Mariners Library ⚓️

Which cargo is suitable for COW? this relates to the conditions under which crude oil washing (COW) is not permitted or not suitable due to the nature of the cargo. According to MARPOL Annex I, Regulation 35, the Crude Oil Washing Manual (COW Manual), and industry practice (OCIMF/ICS guidelines), certain cargoes make a tank unsuitable for COW operations. Here’s a clear summary: ⚠️ Cargoes not suitable for crude oil washing Crude oil washing must not be carried out if the cargo has any of the following 1-characteristics: Waxy or high-pour-point crude oils If the crude tends to solidify or form wax deposits at normal tank temperatures, it may clog lines, pumps, or washing machines. Example: Iranian Heavy, Arabian Heavy, Venezuelan crude. 2- High sediment or water content If the crude carries large amounts of sediments, asphaltenes, or water, it increases the risk of nozzle blockage and contamination.

Useful book about the LPG mixing practices.

Safety and stability: Starting with butane keeps the initial tank pressure lower and easier to control. Loading propane first could lead to overpressure and the need for venting (releasing excess vapor), which is unsafe and wasteful.

Which should be loaded first when making an LPG mix — butane or propane? ✅ Answer: When preparing an LPG mix (a mixture of propane and butane), butane should be loaded first, followed by propane. Technical reasons: Vapor pressure difference: Propane has a much higher vapor pressure than butane (around 8–10 bar at ambient temperature, compared to about 2 bar for butane). If propane is loaded first, the tank pressure will rise quickly, making it difficult or even impossible to inject butane later because there won’t be enough pressure difference to push it in. Better pressure and temperature control: Loading butane first (the heavier component with lower vapor pressure) establishes a base layer of liquid at a manageable pressure. When propane (lighter and higher vapor pressure) is added afterward, the total pressure increases gradually to the desired level without exceeding safety limits. Propane also dissolves well in butane, creating a more homogeneous mixture.

In voyage charter parties, the treatment of time when the vessel finishes one parcel, unberths, and waits for the next parcel (at anchorage or elsewhere) depends strictly on the charter party wording and common practice: 1. General Rule on Laytime Laytime counts continuously once notice of readiness (NOR) is valid and laytime has commenced, unless interrupted by an express exception (e.g., weather, strikes, shifting not for charterers’ account, etc.). If the vessel is waiting solely because the second parcel is not ready (charterer’s fault/delay), then the waiting time is normally for the charterer’s account and counts as laytime (or demurrage, if exceeded). 2. Shifting Between Berth and Anchorage Many charter parties (e.g., GENCON, ASBATANKVOY) have a clause: “Time used in shifting from anchorage to berth or from berth to berth shall count as laytime unless shifting is due to owner’s purposes.” Therefore, the time spent unberthing and shifting to anchorage is usually included in laytime, unless specifically excluded (e.g., if shifting is ordered by port authorities for safety reasons unrelated to cargo). 3. Parcel Situation If charterers book multiple parcels under one voyage charter, the entire loading operation (first + second parcels) is normally treated as one continuous operation, and the ship must remain available until all parcels are completed. If the vessel has to vacate the berth to allow others while charterers are not ready, the waiting time generally counts against charterers. ✅ Conclusion: Yes, the total waiting time should be assumed as laytime (and if expired, as demurrage), because the delay arises from the charterers not having the second parcel ready. The unberthing and shifting to anchorage is not an exemption; it still counts as laytime (unless the charter party has a very specific clause excluding it).