Stanchion base removal

[Red Panda]

I'm trying to reinforce the bases of a couple of stanchions on my Albin Nova, as they're a bit wobbly. However, I've come to a halt trying to remove them.
There's a single, central dome-headed bolt that goes through the stanchion base, through the deck, and held in place with washer and nut on the underside. I've removed the washer and nut, but the bolt itself is reluctant to shift. As it's a dome head I can't get a spanner on it from above deck.

From above

From below



I'm reluctant to just thump it loose with a big hammer from below.
Has anyone removed a similar stanchion base, is there some trick I'm missing, or is it time for brute force?

 

[neilf39]

I think a thump or several with a hammer is probably what you will need to do. Put some wood between the bolt end and hammer so you don't damage the end thread of the bolt.

 

[paulajayne]

Put two nuts on it locked against each other and then rotate it side to side - should loosen it,

 

[KINGFISHER 9]

I think a thump or several with a hammer is probably what you will need to do. Put some wood between the bolt end and hammer so you don't damage the end thread of the bolt.

This .... and if it still doesn't work ... get a bigger hammer! ... :encouragement:

 

[Red Panda]

Thumping things with a big hammer is my speciality, but I'm wary of splintering fibreglass and the pain of repairing it!
Thankfully, hammer swinging room is restricted due to the woodwork below.
I've tried the double-nut approach too, but both bolt and stanchion support turn together. They probably haven't been removed since 1985, so I'll have another go at that, and whack it a bit more with a hammer. I think I'll have to recruit a larger model of glamorous assistant to hold things in place topside.

 

[CCJ]

Put two nuts on it locked against each other and then rotate it side to side - should loosen it,

+ 1 + some penetrating oil ( plus gas ) around the head on the outside & leave it a few hrs.