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B&B's first annual "Capsize Camp" July, 20-22

Alan Stewart

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Thanks Alan, for the thoughtful reply. I've thought a bunch about those trade offs, and did have the notion that I could go rent a slip and fill it with a big ol' keel boat. But it's just not what we want, and we love the boat. This will mortify many, but I want to experiment with 3 24" sections of pool noodle secured to the top of each mast, and see just how badly they disrupt air flow. If I can live with it, they should add 24 lbs of lift per mast. That should help.


Paul, my mizzen was sealed, my main mast was open. I've thought a lot about this, and closely studied Amos' (I think) boat video during the last capsize camp. No idea whether his masts were sealed or not, but you can see his masts (last capsize of his) slice through the water when his sails were all the way out as if on a run. I don't think the volume of the mast is enough to provide much flotation, whereas it's clear to me that the sails offer a lot of resistance if they're sheeted in. Yes, I think the masts should be sealed, but again, not sure it's enough to have made any difference.


Steve, I'm not sure. Frankly, by the time I'd gotten around to the stern (within seconds of uncleating the sheets) the CB rolled into the trunk. I'm not sure, if it had somehow been locked, that we could have reached it to make any use of it in time. On a stb roll, it's higher out of the water, and the boat had rolled far enough, and the CB upright enough, that it dropped easily into the trunk.  Under some circumstances, it seems to be less than a minute before the hull turtles.

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Thanks for the link Mike - can't believe you Found this. I'd been pondering just such an idea but figured I'd have to cannibalize a pfd. They're also kind of heavy, what with the CO2 cylinder and all. I'll see what happens with Graham and Alan's float, and/or the pool noodles first, then go from there.

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I have been thinking about this too and have found a couple of additional links. Some of the bulbous devices are really ugly. Flying Scot has a float that fits over the head of the mainsail (https://flyingscot.com/product/mainsail-flotation-mast-flotation-top-of-mast-flotation/); I never saw one in use, thought it was ugly, and wondered about its effect on sail shape. Maybe there are some other ones like it. Seems like you might be able to make something similar with some closed-cell foam and sailcloth.


There are a couple of inflatable masthead floats made by Crewsaver: https://crewsaver.com/au/search-results/?searchTerm=mast+head.     I am not clear on how these attach.


Another self-inflating device that may be an option: https://www.throwraft.com/  I had the idea that this could be rigged to hoist on a spare halyard (think pigstick) and might work. At least it would be significant buoyancy. The fallback would be that it meets USCG requirements for a throwable flotation device and would be usable for that.


But once one of these is used, then what? Lower it and replace the CO2 cylinder? Seems like if you can capsize once you can do it again (my personal best is 14 consecutive capsizes in a Laser). A more 'durable' or permanent device would address that but windage and aesthetics enter my thinking. The B&B option as it evolves is appealing. Maybe Graham and Alan can figure out how to make it add power, like a topgallant ...


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I saw one of these on a 15’ Mutineer. Light weight and fairly low profile. 8 liters, about 16lbs of floatation. You could put one on each mast. It is made for a luff groove, but could be modified to fit over the slugs on a sail track.


I would like to hear from Alan or Designer how much floatation is needed for the various designs.

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This morning I finished a new ground up weight study for the Core Sound 17 Mark 3. You can see the spreadsheet at this link. https://docs.google.com/spreadsheets/d/1FdHRORADYjMWl-AEDNtsJI7Q4Dujp7n38PEjUZcsom4/edit?usp=sharing.


If you would like access to copy and have your own version and add things let me know and I'm happy to share the file.


All of the parts are in there in addition to our calculation for epoxy, masts, track, sails, sprits, ballast (both in and out) rudder and centerboard. I included 20lbs of hardware/rigging applied at approximately deck level. As some may know, we "re designed" the boat in 2018 with a slightly taller cabin. Basically raising the boat from the sheer line up by ~2 1/4 inches to accommodate the taller among us. The same alteration was made to the 20mk3. Here is the difference in scale. While Freds 17mk3 was one of the first, there is little difference between his boat and the 2018 model. The masts are the same height, the ballast is the same. 




