As previously indicated, keep ground as close to welding site as practicable. You could ground on the stanchion, strike arc
on the stanchion and carry to joint. Grind off all paint and rust in area to be welded. Bevel edge of stanchion base to allow better penetration of weld. Burn 1st pass in hot. Chip out slag and grind if necessary. Fillet weld to finish. Probably a 7018 5/32 rod at 150 amps or so, DC. If the stanchion is open on top or might allow ingress of water
, drill a small weep hole in lowest part of the stanchion to allow drainage. This will preclude water accumulating and freezing in the stanchion, or completely fill the void with high density urethane foam. You should be able to find a local who offers on site welding. Worth the money
if you don't have access to the equipment
yourself or are not up on welding - check with your boat yard. They might also frown on individuals welding or doing other major work that is not on their list of vendors. Also, post someone with fire extinguisher while welding and keep an eye on the area for a period after done in case a hot spark wandered off and found something to ignite.
10 years a mill wright and independent contract
welder for another 20 yrs part time. Now retired. Good luck in your endeavor.