Hello, and thank you for your question.
Based upon your description, what you likely have is a painting by the Scottish artist Thomas Hope McKay (1870-1930). His works are mostly that of sea seascapes and landscapes that include bodies of water (rivers, lochs, bays, etc.). His work is good and his style of painting is of a realistic yet slightly impressionistic quality. There is a fairly distinct range of prices for his paintings, but given the size of your piece it might exceed the norm by some measure. On average, his oils sell in the range of about $1,000-$2,000. Yours, however, given its larger scale might be more in the vicinity of $3,000 to as much as $4,000/$4,500 in its original (or period) frame and in excellent condition. The appeal of this sort of work is fairly strong (esp. that of American artists) and, again, his in particular would be considered that of good quality. The appeal of your piece in particular would, as with all art, be a more subjective matter.
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Thank you, again.