The Space Between
An In-Depth Look at Bridgedeck Clearance for Catamarans
– By Sackville Currie of Multihull Design
Bridgedeck clearance (the height of the bridgedeck above the water) is crucial for catamaran’s seaworthiness and crew comfort. Because bridgedeck clearance can be seen at a glance, and is easily measured, even an inexperienced sailor can evaluate it.
Why does a catamaran need high bridgedeck clearance? First, ocean waves need headroom to pass between the hulls. Second, each bow creates a bow wave; these V-shaped waves meet under the bridgedeck and increase the clearance needed. What happens when bridgedeck clearance is inadequate? The one-word answer: Pounding. Visit our article on bridgedeck clearance on catamarans to see a video explanation of the importance of bridgedeck clearance by Stephen of Catamaran Guru as well as a video between the hulls of a Lagoon 450S in heavy following seas with moderate gale force winds.
Pounding causes three problem areas:
- to the crew: physical discomfort, and fatigue
- to the boat and rig: excessive wear and tear (I’ve had multihull design bulkheads break from windward pounding)
- and to the boat speed: a serious reduction.
The potential of the catamaran hull form, which is so impressive when sailing at 8 to 10 knots in 20 knots of breeze in protected waters, can be quickly reduced to 5 knots by pounding. Yes, a very low bridgedeck cat can lose 3 to 4 knots of boat speed with a major pound.
Read more about bridge deck clearance.
2 thoughts on “Bridgedeck Clearance”
It is all about steering so you get the right angle of the waves to your hull.
I did own a Fountaine Pajot Tobago. Infamous for its low bridgedeck clearance. But I crossed the Atlantic with her twice and no poundung whatsoever. Doing 15kts. And waves of 15ft.
The angle of the dangle, as they say. Yes, you are correct and most cats will slam if you go straight into the waves.The short steep chop in the Chesapeake is notorious for exactly that! LOL