Core Sound 20 Mark 3


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………650-700 lbs [295-317]kg
*DISPLACEMENT………1500 lbs (773 kg) @ DWL

*@DWL With people water ballast and gear

Click here to view our Video and builder spotlight gallery for the Core Sound 20 Mark 3

Based on the popular and race proven Core Sound 20, the new "Mark 3" is fully capable coastal cruiser with water ballast that make her self righting from a capsize.

Updated 2018 model: We've just completed some major updates to the 20 Mk3 based on feedback from our builders. In addition to adding a mizzen tabernacle for easier rigging as a standard feature in the kit we've increased the headroom in the cabin for even more spacious accommodations and redesigned many components to make assembly of the kit even easier. While this is not a simple boat to build, the techniques are not any different than any simply stitch and glue kit. 

Why is it called the "Mark 3?" here is a history of the evolution of the Mark 3 series of Core Sound designs. If you're interested in all the same features in a slightly smaller package, check out the Core Sound 17 Mark 3. More pictures click here.

Standard features of the Core Sound-20 Mk3 now include:

  • Kick up rudder and weighted centerboard.
  • A raised deck cabin with sliding companionway hatch and hinged foredeck hatch.
  • Lots of storage space down below.
  • Porta potti easily stows in cabin.
  • Water ballast and a self draining cockpit.
  • Main and mizzen tabernacle for faster rigging.
  • Reefing from the cockpit.

Keep reading for information on all the available options and prices for the Core Sound 20 Mark 3!

CNC Kit base price: $4,150 
This is no ordinary boat kit. After years of development the 20mk3 kit is now the most sophisticated, comprehensive and highest quality 20' sailboat kit on the market today.  This kit includes every plywood part we can cut on the CNC machine and then some. All parts are made of the highest quality BS 1088 okume marine plywood and clear southern yellow pine.

Being a complicated boat, decisions must be made with regard to all design details. Hatches, tabernacles, ports, etc. and the kit represents the best compromises in each area. If you would like to customize your kit in some way just ask and we'll let you know if it's possible.

What is included? Every plywood component is cnc cut and labeled with our custom CNC pen which marks bulkhead and stringer locations directly onto the part which has mostly eliminated measuring during the build. 

  • 21 CNC cut sheet of 6mm okume.
  • Miscellaneous parts in 4, 9, 12 and 18mm okume. 
  • All parts for sliding companionway hatch and fordeck hatch. 
  • Plywood coaming for optional dodger. 
  • CNC cut southern yellow pine components including main and mizzen tabernacle, deck beams, transom stiffeners and tiller. 
  • 3/4" birch plywood cradles and cradle gussets. Just add 2x6 rails as shown in the plans.  

The main and mizzen tabernacles allow the masts to be quickly and safely raised and lowered. You can launch your boat and rig on the water easily with this setup saving time at the ramp. 
The companionway is fitted with a sliding hatch and drop board style companionway opening 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 is not included? 

  • Solid wood: You will need additional solid wood to complete the boat. We suggest southern yellow pine for stringers, cleats, gunwales, etc. We don't include these in the kit because they are best ripped up from long boards which are not practical to ship.
  • Cradle lumber: Standard 2x6's for the building cradle.
  • Ports: Purchase port-lights separately or choose to add-on our lexan porlight option (see below).
  • Epoxy and fiberglass (see below)
  • Paint

Lexan Deadlights: $350
We wanted to offer an alternative to the somewhat expensive plastic opening ports so we came up with 5mm lexan parts for a simple deadlight (non-opening ports) three per side and two in the companionway drop board. These were very popular so they are now standard. This includes the 6 pieces of lexan and two for the washboards, plywood trim rings, and Stainless steel "rivet-nuts" for mounting.  If you prefer opening ports no problem just let us know to NOT cut out the ports in the side panels. Beckson makes opening ports that work well. (link here). B&B sells beckson 5x12 opening ports for ~$125 each. 

CNC Centerboard/Rudder : $675
We offer a CNC shaped rudder and centerboard which includes:

  • CNC cut (shaped) centerboard made of laminated southern yellow pine lumber.
  • 17.5lb cast lead tip for the centerboard ready to install and fiberglass to the board. 
  • CNC shaped rudder made from 3/4" Meranti marine plywood.

Aluminum Mast KIT: $600

  • Aluminum tubing as specified in the plans. 
  • New B&B sailtrack
  • All rivets for attaching track to masts.
  • Starboard (plastic) end caps for masts where applicable.

Sails (Main and Mizzen): $1,100

Main and mizzen sails include 2 reef points each and all battens as well as sail number and logo attached. 

Standard Rigging and lines Package: $950

All rigging for the main, mizzen, center-board and rudder and all running rigging in the standard configuration. 

This kit does NOT include: 

  • Optional cockpit reefing lines
  • Optional second downhaul lines 

Epoxy and Fiberglass KIT: $850

This should be all the epoxy and fiberglass needed to complete the boat based on good practices and minimal wasted epoxy.

  • 9 gal of epoxy (6gal of resin and 3 gal of hardener). Note, we have slow and fast hardener and can supply some of each which is sometimes helpful for small jobs to cure faster. 
  • 3 Metered pumps (1 spare)
  • 3 pounds of our "B&B blend" cabosil epoxy thickener for thickening epoxy when gluing or making fillets. 
  • 3 rolls of 3" wide 10oz fiberglass tape. (50 yards each, 450 linear fee total)
  • 1 Length of extra wide biaxial fiberglass tape for fiber-glassing the keel. 
  • 20 yards of 10oz plain weave fiberglass "finish-cloth" on a 50" wide roll. 

Full Size Templates and Construction Plans ONLY: $220

The plans set consists of full color 11 x 17 sheets that detail all aspects of construction and assembly. 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 foot x24 inch strips of dimensionally stable Mylar sheet that make up the full size templates. In use, 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: The plan sheets are designed to accompany the full size templates or the CNC cut Kit. There is no lines plan because the templates are full size. There is no lofting required. This option is mostly for overseas builders.   

-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
Image Image

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.