Diam 24 vs. F18: How the Two Multihulls Differ and Who Each Suits
From the dock, a Diam 24 and an F18 can look like cousins — both fast, both multihulls, both clearly built for racing instead of cruising. Get one under your hands and the resemblance mostly ends there.
They reward different instincts, ask different things of your body, and honestly aren't competing for the same sailor. Knowing the difference before you pick one saves you a confusing first session.
Two Hulls vs. Three: The Difference That Changes Everything Else
An F18 is a catamaran: two identical hulls, side by side, nothing in the middle. A Diam 24 is a trimaran: one main hull down the centerline plus two outer floats that do most of the work once the breeze is up. That sounds like a technical distinction, but it's the root of almost every other difference between the two boats.
On the F18, power gets managed by lifting the windward hull and sailing on the leeward one — classic beach-cat technique. On the Diam 24, the boat is designed to lift its main hull clear of the water while riding on the leeward float instead, which is a different balancing act, not just a bigger version of the same one.
Why Your Weight Goes to a Different Place on Each Boat
This is where the hull-count difference actually shows up in your hands. On an F18, both crew are on trapeze, out over the windward hull, as soon as there's enough breeze to need it. That outboard weight balances the boat the way it's meant to be balanced.
On a Diam 24, weight moves through a sequence instead. In light air the crew sits forward and often on the leeward side, pressing the bow down. As the breeze builds and the main hull lifts, weight moves toward the center. Only once the boat is fully powered up, around 12 knots, does real hiking start. The timing is the counterintuitive part if your instincts come from a catamaran, and it's usually the first thing a new Diam 24 sailor has to relearn.
One Design vs. Box Rule: Racing Identical Boats or a Fleet of Cousins
The Diam 24 is a strict one-design — every boat on the racecourse is built to the same specification, so results come down to sailing, not equipment. The F18 is a box rule class instead: a range of builders produce boats to the same general envelope of length, weight, and sail area, which means the fleet includes several different models racing against each other under one rule.
Neither approach is better, but they change what you're racing against. A Diam 24 start line is a field of identical boats. An F18 start line is a field of similar boats with significant design variation between them — and reading which is faster in which conditions becomes part of the game.
Who Each Boat Actually Suits
The Diam 24 is the natural starting point. Three hulls make it stable and forgiving, there's no trapeze work to learn, and a crew of three or four means you're never managing the boat alone. It's also the boat behind the Caribbean Championship, so the skills you build carry straight onto a start line. For competitive monohull racers cross-training in the off-season, it's also the boat that rebuilds your instincts fastest.
The F18 is the step up. Twin-trapeze sailing is athletic and unforgiving, two people handle everything, and the boat rewards crews who already have multihull miles. For sailors who want a physical, high-intensity challenge, it's the next boat to aim for.
Not Sure Which One Is Right for You?
The honest answer is that time on both boats tells you more than any comparison article can. SMSC's fleet includes both the Diam 24 and the F18, and a session on each is the fastest way to find out which one matches how you want to sail.