responsible as to her keel

Solution 1:

The question might be clearer if we also include a couple of further sentences of context.

... According to all theory, she ought to have been perfectly responsible as to her keel. In practice, she was frightfully cranky. Sailing the Judas Iscariot was like driving a horse with more vices than hairs in his tail. She always did the unexpected thing, except when bad behavior was expected of her on general principles. ... Start on whatever course she might, the schooner was certain to run before long into one of three things, namely, some other vessel, a fog bank, or the bottom.

This shows that the ship (like a bad horse) doesn't go where it's steered.

So "responsible" is being used here where modern standard English would use "responsive".

If the ship were "responsible" to her keel, she would travel straight rather than unpredictably.

Solution 2:

Responsible can mean 'reliable'.

6. reliable or dependable, as in meeting debts, conducting business dealings, etc.

And as to can mean 'concerning'

Thesaurus: synonyms and related words

Regarding and concerning

Keel may be being used in a figurative sense in terms of balance and stability. So your sentence probably means something on the lines of:

The boat ought to have been perfectly reliable as far as its stability was concerned.

Solution 3:

This appears to be an unusual (and perhaps ironic) extension of "responsible" in the sense of "trustworthy, reliable" to an inanimate object.

As to means "with respect to", and keel is probably intended as a synechdoche for the vessel's entire physical construction, since planking, caulking, spars, rigging and sails are included in the assessment.

So the nautical experts agreed that the Judas Iscariot ought to have been perfectly trustworthy, at least with respect to her construction and materials .