Swan 411 GZ Curve
Hello Lars (Professor) I am new to the forum and I have just read through all threads. My Swan 411 is described by the RORC as having an AVS of 120 and a STIX of 32. My own calculations give an AVS of 130 and a STIX of 44. To be absolutely sure of my figures before I attempt to correct the RORC (Royal Ocean Racing Club) I need to view a GZ curve for the Swan 411 - I used a similar boat for my calculations. I also used a down flooding angle of 100 degrees. Best regards David

Dear David

Here a GZ curve for a Swan 411. The curve is based on IMS measurement which includes taking hull offsets and performing an inclining test.

How do you arrive at the large numbers?

Kind regards

Lars

Hello Lars
I will post the full calculations when I am satisfied that they are correct. Thank you very much for the curve.

David

Dear David

Lars
I am having difficulties reconciling all the numbers. I think I will need to re-plot the GZ curve. In you records do you have the distance from the C of G to the point M?

Regards

David

David

GM is in the order of 1.04 m

Lars

David

Lars
Sorry to be a pain - I also need the distance from C of G to the C of B. Then I can perform the trigonometrical calculation.

Regards

David

David

BG is about 0.32 m

Lars

Hello Lars
All this is making more sense now. Is the C of G just below or just above DWL? What do you have as the the beam at the waterline? My estimate is 3.56m! My estimate for the the draft canoe body (DCB) at 1/8 of the total beam out from the centre line is 2.1M - I will measure this exactly soon.
I have established that the IOR used a down flooding angle of 90 degrees as a default this gives a multiplier of '1' to the STIX calculation. A cut-out model of the 411 shows a down flooding angle in excess of 117 degrees. This would allow a multiplier of 1.25 in the STIX calculation giving the 411 a STIX of around 40 which appears to be about right. Perhaps I can generalise the spreadsheet for all S&S Swans!

Best regards

David

David

The C of G is just below the water surface. BWL is 3.46 m, pls note this is in empty condition. There is likely to be a typing error in the canoe body draught you give.

Kind regards

Lars

Lars
I had given the canoe depth value in feet, I meant 0.64m - sorry.
Should I use the empty BWL or adjust to, say 3.5m?
David

Hello Lars
I have calculated CE above DWL at 7.4m and CLR below DWL to be 1.15m. Have you better measurements?

David

David

The condition which gives the lowest STIX should be used. This usually is the loaded condition.

Your center of efforts are in the right range.

Pls note that portholes are assumed to be closed in STIX calculations. The entrance hatch is always assumed open, as well as ventilation openings without closing means.

Lars

Lars
I will send you a copy of the spread sheet via Matteo - with some pessimistic values.
As you will see the STIX is 38.5 and the AVS is 137. The calculation formula for STIX is from the ISO Standard and the good approximation formula for AVS comes from the UK's Wolfson Centre (Southampton University). The Wolfson method was developed for the UK government following the 1979 Fastnet incident. The Wolfson method is known to slightly over value the AVS - I have adjusted this in the second calculation. Please feel free to comment - anyone else may also have a copy of the spreadsheet - but it is still in draft form.

Regards

David

David

Received the spreadsheet, thank you.

Will check your calculations, expect to report next week

Kind regards

Lars

Dear all
I will upload all my input figures this week and deliver a working spreadsheet the Matteo. It will then be possible for anyone who is interested to calculate the STIX for a S&S Swan.
Regards
David