Cat draft

Discussion in 'Boat Design' started by Saqa, Dec 28, 2014.

1. Joined: Jun 2011
Posts: 2,479
Likes: 136, Points: 73, Legacy Rep: 693
Location: australia

groperSenior Member

The software is leading you up the garden path. A single hull displacement at given draft = 1000lb. Then 2 identical hulls at same draft will give you 2000lb.

If you can't figure out the software settings, just work that part manually and use the software for it's other functions. Or use better software...

2. Joined: Jan 2006
Posts: 2,445
Likes: 178, Points: 73, Legacy Rep: 871
Location: Australia

waikikinSenior Member

Not trying to lead you down the Luddite path but I'd tend to do preliminary stuff on graph paper with a pencil using the grid as a metric representative of a decimetre... every 100mm box equals a liter, you can apply a multiplier(x 1.025) for salt water but hardly worth it, for volumes use trapezoidal rule as cats are pretty straight- it just averages your end areas from station to station- for these you can count the squares & part squares on the paper- say 0.25, 0.5, 0.75. Just feels tangible & real to me.
Jeff.

3. Joined: Oct 2004
Posts: 307
Likes: 16, Points: 18, Legacy Rep: 202

TimothySenior Member

In some 3D software if you mirror an object it will measure as a negative of the other part . If this part is a component of other parts in a complete model then the volume calculations will be wrong.

4. Joined: Oct 2013
Posts: 681
Likes: 18, Points: 18, Legacy Rep: 75
Location: Hervey Bay

SaqaSenior Member

I have come to the understanding that if just the single hull sits fine then if I pair it I wont get any worse draft in the real world

I have started another thread
http://www.boatdesign.net/forums/boat-design/cat-draft-2-a-52182.html

Here I have drawn identical single and paired and posted screen shots as well as cad files. I will appreciate it if you guys could take a gander and see if I am missing something about cat mode or looking at a bug. I will also forward that link to the software developer, maybe its a bug they haven't caught

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.