Sail Skills - ColRegs Free Guide to ColRegs (the International Regulations for Preventing Collisions at Sea, the IRPCS or Collision Regs).  Guidance covers all aspects with animations, pictures and diagrams.  Aimed at small vessel users but suitable for professional mariners.  Especially recommended for RYA examination candidates.
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The following vessels shall sound at intervals of not more than 2 minutes: ColRegs Home>ColRegs>Signals>Fog Signals>Other Vessels So, all these vessels have the same signal: While the towed vessel below is required to sound the additional signal of 1 prolonged blast followed by 3 short: Tug and tow tug sounds 1 prolonged blast followed by 2 short  tow sounds 1 long followed by 3 short Comparison of whistles back to top Power-driven vessel underway in restricted visibility Sailing vessel underway in restricted visibility A vessel at anchor in restricted visibility A vessel under 12m underway in restricted visibility Power-driven underway Other vessels underway Anchored & Aground Vessels under 12m Vessel engaged in pilotage duties underway in restricted visibility Vessels engaged in pilotage duties A vessel under 12m:  need not sound any of the specified fog signals but shall make some other “efficient sound signal” at intervals of not more than 2 minutes if she does not make the specified signal
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