You might be able to grip the stub with locking pliers and slowly ease it out

   Like Kevin said.  Vise grip it very tight and will back right out 

   Just in case the normal cause of stripped screw is too small diameter of drill bit or too shallow of predrill. ( ie...not deep enough) 

When performing operations like you've described (light scantlings being 'stressed' into position) it's helpful having a clamp or two handy. Use 'em to bring things into position, under more control than simply by hand-power alone, then install the screws when they're not doing anything but being driven into place.

Asking screw threads to do all the work of holding stressed bits in position while also being driven home is asking for stripped screws whether pilot holes are properly sized or not.

Clamps are your friend: stronger than your fingers, reliable 24/7/365 & don't get tired.

Thanks everyone, a vise grip did the trick.

Grumpy: A too-shallow drill was indeed the problem. Still getting used to countersink drill bits.

spclark: Yes, I did try to do too much at once. This was at the bow, and the clamps were not large enough to accommodate the breast hook. Next time I'll know, just get bigger clamps.

I may have even gone overboard on clamps elsewhere:

Nope.

This is one pastime with a truism that 'you can never have enough clamps' is indeed the level truth.

(I'm envious of your luck at getting images to appear here., Mine's not been so good but I'll try again with this:)

http://[img]https://forum.fyneboatkits.co.uk/img/members/25548/Clamps_eh.jpg[/img]

 My Waterlust's aka under fabrication a few days ago.

https://forum.fyneboatkits.co.uk/img/members/25548/Clamps_eh.jpg

Better I hope.  

   spclark: I was able to see the photo by cutting/pasting the url (the second one) into a browser.

When you post the image, do you use the special image button? When editing a message, it is the button to the left of the question mark, in the toolbar above the edit window. Put the link in the box labeled URL, and it should then show the photo in the message itself.

Thanks geophile, I'll try that the next time I stick my neck out posting an image w/o an edit button close by.