What does my 68ft narrowboat weigh?

[MtB]

We have just done a deal to buy a 68ft tug style built by Charlie Cox, and we'll be transporting it down here by road. We'll need to have it lifted off the lorry and into the water at this end and the marina have just asked us how much it weighs. Apparently their crane has a max lift weight of 16 tons. Or maybe 18 tons at a push (to quote the office bod). Or maybe he means tonnes. Are crane lift capacities quoted in metric or imperial these days?

 

Thing is, I don't know how much it weighs. I'm sure the vendor would give us a figure if I ask, but how would HE know, other than by Chinese whispers from the people HE bought it from?? This could be embarrassing and expensive if the boat turns out to be too heavy for the crane. What are the chances of an 18 ton (or tonne) crane lifting a 68ft boat? My own fag packet calculation of the displacement of the boat based on draft, width and length is about 16 cubic metres of water. 16 tonnes. Not much margn for error!

 

Cheers, Mike

[Guest]

We have just done a deal to buy a 68ft tug style built by Charlie Cox, and we'll be transporting it down here by road. We'll need to have it lifted off the lorry and into the water at this end and the marina have just asked us how much it weighs. Apparently their crane has a max lift weight of 16 tons. Or maybe 18 tons at a push (to quote the office bod). Or maybe he means tonnes. Are crane lift capacities quoted in metric or imperial these days?

 

Thing is, I don't know how much it weighs. I'm sure the vendor would give us a figure if I ask, but how would HE know, other than by Chinese whispers from the people HE bought it from?? This could be embarrassing and expensive if the boat turns out to be too heavy for the crane. What are the chances of an 18 ton (or tonne) crane lifting a 68ft boat? My own fag packet calculation of the displacement of the boat based on draft, width and length is about 16 cubic metres of water. 16 tonnes. Not much margn for error!

 

Cheers, Mike

Depends on many factors, but I think it will be a close call. An empty fuel/water/pumpout could make a significant difference. I could reduce my boat by half a ton if I removed SWMBO's shoes

[johnthebridge]

We have just done a deal to buy a 68ft tug style built by Charlie Cox, and we'll be transporting it down here by road. We'll need to have it lifted off the lorry and into the water at this end and the marina have just asked us how much it weighs. Apparently their crane has a max lift weight of 16 tons. Or maybe 18 tons at a push (to quote the office bod). Or maybe he means tonnes. Are crane lift capacities quoted in metric or imperial these days?

 

Thing is, I don't know how much it weighs. I'm sure the vendor would give us a figure if I ask, but how would HE know, other than by Chinese whispers from the people HE bought it from?? This could be embarrassing and expensive if the boat turns out to be too heavy for the crane. What are the chances of an 18 ton (or tonne) crane lifting a 68ft boat? My own fag packet calculation of the displacement of the boat based on draft, width and length is about 16 cubic metres of water. 16 tonnes. Not much margn for error!

 

Cheers, Mike

Mike-you're probably not far off with your calculation, but what would worry me more is this marina's apparently slap-happy method of describing their crane. 16 tons? 18 tons? All cranes should be certificated for lifting maximum weight. I would not want to have any boat of mine lifted by these people. Remember too that reach of jib, and the terrain the crane stands on are factors to consider. You really want to get proper information on this, and it might pay you to ask your local crane operator.

I had my Dutch barge lifted some time ago. She weighs about 30 tons, and required a 110 ton crane because of the distance to lift from the water's edge.

[alan_fincher]

I could reduce my boat by half a ton if I removed SWMBO's shoes

Is the maximum safe amount of footwear that can be on board determined by the Plimsoll line ?

[paulcatchpole]

Is the maximum safe amount of footwear that can be on board determined by the Plimsoll line ?

 

Groan....

 

Oh Alan.

 

Presumably, if you're learning how to make such a determination, you need a trainer? Or you'd feel a complete heel.

