Re: PSUBS Crush/Depth Calculator online

[Martin Sanderse <sanderse@interlog.com>]

Ray Keefer wrote:
> 
> Hi,
>         I like it. Very well done interface. I'll link to it from my web page.
>         A question I have is, the "Hull Length". Is the "Hull Length" the
> overall length of the hull or is it the distance between stiffener rings?
>         Maybe add a safety factor option. Like 1, 2, 3, ... x safety factor.
> So the crush depth and safe operating depth can be calculated.
>         You may want to note that these calculations are based on a cylindrical
> hull.
> Just some thoughts,

This is going to be good!

Well, you have to consider whether the ends are unstiffened or not too, and the 
tolerance for out of roundness.  If this is based on the program posted by O'Neil I 
recall it was for unstiffened cylinders with inbound ends. (like it would be if it had 
hemi-head ends)  Also, this assumes no through-hulls or other discontinuities, and 
discounts fatigue, corrosion allowance, local lifting loads, etc.

The ABS standards to do the same calculation are 15 pages long.  I made up a speadsheet 
to do the calculations once.  It took me 2 days since there were a lot of table lookups. 
 (@vlookup in Lotus)  In any case, the numbers ended up different than the O'Neil 
numbers by 25% or so.  What should perhaps be noted is that it would be a good 
preliminary guideline for initial stabilty, displacement and bouyancy calculations, but 
that final design should be done using ABS standards.

I can't emphasize enough how helpful this ABS book has been to me.  I'd recommend that 
everyone get it.

So, I would mention that no safety factors are included because it's the responsibility 
of the final designer to add those.  For this preliminary guess I'd suggest 1.5.  With 5 
it starts to add weight so ast you woun't get below 200 feet before you have to add 
bouyancy other than the hull volume.

-- 
Martin Sanderse
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