I recently heard a great sermon about the miracle that Jesus performed on the Sea of Galilee in the presence of Simon-Peter and other fishermen.  According to the story, they caught so many fish that their two boats almost sank.  I personally find the story believable, but I’ve often wondered how many fish would someone have to catch for their boat to almost capsize?  As Christians we often talk about how we serve a God of miracles. Yet, I don’t think we give much thought to how utterly amazing some of them actually were, and what it must have been like to actually witness this event in person.

Call me a dork if you like, but the scientific, left-brained side of me kicked in and I started pondering if there was any way to estimate how many fish were actually caught that day?  I’m not sure if anyone has ever attempted this before, but I figured it was worth a try.  To my surprise, the details in the story combined with archeological findings near the Sea of Galilee in the last few decades made getting a reasonable estimate possible. Thinking back to my classical physics training I knew that the keys to solving the problem would be finding a reasonable estimate of the boat size, the boat volume, and the boat weight.  Luckily, I was able to research and find some rough estimates for all three questions.  I figured that if I could get a reasonable estimate of all three, than I could back-calculate the number of fish caught using the laws of buoyancy (Archimedes principle).  One of the other main keys to the story was knowing that the boat almost capsized due to the huge catch.  When a boat is stuck in a state where it could either sink or float with added or decreased weight it’s referred to as neutral buoyancy.

So here’s the bottom line: If you combine current archeological understanding of boat sizes during Jesus time with the laws of buoyancy, then it turns out that almost 5,000 lbs of fish jumped into their boats.

So for those interested here’s the math behind the estimate………

Boat Dimensions:

In 1986 an archeological find discovered a boat believed to have been a typical fishing vessel at the time of Jesus[1].  The boat size was approximately 27 ft long x 7 ft wide x 4 ft deep (estimated depth).  Since, I didn’t have the internal boat dimensions or a scale model of the boat’s external body dimensions I slimmed it down to only include the space that I figured was free within the boat, after nets, fishermen, and other items.

20ft long x 5ft wide x 4 ft deep *
* This a very conservative estimate
.

Volume of the Boat:

Volume inside of boat = 20ft x 5ft x 3ft = 300 cubic ft

Boat Weight:

Density of Water = 1000 kg/cubic meter

1meter = 3.28 ft

So, 1cubic meter = 35.29 cubic ft

1kg = 2.204 lbs

Therefore………..

Density of Water (lbs/cu ft) = 1000 kg/cubic meter * cubic meter/35.29 cu ft * 2.204 lbs/kg = 62.45 (lbs/cu ft)

Neutral Buoyancy:

Neutral buoyancy means that the boat is literally teetering on the verge of sinking or floating, meaning that the buoyant forces are perfectly equal with the weight of the boat and the contents inside of it.  That basically means that the Total weight of boat = Weight of water that the full boat body displaces.


Total weight of boat

Total weight of boat = Weight of empty boat + Weight of fishermen + Weight of fish

Weight of boat = 10,000 lbs (estimated from similar sized wooden boats)

Weight of fishermen = 15 men (max boat capacity) * 200 lbs/fishermen = 3000 lbs

Weight of water that the full boat body displaces

Weight of water that full boat body displaces = Volume of boat x density of water

Weight of water that full boat body displaces = 300 cu ft x 62.45 lbs/cu ft = 18,000 lbs(approximate)

 

Total weight of boat = Weight of water that the full boat body displaces.

10,000 lbs + 3000 lbs + Weight of Fish = 18,000 lbs

Weight of Fish = 5,000 lbs

That’s alot of fish!  Stay tuned for Part 2………..

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