Can You Solve This?

[High6]

When a boat crosses an aquaduct does it increase the load on the bridge?

 

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[JohnK]

Great question.
I’d say (guess) no as long as the water the boat displaces can flow away.
If it was like a tank (locks either side of the bridge perhaps) then the weight on the bridge would increase.


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[TheQ]

Generally NO, the water displaced by the mass / weight of your boat, is the same weight as your boat.

 However, there is a slight increase in front of your boat as you push the water forward, and a slight decrease behind your boat as you leave a hole in the water..

[JanetAnne]

23 minutes ago, TheQ said:

Generally NO, the water displaced by the mass / weight of your boat, is the same weight as your boat.

Now I know what my bulldog weighs. They said, when he had his bath at the dog groomers the other day, that he had left a ton of water all over the floor 

 

[High6]

Thanks, JohnK, I kinda thought that although I am not an engineer. I didn't expect TheQ's reply, though, although that does seem to make sense.

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[Vaughan]

We recently discussed this in my thread entitled "the kick of the propellor" in the technical section.

But Archimedes got there before me -

EUREKA!

[High6]

We recently discussed this in my thread entitled "the kick of the propellor" in the technical section.
But Archimedes got there before me -
EUREKA!

Such a brilliant and informative topic - thank you. Recommend to anyone who hasn't read it yet.

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[tjg1677]

you can actually roughly calculate the weight of your boat using this method.

very roughly multiply length by beam by draft and deduct between 15-20 percent for the taper of the bow.

whatever this comes to as cubic metres will be roughly the weight of your boat.

i.e. GK is 12.6 x 3.6 x 0.33 =   less 15 percent = 12.43 or at 20 percent = 11.44. she actually weighs in at just a shade over 12 tonnes so I am told.

Archimedes principle at its simplest. Used to do this all the time in marine engineering when adding steelwork to a ship to enable recalculation of draft and stability curves. all interesting stuff...

when I replated the bottom of my narrowboat I put an extra 3 tonnes of steel in it, using the above method, I calculated the extra draft. when she was relaunched I was only 6mm out.

 

cheers

trev

[TheQ]

An Elysian 27,    8m length *2.8m width*0.6m draft*0.8 twenty percent off=10.7tons ish

An Elysian 27 weighs 2.6 tons....

[grendel]

does it have a deep keel?

[tjg1677]

I did say roughly and what i should have perhaps explained is that the draft used is the mean average depth from the waterline to the turn of the bilge / bottom, ignoring the keel........ 

[TheQ]

Sadly that means it still won't work as an Elysian has a V hull for the front half, and a flat -ish rear half with a beam coming out of the  bottom of the V to the bottom of the steering Gear. 

[Vaughan]

AHA!

1 hour ago, TheQ said:

Sadly that means it still won't work as an Elysian has a V hull for the front half, and a flat -ish rear half with a beam coming out of the  bottom of the V to the bottom of the steering Gear.

This is because the Elysian was designed as an offshore boat as well as river boat, so it is a semi-displacement hull.

This is probably why the formula won't work.