Here is a pretty picture of the Weight study mode. All of the plywood parts are simple surfaces and the solid wood is is green. This model was used to calculate the center of gravity of the boat both longitudinally and the all important vertical center of gravity. 



Below, you can see the 17mk3's resulting CG calculation showing the all important VCG (vertical CG) with ballast in and board down as well as ballast in and board up as well as no ballast or board at all. This solid model was used for the calculation of flotation at various angles of heel. Note that the cockpit coamings are removed and that boat is somewhat simplified to just the sealed volumes.  These calculations are based on sealed masts, and assuming that cockpit lockers don't leak. You can see that an outboard motor would not significantly alter the results because the CG of the motor would be very close to if not below the VCG in all cases. 



First I looked at the 90 degree case. I was hoping it would be still positive but it turned out just slightly negative. The difference between the VCG (red) and the LCB (location of center of bouancy) blue gives us the moment arm for either heeling or righting. In this case the VCG overtook the LCB by about an inch and a half so the boat is going to keep going over. In order to increase righting moment the only options here are increase buoyancy up high or increase ballast.



Next I looked at the tips of the mast in the water. or about 97 deg. At this point we are still going over since now there is an even larger difference between the LCB and the VCG. You can perhaps see the difficulty. To put into perspective the heeling moment of -3300 inch lbs, a 200lb sailor standing on the tip of the board would be able to apply approximately 10,000 inch lbs of righting moment. Easily righting the boat. This was confirmed by Richard's capsize test last year. Also, seen here an 18 lb buoyancy float would prevent turtling with just a bit to spare. 18lbs is the size of the float we used in the latest capzise tests with Will's CS17. 



Now we look at the same setup but with the board up. Either it fell up or was up to begin with. With the same mast head float not we're on our way over....BUT



The masts do provide significant flotation. In fact more than this 18lb float does at an angle of 105 degrees. I chose 105 degrees because that is about the angle  that Richard's boat went to when he flipped his 17mk3 with the baord up in his 2018 capsize test seen in this video. https://youtu.be/s35CfcipAKo?t=206. The boat quickly came to rest with the mast underwater about up to the snotter connection point. Here we see that with a mast float the boat would not go turtle even if the board fell into the trunk as long as the masts were sealed. This doesn't solve the problem of how do you get the board back down so you can pull on it. I think the solution for that should be a "safety line" approximately 2' long that hangs from the trailing edge of the Centerboard which can be pulled to get the board back down. 




Next we have the same 105 degee case but with the board down. This seems an unlikely case since as Fred's test showed, the board will fall back into the boat. A downhaul line could be rigged on the weighed board on a breakaway cleat to prevent this. This could be a better solution than dragging a line. 



Finally, how much mast float should we recommend? Well one calculation is based on the case of NO ballast and NO centerboard down. Which is not inconceivable if you were in the EC racing in light winds downwind . In this scenario I calculate that a 35lb mast head float would be required to prevent the boat from going turtle. This does not take into account any flotation provided by the masts. The boat is lighter without ballast which reduces the heeling moment even though the Vertical center of gravity has gone up to 23.5" above the DWL. 



A 35lb buoyancy mast head float is not too bad. Here it would be in scale. 27" long, 8" tall (to keep it within 4 layers of 2" blue foam), and about 10.5" wide as viewed from the front. The 18lbs float we built came in at right about 2lbs. Unfortunately a mast head tri-color such as the one Graham installed makes the addition of this float a bit more difficulty but not impossible. The floats "mast" is 3/4" aluminum tubing and it could be mounted to the front side of the mast on a pair of brackets and I think not interfere with a tri color. 




One final thought that has me leaning toward the larger float size is sailing the 17 mk3 in the EC at night with a crew member sleeping down below. However unlikely, a capsize then could trap the crew member in the cabin. Keeping the drop boards out when a crew is sleeping below would be a good standard practice. The larger mast head float would eliminate that concern with ample buoyancy when combined with the ballast. Remember the 17mk3 with ballast is still a lot more stable than the original 17 so I'm not trying to alarm anyone but we also don't want anyone getting water in their cabins. 


