GZ curve

Guest · Post by **Guest** » Apr 13th, '10, 15:22

Has anybody ever seen a GZ curve for a cape dory 30? and if so how could I find it (short of calculating it myself)?

The reason I ask is my boat is in Europe and it has to meet legislation that some suit decided would be a good idea to prove my boat is seaworthy (it has sailed the Atlantic but that doesn't seem to count for anything). I have to compile a folder of data including a stability curve.

Thanks for any help.

DaveCD28 · Post by **DaveCD28** » Apr 13th, '10, 16:00

I have never heard of that before (having to show this data to someone). What difference does it make to anybody? I believe they let open dinghys sail in the English Channel.

It would be interesting to know your circumstances and why you would have to prove this to someone. Is it to aquire insurance or something?

-David

Guest · Post by **Guest** » Apr 14th, '10, 09:39

David

All boats being built withing the European Union since 1998 have to have a CIN plate attached (Craft Identification Number) and be registered to a certain design catagory ( A for Ocean going through to D for lakes and canals). Having the CIN plate means they comply with the Recreational Craft Directive. This means they have been built to a certain set of standards eg - hull composition, electrics, fire safety, stability, gas installation etc. All boats built prior to 1998 were excluded but unfortunately my Cape Dory is classed as an import after 1998 and although it is an older yacht it has to comply with this legislation.

You can still take a design catagory D boat across the Atlantic but the politician in the office wouldn't approve of course - he might dream up some more paperwork for us all to do.

DaveCD28 · Post by **DaveCD28** » Apr 14th, '10, 09:49

Oh, I see.

I thought you were simply cruising over there, I didn't realize you were trying to register it as a European boat.

It's interesting that they don't exclude it due to it's age. Good luck getting it resolved.

-David

Russell · Post by **Russell** » Apr 14th, '10, 10:31

The funny thing about this is according to the politicians boats like Beneteus and Bavarias are class A boats. Yet a solid design like a CD and many many others have trouble proving they are as seaworthy as those highly respected Beneteus and Bavarias.

There has to be a way around it? There are thousands of imported older boats and home built boats plying the waters of the EU.

Cathy Monaghan · Post by **Cathy Monaghan** » Apr 14th, '10, 11:51

This is all Greek to me, but maybe it'll help somebody. Hopefully some of you mathematicians, engineers and physicists can figure it out, otherwise you'll need to hire a naval architect.

Ship's Stability Info: http://www.mcaorals.co.uk/Stability.htm
Definitions: http://www.mcaorals.co.uk/Stability%20Definations.htm
Stability Formulas: http://www.mcaorals.co.uk/Stability%20Formulas.htm
Stability Sums: http://www.mcaorals.co.uk/Stability%20Sums.htm
Equilibrium: http://www.mcaorals.co.uk/Equilibrium.htm
Calculate Stability Curve: http://www.mcaorals.co.uk/Calculate%20S ... 0Curve.htm

Good luck.

Cathy Monaghan · Post by **Cathy Monaghan** » Apr 14th, '10, 14:25

I found this $50 spreadsheet if you're interested. I have no idea how reliable it is nor do I know anything about the company providing it.

http://www.hawaii-marine.com/templates/ ... iption.htm

Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

Guest · Post by **Guest** » Apr 16th, '10, 09:03

Thanks for all your interest and thanks for the links. I'll look through these. I'm sure my boat will be much more seaworthy when all the forms are filled in and stored in an office somewhere! (although Carl Alberg might feel slightly offended).

2tocruise · Post by **2tocruise** » Apr 16th, '10, 09:51

While I'm sure the $50 spreadsheet will produce the numbers as promised, it is only going to be as good as the data put into the calculations.

In order to properly calculate the stability curve you will need a lot of information not readily available to us Cape Dory owners. Many of the measurements can be obtained by close approximation using the sail plan sketches from the owners manual, but not everything. Inputs such as wetted surface area and cross sectional area would require a lines plan or offsets. Since these are not really available, it would mean taking the lines off your hull, a time consuming process at best.

To further complicate things, a stability curve is based on one value of displacement (weight) and one value of the vertical center of gravity (KG, the overall average location of all weight on the boat). Figuring out the proper KG value would involve conducting what's called an "incline experiment". Another time consuming and potentially expensive process.

What I don't understand in all this is the bureaucracy. I fully admit that I am ignorant of EU laws and regulations, but to me the key phrase you mentioned is that a vessel built within the EU must have a CIN and be classed. New England is certainly not part of the EU. It is my understanding that the majority of US built boats, even today, are not classed by the EU regulations unless there is potential to race in a EU race or the manufacturer wishes to sell the boat in the EU.

Parfait's Provider · Post by **Parfait's Provider** » Apr 21st, '10, 07:59

From
http://www.boatdesign.net/forums/sailbo ... 492-5.html

Alberg Sea Sprite AVS = 138.6Â°

Alberg Cape Dory 28 AVS=133.3

Alberg Cape Dory 30 AVS = TBD

Practical Sailor might have some info.

The Cape Dory Board

GZ curve

GZ curve

Recreational Craft Directive

It's all Greek to me....

Spreadsheet...

GZ

Stability Curve