Slightly off topic, but at a concert a few weeks ago, I started singing one of my fellow shanty singer's verses in Johnny Leave Her- The audience noticed, since "Oh the skipper was bad but the mate was worse" had just been done. I had a "Leave her Johnny, leave her" to rhyme in "I believe I've sung the very wrong verse." It rhymed, and we got a good laugh.
    Learning all the easy to rhyme words is a good idea. (E.G. That chair rhymes with stair, mare, bear, there, hair, air, rare, tear, impair, compare, &c...) It's how improvisers can write whole blues songs on the spot, with a subject provided by the audience, no less.
Best,
    Kristoffer