RDM vs SDM - Reduced Diameter vs Standard Diameter Masts


Type Description Inside Diameter (metric) Inside Diameter (imperial) Outside Diameter (imperial) Mast Pieces
RDM Reduced Diameter Mast 33 mm ~1 19/64" ~1 5/8" 2
SDM Standard Diameter Mast 48.5 mm ~1 29/32" ~2" 2


Masts come in 2 base diameter types: SDM, and RDM. Mast extensions need to be compatible with the mast type. Buy a SDM extension for standard diameter masts. Buy a RDM extension for reduced diameter masts.

SDM - Standard Diameter Masts

SDM standard diameter masts are the original style masts. Starting around 1990 they were manufactured using a semi organized industry standard.

SDM masts use SDM mast extensions and SDM boom heads.

SDM masts are lighter because the walls are thinner. Race and freeride sails over 6.0m should use SDM masts.

RDM - Reduced Diameter Masts

RDM reduced diameter masts are designed for smaller sails, thicker mast walls, and stronger construction for wave sailing. The smaller diameter helps make rigging your sails easier. Sail handling is easier - especially water starting.


Start out with RDM masts and extensions, especially for learning. RDM masts and extensions for sails under 6.0m.

If you are buying your first mast - buy RDM and look for masts with a carbon content between 40-80%.

Free-race and race sails should use standard diameter masts. 

Mast Lengths

Length Imperial Reduced Diameter Standard Diameter Notes
270 cm 8'10" Common Kids Mast
300 cm 9'10" Common Kids Mast
315 cm 10'4" Common Kids Mast
340 cm 11'1" Common Wave Sails
370 cm 12'1" Common Wave Sails
400 cm 13'1" Common Common Wave Sails
430 cm 14'1" Common Common Free Ride Sails
460 cm 15'1" Common Common Free Ride Sails
490 cm 16'0" Common Race Sails
520 cm 17'0" Common Large Race Sails
550 cm 18'0" Common Formula Race Sails