15/9/10

Business Name

Drop Weights

The drop weights are supposed to be 56 inches long and weigh 150lb.  Due to the alternative fitting of the battery pod ends, the standard weights shown on the plans will not fit.  The sealing rings for the pods are in the way.  So I had to resize the weights to be shorter but still at the required 150lb weight. 

 

The website is also for my own reference so I can remember how I did things, so here is how I calculated the size of the new weights.

 

First, I calculated the volume and weight of the “standard” weight.

 

Changing everything in metric and using CM as the units.

 

Using the formula for the area of a trapezoid ˝(A+B)h

 

Cross sectional area.  ˝(4+9)6.5 = 42.25cm2

Multiply by length to get volume. 42.25 x 142.24 = 6009.64cm3

=6KG or 13.22lb

Multiply by specific gravity of lead (11.34)

6 x 11.34 = 68.04KG or 150lb

 

Next I experimented by adjusting the lengths of A,B and h until I got more or less the same volume for my shortened length which is 127cm.

 

Cross sectional area.  ˝(4+9.5)7.3 = 49.275cm2

Multiply by length to get volume. 49.275 x 127 = 6257.925cm3

=6.25KG or 13.77lb

Multiply by specific gravity of lead (11.34)

6.25 x 11.34 = 70.88KG or 156lb

 

I know it calculates out slightly heavier, but hopefully that will take into account the slope at the front of the weight, the steel insert and any less than perfect fills which haven't been calculated for.  If they do end up a bit to heavy, I don't think it would matter and I can always drill or shave some material off.  Much easier to remove material after than try to add it on.

 

Anyway, I think that’s going to be ok.  Adding the additional volume to the weights only meant having to increase the height of the weights by 8mm.  Not too much difference.

 

I hope this adjustment of weight distribution won’t upset the trim of the sub to much.

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