You can also see how vitally important it is to keep the weight down especially on deck. We might want to think about switching to the much lighter flexible solar panels as opposed to the heavier glass ones for example. 


We want to do a dockside test where we pull the boat over on it's side at the dock with all rigging in place, ballast in and board up. then use a fish scale to measure at the tip of the mast. Presumably the mast will be pulling down and we could directly measure the heeling moment as a check against these numbers. It seems like it could be as much as 19lbs based on my calculations. This is a test we should have done with Graham's boat but the only test we did was without sails. 


Adding MORE water ballast is of course another option but this is the problem with a shallow draft boat, the ballast is not very effective at 90 deg of heel due to the very short moment arm. An extra pound of lead on the tip of the centerboard would be more effective but the board already requires a fair amount of purchase. Making the board heavier is not very difficult but it also only works if it's down where as the mast float is always there. 


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Thanks, Alan, for the well thought out analysis and illustrations. 


Was the lead tip on the cb designed as a means of holding the cb down without needing to cleat it down? Or was it designed to provide righting moment and ballast? My CS20 Mk1 does not have the lead tip but I do use the breakaway cleat.


Could you do an analysis of the CS20 Mk1 with respect to inversion, assuming board down? It would be good to know what size mast float would be needed.



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Here's some decidedly vague info that may be a bit helpful.  I obtained a masthead float from Alan and Graham last winter for my CS 17 MkI.  I was going to get a kit, but they had one made up and basically sold it at cost (thanks!).  I put it on the mizzen, even though they advised putting it on the main, since if I had put the extension tube on the main the outfit would no longer fit under my trailer cover.  The recommendation to use the main was in order to get the greatest righting moment.  I had to sacrifice about a foot of moment, I suppose, by moving to the mizzen.


In any event, I do notice a slight added windage when stepping the mizzen.  How much is very difficult to quantify.  A "slight extra push"? Maybe?  So I assume there is a corresponding *slight* decrease in windward performance, but I certainly have not noticed anything, and I have not noticed any visible signs like added mast bend.  I take the float on and off each launching.  It just takes a minute.  It turns out the hardware store had a car air filter wing nut with a quarter-inch threaded bolt that fits perfectly, so I don't need to install a screw to hold it on, just twirl in the wing nut.


The float has a name:  Moby Turtle.


I've also been very careful to make sure my masts are sealed.  When I did capsize and turtle last year, one filled and one didn't.  The one that filled had a 1/8" hole at the top that I had drilled and abandoned.  That's apparently all it took to fill.


So, having capsized and turtled and not wanting to repeat, I certainly feel safer with Moby T at the masthead, and it's worth the peace of mind for the negligible loss, if any, in performance and the added minute or less of setup time.  Obviously the float is not the only option, given some of the other devices folks have found, but it is easy to use, out of the way, and does not seem to interfere with getting anywhere.


Here's Moby Turtle at the mizzenhead.  (Plus I love this picture.)





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59 minutes ago, Steve W said:


  1. I always thought a square foot of air supported 62 pounds. Am I wrong?



You probably mean cubic foot. A cubic foot of fresh water weighs just over 65 pounds.  So your statement is at least a good approximate. What people have trouble visualizing is how big that is.  A 5 gal. bucket is 2/3 of a cubic foot.

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12 hours ago, Steve W said:

A couple of questions.


  1. Would you expect similar results with the 20.3
  2. How do I make my masts float? I followed the plans and rivited the track, but I am sure that the mast isn't water tight. Pool noodles?
  3. I always thought a square foot of air supported 62 pounds. Am I wrong?




Answer to question 1...

I've now also done a complete re-do of the 20mk3 weight study this morning. This weight study has the raised bunk tops mod which is now standard in the kit. Here is a link to the spreadsheet. https://docs.google.com/spreadsheets/d/1rqaVj7Ncj45HQtIq8PMWILgZhQCXYuGpHj3qkUgu6DU/edit?usp=sharing






In that spreadsheet is another sheet with some stability curves I did last year. They are still fairly valid in that they show the heeling angle of max righting moment in various stages. For example without ballast, the 20mk3 has positing righting until about 60 degrees (angle of vanishing stability). With the ballast in it goes to about 90 degrees depending on "factors". Factors meaning basically what other stuff is in your boat.


