Drilling a screw out is not an easy task and it is usually not cheap.

*Grind the broken screw flat

*Mark the center with a punch

*Use a center drill to start the hole

*Drill a pilot hole all the way through the screw. The pilot hole should be no larger than 1/2 the dia of the screw

*Drill the screw out in at least 2 steps

To drill out a 1/4 inch screw you start by drilling a 3/32-1/8 hole all the way through the screw without breaking the bit. This takes a steady hand, lot of sharp bits, cutting fluid, constant pressure on the drill and the right drill speed. Never ever try to drill with a dull bit. The normal SS screws work harden. Just spinning a dull bit, will harden the SS until steel bits will not cut(cobalt bits are cobalt steel by the way). You need a solid carbide bit to drill through it.

There are kits that promise to make this easy and there much more expensive kits and tools that center the hole and keep the drill aligned and square.

There are alternatives

Use a Dremel tool with a 1/4 in cylinder grinding stones and just grind the screw away. This produces a lot of heat, don't set the boat on fire. This will take several aluminum oxide stones. They make a carbide bit that has smooth sides just to do this(expensive). This takes about an hour and you have a ragged hole to fill.

My newest favorite is the diamond one piece hole saw. There is no center drill. You fit the hole saw over the screw and just cut a hole around the screw. Then I used a bigger hole saw to make a plug out of G10 and drilled it for a helicoil. The saw has a limited depth of cut. You may have to do this in stages.

If there is a Hobie dealer in your area that does repairs you might get an estimate and then compare that to what it will cost for you to remove the screws. If it were my boat I would estimate $30 per side to remove the screws and put in helicoils