How much does a narrowboat weigh?

[rusty69]

9 hours ago, Mike the Boilerman said:

 

Again, I ask you to point out where the error in my calculation lies.

I suggest you can't, and your list above is just blokes willy-waving. Blokes love to claim their boats are heavier than they actually are, as we all well know.

I've never tried to weigh my willy, but haven't had a bath in years. 

[frahkn]

10 hours ago, ditchcrawler said:

My boat weighs around 18 ton from calculation and crane weight, its about 28" at the stern and 24" at the bows and 57 ft overall

Mine says 22 tons in the builder's (Orion) paperwork and weighed 23 on the crane. It is 70' but a tug so less cabin than most. It has a modern engine not a heavy lump. Draws 28" at the front and 31" under the skeg.

[Machpoint005]

There's a great deal to be said for a consistent system of units.

[MtB]

On 05/06/2017 at 09:08, frahkn said:

Mine says 22 tons in the builder's (Orion) paperwork and weighed 23 on the crane. It is 70' but a tug so less cabin than most. It has a modern engine not a heavy lump. Draws 28" at the front and 31" under the skeg.

 

My point exactly. Archimedes would ask how can a boat 12 ft shorter and drawing 30% less than yours also weigh 22 tonnes?

Actually he wouldn't ask. He would say it doesn't.

[mross]

17 hours ago, Murflynn said:

or, to put it another way, the word 'tonnage' in use today to define the size of a ship is misused.  The correct word is 'tunnage', which quantifies the number of tuns a ship could carry in its cargo hold.  A tun was a standard sized barrel used as a container in medieval times.

This is outdated.  Merchant ships are measured in Gross Tonnage, no longer Gross Registered Tonnage.  Gross Tonnage is a measure of the volume of a ship, measured to the outside of the hull. As a 'rule of thumb' the ship's weight will be about half it's Gross Tonnage.  Newspapers always get this wrong.  QE2, for example, has a Gross Tonnage of 70,327.  But if it had weighed that much it would have sunk rapidly.  She displaced 48,923 fully laden and this is a true measure of her weight (albeit calculated by inclining).

[Murflynn]

this discussion could have been avoided if post #2 had read ....................... "as much as the water that it displaces".  

 

.............  coat 

[ditchcrawler]

16 hours ago, Mike the Boilerman said:

 

Again, I ask you to point out where the error in my calculation lies.

I suggest you can't, and your list above is just blokes willy-waving. Blokes love to claim their boats are heavier than they actually are, as we all well know.

No one has mentioned Plimsoll Lines yet  http://oceanservice.noaa.gov/facts/plimsoll-line.html

There is no error in your calculations but we don't know what raw data we should be using, length of swims, boat draught will have an effect.

[howardang]

4 minutes ago, ditchcrawler said:

No one has mentioned Plimsoll Lines yet  http://oceanservice.noaa.gov/facts/plimsoll-line.html

 

Tropical Fresh or Winter North Atlantic etc don't have great relevance on the cut!

Howard

[Scholar Gypsy]

20 hours ago, Mike the Boilerman said:

 

At first sight I'd have expected some factor to take into account the viscosity of the water but on reflection, it probably cancels itself out.

The one thing I'm not sure about is the thrust. You started with a bollard thrust of 50Kg and it looks to me from your notes as though this was assumed to be a constant force during the acceleration. It isn't. The prop thrust reduces as the speed of the boat increases, assuming your instructions were to leave the throttle setting alone. This would, I think, lead to an overestimation of the mass accelerating and stopping.

Somehow this feels rather basic though, and I imagine your friend took it into account. I just can't see how though.

When the boat is accelerating, T-D = ma  where D is the drag (which will vary with speed and will be affected by viscosity, shape of the channel etc)

And then when decelerating D = md, and so T = m (a+d) - just add the two equations together.  One would need to add the factor g if T is measured in Newtons. (1 kg of mass weighs 9.81 N, although most scales will express a force in kg, which is strictly speaking a unit of mass not of force!).

This result is true at each speed, so then as you note one has to assume that T is constant.

a, d and D will also vary with speed and so one is estimating average values of a and d. There are several ways of estimating them from timing when the boat passes the various markers.

Another experiment would be to hit the stationery boat with a large sledgehammer, and observe the speed at which it moves, or (more practical) hit it 1with a narrowboat of known mass and speed and then measure the speeds (velocities) of the two boats after the collision. The principle of conservation of energy would then enable to work out the mass of your boat.

PS One has to assume no wind, and no current!

[matty40s]

2 widebeams out today, 10ft x61ft and 12 ft x 60 ft. The first was 22tonnes, the second 32. 

