20 knots is not all that slow. According to google average container ship speed is about 24 knots. Even the navy destroyer I used to sail on topped out at 30 knots using its gas turbines, which were only to be used for "serious purposes".
Very rough scale with respect to sailing vessels around 30-55 foot length... multihulls (fast = 20 knots, common = 15 knots, many = 10 knots), monohulls (fast = 12 knots, common = 8-10 knots, many = 6-8 knots). For an ocean-going trimaran, their 10 knot speed is not fast. It is quite likely the vessel's apparently near-fixed "wingsail" represents a very conservatively-rigged configuration that is biased for stability instead of speed.
Thinking about it in the context of the colregs, 10kts is above the hull speed of a 40ft sailing yacht, and is probably plenty fast enough to sink that yacht in a collision.
The documents on the website mentioned 20 kts, so that's what I went with.