HDPE canal boat

[agg221]

52 minutes ago, IanD said:

HDPE is far less stiff than wood, even pine is about 15x stiffer -- which is why wood is an excellent construction material for boats (or buildings, or aircraft), and plastics aren't...

 

(a thick wooden panel or hull the same weight as a thin steel one is about 3x stiffer)

Having had a look at flexural modulus values I am not sure your figures are quite right.

 

White pine is around 7.8GPa and whilst unfilled HDPE is around 0.85GPa (~9x less stiff) a conventional chopped glass fibre filled HDPE is around 6GPa at 40% loading. That's probably close enough to design around HDPE as equivalent to wood.

 

@stagedamager - how about having a go at a filled HDPE replica when you are done with Norway? It welds nicely and very fast!

 

Alec

[ditchcrawler]

16 minutes ago, agg221 said:

 

@stagedamager - how about having a go at a filled HDPE replica when you are done with Norway? It welds nicely and very fast!

 

Alec

I like that idea, it would probably work better than the design they have used with flat sides and bottom, A more ridged construction 

Edited September 25 by ditchcrawler
Spilling

[IanD]

9 minutes ago, agg221 said:

Having had a look at flexural modulus values I am not sure your figures are quite right.

 

White pine is around 7.8GPa and whilst unfilled HDPE is around 0.85GPa (~9x less stiff) a conventional chopped glass fibre filled HDPE is around 6GPa at 40% loading. That's probably close enough to design around HDPE as equivalent to wood.

 

@stagedamager - how about having a go at a filled HDPE replica when you are done with Norway? It welds nicely and very fast!

 

Alec

The wood figure I gave was a bit high, as you pointed out. If you stuff enough glass fibre into it HDPE does get a lot stiffer, but I hate to think what the cost of 20mm thick HDPE with that much glass fibre in would be -- far more than wood, probably more steel for building a hull. Conventional laid-up GRP would be thinner, lighter and cheaper for the same strength.

 

If you want to use plastics for structural purposes, the best way is to use it to make panels with deep stiffening ribs moulded in, not thick solid sheets -- for example, this is what all those plastic moulded PA speakers you see do, they can be injection-moulded much more cheaply than building a wooden cabinet -- but are still if anything acoustically inferior unless very carefully designed.

 

Big solid sheets of unfilled HDPA are just not a good way to build something like a boat hull, unless you add on things like a properly designed internal steel stiffening frame -- and by the time you've done all this it'll probably cost more than a steel or GRP hull.

[Peugeot 106]

31 minutes ago, Momac said:

https://www.bulldogboats.co.uk/#:~:text=Bulldog Boats are designers and,in an almost indestructible workboat.

These are work boats and not canal boats of course but they do demonstrate the possibilities. 

 

 

Impressive. I wonder if anybody has any price comparisons

[stagedamager]

51 minutes ago, agg221 said:

Having had a look at flexural modulus values I am not sure your figures are quite right.

 

White pine is around 7.8GPa and whilst unfilled HDPE is around 0.85GPa (~9x less stiff) a conventional chopped glass fibre filled HDPE is around 6GPa at 40% loading. That's probably close enough to design around HDPE as equivalent to wood.

 

@stagedamager - how about having a go at a filled HDPE replica when you are done with Norway? It welds nicely and very fast!

 

Alec

hold my beer........

[IanD]

25 minutes ago, Peugeot 106 said:

Impressive. I wonder if anybody has any price comparisons

If you can shape a (relatively short and deep) moulded hull with curves, ribs, tubes and reinforcing sections like that, you can make something pretty strong out of HDPE. If you use thick sandwich-type sections filled with foam then even better, that's a classic method to make stronger lighter structures or panels.

 

The problem is that this doesn't really work for a long narrow flat-sided flat-bottomed canal boat made from simple HDPE panels... 😞

Edited September 25 by IanD

[nbfiresprite]

One thing that no one has taken account of is the high thermal expansion of HDPE as regards to both licensing and fitting the canal gauge.

For example Densetec HDPE expands 1.5mm per linear metre for every 10 degrees C, approximately that means a 2.4m strip of this material can expand and contract 10.8mm between a temperature range of 0 and 30 degrees C

 

Take a Narrowboat with a length of 17m and a width of 2.1m using a temperature range of 40 degrees -10 to +30.

