Jump to content

Core Sound 20 Mk3 #23 - Williamsburg, VA

Todd Stein

Recommended Posts

On 02 April we drove to the factory and picked up the kit using the modified catamaran’s trailer. As predicted, upon arrival the skies opened up and made for a drenching experience while loading.  Prior to arriving Alan recommended picking up a poly tarp which we draped over the crate followed by numerous wraps of shipping film around the circumference. After skillful loading I was impressed the trailer was in darn near perfect trim and balance for a very wet drive home.  The next day under clear blue skies I removed the tarp and film to find the crate dry and the contents unaffected. Thank you Alan!


As parts were unloaded, inventoried, stowed and somewhat organized in the garage, it subtly came to me just what a huge project I’ve taken on. My mantra is to enjoy the journey and destination will be that much sweeter. Thank you all who have contributed to this forum, your posts provide me with such great amount of information and knowledge that provides me the confidence I can achieve one of my bucket-list goals.





  • Like 2
Link to comment
Share on other sites

2 hours ago, Chick Ludwig said:

I didn't know that a dog came in the kit!

Welcome to the forum. Take it one step at a time and enjoy the journey!


The only dogs associated with my kit were Lee Valley Bench Dogs; I'm jealous of the new addition to the kit!



Link to comment
Share on other sites

Between all the Springtime yard projects and the honey-do’s I’ve been slowly and steadily making progress as per plan recommendations. Bulkheads 1&2, transom and hanging knees. Many little lessons learned thus far and I’m becoming more confident in trusting the process as well as myself. I’m wasting a lot less epoxy goo now that I can better judge amounts. 


I purchased 2 Beckson ports for ventilation and access under anchor locker. I cutout the ventilation port on bulkhead 1, should I now also cut out opening for underneath anchor stowage? I plan to mount actual port itself post final epoxy coating using silicone and magic fasteners.


Once again I reiterated how much I appreciate the sharing of information in this forum, without which I do not believe I could have taken on a project of this magnitude by myself. Despite many decades of sailing, racing and cruising all manner of boats, I’m graciously humble to be a “newbie” boatbuilder. This build has already assisted me personally as I transition into semi-retirement, which I finding to be an oxymoron.


Happy Easter to All!


Altus Tendo





Link to comment
Share on other sites

I didn't cut out the opening ahead of time; I probably should have, it would have been easier (I used a keyhole saw after the bulkhead was fiberglassed in place). 


If you cut out the opening prior to installing the bulkhead; you may want to temporary reinforce the opening.  When you install the bulkhead after unfolding the boat, there is significant pressure on the lower portion of the bulkhead as you conform the panels to the shape of the bulkhead. 


Consider temporarily clamping a board across the hole to keep the plywood from bending during installation (since I didn't go this route, I can't say for sure that this is necessary). 

Link to comment
Share on other sites

Worthy considerations Amos.  Though built very differently, the mold for a Lapwing becomes part of the boat, bulkheads and inboard sides of side seat/tanks.  One of the bulkheads gets a major portion of it cut out, but the same issue of deforming under strain during construction exists.  I cut out the corners of the holes with hole saw blades of appropriate diameter before, so that I had easy straight cuts for after.  I calculated my jigsaw would fit for doing these straight sections.

  • Like 1
Link to comment
Share on other sites

  • 3 weeks later...

Todd,  as a side note I would keep silicon sealant far away from your boat build.  Lots of good sealants around but silicons can cause headaches then you start painting.  May years ago I bought a Columbia 26 that the ports had been silicones into place, still leaked and it was the absolute devil to decontaminate that area, and apparently where the installer had some on his hands and touch random places on the boat. 


I installed the anchor well/ cabin vent with mosquito netting after the first long weekend aboard.  Very effective!  

