Performance 40 vs 38

Hi!

Looking at tall rig versions of the Swan 40 and Swan 38, the measurements are similar, but naturally the hull shapes are different. The polar diagrams indicate that the Swan 40 is the quicker of the two. Can anyone provide information on performance of the 40 vs 38 under sail? Also, if anyone has information on performance of other swans that have different hull shapes, but similar rig measurements, I would eagerly like to know about those.

Cheers,

niklas

Niklas
The main particulars show that the 40 is a little narrower, but has more ballast to compensate, and slightly more sail area, as P is 0.75 ft longer.
The speed differences can be expected to be rather small, and may in practice be hidden by good or bad sails, or more or less skill. I would therefore suggest a scientific approach, i.e. using IMS as a gauge. This rating system has been developed particularly for this purpose.
It would be helpful to analyze IMS or ORCi certificates for both models, with the correct rig lengths and issued the same year. Unfortunately I do not have certificates for the 40, but could make a comparison if some are found.
IMS is the most scientific speed prediction available, and is based on full measurement of the hull as well as stability measurement.
The same approach is suggested for the comparison of other models, for example Swan 47 and Swan 48 have dimensions which are fairly close. Also variations of the same model can be evaluated in this way
Best regards
Lars

Lars,

Thank you for your quick and accurate reply. This would be very interesting. Does anyone have IMS certificates for the Swan 40. Also, comparison of the other models with similar values would be very interesting.

Cheers,

niklas

Lars,

I have IMS rating certificates from 1990, 1992 and 1993 for my S&S Swan 40 Sunniva V (hull #36). If you are interested I can send you a copy.

Leif

40 vs 38. Too many variables to make a statement. Lars was absolutely right as always. They are very close. It depends on

quality of the sailor
quality of sails
how clean the bottom is
Large scientific debate here... smooth like a dolphin or sandpaper like a shark... laminar flow or trapped boundary layer.. then one needs to think about interaction with turbulence in waves and.....
propellor ( effects boat speed as well as pointing)
sea conditions.
crew... mine gets seasick.
How hard you want to push the boat, yourself and the crew. Crew probably the most important variable!


Smooth seas
Storm Svale

Leif
Thank you for your kind proposal. I would appreciate copy of the 1993 certificate, but unfortunately it is not helpful for this comparison as your yacht does not have the tall rig with I =15.54. I will try to find a tall rig certificate elsewhere.
Best regards
Lars

Hi,
Does anyone have a polar diagram for a Swan 38?

Patrick Lund
"Splash" 38/108

Thank you for all the replies. I am aware that there are variables not linked to the hull, that are affecting boat speed. However, I would like to eliminate those from the current discussion.
I am curious on the boat design and what kind of an effect a few years of thought and influence of rules have on the performance of these boats. I suppose both the 38 and 40 are equally seaworthy in any case, or does anyone have an opinion that. I can't wait what Lars will come up with as regards to the analysis.

Cheers,
niklas

Leif
Unable to find a tall rig Swan 40 certificate, pls send copy of yours. The influence of the rig extension then has to be estimated, and this creates some uncertainty.
Best regards
Lars

Patrick
Pls have a look at this thread
Best regards
Lars
http://www.classicswan.org/forum/post_thread.php?thread=655

Niklas
At last the comparison between the tall rig Swan 38 and Swan 40.
According to IMS the GPH (General Purpose Handicap) for the 38 is 3.5 seconds lower, that means she can generally be expected to be that much faster. The GPH does not, however, indicate the strong and weak points for each model, for this additional evaluations are needed.
The differences on specific courses can be calculated accurately based on the certificate information. Here 3 examples - on the wind, off the wind, and reaching at 110 deg true, all over one mile. The base boat is at zero level on the diagram, and when the other boat is above zero she uses more time.
Questions?
Best regards
Lars

Lars,
Thank you very much for your effort. This is indeed very interesting. Will dig into this.

Best regards,
niklas

Dear All,

in the meantime some owners of S&S Swan 38 and of S&S Swan 40 meet on the the Danish harbour "Høruphavn" (54°54,4' N 009° 53,4' E).
The S&S Swan Association Member's boats were:
38/058 Kalliope
38/069 Carissima
38/113 Toge
38/010 Limaremca
38/094 Thyros
40/028 Storm Svale
40/008 Ophelia

what a meeting!

Fair winds!

matteo (38/067 Only You)

Lars,

Hi,

During winter months it would be nice to do some research. As the owner of Swan 40, Becca, I am very interested in a polar diagram and IMS certificate. Read that you Leif have some. Would be really nice!

all the good from a rainy Netherlands

Dear jollinglodema

Hi,

Please find as attachment IMS certificate issued 1993 and polar diagram for my S&S Swan 40  Sunniva V

Best regards,

Leif Hambraeus

Hi Leif,

Thank you very much. Realy kind your share this! I will import in the IOS app IRegatta. Very interesting tool!

Thnx!!

O Leif,

Have a bit of a problem with resolution of the diagram. Cannot read the numbers of the second diagram very well. Do hav a bit higher res?

Maybe mail is better: jolling65@gmail.com

Thnx! Jolling