When a veteran detective takes his son out for a cruise, an old acquaintance looking for revenge shows up. The little detective outsmarts the acquaintance of this dad that happens to be the killer of his mother that his father was never able to catch.

When a boy finds evidence linking a family friend to his mother’s unsolved murder, he must solve the case his father failed to while he was a detective.?(~28 words)

Your version is too long. I cut out the crusie and revenge angle because the cruise is just setting and unless the setting has something to do with the plot then don’t include it. The revenge part I cut because it just seems to complicate matters a bit. Something else is that your logline doesn’t focus on one main character, which from what I got is the detective’s son. So frame other characters as they are in relation to the MC. (rather than say “a veteran detective” identify the man as the MC father.
Take a look at the ‘Training’ tap at the top of the site to see what a good logline formula should include.

I agree that the inciting incident isn’t very strong, but the point of the story, to my understanding, is that years ago his mother died, his father, a detective tried to find the killer, and failed. Now it is the son’s time to find the killer. So in this case his mother dying being the inciting incident probably wouldn’t be as effective because it doesn’t make a clear connection for why he must solve the case now, after all of these years.?Maybe for this story a logline without an inciting incident could work, treat it as the boy determined since he was very young to see his mother’s murderer come to justice.