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Water Ballast Query

Rob Blackburn

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Evening All,


I have a CS 20 and recently was sailing in company with a Bayraider 20 in Tasmania in gusty and windy conditions. What really struck me was when the going got tougher ie over 20knots with gusts, my friends filled their tanks with 300 litres of water and sat back to watch us carry on reefing etc as they sailed away victorious. We soon lost sight of them as the wind got stronger. The wife onboard was calmly knitting a woollie hat just to rub it in. 


Has anyone had a go at retrofitting water ballast to one of the Core Sounds? ie version one, (the classic original flavour).


I have looked at our boat and can fit a hundred litres in each aft side locker and another 100 under the foredeck in front of the centreboard on the cockpit floor. I was thinking in wake boat ballast bags, nicely plumbed in and pretty much hidden. Jabsco wakeboat reversible pump to do the work.


My distant university physics lectures suggest to me that the combined centre of mass of such an arrangement would be 2/3 of the way along the axis of the boat about 100mm off the floor of the keel. ie 100kg fore and 200kg aft. Pretty much perfect.


So would it work?


Reading on the Swallow Boats site it seems to me that Core Sound, having a hard chine out wide would be a prime candidate?


What is the thinking here or have I missed an obvious point?


It is just that at 56 I am trying to find a way to extend the comfortable use of our boat for the pair of us. We are not 25 and bulletproof anymore.


My next plan is to simply try it with a 100kg of wet sand in the front on the floor in bags and fill both aft lockers with a bucket but I wont be able to for about 5 weeks.




Have attached a pdf on the topic. (And a shot of our daughter at the helm down at the bottom of Tasmania in Feb.)The Physics of Water Ballast - Swallow Yachts Association.pdf


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I love the photo of your boat, Rob.  You're sailing on, regardless of the gray, looming skies.    Cool!  I am 68, and have long since shed the sense of immortality I had in my youth-- I hear you!  But Graham has addressed this consideration in another post.  The gist of it is this:  the lower freeboard of the mk1 allows water to enter over the side at just about the point that the water ballast begins to be effective.  If you look at the lines of a mk3, you'll see the freeboard is significantly higher than a mk1.  So, it looks like you're going to have to build another boat!

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Thanks for that. It is all very confusing to a non naval architect. I guess the proof will be to get the boat back in the water and simply try it. The only cost will be the plastic bags for the wet sand. I am proposing an R and D budget here of about $20.


I get what you are saying about the freeboard but when I watch the Bayraider in action, the key thing is that it seems to sit about 1 inch deeper in the water and stiffens up. So a gust won't put it on it's ear as much. If a capsize is looking imminent, then the freeboard is definitely an issue.


I guess the other question is really, would the CS 20 be an easier boat to live with for a middle aged couple in gusty conditions if it had 300kg of ballast aboard. I suspect the answer will be yes. The boat won't know if the resulting mass increase is from water, boxes of wine, lead, spent uranium etc. I get the feeling that 300kg of lead in two ingots bolted to the sides of the centreboard case would alter the boat's response quite a bit so shall see.


We had 12 people aboard to ferry them to boats one morning (see attached)  and the boat was anchored in the water. That would be about a 1,000kg with outboard and jumpers and clothes etc that day. It floated lower of course but not diabolically.


Anyway. Thanks for the reply, will report back after sea trials.





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Hi Rob,


It is good to hear from you again and that you are still active with the boat. You must have sailed a lot of miles in her by now.


I think that water ballast would be still helpful. As you pointed out, testing with sand bags is a cheap effective test. Having to put the ballast out under the side seating raises the CG of the ballast versus being on the centerline due to the deadrise of the boat. Putting lead on the tip of the centerboard would give the most righting moment for the increase in weight. Perhaps some of each method would be the best compromise.


The big boats of course pump the ballast up to windward, or drain the water to the lee tank just before tacking but they usually stay on one tack for a long time. It would be tiresome on a small boat if you had to so a lot of tacking. 


On the last EC with the wind fresh out of the east, we would be on a port tack predominately so I put all of my heaviest gear on the port side of the boat. It might have helped if my back did not give out. I still have trouble accepting that I am not 25 anymore either.

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Kids and sailing could be a whole separate thread. Back when the wife and three kids used to pile into the CS17 I had thoughts of a larger boat.  The reality is that the window of time where you can sell sailing to the whole family is all too brief, and then you 'd be stuck with a 20 foot boat that is more challenging to row.  When they're little they fit into the bow compartment. 

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Yes Graham, I'm still extant as they say.


The boat is going fine and bang for buck I have never had such a good return over the years. It has been a great asset to the family and has been a 'passport' to other things/people/places that would have been denied to us with a smaller one or a bigger one. So very happy. Still think it is a bit wet though... lol.


I think the bit you have pointed out about the moving water around is really what I have in mind if this all comes together. The jabsco wake boat pump is reversible so I figure a set of 3 taps to direct the flow, a battery, solar panel and regulator which I have will be about all it needs.




It was just so apparent to us the difference 300kg made some days on our friends boat.


