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Old 12-12-2016, 03:38 PM   #46
waddenkruiser
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City: Southern Baltic
Country: Europe
Vessel Name: Sømarken
Vessel Model: AMS 40'
Join Date: Jul 2012
Posts: 187
Nordig Tug 37 stability

There is a lot of generic information available about boat stability. One I found very handy and which describes the basic rules and aspects to be considered is here:
http://www.fao.org/3/a-i0625e.pdf

However I wasn't able to find a specific stability curve for our boat (what a pity for an engineer like me). But which additional value would I gain with such a curve describing only the static stability? In practice the dynamic stability gives the limit!
What we really have to avoid is periodic roll and are braking waves equal to or higher than our beam ...

Most of our trawler yacht hulls have an AVS (heeling angle of vanishing stability) quite below 90 while flooding starts already at a heel angle which is typically in the range of 50 (or even lower). And we know that most of our hulls are reasonably stiff (e.g. roll Eigenperiod in seconds is typically lower than beam in meter), i.e. they have a reasonable metacentric height.
If you really want to you can calculate the metacentric height of your boat based on the results of a heel test (performed at your dock) and correlate this with your roll Eigenperiod measured at the same time.
Doing so you would be able later to check whether metacentric height / roll Eigenperiod have been influenced negatively due to a changed weight distribution, a new heavy antenna in the mast top, ice on deck, added heavy load on the cabin roof or whatever.
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best regards / med venlig hilsen
Wadden
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