The GSC Regulations at point 3.11 require that a boat is fitted with watertight bulkheads that divide the boat in several watertight areas. This, to ensure that if any subsections becomes flooded as a consequence of a collision or through-hull failure or other damage such as rudder loss or damage the boat will preserve sufficient reserve buoyancy to allow a skipper to assess the situation, attempt repairs and in any case be in a position to avoid the immediate need to abandon the boat for the liferaft. A liferaft may provide less shelter than a damaged boat fitted with appropriately placed watertight bulkheads.
Complying with the Regulations is a requirement, however the range of situations that may arise following an accident or structural boat failure is so vast that skippers are also required to carry a survival suit. This will provide additional protection against the risk of hypothermia whether a skipper remains onboard their partially flooded boat or is forced to abandon.
Watertight subdivision is a common technique for increasing safety on commercial and military vessels but is very rare on yachts. Only Events held under World Sailing Offshore Special Regulations Category 0, as well as the Global Solo Challenge, require this.
Fore and Aft bulkheads
The GSC Regulations require that:
3.11.1 Either a watertight “crash” bulkhead within 15% of LH from the bow and abaft the forward end of LWL, or permanently installed closed-cell foam buoyancy effectively filling the forward 30% LH of the hull
3.11.2 It is strongly recommended that a boat is fitted with a bulkhead within 15% of LH from the stern. The sub-section should include the rudder stock(s) through-hull(s) if fitted within 15% of LH from stern
3.11.3 Any required watertight bulkhead to be strongly built to take a full head of water pressure without allowing any leakage into the adjacent compartment
3.11.4 At least two watertight transverse bulkheads in addition to any bulkheads positioned within the forward and aft 15% of LH
3.11.5 Outside deck access for inspection and pumping shall be provided to every watertight compartment terminated by a hull section bulkhead, except that deck access to extreme end “crash” compartments is not required
3.11.6 An access hatch in every required watertight bulkhead (except a “crash” bulkhead). The access hatch shall have means of watertight closure permanently attached to the main panel, or lid, or cover of the hatch. The closure shall not require tools to operate
If the installation of the above bulkheads cannot be achieved, a Skipper shall submit to the Organiser by the 30th of April 2023 or earlier a written statement confirming they have made alternative provisions for watertight bulkheads to divide the Boat in watertight sub-sections that are of a sufficient standard quantity and volume and are equal to or exceed the protection against sinking or flooding that compliance with 3.11.1 to 3.11.6 would provide and that they have consulted with a marine architect or other suitably qualified person who has confirmed that such alternative provisions are of sufficient standard quantity and volume and are equal to or exceed the protection against sinking or flooding that compliance with 3.11.1 to 3.11.6 would provide. Please refer to the GSC Regulations 3.11 for full details.
You can find additional insights on this topic in this Proboat Article.