VPP Catamaran

hi everybody

I am a Naval architect student at the polytechnical institute of delft (www.inholland.nl) .
For my final year project I am designing a 17 meter cruising catamaran.
This catamaran has to be (glass/carbon/epoxy )semi custom build high performance luxury cruiser .
But we use maxsurf at school and their Velocity Prediction Program does not work for Catamaran . DOes anyboady know or have a VPP for catamaran because i could really use it .


Maurits Weyschede
Email : Weys@hotmail.com ,

 

VPPs do no more than equate a hydrodynamic and aerodynamic rig model. Hazen's Aerodynamic model is pretty typical, but for the hydrodynamic model you want to consider using Insel and Molland's work on catamaran resistance prediction. You might also want to contact Leo Lazauskas about the work he has been doing on multi-hulls.

There should be enough info around to write a VPP.

Tim B.

 

I'm sure Maurits has enough on his plate without having to write his own VPP.

Sorry, I can't help beyond asking "do you really need a VPP to do this work"?

 

download michlet at http://www.cyberiad.net/michlet.htm print the manual and you may want to read the rest of Leo's site also

 

a VPP does not need to be complex, if a particular angle and wind speed is needed, this can be done easily enough in excel. You just need to get the good algorithms. As Tim explained, Hazen's (or IMS) aerodynamic model works well enough. You should already have a fair idea how to estimate resistance for your boat, so the hydrodynamic part is almost done. This is a very good exercise to see how well you understand sail theory. And algorithm in commercial vpps won't be much better.
If you choose to pursue this route, i am sure a few people would be happy to help if any problems arises.

 

Leo's Michlet program (yipster's already posted the link) will give very good estimates of the drag on the hulls. Its output is easily read by all common spreadsheet programs. I haven't tried to model a heeling catamaran yet though.... not quite sure how that'd work.
It only deals with the hulls, but if you have a means of estimating the forces on the rig in a given wind condition, it should be a simple matter to combine the outputs (resistance curve known, sail power known, speed calculation becomes trivial). The question is, how accurate do you need to get.... slight gains in accuracy come at the cost of huge amounts of time and effort to account for all the fiddly little details.

 

I followed your advice i am making my own VPP , but the trouble is finding the right value's , for instance i only have 5 hazen'value's sail coefficients at 27 , 50,80,100,180 , does anybody know where i can find more of these?

 

It should be fine (for a first round) to interpolate between these values. The IMS coeffs might be a bit better.
You can also have a look at some java code at http://www.wb-sails.fi/news/SailPowerCalc/SailPowerCalc.htm#Results (check source code).

 

Catamaran VPP

Maurits
You can use Michlet for catamaran drag prediction. The software is available from this site:
http://www.cyberiad.net/michlet.htm
The user interface looks very clunky but the software is powerful and yields good results. Just takes a bit of reading to get used to it. There is an optimising function available called Godzilla that can determine the optimum spacing for catamaran hulls.

You can readily set up an Excel program with a goal seek macro using the Michlet data and your propulsion system data to do performance prediction.

Rick W.

 

Windesign, the VPP developed by the Wolfson Unit has a multihull function. I have never used it on multis, but seems to work well on monos.

 

The Michlet interface was designed for left-hand operation by slouching pirates. It is not meant for people who sit up straight because that's what they were told to do by the nuns at their gurly school.

 

Ohhhh Geez!

Please stop, Leo, you're knocking me off my chair, here.

This has to be some of the best material I have ever seen on the Boatdesign.net pages and that includes everything ever written by Doug Lord.

Seriously, though... great quip and it surely brightened my Friday in snowville.

Chris Ostlind

 

Left Handed Pirates

Leo
For the record I find Michlet very easy to use and it did not take me very long to pick it up so it is intuitive for left handed pirate types.

Sadly Apple and Microsoft have a lot to answer for in adding complexity to their software so we have user interfaces that appeal to other types (note I have avoided any politically incorrect references). This has set the expectation. If you do not have a few hundred megabytes dedicated to the user interface then it does not get a foot in the door for a lot of people.

By the way I have started my twelve boat. It is a product of Godzilla with a stability constraint. I have attached a rendering produced using FREE!SHIP. I have been working on a low centre of gravity drive unit for it.

Rick W.

 

I have some programs that are much more powerful than Michlet (e.g. they can calculate the dynamic sinkage and trim and other near-field effects of multihulls, hovercraft and SES) and that are about 300Kb in size. I tried adding a Windows graphic interface and it blew out to 5Mb, loaded slowly, and was a pig to debug. I ended up dumping the whole idea of a pretty interface and now I just use a text version. Professionals (e.g. the US navy and some other navies) have never complained that the code lacks a mouse-driven interface with lavender curlicues at the corners of every window. They are quite happy with a couple of columns of numbers in a text file.

Good luck with the floating needle!
Regards,
Leo.

 

What are you writing the interface in, Leo?

My experiences with writing GUIs have been good so far with QT. Small, light and multi-platform.

Tim B.