Design Hydrostatic Report

[Hector MacNeil]

Does the design hydrostatic report show the area, thickness and weight for both sides of the model, or just one side?

I have four fuel tanks, two on either side located in the sponsoons (Marvin). The total capacity is 92litres and taking the SG at 0.77 kg/litre this gives me a total weight of 0.07084 tonnes. Since I can’t add this mass directly I have to use the layer properties to simulate this condition, ie using thickness and density. I’ve tried several combinations but never end up with my total tonnage…….my brain is beginning to seize up!

I have the same problem with my twin batteries, one either side.

If I knew whether the design hydrostatics shows one or two sides it would at least narrow the unknowns.

[Jesus Cruz]

The design Hydrostatics report has a legend that clearly says “The following layer properties are calculated for both sides of the ship” is rigth above the table with the layer´s data.

So bottom line the data is for both sides of the ship. I supose you are using the free version because the loadcases extension allows you to include any weigth and the modelling tanks extension allows you to model any tank and use any percentage of fill for a loadcase.

Best regrads

[Hector MacNeil]

Thanks for the information.
I did actually read that sentence a while back, but when my totals looked wrong I started to have doubts.
So when you confirmed the sentence I looked again at the data and all I had to do was double the thickness and hey presto, my weights are exact.
Thanks.

[MICHAEL KERR]

I dont know if this will work its been a while since I fiddled with it, in layer properties tick the box under Symmetric next to your tank layer and untick Hydro, look at the wight window at the top to see if the weight doubles.

[Hector MacNeil]

Thanks Mike. It works just as you said.

At first glance the symmetric box is greyed out, but if you untick the hydrostatic first then you can click on the symmetric one. The area doubles and so does the weight. The VCG and LCG remain the same but the TCG changes to zero.

The problem is I don’t know what to do now. Do I leave my model with the hydrostatic box ticked or do I tick the symmetric box?

[MICHAEL KERR]

Hi Clansman,
as I said before its been a long time since I fiddled around in that area as I have the Tanks module and the Load Case module to do my tanks and balance the hull. I cant see why you need the hydro for your tanks as they are internal and they make up part of the overall displacement. What is important is the weight of the tanks, contents and their centre of gravity but with out the Load Case module you will have to balance your vessel mathematically.

[Hector MacNeil]

Hi Mike,

Thanks for the input.
So to recap, what you’re saying is that anything inside the hull, such as tanks, batteries, the cabin, the floor etc. doesn’t need the hydrostatic box ticked, just the symmetric one. That is provided the thickness and density are input.

As you can see I’m pretty much a layman as far as boat design is concerned, but I’m trying………

When I saw hydrostatic I assumed hydrostatic pressure exerted on the water by the boat. Since in reservoir engineering which was my forte, one calculated the hydrostatic pressure at the bottom of a wellbore with pipe and kill fluid in place.

Anyway, thank you kindly for the information and the patience.

[Author]

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