Anomaly in longitudinal buoyancy distribution curve

I have a strange anomaly in longitudinal buoyancy distribution curve where it all looks reasonable until the stern platform immerses, at which point the area at one point drops to zero.
This is in the only appendage which does not have evenly spaced frames. Could this be a factor?

( I tried moving the intermediate frame to give equal spacing and the anomaly remains. It is also apparent when the appendage upper surface partially immerses due to trim)

I also tried with the demo barge. It has the same problem: When the draught is greater than the freeboard for an appendage, there is a sudden drop of area produced for the second frame of the submerged appendage, then the area jumps back up to what looks like a reasonable value. Try loading the simple wedge hull and running longitudinal area for draught 6m and 6.1m to see what I mean.
The trawler model shows similar effects. if you run a draft that is deeper than the main body portion, there are spikes in the area curve that look like they may be related to the intersection of the waterplane with the top surface of the appendage/hull. if there are two intersections there will be two spikes, not neccessarily of the same magnitude.
Further investigation shows that the volume and displacement curves (and any other curves using volume and displacement as a factor) have anomalous jogs where the waterplane is above the appendage. There seems to be a bug affecting area integration where the waterplane is at or above the top of the appendage


Hi Peter,

You are correct and thought I had caught this bug in the latest release I am working on just now but it is only partially solved.

Am looking into it. All registered users get an email updating them when a new version is released. If you are not a registered user, drop me a line with your email address so I can keep you posted.

Many thanks for your feedback,


Site Admin
email - info_at_naval-architecture_dot_co_dot_uk

E-mail address

Hi John,
I have e-mailed you with my address.