1970’s YA Fiction. MC is boy who works one summer at a dock in order to buy a boat. Possibly learns to water skiing Bests older brother.

[Teri]

1970’s YAL. MC is a boy about 16 who isn’t very confident. He gets a job working at a boat dock near his house. He possibly learns to swim or water ski? He and a friend buy a small boat together. His brother is good at everything and I believe had also wanted the boat. There’s some conclusion in which the boy beats the brother at something big. That’s about all I remember.

[bookel]

First thought, pictured a Scholastic cover, orangish with a boy, dog on a dock. Haven't read it. Title was ... it has Young in it I think.
Worldcat.org title Young, keyword Scholastic, year range and filters.

The young loner
Authors:Bianca Bradbury, John Gretzer (Illustrator), Scholastic Book Services
Summary:A summer's new relationships and experiences lead Jay to new self-discovery and a better relationship with his older brother
Print Book, English, 1971, ©1970
Publisher: Scholastic Book Services, New York, 1971, ©1970
https://www.librarything.com/work/855...
Yes that's the cover.
144 p. New York : Scholastic Book Services, 1971, c1970. Paperback. TX 1856.
Original title: The Loner.

Summary: A summer's new relationships and experiences lead Jay to new self-discovery and a better relationship with his older brother. "Come on, Squirt, hit me! Fight back!" Jay's brother Mal teases him. But Jay is afraid. How can he win over an older brother who does everything better? Then one day, down at the dock, something happens that changes everything...
The Young Loner