[mark99]

3 hours ago, matty40s said:

2 widebeams out today, 10ft x61ft and 12 ft x 60 ft. The first was 22tonnes, the second 32. 

Can you keep em out?

[Murflynn]

during water shortages they should be encouraged because they displace so much of it.

 

.......................  of course not needed this week.  

[sharpness]

23 hours ago, Mike the Boilerman said:

 

Again, I ask you to point out where the error in my calculation lies.

I suggest you can't, and your list above is just blokes willy-waving. Blokes love to claim their boats are heavier than they actually are, as we all well know.

I would suggest that there is no error in your maths but that your estimation of the average draft is incorrect. The draft on the stem post may be 350mm but go back 6ft & it is much deeper because, on mine anyway, the base plate curves upwards.

Steve

[nb Innisfree]

I lost count of the times I punched the calculator keys to find the weight of Innisfree, I went into the utmost  detail in finding the displacement allowing for hull sides that we're out of square with the bottom plate,  took account of swim and bow shape, measured draught over and over again at different points. 

Kept coming up with 18.5 tons {60' Narrowboat fully fitted out and complete with all tools and full tanks etc) 

[Scholar Gypsy]

My fuel tank is an easier calculation: 170 litres.

[Boat&Bikes]

7 minutes ago, nb Innisfree said:

I lost count of the times I punched the calculator keys to find the weight of Innisfree, I went into the utmost  detail in finding the displacement allowing for hull sides that we're out of square with the bottom plate,  took account of swim and bow shape, measured draught over and over again at different points. 

Kept coming up with 18.5 tons {60' Narrowboat fully fitted out and complete with all tools and full tanks etc) 

17.4 for mine..58 footer. Interestingly I worked out the steel plate only as weighing around 10 ton. 

[MtB]

1 hour ago, nb Innisfree said:

I lost count of the times I punched the calculator keys to find the weight of Innisfree, I went into the utmost  detail in finding the displacement allowing for hull sides that we're out of square with the bottom plate,  took account of swim and bow shape, measured draught over and over again at different points. 

Kept coming up with 18.5 tons {60' Narrowboat fully fitted out and complete with all tools and full tanks etc) 

 

What draft is your bote?

And is it trad, or cruiser stern?

[dor]

Quote

 

17.4 for mine..58 footer. Interestingly I worked out the steel plate only as weighing around 10 ton. 

Kept coming up with 18.5 tons {60' Narrowboat fully fitted out and complete with all tools and full tanks etc) 

 

So,. Roughly one tonne per metre ... .

[Boat&Bikes]

25 minutes ago, dor said:

So,. Roughly one tonne per metre ... .

Well 2 metres wide X .5 deep is a tonne. As you and most people here seem to accept. Ian. 

[ditchcrawler]

4 hours ago, ianali said:

17.4 for mine..58 footer. Interestingly I worked out the steel plate only as weighing around 10 ton. 

I think that was about what mine weighed when the hull was delivered, it may have even been slightly less I can't remember exactly

 

[nb Innisfree]

19 hours ago, ianali said:

17.4 for mine..58 footer. Interestingly I worked out the steel plate only as weighing around 10 ton. 

Sounds right, I came up with 10.5 ton

18 hours ago, Mike the Boilerman said:

 

What draft is your bote?

And is it trad, or cruiser stern?

Was my boat. 

Cruiser stern and about 22" average draught IIRCC,  it was a few years ago now and exact details are starting to leak out of my head. 

[JohnEW2912]

For what it's worth we had our boat on the back of a lorry in late April - it was 18 tons for a 58' Tim Tyler hull fully fitted with empty water tank and maybe 1/3rd full fuel tank.

[Alan de Enfield]

18 minutes ago, John Wareing said:

For what it's worth we had our boat on the back of a lorry in late April - it was 18 tons for a 58' Tim Tyler hull fully fitted with empty water tank and maybe 1/3rd full fuel tank.

Very similar to all other 58-60 footers then.

Presumably the draft was a fair bit more than 14"

[hansd]

On 04/06/2017 at 12:38, Scholar Gypsy said:

The precise density of water here. So at 10 deg C it's 999.7 kg per cubic metre.

http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

[And strictly speaking kg and tonnes are measurements of mass, not weight. So the weight of your boat will vary according to  where you are - at least six different effects described here:

http://geol-amu.org/notes/m10-1-1.htm

 

hey, if you want more precise calculate about density of water you can use this one density of water converter

Edited May 26, 2021 by hansd

[ditchcrawler]

5 minutes ago, hansd said:

hey, if you want more precise calculate about density of water you can use this one 

On his way