If you have the 3 separate blocks of water you could run with bow and windward side on a tack. Open the remaining tap for the empty tank, run the pump and fill the leeward one when you are approaching the tack, then tack, then pump out the new leeward tank. 100 litres will only take a couple of mins to shift too with the pump. So you are not vulnerable to having weight on the wrong side.


Same with downwind, don't fill the bow one if it is boisterous.


Anyway will see how this all pans out. 




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Ah Randy. I think you are right. As it is, they are already (at 8, 10, 12, and 14) going 5 different directions. Most of the time I am lucky to get one to go with me. They got good and wet one day when we came back on the west side of Camano and the chop picked up with some wind. I was only using the motor at this point and the spray was pretty cold. I had a blue poly tarp that I gave them and they huddled under it with the Mrs. but that almost made it worse because they all were up in the bow which made it worse. I was staying pretty dry back at the tiller. But unless I have a cooler of snacks and the dolphins or seals (or whales) are out, they get bored pretty fast. 

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Graham, Rob, or anyone with knowledge of the subject,  


Do you consider the single mast main/jib rig to be equal or better than a cat ketch rig in the conditions Rob encountered. Or vice versa. Or does the Bayraider 20 simply have some advantages at times?

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The first day of our trip to Tasmania we had 2 Bayraiders on the raid arrive. (Tawe Nunnugah 2017... google it  https://goo.gl/photos/mQsctBKu1TNzgcma6 )


(We also had a CS 17 along and they were great company. (Wyvern))


Here is a set of photos I sent to the owner of one of them that I took of them sailing in a fairly strong breeze. 




The video in this set is instructive. 

They put the water in and if you look at the video the boat just sits in the water. We would have been on our ear I suspect. 


Mind you I have come to the conclusion we have made a fundamental error when we put the sloop rig on the boat. We should not have put a fully battened main on. I think the BR yawl would have been better (bigger main, small self tacking jib, mizzen). With a soft main, so it is easier to feather etc in stronger winds. (we are approaching 60 years)


I loved our cat ketch but for down in places like Tasmania with very variable and gusty cold wind it was just a big ask for the two of us to be reefing it the way we had it setup. We did not put tracks on the masts and paid the price. It was a pity I did not understand it all better at the time.


The day after that was taken we sailed up the coast and the wind came out of the NW at 35 knots after lunch. We had 2 boats swamped but the Bayraiders dropped their mains and sailed up on jib and mizzen with the water in without a care in the world. 

So which rig is best, that is an impossible answer but I guess all I saw was the effect of the water going in, the boat stiffening up and the crew looking cheerful. (The hull really does not know what sort of rig is on top IMHO, it is the sum of the forces that count.)


We put the motor on in the end that day, served out rum and raisin chocolate and glasses of Liqueur Muscat. So it was still a fun day. Won't forget it for a while.





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Consider casting up some lead plates to lay flat on the bottom of the boat, adjacent to the centerboard case (near the pivot pin, I'd venture to guess). Do this after your sandbag testing. The plates can be bedded in some 3M-5200 or simply "dogged" down with some swivel clips. This will get the mass as low as practical and will make a significant difference in her roll moment. Additionally, depending on how much you find the boat likes, consider placing 1/3rd of this in the very tip of the centerboard. The Case can take some board ballasting without tearing stuff up, but there's a point of no return if you're in heavy air a lot and the board is heavily ballasted. I put about 40 pounds in a CS-17 some years back, with no harm to the case. I think you can double this easily, simply because of the way the case is supported above its pivot (seat stringer), which will resist a lot of torsional loading.

   Rig choices tend to be much like what your other half thinks are a pair of sensible shoes. Lower aspect rigs seem to do better in heavy air, but there are a lot of other variables that can come to play in the equation. There's a reasonable argument for simple rigs and also self vanging boom arrangements. I've found heavy air sailing is about skipper mind set and rig setup, than any particular rig over another.

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I would buy or build a smaller sail before I'd add ballast to a Core Sound.  I think you'll get more bang for the buck by reducing sail and finding a comfortable way to sit on the rail.  That way your ballast (crew) is always where it is doing the most good and you're not reducing freeboard unnecessarily.

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  • 4 months later...

Well, sea trials have finally been had on the new arrangement and I am pleased to report it all worked a treat.

The aft side lockers on our boat take exactly a hundred litres so started by filling them with a bilge pump dangled over the side with a hose attached. Immediately settled the boat.

Then filled the forward lockers as well, another 65 litres per side. So all up 330litres on board. Perfect. Balanced nicely fore and aft and just was not bothered by the gusts coming around buildings etc on the river.


The boat was so much more stable with just the wife and I aboard and did not heel much at all with the gusts.

We did not have a lot of time so then did a few runs with only water in the windward side and that too worked a treat. I can't believe I have not tried this at some point in the past 14 years we have had the boat. All you really need is a bucket to fill it really.


Was standing in the queue at the hardware store looking at the display of bags of cement. Each 20kg. So sixteen bags of cement on board was effectively the load, down low and out of sight. It is a worthy experiment.



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