).

Standard Diameter Masts (SDMs) were the ‘original’ windsurfing mast diameter until the early 2000s when RDMs first appeared on the scene.

Reduced Diameter Masts (RDMs) were originally introduced for wave-sailing as a solution for durability in waves due to their extra wall thickness that is more resistant to breaking when exposed to extreme flex in surf conditions.

RDMs have an internal diameter of 32-33 mm. at the base.


Masts are the backbone of the rig and rig character changes significantly depending on the mast type used.

The two mast types are different in the way they work when windsurfing.

The differences between RDMs and SDMs can be a positive or can be negative depending on many factors.

For any given sail size here’s a summary of the contrasts:


  • Feel more forgiving generally compared to SDMs. Their more elastic dynamic character is better suited to lighter windsurfers.
  • Smaller sail sizes are likely better on RDMs
  • Their dynamic softness making the rig more forgiving for the stronger winds associated with smaller sizes.
  • Are generally better suited to rough conditions, especially severe chop, where their softer character gives a ‘dampened’ feeling to the rig.
  • Cam-equipped designs rotate more easily on RDM masts than on SDM masts.
  • Tend to set the sail flatter through the lower body on RDMs compared to SDMs.
  • Generally allow the rig to set lower down onto the board compared to SDMs because their softer character results in slightly more mast bend through the middle, which in turn allows more twist through the lower leech that lets the sail twist off more just above the boom, so that the boom settles in, ‘closing the gap slightly more than SDMs do. This can make upper end sailing more efficient and more comfortable.
  • Are more durable than SDMs. RDMs can flex much farther than SDMs, which is especially important for wave sailing.
  • RDMs also accept cam pressure without problems due to their thick walls.
  • Are of similar weights compared to SDMs in shorter lengths – but become heavier than SDMs in longer lengths
  • Are more likely to be more accurate regarding flex-spec matching because the greater wall thickness makes RDMs less production-tolerance critical.


  • Make the rig feel stiffer and less forgiving.
  • Can produce better upwind & flatwater performance compared to RDMs.
  • Will set the sail with a slightly more defined, fuller profile through the lower body compared to RDMs.
  • SDMs, with their thin walls, can be sensitive to cam pressure. This can become an issue in hot weather or direct sunlit where SDMs can sometimes loose their integrity.
  • Large sail sizes are usually better rigged on SDMs and are better suited to the stiffer character of SDMs, just as a large backbone is better suited to large-sized body.
  • The sail size where this transition happens is relative depending on the size of the sailor, sail design details and trim. However I would suggest 7.0 and down on RDM, larger sizes on SDM as a basic parameter for most windsurfers.
  • Are generally less likely compared to RDMs to be accurate regarding flex-spec matching because the thinner wall thickness make SDMs more production-tolerance critical.

Back in 2005 I decided to bring cam-equipped designs into the Loftsails product range.

I am 78 kg.and appreciate the softer feeling, durability and spec-matching associated with RDMs.

Consequently, early Loftsails Blade designs were RDM-only.

As the Blade designs evolved, SDM compatibility became necessary.

Providing both cam types with Blade designs has been a feature of Loftsails Racing Blades since 2009.

RDM/SDM compatibility is a unique feature of Loftsails Blade designs and I hope that you find the information above useful in choosing the right mast for your sail!

Good winds,