 

PC

[koukouvagia]

We have just done a deal to buy a 68ft tug style built by Charlie Cox, and we'll be transporting it down here by road. We'll need to have it lifted off the lorry and into the water at this end and the marina have just asked us how much it weighs. Apparently their crane has a max lift weight of 16 tons. Or maybe 18 tons at a push (to quote the office bod). Or maybe he means tonnes. Are crane lift capacities quoted in metric or imperial these days?

 

Thing is, I don't know how much it weighs. I'm sure the vendor would give us a figure if I ask, but how would HE know, other than by Chinese whispers from the people HE bought it from?? This could be embarrassing and expensive if the boat turns out to be too heavy for the crane. What are the chances of an 18 ton (or tonne) crane lifting a 68ft boat? My own fag packet calculation of the displacement of the boat based on draft, width and length is about 16 cubic metres of water. 16 tonnes. Not much margn for error!

 

Cheers, Mike

 

Years ago I saw the following method for weighing a narrowboat using only a spring balance, a stopwatch and a measuring tape. I'm not a mathematician, so please don't ask me to explain the details. All my part in the experiment was to provide a narrowboat while a colleague of mine and his A level maths class took all the measurements and made the calculations. The method was for me to tie a line from the boat to a spring balance which itself was tied to a bollard. I started the engine until a thrust of about 50kgs was measured on the spring balance and the boat was released. For the next 50 metres I drove the boat at a constant speed past markers at 10 metre intervals, then cut the engine until the boat drifted to a stop past further markers. This gave the acceleration and deceleration rates.

The results were as follows:

Thrust (T) = 46 kgs; Accel. (a) = 0.0346m/sec/sec; Decel. (d) 0.0231 m/ sec/sec; Gravity (g) 9.8 m/sec/sec

My colleague used the formula W=Tg/(a+d) and the weight was 7.8 tonnes. I reckoned this was spot on because at the time I had a 38 ft Springer.

The full explanation which my mathematical friend wrote up is several pages long. We submitted the article to the waterways press, but none of them could understand what we were saying so the article has languished in a drawer for nearly 25 years.

No, I don't understand it either - but it did seem to work!!

[US Marines]

Years ago I saw the following method for weighing a narrowboat using only a spring balance, a stopwatch and a measuring tape. I'm not a mathematician, so please don't ask me to explain the details. All my part in the experiment was to provide a narrowboat while a colleague of mine and his A level maths class took all the measurements and made the calculations. The method was for me to tie a line from the boat to a spring balance which itself was tied to a bollard. I started the engine until a thrust of about 50kgs was measured on the spring balance and the boat was released. For the next 50 metres I drove the boat at a constant speed past markers at 10 metre intervals, then cut the engine until the boat drifted to a stop past further markers. This gave the acceleration and deceleration rates.

The results were as follows:

Thrust (T) = 46 kgs; Accel. (a) = 0.0346m/sec/sec; Decel. (d) 0.0231 m/ sec/sec; Gravity (g) 9.8 m/sec/sec

My colleague used the formula W=Tg/(a+d) and the weight was 7.8 tonnes. I reckoned this was spot on because at the time I had a 38 ft Springer.

The full explanation which my mathematical friend wrote up is several pages long. We submitted the article to the waterways press, but none of them could understand what we were saying so the article has languished in a drawer for nearly 25 years.

No, I don't understand it either - but it did seem to work!!

Hey - that's clever !

 

(Essentially, its based on the fact that the boat's momentum when you cut the engine is its mass x its velocity. However, you also need to know the resistance of the water/air to the movement of the boat, which is why you need the thrust and acceleration numbers as well).

Edited November 15, 2008 by US Marines

[david and julie]

Unless its an old crane(possible in a boatyard)it will be in tonnes.

