Not really sure about the time frame for this story. I'd guess 1960's or earlier.
The story centers around an alien being (humanoid) who is sailing the sea on his homeworld in his small sailboat. Said world is many times larger than Earth, and has crushing gravity (by our standards). The gravity is so high, that the atmosphere is very thick near the ocean's surface, blurring the line between liquid and gas (somewhat akin to a gas/ice giant like Saturn or Neptune, etc. though this planet is temperate in nature). The boat sometimes rises with a breeze, cresting above the water before settling back down.
The sailor in question is patrolling his area, on the look out for signs of some enemy people who share the planet. While doing so, he finds the wreckage of what is assumed to be a Terran spaceship. I believe the ship is described as silver and needle-like. It's crashed onto the planet, and has been hulled by battle damage, IIRC.
The sailor/protagonist investigates the ship. He remarks that the material of the hull is very flimsy. He thrusts his hand into the breach in the hull and rips a long tear in the hull to equalize the pressure and keep the ship from being crushed. Carefully boarding the vessel, the protagonist finds the remains of the crew. They've all been crushed by the atmospheric pressure. The protagonist also finds the ship has a powerful looking energy weapon as a broadside deck gun, and that the ship is nuclear-powered. I believe the term he uses is "atomic", which leads me to believe the story is an older one.
We learn that this is a great find for the protagonist, as his people society have not mastered nuclear technology, and that has prevented them from venturing into space. Conventional propulsion designs cannot escape the planet's extreme gravity.
The crisis in the story comes when a group of the enemy people arrive in the area in their own boat(s). Fearful that the enemy will get the starship, the protagonist (IIRC) attempts to flee and/or hide from the enemy. This crisis is resolved when the protagonist returns to the starship and figures out how to use the energy weapon on the ship. He blasts the enemy boat and they are completely annihilated, with no remains at all left.
The story ends with the protagonist heading for shore, confident that a new era is opening up for his people.