Rating the Coresound 20 Mk3

[Drew]

Has anyone attempted to get a rating for their CS 20#3 to enable club or event racing? I am faced with the dilemma of whether to apply to Australian Sailing, the body that determines local rules and handicaps, for what is known as a class-based handicap (CBH). It is needed to participate in any point scoring racing and seems to be quite a process. If anyone has done anything similar and succeeded elsewhere the details could be helpful to me if I pursue this here.

Interested to hear your experiences, especially those who have participated in events such as the Everglades Challenge.

[Alan Stewart]

Since there are only a few 20mk3s out and about I think you may be the only one blazing this trail. As far as the Everglades Challenge goes it's very non-ratings based. In fact it's not even a consideration. "Run what you brung" as they say. All sailboats are lumped together and only differentiated by number of crew (1 person or 2 people or...now...3 people aboard) since that is a much larger factor in speed for the sailors since a two person crew does not have to stop if they have a cabin or shelter for sleep aboard. The only thing that matters is finish time. 

 

 

[Drew]

Thanks for your reply Alan. I will keep you posted on progress. Can you tell me the designed waterline length (DWL) as I can't find it in the plans data.

[Alan Stewart]

223 1/2" or 5.67m. Good Luck!  We are interested to see how it goes. We have some buoy racing here in our area on the Neuse river but we tend to just go camping or to the beach when we have free time and haven't gotten into the social racing scene yet. Back in the day Graham used to race Spindrift 10s with all the builders here. I wish i was there for those days. I would love to have an active Spindrift race fleet again. 

[PAR]

I'd suspect the CS series in general would get spanked pretty bad, by the current rating systems, so you might be better off just letting your local committee offer you a rate, on observed performance potential and race finishes. Depending on politics within the committee and your experiences with them, the rate will move around, but after a season, they'll get you reasonably sorted.

[Hirilonde]

I would build a Spindrift 10 in a heart beat if racing it was an option.

[Drew]

OK guys, next question (Alan). I know the CS20 Mk3 self rights from over 90 degrees but have you worked out a self-righting index for them?

[Alan Stewart]

Drew,

 

It took me a  google or two to see a reference to that index rating. I'm still not sure how its calculated but I had done some analysis of the 20m3k hull with and without water ballast previously. Attached below is a pdf of the graphs (imperial units at the moment sorry).

 

Both the ballasted and un-ballasted cases assume no crew aboard and i did one with two crew sitting on the wrong side which could simulate a very poorly executed gybe perhaps.

 

Interestingly the masts (if sealed) provide a not insignificant amount of righting just after capsize. A good reason to seal all those rivet holes. This effect presents as a second "hump" in the righting moment curve after 90 deg is passed again assuming the masts don't take on water. 

 

While not shown, the weight of the sails is accounted for. It is assumed that the centerboard stays in the down position. Which may or may not be the case. We have thought about adding a cleatable downhaul line for the CB to make sure it stays down in a situation like this when sailing in deep water. Also note that the cockpit coamings are not included at all as part of the buoyant volume although they would help the down-flooding angle slightly. At 110 deg, the cockpit hatch is still above water.

 

Here is a link to the files, they were too big to upload here....

https://drive.google.com/drive/folders/1a5RWgDJGvyTCfyEOj0PosHYcIn2pxI0B?usp=sharing

 

 

[Drew]

Wow! You are truly amazing. This should b encouraging to all of us. I am about to submit the initial paperwork and will let you know the outcome.

[ipeband]

On 25/02/2018 at 9:19 AM, Alan Stewart said:

Drew,

 

It took me a  google or two to see a to that index rating. I'm still not sure how its calculated but I had done some analysis of the 20m3k hull with and without water ballast previously. Attached below is a pdf of the graphs (imperial units at the moment sorry).

 

Both the ballasted and un-ballasted cases assume no crew aboard and i did one with two crew sitting on the wrong side which could simulate a very poorly executed gybe perhaps.

 

Interestingly the masts (if sealed) provide a not insignificant amount of righting just after capsize. A good reason to seal all those rivet holes. This effect presents as a second "hump" in the righting moment curve after 90 deg is passed again assuming the masts don't take on water. 

 

While not shown, the weight of the sails is accounted for. It is assumed that the centerboard stays in the down position. Which may or may not be the case. We have thought about adding a cleatable downhaul line for the CB to make sure it stays down in a situation like this when sailing in deep water. Also note that the cockpit coamings are not included at all as part of the buoyant volume although they would help the down-flooding angle slightly. At 110 deg, the cockpit hatch is still above water.

 

Here is a link to the files, they were too big to upload here....

https://drive.google.com/drive/folders/1a5RWgDJGvyTCfyEOj0PosHYcIn2pxI0B?usp=sharing

 

 

Hi Alan,

 

Really nice analysis! I was thinking about a floating topedo at mast top and forgot about the air inside sealed mast. Got surprise about how big is the varnishing stability angle for a water ballast boat.

[Drew]

Thanks for the comments to date. I have made a request to Sailing Australia for a class based handicap and they have been helpful so far. Fortunately, my club in Canberra has two national inspectors as members so we have made a tentative date later in the year for measuring. The one issue that keeps coming up is the low centerboard to total weight ratio. I have said that, as well as Alan's righting graphs, I am willing to emulate the righting experiment and take the masts down to water level, but there is a bit of skepticism on that, arguing that it might not represent what could happen in a sudden squall (a la the incidents recently in the EC). I guess some people feel uncomfortable with water ballast as a substitute for centerboard weight.

Comments from you guys, especially from Graham, about the potential effect of adding say 100lb to the centreboard mass in the form of a steel plate CB with a heavy bottom end would be much appreciated. I note that the Norwalk Islands Sharpies seem to carry a lot of ballast weight.