For example, below is the 90 deg case. Although it came out negative it is very marginally so. the 1/2" difference in the vertical center of gravity from the LCB could swing the other way if say for example you have a ~50lb house battery secured just in front of the ballast tank. OR on the flip side, if you have mast head tricolor light that weighs 3 lbs with wires in the mast then that pretty much cancels out that house battery in this case since it's so far away from the LCB. Weight is the killer and the farther from the CG that weight is, the more effect it has. Note also that my weight study did not include a solar panel, toe rails, tabernacle bolt, halyard block, running rigging like halyards, or the lexan ports for that matter. 




So, we're going over. Below shows the masts now in the water at 100 deg. and the board fallen back into the boat. In this case the 20 mark 3 should have enough buoyancy provided by the submerged masts to prevent turtling but only juuuust barely. Since it's hard to know where we are on the curve at this point. I did one more at 2 deg more heel. 103 degrees. 




Below is the same situation but just 2 more degrees of heel. The calculations show an increase in righting moment which means we haven't reached the max yet which is good. So the 20mk3 shouldn't turtle as long as the ballast tank is full even if the board is up provided there isn't a bunch of heavy stuff at the top of the mast and all of the stuff stored under the bunks doesn't fall to the cabin roof and weigh the top down. Note also that the cabin hatches are clear of the waterline. 




So getting back to the 20 vs the 17 mark 3. Why does the 20 seem to have enough mast buoyancy and the 17mk3 not quite enough in this case? Below we see them side by side both at 100 degree of heel. The smaller 17mk3 has a bit less ballast (300lbs vs 430lbs) but even if we increase the ballast on the 17m3k by 130lbs so that they have the same amount of ballast water, it's not quite enough to make the 17mk3 positive at this heel angle. The masts are shorter so the force they apply is not quite as effective. And, for another perspective check,  the negative 1750 inlbs of heeling moment seen in the 17mk3 here could be countered with just 7-10 lbs of flotation at the top of the mast or 270 cubic inches which would be about a 4 inch sphere of foam (again assuming no mast head lights or other mods to the boat). This once again highlights the design challenge with such a shallow draft hull with lots of primary stability.




The case of no ballast and board up for the 20mk3. I calculate a similar amount of flotation about 33lbs required to keep the boat on its side with no ballast and no board. At -8700 inlbs it should be no problem for one person to right the boat by standing on the centerboard. I am not sure about using a righting line but with 2 people on a righting line I think it would be enough. I plan to test this extensively on my boat. 




One last one (below), the boat is capsized to starboard so the board is way up high and falls back into the trunk. In this case, cockpit and mizzen mast are used to climb onto the top of the hull so that the board can be reached and pulled back out of the trunk so that you can then stand on the board. In this case, we would need at least a 17lbs mast float to support the additional weight of a 200lb crew member climbing in the cockpit. A 35lbs buoyancy mast float as discussed earlier for the 17mk3 would almost be enough in this case even if we discount the flotation provided by the sealed masts. An alternative to this situation would be to have a righting line in the cockpit that is thrown over the high side and then hung on by the crew to right the boat regardless of the position of the centerboard. 


Here is a video of Joe and Aaron demonstrating the "climb over" technique on his EC-22 https://youtu.be/4y19ckyZNgI





Answer to question 2. 

We are coming out with a mast float kit and I think we will be offering it to all of the Mark 3 owners basically at cost to any who want it. We don't want to see any Mark 3's going turtle. Here is a screenshot of the float design. It is made of 4 layers of 2" blue foam laminated together. The teardrop shape is cut on the CNC machine. There is a starboard collar top and bottom that is glued into the top and and bottom. A 3/4" aluminum tube is the float's mast and a modified mast cap supports the mast. The float sits on the little mast with a nylon washer and a clevis pin makes it quick to remove. The foam layers are hollowed out somewhat on the inside. The exterior of the foam can be fiberglassed but based on our first test done at the most recent capsize camp, this is not necessary. Simply epoxy coating the foam and then painting the float is sufficient. It cannot absorb water or leak. The tail fin is made of thin pre laminated fiberglass cloth and glued into a slot in the foam. The float should weigh less than 3 lbs and rotates easily into the wind. 




