Good Question: Max boat speed is dependant on the hull shape and boat length. Most most cruisers, you won't get them over about 12 knots in speed as a general rule. A cruiser has a displacement hull which means it is always displacing the amount of water according to its weight. This tends to limit its max speed. A planning hull means that the boat gets lift from the speed of water underneath. Since it does not displace so much water now it can go faster. And in some cases much faster than 12 knots. Volvo ocean race boats can get to 30 knots. We saw 48 knots in Americas Cup Foiling Catamarans.