Maybe if you change the ability you'll succeed.
I've been looking for another type of Speed increase when you posted this and found out that you can make the Rune of Speed an Ability.
For this, you must go to the Object Editor and click in the Abilities Flap, then create a new ability. Put the name you want and find the Rune of Speed in Items (Base Ability: ). When you click OK, the ability will be created, but you must change some stuff, like: "It's a Hero Ability" (True). Also change the levels as much as you wish to put, because you'd only have a single level. Don't forget the cooldown, the speed bonus for each level, etc.
It's very important you put TOOLTIPS, or else in the game it'll be shown as "ToolTip missing!"
Then add it to your boat and... Done! You have a new Speed Bonus Skill.
PS: Don't mind if in the Skill Learnings the icon is shown as a Green square, it always happens. Anyway, it will be shown as the icon you selected when you learn it.
Greets.