Vernacular voyaging canoe design

The length to overall beam ratio affects the wave drag between hulls.

 

P.S. Are you Belgian, or just living there? Any catamaran design forums en francais?

 

http://www.multihull.de/technik/catdimension.pdf

How to dimension a sailing catamaran? https://www.boatdesign.net/threads/how-to-dimension-a-sailing-catamaran.22274/

Catamaran drag rise at less than hull speed https://www.boatdesign.net/threads/catamaran-drag-rise-at-less-than-hull-speed.36179/


Catamaran Hulls - South Bay Simulations, Inc. http://www.panix.com/~brosen/catamarans.html

 

That simulation at S/L=0.2 -- how close is that to Neel 51 ama separation?

 

Neel 51 has an overall width of 29 ft. Eyeballing it, the spacing isn't proportional, but guess about 6 feet, if that? .2 would be what, 10.2 feet? No way in hell it's that much. 6/51 would give .11.

 

Neel 51 ---> Specs​

‘‘ - - - Overall length 51 ft

Overall width 29,18 ft
Draft 4,9 ft
Displacement 14 T
Self tacking staysail 332 sq ft
Furling genoa 760 sq ft
Battened gaff mainsail 1 039 sq ft
Inboard engine Volvo 75 hp sail drive
Freshwater 160 us gallons
Diesel 160 us gallons - - - - - - - ’’​

Maybe a good estimation of the S/L ratio can be made from this below deck floor plan....

click pic to enlarge​

And what could be the reason for the marked ama dents . . ? ?

 

This image actually gives a really good view of the wake generation from the rear. It actually matches the cfd renders pretty well, I think.

FWIW, the Neel has an average cruising speed of 10 knots, and 15-18 knots "when the wind picks up".

 

I was thinking that too, except I'm not sure that is representative of the waterline.

I think the dents may have to do with a change in the slope of the hull near the deck height. Not necessarily the vicinity we care about.

 

Yes, Belgian nationality, but I live in the Netherlands for some time now, but I often go back to visit my mother and to take care of the house and the garden.

My first language is Dutch, I speak read and write only very limited French, I do even better in Friesian, which I also manage only very limited . .

 

You could say that hare was neither here nor hair.
As to the Heel 51 indent, got no idea. But the whole boat is exceeding strange.

 

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!

 

of more interest I think is its minimum practical sailing wind speed.

 

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 would say the dent is just how they show a cabin top cut away view of the inside . The Horstman tristars are conoe design , on a 31' 4" overall width 19' 1" , the bulkhead,s are set at 8' 7 1/2" center line of ama at Designed W/L to center of center hull .

 

Ok, so here, I suppose, is a more specific scenario.

Given identical beam between hull centers, and given identical displacement, what is the difference in drag at various speeds between a catamaran of Length/Beam ratio of CL of 3.4 versus that of one with a Length/Beam ratio of CL of 2.2? I'm not sure whether to hold the beam of the individual hulls and/or the draft constant. It seems to me that if one held the beam for an individual hull constant, and increased the hull length, while keeping displacement constant, that would affect either the draft or the prismatic ratio?

So here are the numbers so far between the two cats, based on the spreadsheet Manfred.pech linked above:

12.2 meters for Cat #1, with a length to beam ratio (measured from centerline to centerline) of 3.4:1. Beam of one hull is 1.5m, beam between hull centers is 3.59m. Light loaded displacement is 9920 kg.

7.9 meters for Cat #2, with a length to beam ratio (measured centerline to centerline) of 2.2:1. Beam of one hull is 1.5m, beam between hull centers is 3.59m. Light loaded displacement is 9996 kg.

I had to mess with a few of the other numbers to get the displacements to match, namely the beam:draft ratio of the individual hull.

I'll let you all read the results for yourselves, partially because I didn't mess with the rigging or the rudders/centerboard, etc. because I haven't gotten that far yet.