Your explanation of your dilemma is inadequate. Since it takes no stamina to sit at the rudder and steer a boat, I must assume you were either on the boat but not at the rudder or in the ocean next to the boat when you ran out of stamina. At that point you could not move to the rudder if you were on the boat or swim to the boat ladder in you were in the water.

If you were on the boat, the scrap iron apparently slid off ithe deck into the ocean when you tossed it. If you were in the water next to the boat, the scrap iron apparently bounced off the gunwhale instead of landing on the deck.

In either case, the simple solution is to log out of the game and immediately log back in. If you are quick, the boat will have moved only slightly in the interval. You will lose all your rested bonus when you log back in but you will regain your stamina.

At any rate, you should have learned a very valuable lesson: don't screw around in the water.