VPP's and wave drag...

[dionysis]

Hi all,

I am in the process of developing a VPP for design purposes, and apart from the Havelock-Castles equations in Norwood's "High Speed Sailing", I can find little information on calculationg wave resistance for monohull sailing boats.

I like to be as exact as possible, so that changes to hull design are reflected in the vpp's results.

Am I forced into having to come to terms with partial differential equations, or is there a simpler way?

Cheers, and thanks in advance, dionysis.

[nico]

Hi,

For the wave resistance you should have a look at the Delft series. It is a regression of the tank testing of around 50 boats and includes effect of (LWL,Cp,LCB,...) . I think it is what you re looking for. it is available in the Chesapeake Sailing Yacht Symposium proceedings and/or Larsson books and several others. If no one is availble to you , a can email you the set of equations and coeficients.

Nico

[dionysis]

Thanks nico,

I have heard so much about this series, but have not been able to get my hands on it. Yes, your email would be much appreciated.

[Mike D]

Nico

Like dionysis I too would appreciate a copy of the Delft series.

Thanking you in advance

Michael

[nico]

Here it is

It is an excel spreadsheet

[dionysis]

much appreciated nico, will sit down and make a study of your spreadsheet. Thanks again

dionysis

[dionysis]

Hello nico,

Excellent spreadsheet, just some questions to clarify it's use:

On the data page:
for hull data : what does Tc, WA, T and form factor mean?

On the calc page:
1. What does Rv mean?, and in say, the formular Rv=Q4*hff, what does hff stand for?
2. What does the column Rresidual mean? Induced drag of hull, or wave drag?

Just two more questions:

I think the data: a0, a1,...a8 have to do with the 9 hull shapes of the delft series, but what do these represent? Do I need to know what they mean?

cheers dionysis

[nico]

Hi

Tc canoe body draught
WA waterplane area ( not wetted area)
T total draught

Rv is the viscous resistance ( frictionnal + pressure)
hff is hull form factor ( account for pressure resistance)
Rv = Rf * form factor ( Rf = Rfrictionnal)

You don't need to know what a0,a1... mean, they are the factor of the polynomial regression to get the residuary resistance (=wave resistance)


Nico

[dionysis]

thanks nico, I owe you one

dionysis

[MGLARRIBA]

Hi Nico

I have some information on the LARSON and ELIASSON formula to calculate residual resistance that i feel mest be wrong.

I have seen in an Excel sheet that you have offeres within this forum, that the third term, that says a2*LCB, comes with a minus (-) in my formula comes with a plus (+), can you confirm me the right one.

Also, can you tell me if the LCB dimension shown in the formula it's the position of the Center of Bouyancy as a percentage of the Lenght or it's an absolute value?, is it measured from the fore perpendicular or from the main frame in either of my previous question.

[nico]

hello,

In the paper LCB is a % value and = (Lcb/Lwl)-0.5 with absolute value of Lcb and Lwl. In the paper a lcb aft of midship is by convention negative, so i just changed sign to put it positive (to my own convention: lcb aft is positive). (-*-=+)

Nico

[MGLARRIBA]

Hi Nico:

Thank you for your comment

MGLARRIBA

[grob]

Does anyone know where I can get info on the Gerritsma drag calculation scheme?

[nico]

My spreadsheet actually uses the Delft series resistance scheme developed mainly by Prof. Gerristsma.
Several papers are at http://www.hiswasymposium.com/symposium_papers.asp

[dionysis]

Grob, thanks to Sorenfdk, go here:

http://www.hiswasymposium.com/symposium_papers.asp

There is a wealth of good info, but scroll down to the 1998 symposium papers and download 6- Approximation of the hydrodynamic forces on a saili...

It is a large 13 Mb pdf file, so I cannot attach it here. I think it is exactly what you want.