6.5.1 - DESIGN CONCEPTSThe following FO systems are to be provided for the main generating set engines and boiler services:- FO service systems (See section 13.6.1.)- FO purifying systems (See section 13.6.2)- FO transfer systems (See section 13.6.3)- FO drains system (See section 13.6.4)- Sludge system (See section 13.6.5)The machinery and piping installation including FO transfer and purification system will be designed for operation on the following fuels:- Heavy fuel oil to ISO 8217:2010 with viscosity up to 380cSt/50°C;- Marine distillate fuel to ISO 8217: 2010 Fuel Standard type DMA with viscosity 2 cSt.The fuel handling systems is to be such to allow the alternate use, according to Operator’s choice, of the following types of fuel:1) Fuel type A, MGO2) Fuel type B, with sulphur content limit of 1,0%3) Fuel type C, with sulphur content limit of 3,5%