Core Sound 20 Mark 3

Based on the popular and race proven Core Sound 20 hull the new “Mark 3” is fully capable coastal cruiser.  If your interested in all the same features in a slightly smaller package, check out the Core Sound 17 Mark 3. More pictures click here. There a number of 20 Mark 3’s currently being built so we will add more pictures when we get them. Standard features of the CS-20 Mk3 include:

  • Kick up rudder and centerboard.
  • A raised deck cabin with spacious bunk and storage space below.
  • Porta potti storage in cabin.
  • Water ballast and a self draining cockpit.
  • Main tabernacle for easy rigging.
  • Cockpit reefing capability.
  • Outboard storage out of sight in the cockpit lockers.

The cabin can be built with a trench style hatch giving headroom and access to the main mast and for anchoring in good weather. A conventional sliding hatch aft and fore-deck hatch arrangement allow for the addition of a dodger turning her into a proper little cruiser. The centerboard is completely clear of the cabin and cockpit. Extra large cockpit hatches and berth storage allow for an outboard to store out of sight. Thanks to her integral water ballast, the Mark 3 is self righting from a 90 degree capsize and the elevated cockpit is self bailing. All this in a package that can be towed by a mid size car.

CS-20 Mk3 Specs:
LOA………20′-0″ [6.1] m
BEAM………6′-4” [2.16] m (Trailer-able width)
DRAFT………9″ – 3′-614” [0.23 -1.07]m @ DWL
SAIL Area………180 sq. ft.
WEIGHT………600-650 lbs [272-295]kg
*DISPLACEMENT………1500 lbs (773 kg) @ DWL

*@DWL With people water ballast and gear

Video Gallery


To understand the history and development of the Mark 3 , you need to know some history about the Everglades Challenge. The Core Sound series of boats have been competing successfully for almost 10 years in the annual Watertribe Everglades Challenge. This 300 mile distance race from Tampa Bay to Key Largo, Florida is open to all boat types and typically has over 100 entrants. Kayaks and small sailboats make up the majority of the entries and all boats must be able to push off from above the high tide mark which is intended to limit the entries to small trailer-able crafts. From 2006-2009, the race was won by Graham Byrnes in class 4 (sailboats) fist in a  Core Sound 17 ‘Green Heron’ and later in the EC-22 ‘Southern Skimmer’ . Since then it is a common sight to find B&B designed sailboats in the lineup. The current course record for class 4 was set in 2013 by Paul and Alan Stewart in Core Sound 20 ‘Dawn Patrol’ with a time of 2 days and 2 minutes followed closely that year by a new Core Sound 17 ‘La Perla’ sailed by Phil Garland and Dan Neri.

The success of Southern Skimmer and Dawn Patrol can be partly attributed to their cuddy cabins allowing the sailors a safe haven from the wind and spray to rest between watches. Paul and Alan retrofitted their Core Sound 20 with its cabin during the build but there were no plans available and it was a one off design modification. An attempt to copy the shapely cabin on Graham’s EC-22.

As followers and entrants of the Everglades Challenge began to take note of the Core Sound’s success, more and more requests were made for a boat with a small cabin similar to the EC-22 and Dawn Patrol. In 2013 Chick Ludwig, long time friend and builder of many B&B boats (like the first OB-20 ‘Princess’), officially requested the design and kit for a new Core Sound 20 with a cabin! Now discontinued, this boat was called the Core Sound 20 Mark 2 and featured a cuddy cabin, raised cockpit seating, water ballast, and a self draining cockpit. Click here to watch a video of the Mark 2 proving her self righting capability. This boat was later campaigned successfully in the Watertribe North Carolina Challenge by Julie and Frank Miguel. More pictures and video on his blog.

Graham saw room for further improvement in the Mark 2 and very soon after the Core Sound 20 “mark 3” (hence the name) was drawn and hull #1 was built by former Core Sound 20 builder/owner and watertribe racer Doug Cameron. His blog has more pictures of construction and sailing videos.

Above: Carol and Jay Knight’s CS-20 Mark 3 at the 2015 B&B Messabout. More picture here and a link the their construction log on the forum.

