Blanketing factor - VPP

Hi,

I am looking for modern values for upwind/downwind blanketing factor used in VPP.

Thanks for any help


Nico

 

Hi Nico,

There seems to be a paper regarding this subject by C.L. Poor. This is mentioned in Principles of Yacht design in the part regarding the calculation of sailforces using the HAZEN model.

I have been looking for this paper but have not yet found it. If you find this paper or other any study paper or calculation method covering the calculation of sail forces (more accurate than the HAZEN model) please let me know.

I hope that you or maybe somebody else on this forum will be more succesfull than i have been untill now.

regards,

 

Hi,

I never found the paper from C.L. Poor, if anyone knows where it can be found, thanks.
I have seen the paper from Hazen but there was nothing on the coefficients. This appear to be a subject not often talked about because in every paper talking about VPP or Sail coefficient, blanketing coefficient are shown in equations but no value or more data is given.

Nico.

 

I seem to remember from one of Marchaj's books that there is no suitable cross-sail interference effects (for upwind sailing especially). From my own experience, I have found that the Hazen model provides a very reasonable estimate of forces regardless of other effects.

One suggestion. In the Chesepeake Sailing Yacht Symposium (I think the 14th), there was a paper by Andrew Claughton which included lift and parasitic drag curves which are used in the IMS VPP.

-Jon

 

Hi Jon,

Thanks for your reply. Te paper you are mentioning is that also available online? If not is how can i get this paper or is it possible to mail a copy?
Does, in your experience, the information presented in this paper add more accuracy to the hazen model?

thanks

 

For a paper, check out this link:

http://wseweb.ew.usna.edu/nahl/csys/default.htm

This is the homepage for CSYS. You can order past proceedings from John Zseleczky, but I know they are also coming out with a cdrom with pdf versions of all proceedings ( I don't know if it is publically available yet ).

On the other hand, I have some of the same information on lift and parasitic drag coefficients on my site:

http://www.redcoopers.net

If you have the time, I would recommend downloading the full pdf file: the graphics are better. Otherwise, you can check out the section on VPPs. In figures 47 and 48 I have the coefficients of lift and drag. I would recommend just pulling the numbers from my chart.

-Jon

 

I realise this is already an Old thread but starting a new one with the same question does not make any sense.
Recently I have been looking for blanketing factors but unfortunately with no result at all. I am interested in blanketing factors for:

Main - Jib/ genoa
Main - Spinnakker

As far as I would expect there should be some formulea to calculate the blanketing factor for differend aparant wind angles.

Is there anybody with a solution or having practical experience how to adress this problem and account for blanketing when calculating sal forces?
How do for example the VPP's thake this in account there must be some documented solution I would expect.

Any help is much appreciated!