 

The 16-18T comment by the office bod is a fair comment, he may actually be being reasonable. I've not driven a crane for years and they will have changed, but it used to be that you got a warning when nearing the limit(used to be an orange light IIRC) this was followed by a red light and a bell. There may be 2 tonnes between these warnings on his crane and he's prepared to go to the limit. As others have said, reach is everything to a crane.

 

As you recognise you could end up on the spot. Many modern cranes can weigh the load and the selling boatyard(particularly if they sub the lift out)may use one of these. 68Ft is a long boat so I assume your using a specialist for transport, they may have onboard weighing systems or be prepared to go to a weighbridge for you(for a bit of extra cost)they may even have a good working knowledge of average weights.

 

My gut feelng is your on the limit especially if your talking thick base plates and vintage engines.

 

I would find out any yards locally that could handle the lift at short notice just in case your stuck and then find out the true weight as I said above. At leat that way you have a few hours to sort the problem out before the wagon arrives otherwise waiting time, lost work costs etc for the wagon could be high.

[RLWP]

We have just done a deal to buy a 68ft tug style built by Charlie Cox, and we'll be transporting it down here by road.

 

Hi Mike,

 

What a shame! The most enjoyable cruise we ever made with Tawny Owl was bringing her home from Anderton to Hatton. It took a while at a few days moving a time but we cruised waterways that we will probably never cruise again.

 

Richard

 

Like the Weaver navigation and the Manchester Ship Canal...

[MtB]

Hi Mike,

 

What a shame! The most enjoyable cruise we ever made with Tawny Owl was bringing her home from Anderton to Hatton. It took a while at a few days moving a time but we cruised waterways that we will probably never cruise again.

 

 

Hi Richard,

 

Yes 'tis a shame indeed. We'd LOVE to bring the boat down ourselves but the only reason we can afford it in the first place is that I'm so busy with work at the moment and taking that amount of time off is not an option!

 

This will be twice now we've bought a boat from the midlands and missed out on a long, one-way trip through waterways we're unlikely to ever get a chance again to cruise. Maybe next time we change the boat....

 

Thanks for your replies everyone. We'll probably end up using the 50 tonne cradle-crane thingy at Thames and Kennet marina. It's just that it's not available the weekend we wanted it. It worries me to see a long narrowboat lifted by a conventional crane with straps below a frame. The boat looks so unstable. When they cranes our first narrowboat into the water years ago the driver lifted the boat with the straps placed centrally along the length of the boat. He insisted this was fine despite an engine in the back. I still think he (we?) were lucky the boat didn't slip out of the slings, so far out of horizontal it tipped as he turned the crane....

[Rick-n-Jo]

Hi Richard,

 

Yes 'tis a shame indeed. We'd LOVE to bring the boat down ourselves but the only reason we can afford it in the first place is that I'm so busy with work at the moment and taking that amount of time off is not an option!

 

This will be twice now we've bought a boat from the midlands and missed out on a long, one-way trip through waterways we're unlikely to ever get a chance again to cruise. Maybe next time we change the boat....

 

 

I'd guess the whole exercise (two BIG crane lifts + haulage) is going to set you back a couple of grand or more.

 

If you can't cruise it back yourselves, and you're not in a desperate hurry for it, why not get someone else to bring it by water for you. Several people advertise this service.

 

I'd do it for half what it would cost you by road!

 

Rick

[chris w]

I believe your boat will weigh considerably more than 18 tons.

 

Let's say it has a 2ft draft and the length at waterline is about 60 feet and it's a conventional 7ft beam.

 

Then the volume of water displaced = 60 x 7 x 2 = 840 cu ft

 

The weight of this water displaced = the weight of your boat.... that's why it floats!!! (Archimedes Principle)

 

Since 1 cu ft weighs 62.5 lbs, your boat weighs 840 x 62.5 = 52,500 lbs or 23.5 tons, much more than the crane's capability.

 

Chris

 

I also think the "Springer" mentioned above weighed closer to 12 tons, based on the volume of water it would typically displace, rather than the 8 tons estimate above.

