Hi! Lets fix your sentence and explain why.
Original: with a powerful engine and a smooth body, the speedboat moves fast and is easy to steer.
Corrected (best): With a powerful engine and a smooth body, the speedboat moves quickly and is easy to steer.
- Capitalize the first word. Sentences start with a big letter, so change with to With.
- Keep the comma after the intro phrase. The phrase "With a powerful engine and a smooth body" comes at the start and describes the boat, so we put a comma after it.
- Choose an adverb. Quickly is an adverb (it tells how the boat moves), so it sounds a little more correct in writing. Saying fast is also okay when talking, but quickly is better for clear writing.
Another simple correct option: With a powerful engine and a smooth hull, the speedboat moves quickly and is easy to steer.
Great job — your idea is clear and just needed a small capital letter and a word choice change!