Catamaran Bridgedeck Clearance Calculator

What is catamaran bridgedeck clearance?

Bridgedeck clearance is the vertical distance between the loaded waterline and the lowest part of the structure connecting the two hulls. More clearance generally reduces the likelihood of waves striking the underside of the bridgedeck. :contentReference[oaicite:1]{index=1}

How do you calculate minimum bridgedeck clearance?

One commonly cited rule of thumb uses approximately 0.7 inches of clearance for every foot of LOA:

Another commonly cited check for a very wide catamaran is based on the clear span between the two hulls:

The calculator uses the larger of these two values as its conservative rule-of-thumb recommendation when the catamaran is particularly wide.

What is a good bridgedeck clearance?

There is no universal value that is correct for every catamaran. Published design guidance commonly places comfortable offshore clearances around roughly 6% of LOA, while other rules use about 0.7 inches per foot of LOA. :contentReference[oaicite:2]{index=2}

The real requirement depends on hull spacing, bridgedeck geometry, loading, wave conditions, vessel speed, and the intended operating environment.

Bridgedeck clearance example

Consider a 45 ft catamaran with a 25 ft overall beam and 5.5 ft hulls.

The wide-catamaran check produces the larger result, so the calculator would use approximately 33.6 inches as the rule-of-thumb minimum in this example.

Why does hull spacing affect bridgedeck clearance?

When the hulls are spaced farther apart, waves can develop and rise in the central tunnel between them. For a wide catamaran, this can make additional bridgedeck clearance desirable. :contentReference[oaicite:3]{index=3}

What is clearance ratio?

Clearance ratio compares bridgedeck clearance with overall length. It provides a simple way to compare different catamarans:

Some catamaran designers use a bridgedeck-clearance ratio of roughly 6% of LOA as a useful benchmark for good clearance. :contentReference[oaicite:4]{index=4}

Does a loaded catamaran have less bridgedeck clearance?

Yes. Adding people, fuel, water, equipment, or cruising stores can lower the loaded waterline, which reduces the vertical distance between the water and the bridgedeck. Published guidance specifically emphasizes checking clearance at the loaded waterline. :contentReference[oaicite:5]{index=5}

Why is low bridgedeck clearance a problem?

Low clearance increases the likelihood of waves hitting the underside of the bridgedeck. Repeated impacts can cause uncomfortable slamming, noise, loss of speed, and significant structural loads. :contentReference[oaicite:6]{index=6}

Can a catamaran have too much bridgedeck clearance?

More clearance generally helps reduce wave contact, but raising the structure can increase windage and affect practical aspects such as boarding and low-speed handling. :contentReference[oaicite:7]{index=7}

Bridgedeck clearance reference chart

The following values come from the 0.7 in per foot of LOA rule-of-thumb and are intended as a design reference, not a universal offshore safety requirement.

What is wet deck clearance?

Wet deck clearance is another term used for the vertical distance between the water surface and the underside of a multihull's connecting structure. The terms bridgedeck clearance, underwing clearance, and wet-deck clearance are often used in closely related contexts.

Does bridgedeck clearance affect catamaran comfort?

Yes. Higher clearance reduces the chance of the central structure repeatedly contacting waves, which can reduce pounding and improve comfort in rough water. :contentReference[oaicite:8]{index=8}

Does speed affect required bridgedeck clearance?

Speed can matter because faster vessels can experience different dynamic trim and wave-impact conditions. Power and high-speed catamarans therefore need to consider their operating speed and tunnel geometry rather than relying on a single clearance ratio. :contentReference[oaicite:9]{index=9}

Catamaran bridgedeck clearance FAQ