Overplating my narrowboat?

Question

I am currently overplating my 35 ft Springer Narrowboat

I have sat her on a 35 ft lenghth of 8mm plate by 6 ft 6 in wide.

I will then be welding on to the base for the full length of the boat on both sides 6mm plate approx 18 in wide.

Can anyone tell me how much deeper she will sit in the water when I crane her back in ?

Answer 1

The added weight will not displace much more water than it before. a mater of inches, or less. I assume the original hull was failing and your satisfied with the boat and so over plating makes sense.  Don't worry about it!

Answer 2

There really is no way to tell that untill you get it the way that you want it and put it in the water.

Answer 3

You can work it out.

You need to know the area at the current waterline.  If you assume that is a rectangle it will give you an idea but if you do it more precisely the answer will be better.  Presumably you know the weight of the plate?  if not then weigh another bit and work out the big bit's weight or calculate it fromt e dimensions and the density of steel - 8000Kg per cubic metre.  

The boat will sink lower until the weight of water displaced is the same as the weight you have added.  Water weighs 1Kg per litre, and as you know the area at the waterline, you can work out the depth the boat beeds to sink to displace that much water.

Of course there are a few assumptions.  Your area calculation for one, and the density of water for another, but it should be reasonably accurate.

from the info in your question:

Your big piece is 10.8 metres by 2m by 8mm = I make that 1.4 tonnes.  

the two side bits are 10.8*.5*.006 *8000= 250Kg each so the total weight you are adding is the best part of 2 tonnes.

If the boat was just a rectangle, then the area if the sides are straight is 21.6 metres squared.  2000Kg of water occupies 2000 x 1000cm3  so to get that  from the area, we end up with 9.26cm

I would say about 10 cm lower in the water.

Answer 4

about 4-6 inches.

it'll look better.

Springers have a fairly shallow draft anyway so it'l be no issue.