Cal's Evals » RADICAL BAY 8000

Release Date: 12/5/2005

Radical Bay 8000

The Radical Bay 8000 is a 26 foot long racing catamaran with as much cruising accommodation as could be expected in a small catamaran sailboat. It has twin free-standing masts for a biplane rig plus high aspect ratio dagger boards. The hulls are made from glass/epoxy covered end-grained balsa cored panels. The hulls are connected by alloy pipe crossbeams. It a trampoline deck with an optional hard deck between the main crossbeams. There is a good deal of information available about the boat on the internet. Just Google Radical Bay 8000. The designer, Jeff Schionning, has an article about the twin rig that is worth reading on his site at www.schionningdesigns.com.au.

The following figures show this boat in comparison with the average values of 20 other catamarans with waterline length between 25.5 and 26.75 feet on the Multihull Dynamics, Inc. website. The RB8000 is the lightest boat of the lot.

Displacement: 1.08 tons [2.11 tons]

Length Overall: 26.25 feet [28.21]

Length at Waterline: 26.25 feet [26.17 feet]

Beam Overall: 18.92 feet [16.53 feet]

Sail Area (Twin mains - Main plus jib for others): 441 sq. ft. [422 sq. ft.]

Displacement-Length Ratio: 29.85 [58.72]

Sail AreaDisplacement Ratio: 39.15 [27.46]

Beam between hull centerlines: 16.92 feet [13.29 feet]

Base Speed: 10.35 knots [8.89 knots]

Texel Rating: 108 [135]

Bruce Number: 1.57 [1.29]

Stability Speed: 16.09 knots [16.79 knots]

The numbers show that the RB8000 should be a very competitive racing catamaran with exceptional stability. The stability results from a combination of wide beam and the twin rig. Even though the sail area is greater than average, splitting it into two sails lowers the height of the center of effort of the sails by over 45%, more than five feet and raises the Stability Speed by nearly three knots. Schionning's article tells how this rig can be used to manage sailing in various wind conditions.

This boat is clearly in the racing category with its Lwl/Bh ratio of 13.14 (see Classifying Multihulls in the Technical section of the Multihull Dynamics, Inc. website at www.multihulldynamics.com). There are four boats in the 20 used for comparison that have marginally higher Base Speeds, but the use of the biplane rig may allow the RB8000 to be sailed in stronger winds before reefing, potentially giving it a racing advantage.

Calvin H. Markwood
Engineering Analyst
Multihull Dynamics, Inc.

Contact Cal: multihull.analysis@comcast.net