Sacrificial electrode mounting structure

A sacrificial electrode mounting structure for mounting a sacrificial electrode in a cooling water passageway provided in a cylinder block of a water-cooled engine for an outboard engine unit, the sacrificial electrode mounting structure comprising:

• the cooling water passageway defined by a groove portion provided in the cylinder block and a lid member closing an opening of the groove portion;
• a gasket member provided between the groove portion and the lid member;
• and
• a threaded fastener member that fixedly fastens the sacrificial electrode to a bottom wall of the cooling water passageway, the gasket member having an extension portion opposed to a surface of a head of the fastener member located remote from the bottom wall of the cooling water passageway, so that the fastener member can be prevented, by the extension member, from falling off from the cylinder block.