We currently carry 2 x 1kg ABC dry powder extinguishers and a fire blanket in our 10 metre sailing yacht. I believe the 3 major potential sources of a fire are the diesel engine, the gas cooking stove and the 12volt lead acid batteries. I am sure that the dry powder extinguishers would be effective for all these sources however I am concerned at the collateral damaged that would be caused by the powder, especially to the engine. we do not have space for additional fire extinguishers. My query is that if we changed the dry powder extinguishers for 1.4kg watermist types, would they be effective in the case of a battery fire?

 I would welcome some objective advice on this issue.

Michael Gill 

Hi Michael, if collateral damage is key then water mist is the best bet. While powder is still the most commonly used extinguisher for engines, the water mist will deal with the flames and cool down hot surfaces that could re-ignite the fuel. However, 1.4ltr seems insufficient. I would go for two small units (assuming it's a small engine). They are easier to handle and store.

Harry

Before changing extinguisher types be aware that there are stringent legal requirements for extinguishers on both inland waterways and ocean going craft (including yachts) and Water Mist extinguishers wouldn't meet the minimum fire ratings for use if your yacht requires a Boat Safety Scheme license.
If you are only using it outside waters requiring a BSS license and it is only ever used as a Class XII private pleasure boat, then being under 13.7m it escape the requirements under the UK Merchant Shipping Regulations of having any extinguishers (if it did then the Water Mist extinguishers would need to be 3 or 6 litre) and you could swap as you desire, although I'd check with your insurers first.