Edited November 16, 2008 by chris w

[US Marines]

Chris's general method is sound (Archimedes was a clever chap !) but its very sensitive to the precise draft.

 

For example, if the average draft was 18 inches, the answer would be approx. 17.5 tons.

 

You've also got the fact that the boat probably won't be quite as wide at the waterline as at the gunwhale - and, of course, you need to take the swims into account in terms of the width.

 

When our 70 footer was craned in the summer, the numbers from the cranes at both ends differed significantly. The lower number was around 18 tonnes (metric), but I don't think this is right. The higher number was between 20 and 21 tonnes, which is the one I believe.

 

Since its been on the water, we've ballasted it and filled the water tanks, so I'm guessing it now weighs about 22 to 22.5 metric tonnes. (Metric tonnes are slightly smaller than imperial tons : 1 tonne = 2,205 lbs : 1 ton = 2,240 lbs).

Edited November 16, 2008 by US Marines

[alan_fincher]

Also, don't underestimate the difference that will be the case if the base plate is significantly less than the maximum beam, nor the differences between a nominal "seven foot" boat, and one built strictly within "6 foot 10 inches").

 

Most modern purpose built boats are very significantly narrower at the base plate than at the top strake, and often the bottoms are made from 2 metre sheets, (so less than 77 inches), of which maybe one inch is lost by the half inch overhang each side. So instead of 84" across the hull sides at the lowest point, you end up with just 76", about 9.5% less than a nominal "seven feet".

 

Even at the top a "6 foot 10" boat will only measure less than 6 foot 9 inside the strake, (so maybe 81"). If it's 81" at the widest and 76" at the narrowest, then it's probably around the average of those at waterline (78.5"). So the average underwater width is based on 78.5" (waterline) and 76" (base plate), which is 77 inches, to the nearest inch. This means you need to reduce any estimate you make assuming a 7 foot average width by over 8% - which seems to be around a ton and a half if you are taking around the 18 ton mark - a big difference if you haven't estimated your cross section right.

 

As to the Springer, they are usually sufficiently shallow draughted, are usually lightly ballasted, and above all almost all have a Vee not a flat bottom. They certainly can't be treated as a seven foot wide flat bottomed hull drawing anything like 2 feet. I'd be surprised if many of the "sub 40 foot" Springers went into double figures for tons, unless over-ballasted or maybe heavily over-plated.

 

I'm sure if my maths is wrong somebody will be only to quick to tell me!

 

I sold my first boat in the 1970s - a 40foot riveted iron "Joey" conversion, I know recognise to have been a "Bantock" boat. It had a heavily constructed wooden top, and a big Perkins P3 diesel. The new owner wished to crane it, and remove on a low loader, and was trying to convince himself that an 8 ton crane would do, as to hire a 15 ton one was double the cost. I was not convinced a 40 foot boat like that could be lifted by an 8 ton crane. In practice it was, although all the alarms and bells were on, the driver just kept lifting. It made a couple of very large two foot diameter holes in the pavement where the stabiliser pads sunk in though!

 

Alan

[MtB]

Just to finish off this thread, the boat weighed, according to Mike the crane driver at Reading, a shade under 22 tonnes.

 

Here's a pic of the boat in the slings, and as you can probably see from the waterline mark my original estimates of the draft front and back were a bit low.

 

Total cost for lifting onto the lorry at Newark, transport down and launching at Reading was £1,693.

 

Cheers, Mike

 

 

[chris w]

So my original prediction of 23.5 tons was only 7% out.

[robkg]

Just to finish off this thread, the boat weighed, according to Mike the crane driver at Reading, a shade under 22 tonnes.

Be slightly cautious of crane weights. Grace (70' and 2'3" draught) was declared 18.5 tonnes by the crane that lifted her on to the lorry and 21.5 tonnes by the crane that lifted her back off the lorry at the other end! (I suspect that the latter crane was closer to the mark)