Answer to question 3. 

Fresh water is 62.4lbs per cubic foot 

salt water is denser 64 lbs

I used 62.4 lbs for the ballast tank calculation because that is "worst case" if the boat is being used in fresh water. 




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Nothing wrong with using two mast head floats (one on each mast) but it's not really close with a 35lb buoyancy float so one should do it. 2 means double the time to build and double the cost. Graham's boat has a mast head tricolor light in the main mast and so he might put his float on the mizzen mast only.

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This is all good stuff and being forewarned is forearmed but I do not think that we need to get hysterical. I have capsized probably more than anyone here so you could say that I know something about the subject. If I was venturing far afield alone on a mk1 I would definitely have a mast float. I never capsized a 17 or 20 that was not a test even though I have had them in pretty bad weather.


On a mk 3 it is still a good idea. I have singled handed Carlita a lot and been in some scary weather and never felt insecure. I have sailed her upwind with ballast, deliberately overpowered to see what she will do. As the boat heels over, the wind force is reduced but the righting moment is increasing all the way to about 60 degrees where it starts reducing. 60 degrees is huge and it would be a foolish skipper that did not reef long before. Typically it is hard to get her to heel much past 40 degrees while on the wind.


On an open boat the down flooding angle is reached by 35 to 40 degrees which is easy to achieve as they do not have ballast. The exact downflooding angle depends on beam and freeboard and inherent stability but once you reach it is over.


Down wind is the wildcard because dynamics play a larger factor. Any racing skipper knows, in heavy weather the gybe mark is where most boats capsize. This is because inexperienced skippers bring the helm up quickly to gybe and just when centrifugal force is heeling the boat to the max, over comes the sails adding to the heeling force and suddenly you have reached the down flooding angle and over you go. The smart skipper gybes before the mark by sailing slightly by the lee and holding a straight course, waiting for the gust to pass and pulls the sails over one at a time. He can now approach the mark with full concentration and easily dodge capsized boats and do a tactical rounding of the mark with the sails properly trimmed with no drama.


For a cruising boat the downwind lesson is, reef early, reducing sail reduces wind force and lowers the heeling arm. Avoid gybing in high winds. If you have to gybe , do it carefully as described above. Avoid running dead downwind if you can. If you must, let you sails go forward of the beam by about 15 degrees which reduces the dreaded deathroll and makes it hard to accidentally gybe.


Sailing in large waves also adds to the dynamics. Follow the paragraph above but reef sooner. 


Remember you are sailing one of the safest boats around but common sense is still required.

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Graham has a good point (as usual) and it is good to put the stability into perspective after seeing screenshots of the boat on it's side. There are quite a few mark 3's out there and no reports of stability issues. It is by all accounts a very stable boat and takes quite a lot of effort to capsize. I agree with Graham 100%. 

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Alan and Graham,


Thank you for taking all the time to answer all of these questions. I am very impressed with the sailing characteristics of Skeena. Sunday I sailed up Sodus Bay on Lake Ontario. I told my crew we should get 2/3 of the way upwind to Sodus point and we could motor the rest of the way to catch the Bills/Jets game at 1pm. At 1:04 we walked into the restaurant just in time for kickoff,  having made it under sail alone. Amazing performance.


I recognize the design challenges. I am comfortable for day sailing and short overnight trips not changing anything when I can watch the weather window. I built the boat mostly stock. I do have some of the things Alan mentions (solar panel, masthead anchor light, anchor roller (yikes!)) that puts weight higher.


For longer trips where the weather isn't predictable enough, I'm planning to make some changes.

  1. putting hinges and latches on the bunk lockers. I can see all the contents running  all over the cabin in a knockdown.
  2. Using the WB more.
  3. Being careful how I load gear.
  4. Adding the mast float. I think it will have to go on my mizzen as my main has a windex and 360 nav/anchor light already. How do I get one?

I also think Graham is right in tempering hysteria. I think the being prudent with the mainsheet in hand and reefing properly is still prudent. 




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