Methylene Chloride is a very nasty chemical and should not be used unless you're wearing a respirator and heavy gloves, full face mask... as it is skin absorbable and highly carcinogenic.
It can also eat paint, was the active ingredient in many paint strippers before they removed it due to its cancer causing attributes as a carcinogen, and it can melt certain plastics including softening gelcoat if left on long enough to actually melt the silicone. In short duration, like Acetone, it will not harm the gelcoat much but if left on the surface long enough to soften the silicone you might also soften the gelcoat with it.
Remember you're not working on steel automotive panels or cast iron brake rotors and most hulls are not made of epoxy.
Methylene Chloride is often used to remove silicone conformal coatings on PC boards. In order for it to remove a 0.010 mil thickness it may take 15 minutes to an hour for it to soften the silicone enough for removal and this is submerged in a bath of it.
Here's an excerpt from a study done on removal of conformal coatings:
"As in the case of the polyurethane’s, the coated board is immersed in the solvent at room temperature and allowed to stand
until the silicone has dissolved or can be easily brushed off. The time required will vary with the solvent used, the type of silicone
coating, the coating thickness, and the amount of surface area exposed.
Typically, most coatings of 0.010 inch or less will be
removed in 15 minutes to one hour. Certain chemically-resistant silicones may require extended immersion for several hours. The
use of ultrasonics or agitation will reduce dissolving time.
After coating removal is complete, it is very important that the board be thoroughly washed in alcohol (isopropanol or methanol),
then rinsed in DI water and dried. A saturated cloth or cotton-tipped swab may be used for spot removal. Repeated applications
and brush may be necessary.
Some of the newer silicones will not come off with any form of chemical. Make sure you check with the manufacturer before
you use any chemicals on newer silicones."
On a boat you do not have the ability to submerse the deck for 15 + minutes and rags are not going to cut it. Marine based silicones are designed to be of the chemical resistant type and are generally more resistant to chemicals than PC board conformal coatings.