Construction Plans:

Assembly Manual: $10
As our first few builders start to finish the their new Mark 3’s we have been working hard to complete a detailed assembly manual. The current version of the manual is available to download on our downloads page for a modest fee. If you end up purchasing a complete set of plans or kit, remind us to credit you the cost of the manual!

Full Size Templates and Construction Plans: $220
The plans set consists of 18 full color 11 x 17 sheets that detail all aspects of construction. Kit parts are labeled in each drawing referencing the kit parts throughout. The deck framing and Main Rigging sheet are available to view as a sample by clicking in the list below. We have taken all of the parts from the CNC kit and nested them in two 21’x24″ strips of mylar sheet that make up the full size templates. The sheets are taped together aligning the strike up marks to produce a templates sheet that can be used to transfer all of the part outlines onto plywood for cutting with a jigsaw. Recommended methods and sheet count are shown in the included detail sheet that accompanies the templates.
Note: This plans pack covers assembly only and does NOT include a lines plan or dimensioned parts. The plan sheets are designed to accompany the full size templates or the CNC cut Kit. 

-Parts list
-Cradle assembly
-Main Assembly
Deck Framing
-Deck Plan
-Bulkhead Detail
-Tabernacle Detail
-Cabin Hatch Assembly
-Cabin Hatch Detail
-Cockpit Hatch
-Rudder Detail
-Centerboard Construction
-Centerboard Rigging
-Spar Detail
-Sail Plan
Main Rigging
-Mizzen Rigging
-Optional Reefing Detail

Kit Pricing and Information:

Basic CNC Kit: $3,100
We have spent many many hours developing this kit and it has reached a high level of precision. We think there is no other 20′ coastal cruising boat with the features offered in the 20 Mark 3, kit or otherwise.

The basic kit parts (shown below)  include every plywood part of the kit densely packed into twenty sheets of BS 1088 marine plywood. Just add some solid wood and epoxy and your off and running with your build.

Also included with the basic kit is a full size mylar template providing an easy way to produce some of the solid wood parts not included in the basic kit. Outlines for the tiller, tabernacle parts, rudder cheek spacer, as well as centerboard and rudder shaping detail are shown in this template.

The basic kit also includes the three cradle parts and plywood corner gussets shown below on the building cradle. These are attached to a shop made frame of 2×6 rails and 2×4 legs all detailed in the plans. Below, a CS-20 Mk3 sits nicely on her cradle.

B&B Companionway kit: $275
The basic kit comes with solid cabin top panels which can be fitted out however the builder desires. Some builders have expressed interest in a long “trench” style of companionway allowing for walking forward in the cabin. A trench opening however creates a unique design problem of how to seal the hatch for heavy weather sailing and also make it easy to open and easy to secure the boat while away. In the end, our stock companionway kit was developed after thinking long and hard about the boat’s potential and what we felt the majority of builders would want.

We settled on a drop board style companionway opening with a sliding hatch for accessing the cabin. Forward, an 18 1/2″ x 22″ hinged hatch provides a secure location to deploy an anchor, hank on the mainsail and tie up reef points. This hatch layout also allows for the future installation of a soft dodger over the sliding hatch “garage” as well as a solar panel over the hinged forward hatch.

What else will I need?
Solid wood for stringers and cleats is not included. We prefer our builders to locally source this material and rip into long lengths for stringers, inwales, and gunwales. . It is not practical for us to ship these long pieces. If you are picking up your kit from our shop we can rip these pieces for you and include them in the kit. Just let us know ahead of time so we can put together these extra parts.

Other items to be purchased separately: All available from B&B.
-Mast kit
-Hardware kit
-Lines pack

CS-20 Mark 3 Build Logs:

Have a build log you’d like to share, send us a link.

The first 20 Mark 3 built by Doug Cameron. Build log for Hull #1. Don’t forget to check out Doug’s blog.

Jay and Carol’s build log of their CS-20 Mk3 #2. Installation of a water pump used in ski boats as her ballast pump allows water to be added or removed with the push of a button.

Here is Steve’s build log of his CS-20 Mk3 #3.

Here is Peter Mcray’s build log of his CS-20 Mk3 #5. Peter asked us to preassemble the hull at our shop which we did and he picked her up on a trailer and took home the rest of the kit. His build is going well.