# Formula for percentage of old ships being empty space.

Discussion in 'Boat Design' started by Bishiba, Oct 14, 2023.

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1. Joined: Jun 2022
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### BishibaNew Member

So, I was here about a year ago before I began medical doctor school, and since then it's been quite busy. Had a few weeks of relative calmness (or I am procrastinating the studies, either which way). At the time I was asking for help with how to calculate lift and drag coefficients for sail boats. I was ultimately unable to implement ultra-realistic ways of doing it, but I did implement really good psuedo-realistic ways of calculating ship speed and acceleration, but it's stilla a work in progress.
Decent way of getting lift coefficient and drag coefficient for game design https://www.boatdesign.net/threads/decent-way-of-getting-lift-coefficient-and-drag-coefficient-for-game-design.67094/#post-930671

However, I have from the start been using a formula for calculating the weight of a ship which is based on the length of the ship excluding the bowsprit, the beam of the ship and the height of the ship excluding the masts multiplied by the wood density. Lastly I would multiply the value by an imagined number of actual wood in this volume. The value I chose was 0.2, or that it's 20% of wood in the volume. I doubt this is accurate, but I rather went above than below.

Yet, I've been trying today to get a more correct value, especially as the value will not be constant - bigger ships will have more empty space than smaller ships.

My calculations have born clearly inaccurate results.

Now, 39% of the HMS Victory is certainly not wood. I'd imagine, purely speculative, it would be closer to about 5-10%. But to get a value of 11 %, I need to remove 2,500,000 kg... Which, I mean, I doubt it weighs only 1,000,000 kg without cannons, masts, bowsprit etc.

So, I am now curious if anyone has a good curve or solution for what would give a realistic value for any size ship.

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### gonzoSenior Member

All you do is calculate the submerged volume and multiply it by the density of water.

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