Resistance - Racing yacht

Hi,
I m trying to find out which is the resistance prediction method the most accurate to use for a fast racing sailng yacht. What about planning for this type of hull?
Would appreciate if someone could share his experience in this topic

 

Question is too broad. You need to at least define the hull type and size so we can point you in the right direction.

 

Hi jehardiman,thanks for Your reply!
The boat is 10m long..the hull is something in between pogo30 and Xp33(so not purely racing)..
I would like to use Maxsurf Hullspeed for the calculations if it might help..
should i specify st more?
thanks again

 

anybody?

 

The hullform you asked for is not in the Delft Systematic Yacht series. Though there are other ways to estimate using available data (such as evaluating on the sailing hull form vice the total hull form), and that I'm willing to bet that somebody has paid for some hydro work (see the Open 60 and other works), it appears that there is not much data in the available literature.

Seems like a graduate paper looking for an author.

 

Hi Jehardiman, thanks so much for your reply..
This is ecxactly what i was afraid off..
Do you think that i could use the Delft series at least aproximately? considering that anyway for the classic hull the resistance was much higher then for my 'performance' hull of the same size..or the results im getting are totaly mistaken?
Do you know if the slender body type approach can have some applicability for this design? (in the manual of Maxsurf's Hullspeed for exemple the wave patern of a sailing yacht is calculated with this method)..
thanks again for sharing your opinion and knowledge!!

 

skey, about the accuracy of Delft polynomials, this is extracted from "Sail Yacht Design: Theory" by Claughton

http://www.amazon.com/Sailing-Yacht-Design-A-Claughton/dp/0582368561

According to it, some kind of hulls (like this rather old BOC hull) that are off the DSYHS limits, still correlate very well with measured data.

 

Thanks quequen

 

For high-end racing yachts with new hullforms, full 3D multiphase CFD simulations are used to analyze and optimize the hull shape, then scale models are built and tested to validate the simulation results. This is not cheap, but it is highly effective.

For a lot of more accessible yachts, much more classic, analyzed hulls are used most of the time, with minor variations. Sometimes major variations are made, based only on the designer's physical intuition when it comes to drag.

And everything in between.

Outside of many specific shapes, there are no methods that are accessible to the non-expert. The Maxsurf features you reference are based on Delft systematic yacht series and various other shapes for power boats. If your hull doesn't look like the Delft yacht hulls, then the method isn't valid and its results may be slightly or greatly wrong for your case.

 

Thanks Mike..this is what i was afraid off..but was hoping that maybe for an apoximate optimization exists some way in the middle, not necessarly CFD aplication or the tank tests..
In this case what about Vpp?For hight performance boats seems i cannot rely on it neither?

 

There are lower-fidelity codes using simplified methods instead of full, 3D CFD. These tend to work okay for low-speed vessels, worse for high-speed craft. It's usually a bad idea to use them if you don't understand them very well.

I am not too familiar with the various VPPs out there, but I know that at least some of them use the Delft series to predict resistance. This may or may not be super-kosher of them.

What's your goal? Are you hoping to build a boat of your own novel design? Are you hoping to do this with no model tests?

 

Hi Mike,
let's say that yes, i m going to make my own project, and it should be 'buildable'.. my only concern is if this boat is going to be reasonably fast (without tank testing).. i modeled already the hull and was comparing it in maxsurf hullspeed with some designs of really nice racing yachts..seems to be quite good..just as you said 'results may be slightly or greatly wrong' in this case well, i m already reconciled with the fact that i won't make a winning racing boat before i will get in touch with CFD, but hope it's gonna be at least an average one any tips?

 

skey, this thread coud be of interest for you:

http://www.boatdesign.net/forums/hy...resistance-changes-help-47580.html#post638619

there you'll find many spreadsheets about hull resistance according to different Delft series, ORC 2011 and ORC 2013. These tools are useful to glimpse the potential performance of your hull and (to a lesser extent) appendages design, at least in comparisson whit other existent designs.

VPP is a wide scope tool, that involves aero and hydro models interaction, so as Mike states, you must know it very well to use it as a hull design tool. If you want to try some of them by free, use 06-VPP by Paul Kotzebue. It uses formulae from "PYD" (Larsson, Eliasson) 3dt edd. so it's the best documented one! moreover, it's in excell so you can modify it, add charts etc.

 

I know this thread's a bit dusty, but... there are a LOT of variables which go into predicting how fast a vessel will be. One needs to quantify under what sort of sea & sailing conditions are "on the table". Flat water bouy race, best design for average conditions encountered in a round the world race, & a bunch of other factors numbering in the 2 to 3 digit range.
That said, the best bet might be some version of VPP software, in addition to comparing the design in question to similar vessels already out there, & their performance.

 

tow test

If you have access to one or more similar hulls you can directly measure the hull's resistance with a simple tow test. I have found this very useful for injecting some reality into modeling work. The scale I used cost about $30 on Amazon. There is a picture of the scale and the results of one test at:

https://sites.google.com/site/sailcfd/home/boat-speed-calibration