Learn Russian: Мальчик накатался на лодке, так как сегодня прекрасная погода. - The boy rode on the boat to his heart's content, since the weather is fine today.

The base verb is кататься, which means to ride for fun or leisure. By applying the pattern from this lesson, adding the prefix на- to a verb with the postfix -ся, you create a perfective verb that means to do an action until you are completely satisfied, tired of it, or have simply had enough.

Why do we use the prepositional case in на лодке instead of the accusative?

When talking about riding a mode of transport for leisure with verbs like кататься or накататься, Russian uses на plus the prepositional case. You are treating the boat as the location where the activity takes place, rather than a physical destination you are traveling toward.

Could I use потому что instead of так как in this sentence?

Absolutely. Both mean because or since. The phrase так как is slightly more formal, but it is completely natural in everyday speech too. Note that while потому что almost always connects two clauses in the middle of a sentence, так как is also very commonly used at the very beginning of a sentence.

The boy's ride is in the past tense (накатался), so why is the weather described in the present tense?

Russian is very literal with time across different clauses. Even though his boat ride is already finished, the day itself is not over and the weather is still beautiful right now. English often forces both verbs into the past tense to match, but Russian simply states the current ongoing condition that allowed the past action to happen.