Choose the Location
This photo is showing the spot for the new seacock & thru-hull as chosen from inside the vessel. Care should be taken when considering anew location for an additional seacock which includes, easy access, hose routing and seacock location for valve movement..
Once you have chosen your new location drill through the hull from inside using a 1/4″ drill bit. The reason for the 1/4″ bit is that it matches the size bit used on most hole saws.
You then drill into the hull from outside using the proper sized hole saw to match the thru-hull.Be very careful to drill perpendicular to the hull or the thru-hull fitting will not fit flush.
TIP: Start the hole saw in reverse, as I have done here, and you’ll greatly minimize or remove the possibily gelcoat chipping. Once the hole saw is through the gelcoat, switch to forward and drill up through the hull making sure you are perpendicular to it.