Vessel size and technical details are available on the Vessel details page, under the Vessel information tab, accessible with a Mobile Pro Plan subscription.
What you can see:
Length & Width — the vessel's physical dimensions in metres
DWT (Deadweight Tonnage) — the maximum weight the vessel can carry, in metric tonnes
Gross Tonage — the overall internal volume of the vessel
Engine power — the vessel's engine output in kilowatts
Year built — the year the vessel was constructed