  • Like 1
Link to comment
Share on other sites

So it’s been a little over a month since starting on the CS20.3 and it has provided me opportunities for growth by learning new skills and developing a mindfulness of patience and appreciation of design. This is becoming a cathartic process which I experience genuine humility, gratitude and peace. It’s been very satisfying constructing this boat and I’m enjoying the process overall. I’m not rushing through and have no expectations of a completion date, rather taking it day by day and marking the journey. Although in the back of my mind says I should have it done by October’s Messabout. Currently I’ve been working on the centerboard well and bulkheads where improve my fillet and glass laying skill. I chuckle at my gooey epoxy snot slung everywhere compared to Alan on his video making it all look so neat and easy. I’m continuously pushing play/pause/stop/rewind; play/pause/stop/rewind watching the B&B YouTube videos which has provided a wealth of information and techniques. I’m fortunate for all the shared information here,  without which would have a significant deterrence to build.

Thank you all whom contribute to this forum.







Link to comment
Share on other sites

 So today I’ve taken the opportunity and have been scarfing the finger joints using drywall screws and nylon peel-ply. The first scarf was pretty messy with excess putty but it seems I’m getting dialed into better techniques as I proceeded along. I’m  a wee concerned about this boat fitting fully in the garage but grasping shes longer in single dimension, nevertheless it’ll be close. I’m planning to go 3D next week or so as I time and tide allow for.  While the epoxy was drying today I had time to think and read through the plans until a loose marble lodged itself in my noggin seeding a thought to share.


The long stowage space behind the cockpit combing seems great for stowing oars, however What if it were sealed chamber? I’m considering the inherent buoyancy of an air bladder or several XL sized pool noodles,  conceptually to improve capsize “right-ability”.

My question for discussion is would the provided volume in the cockpit combing to adequately increase the center of buoyancy while capsized? I haven’t started a volume calculation which would begin me calculating buoyancy to see if the center of buoyancy would move  further away from CG? 


B = ρ * V * g




I humbly admit I ‘ain’t no NA, and I’m somewhat lousy at physics and quite possibly adding any buoyancy might/could have a negative effect, causing masts to angle ever further downward increasing possibility to turn turtle? Well it’s these thoughts which will put me to sleep tonight, hopefully. 









Link to comment
Share on other sites

Looking real good Todd!


A while back I looked at many cases for the 20mk3. You can see some of the results in the form of stability curves here. 



Sealing the cockpit comings entirely would certainly add some positive buoyancy to the boat in a capsize. The stability curves we calculated assumed the coamings were flooded. Basically you would be increasing the angle of vanishing stability. The water ballast however is by far the largest determinant factor. We think the boat should always be sailed with the water ballast filled unless you are motoring in a dead calm or sailing in drifting conditions. The numbers don't lie and I am confident that the 20-mark 3 WOULD turn turtle without the water ballast in even if the cockpit comings were completely sealed. A small mast had float on the 17 mark 3 and 20 mark 3 can be added to prevent the boat going turtle in all scenarios which would be a good idea if you like to sail the boat without the ballast of if you plan to participate in say the Everglades Challenge for example. I plan to have a mast head float on my CS-20 Mark 3 because I like to sail without the ballast because it's faster! and I don't want to worry about turning turtle when I don't have the ballast in. If you always have the ballast in then no need. 


With the water ballast filled the boat should not be able to turtle even if the centerboard is up on the 20 mark 3. (maybe not true for the 17 mk3...see below) This is I think attributed to the taller masts which (once partially underwater) provide the missing righting moment lost from the CB which is good because it remains to be seen if the centerboard could be reached from the water if the boat capsizes to starboard (putting the offset board higher up in the air). I intend to test this extensively with my boat. 


We have only been able so far to test capsizing a CS-17 Mk3. Based on these few tests, the 17mk3 was easily righted by one person with the tank full and the board down and even while at the same time scooping the crew into the cockpit. The one test we did with the board UP it looked like she wanted to turtle even with the ballast tank filled. The boat tested did not have sealed cockpit coamings. There were a few extra variables in this test though such as the mizzen being flipped over and could have been scooping water as they tried to right the boat with no CB. Also this test pointed out the possible usefulness of a line tied to the trailing edge of the CB that could be pulled on from the water to re-lower the centerboard.



The 17mk3 is still quite stable without the ballast with an angle of vanishing stability of around 70-80 deg or so. We tested the angle of vanishing stabilty of Grahams 17mk3 here but with no sails at the time and got 85 deg w/o ballast. 



And we did a similar test of the first CS-20 Mark 3 with the ballast in only here. 




