RCC

 Rescue Coordination Centre

RCDS

 Raster Chart Display System

RDC

 Run Down Clause

RDF

 Radio Direction Finder

RED

 Rate, Extras, Demurrage

REC

 Spain's Special Register of Vessels of the Canary Islands

RECD

 Received

REDELY

 Redelivery

RF

 Range Finder

 Radio Frequency

RH

 Relative Humidity

 Right Hand

RINA

 Registro Italiano Navale (Italian Classification Society)

 Royal Institute of Naval Architects

RINAV

 Registro Internacional Naval SARL (Portuguese)

RLS

 Royal Lifeboat Society

RMS

 Root Mean Square

RNR

 Registrul Naval Roman (Romanian Register of Shipping)

 Rate Not Reported

ROB

 Remaining On Board

ROC

 Restricted Operator Certificate

 Reference Our Cable

RORO

 Roll On/Roll Off

ROV

 Remotely Operated Vehicle

ROT

 Reference Our Telex

RPC

 Remote Position Control

RPF

 Radio Position Finding

RPM

 Revolution Per Minute

RPS

 Revolution Per Second

RPT

 Repeat

RS

 Russian Maritime Register of Shipping

 Radio Station

R/T

 Revenue Ton

RT

 Radio Telephone

RTN

 Return

RTW

 Round The World

R/V

 Round Voyage

RVP

 Reid Vapour Pressure

RVT

 Revert

RVTG

 Reverting

RX

 Receiver

RYC

 Reference Your Cable

RYT

 Reference Your Telex