What is freeboard on a boat?
Freeboard is the vertical distance from the waterline up to the deck edge. It is the dry side of the hull—the opposite of draft—and it represents the reserve buoyancy that keeps waves and spray out of the boat.
Related terms
How it works
Freeboard and draft share one waterline: whatever sits the boat deeper takes freeboard away and adds draft. The watertight volume above the waterline is reserve buoyancy—it is what lets the hull rise to a wave instead of shipping it aboard, and it is consumed as the boat is loaded.
Low freeboard means the deck edge submerges at a smaller angle of heel and waves board sooner. That is why small craft carry capacity plates limiting persons and load, and why heavily loaded or heeled boats deserve calmer water. Large ships carry load line marks that set the minimum legal freeboard for the season and zone.
Reserve buoyancy above the waterline
Freeboard literally names the amount of the board—the hull side—that remains free of the water. Naval architects treat it as stored safety: the more watertight hull above the waterline, the more the boat can heel, load, or take a wave before water finds a way in. Load lines, introduced in the nineteenth century, made a minimum freeboard a legal requirement for cargo ships.
On the water
- Six adults aboard a small runabout visibly lower its freeboard—check the capacity plate before loading a seventh.
- Heeled hard over in a gust, the leeward deck edge nears the water; reefing restores the working freeboard.
- A loaded cargo ship floats down to her load line—the deepest she may legally sit for that season and zone.
Common mistake
Freeboard is not a fixed number from the brochure. Every added person, tank, and locker of gear sits the boat deeper, trading freeboard for draft—an overloaded boat has quietly spent the reserve buoyancy her deck edge depends on.
Remember it
FREEBOARD is the dry side: waterline UP to the deck. Draft is the wet side: waterline DOWN.