Only because it is pertinent to the above we are also working on a new design...(spilling the beans here) we are currently calling the  Core Sound 17/20 SR. (SR stands for self righting). We're pushing the limits of the water ballast in a remake of the original CS-17 and 20. The boat below has almost the same hull shape as the CS-20 mk3 but with added sheer height to gain the maximum righting moment from the cockpit coamings which are now completely sealed. The water ballast tank is a full 550lbs in the CS-20 SR and there is 4 inches of blue closed cell foam blocking between the underside of the cockpit sole and the top of the water in the ballast tank. The purpose of this is to push the center of volume of the water ballast lower in the boat thus reducing the vertical center of gravity. It has the added benefit of being able to fill the tank without topping off with buckets or pumps since the entire tank is below the waterline. It is very hard to get a shallow draft boat to self right and it's impossible to do it without sealing the cockpit coamings. That also makes the boat very stable in the inverted position. To solve that problem. One of the coamings is flooded automatically if the boat turns turtle allowing the boat to be rotated back on her side and then righted. If I had this boat, I would also have a mast head float on it for the same reasons as above. I like to sail w/o the ballast (because it's fast) and don't want to worry about turtling. The 17 and 20 SR will also have an integral outboard well in the stern of the cockpit, a longer forward cockpit seating area for camping under a dodger and we're shrinking the weighted CB down so just the top of the trunk sticks up above the sole.  






Link to comment
Share on other sites

Hahaha, it's something we've been thinking hard about. Steve, I agree it would be nice to have some kind of prevention line on the centerboard but on the flip side it's a rare enough event for a regular Core Sound to capsize let alone a Mark 3 Core Sound so it wasn't a top concern in the design process and Graham I think still isn't convinced it's necessary. 

Link to comment
Share on other sites

@Todd Stein— my first stitch and glue project was a Willow kayak featured in Woodenboat magazine (a three part series).  I kept telling myself that it was “only” 95 simple steps.  Your project has a few more than 95, but the approach is the same.  Try not to look at the whole big picture.  Focus on the next 5 steps.  Enjoy the journey!  We’re as good as there, building with you.  (You’re always alone when it comes to the sanding steps, though.). By the way— I still have your military blanket.  See you in October.

Link to comment
Share on other sites

Ok Sports Fans;

One time as a young Petty Officer I was asked by a crusty old Master Chief, “How would I go about eating an elephant?”. The answer, plainly enough has been incorporated into my ethos and one of my watchwords. Just the same, thank you for saying the encouraging thoughts. Although Im physically alone during this build, I can state with confidence I feel more connected to the collective consciousness of boat builders far and wide. This has been a goal/dream since a cold January day in Holland, Michigan back in 2004.


Im at the point where I’m finger scarfing the sheer strake which got me started on the whole Center of Buoyancy question. I must admit I enjoy talking theories and developing scenarios to apply them. Any rate after sleeping on it and chewing on the idea I did a rough calculation which showed there’s not nearly the significant amount to affect buoyancy thus change the stability curve. I estimated 4 cu/ft of volume within the cockpit coaming/sheer strake area. The equation shows a result of 1138.5 Newton’s of force with 256 lbs of displaced fluid. Initially I found this interesting however as Alan stated earlier the  water ballast however is by far the largest determinant factor. Further observation is location, location, location. That amount of force is seemingly a good thing but is it in the desired location?

As mentioned above, just how would it play out if the boat turns turtle, la saman Allah. I’ve learned in other reading where buoyancy placed incorrectly had negative and fatal results. So as it stands I’m doning respirator, goggles, gloves and headphones, (PPE) and recommencing sanding ops. On a final note I’m finding the random orbital sander used together with the  1/4 sheet oscillating sander does a good job fairing the scarfs. KIWTG.


No relation just a salty old Jack.



  • Like 1
Link to comment
Share on other sites

  • 2 weeks later...

I’m about to begin attaching the longitudinal stringers to the hull sides and bottom. I’ve pre-drilled and attached block and drywall screws on outboard side. My question is how do you recommend positioning the plywood while applying the epoxy filler, vertically or horizontally? Initially I had the plywood piece hanging vertically so I could work both sides, but wanted see if there’s a better way?



Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.