Vernacular voyaging canoe design

[Angélique]

Ha! My wife's a descendant of Friesians. Her Grandpa's a Cupery, and her Grandma's a something-sma. We met at a college in Michigan where all the names are either Dutch or Friesian. When I was taking a tour before I went, I asked about diversity, and they were very proud of being "only" 50% Dutch students. This is in 2004 in the US!

Grand Rapids ?

 

[dsigned]

Yeah. Calvin, although her family is from Wisconsin.

 

[Manfred.pech]

And/or what speed wind is needed to achieve various speeds. I'm interested in whether the wave interference drag limits its speed, and to what extent.

A lot of tests have been done concerning interference between catamaran hulls under various conditions. For instance here: http://mararchief.tudelft.nl/file/35511/ .
At low speeds there is not much increase in resistance. But at fr ~ 0.5 more than 30% depending on trim and sinkage. From my experience I would avoid too much gradient of curvature and reduce the wetted surface as much as possible. This can be done by hydrodynamic lift from an optimized waterflow around the hull. May be you can avoid the bow wave and stagnation point and the whole crap of whorls, vortices and eddies.

More:
http://www.maths.adelaide.edu.au/yvonne.stokes/Tuck/pdfiles/tuclaz.pdf

https://www.researchgate.net/publication/263925728_URANS_Simulation_of_Catamaran_Interference

catamaran interferences 30% drag - Google-Suche https://www.google.de/search?q=catamaran+interferences++30%25+drag&client=firefox-b&dcr=0&tbm=isch&imgil=KFvPAELRvckZQM%253A%253BLOOzR4LppJ640M%253Bhttp%25253A%25252F%25252Foffshoremechanics.asmedigitalcollection.asme.org%25252Farticle.aspx%25253Farticleid%2525253D1456674&source=iu&pf=m&fir=KFvPAELRvckZQM%253A%252CLOOzR4LppJ640M%252C_&usg=__EQezSYUhNUPXydLutavyN7F9Np4%3D&biw=1070&bih=588&ved=0ahUKEwiJwNCchJ3WAhWDvxQKHeWOAMIQyjcIMw&ei=AHS2WYnAPIP_UuWdgpAM#imgrc=KFvPAELRvckZQM:

 

[Angélique]

http://www.maths.adelaide.edu.au/yvonne.stokes/Tuck/pdfiles/tuclaz.pdf

If there are questions about this paper, then best invite [U]Leo[/U] to join the discussion I'll guess, since he's one of the authors . .

 

[dsigned]

Is there something I'm missing about calculating Froude number for a multihull? Getting a Froude number in the .5 range for even the "wide" cat using the dimensioning comes out to about 3 knots. A froude number of .80 seems to equate to about 5 knots? If that were true, it seems it would be over the hull interference "hump" in about 10 mph of wind, but that seems unlikely to me, so I'm assuming I've made an error somewhere.

 

[dsigned]

Looks like Bob Oram beat me to it:

Bob Oram Design | Welcome to my site https://www.boboramdesign.com/14rslim

 

[tspeer]

And/or what speed wind is needed to achieve various speeds. I'm interested in whether the wave interference drag limits its speed, and to what extent.

I think for most sailing catamarans, the beam is wide enough that there is little hydrodynamic interaction between the hulls. The shift of wetted area and buoyancy from one hull to the other due the heeling moment from the rig is likely to be more important to the performance than the interference between the hulls. John Shuttleworth discusses the change in wetted area with heeling moment in this article. If there is a significant hydrodynamic interaction, you'd need to take into account the displacement of each hull as a function of speed - it's not going to be a simple relationship. You'd need to use something like Michlet to make many runs at a variety of different loading conditions to see how the drag shakes out over the speed range. A velocity prediction program (VPP) would also be quite useful for solving for the equilibrium loading conditions.

As for the beam/length ratio to balance longitudinal, lateral and diagonal stability, John Shuttleworth also addresses this through his stability indices. I highly recommend his article on Multihull Design Considerations for Seaworthiness.