 

a = ΔL / (L0 * ΔT)

1. a is coefficient of linear thermal expansion per degree Celsius.
2. ΔL is change in length/Width of test specimen due to heating or to cooling.
3. L0 is the original length/Width of specimen at room temperature.
4. ΔT is temperature change, °C,

Material: Steel CTE 13 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.00884m

Final Length (L + ΔL): 17.00884m

Change in Width (ΔL): 0.001092m

Final Width (L + ΔL): 2.101092m

 

HDPE typically exhibits a linear expansion behavior, with its coefficient of thermal expansion ranging from approximately 100 to 200 x10^-6/°C.  So have used the mid range value of 150

 

Material: HDPE CTE 150 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.102m

Final Length (L + ΔL): 17.102m

Change in Width (ΔL): 0.0126m

Final Width   (L + ΔL): 2.1126m

 

While there is little expansion in steel beween Winter and Summer temperatures. With HDPE there is enough expansion to cause problems passing through narrow beam locks if the boat has been built in winter and then there the problems with inside the cabin with gaps opening up due to the thermal expansion. Fitting standard boat windows could also be a problem.

 

 

Thermal Properties of Plastic Materials

[Jon57]

8 minutes ago, nbfiresprite said:

One thing that no one has taken account of is the high thermal expansion of HDPE as regards to both licensing and fitting the canal gauge.

For example Densetec HDPE expands 1.5mm per linear metre for every 10 degrees C, approximately that means a 2.4m strip of this material can expand and contract 10.8mm between a temperature range of 0 and 30 degrees C

 

Take a Narrowboat with a length of 17m and a width of 2.1m using a temperature range of 40 degrees -10 to +30.

 

a = ΔL / (L0 * ΔT)

1. a is coefficient of linear thermal expansion per degree Celsius.
2. ΔL is change in length/Width of test specimen due to heating or to cooling.
3. L0 is the original length/Width of specimen at room temperature.
4. ΔT is temperature change, °C,

Material: Steel CTE 13 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.00884m

Final Length (L + ΔL): 17.00884m

Change in Width (ΔL): 0.001092m

Final Width (L + ΔL): 2.101092m

 

HDPE typically exhibits a linear expansion behavior, with its coefficient of thermal expansion ranging from approximately 100 to 200 x10^-6/°C.  So have used the mid range value of 150

 

Material: HDPE CTE 150 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.102m

Final Length (L + ΔL): 17.102m

Change in Width (ΔL): 0.0126m

Final Width   (L + ΔL): 2.1126m

 

While there is little expansion in steel beween Winter and Summer temperatures. With HDPE there is enough expansion to cause problems passing through narrow beam locks if the boat has been built in winter and then there the problems with inside the cabin with gaps opening up due to the thermal expansion. Fitting standard boat windows could also be a problem.

 

 

Thermal Properties of Plastic Materials

That will be a nightmare for crt licence 🤣

[IanD]

19 minutes ago, nbfiresprite said:

One thing that no one has taken account of is the high thermal expansion of HDPE as regards to both licensing and fitting the canal gauge.

For example Densetec HDPE expands 1.5mm per linear metre for every 10 degrees C, approximately that means a 2.4m strip of this material can expand and contract 10.8mm between a temperature range of 0 and 30 degrees C

 

Take a Narrowboat with a length of 17m and a width of 2.1m using a temperature range of 40 degrees -10 to +30.

 

a = ΔL / (L0 * ΔT)

1. a is coefficient of linear thermal expansion per degree Celsius.
2. ΔL is change in length/Width of test specimen due to heating or to cooling.
3. L0 is the original length/Width of specimen at room temperature.
4. ΔT is temperature change, °C,

Material: Steel CTE 13 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.00884m

Final Length (L + ΔL): 17.00884m

Change in Width (ΔL): 0.001092m

Final Width (L + ΔL): 2.101092m

 

HDPE typically exhibits a linear expansion behavior, with its coefficient of thermal expansion ranging from approximately 100 to 200 x10^-6/°C.  So have used the mid range value of 150

 

Material: HDPE CTE 150 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.102m

Final Length (L + ΔL): 17.102m

Change in Width (ΔL): 0.0126m

Final Width   (L + ΔL): 2.1126m

 

While there is little expansion in steel beween Winter and Summer temperatures. With HDPE there is enough expansion to cause problems passing through narrow beam locks if the boat has been built in winter and then there the problems with inside the cabin with gaps opening up due to the thermal expansion. Fitting standard boat windows could also be a problem.

 

 

Thermal Properties of Plastic Materials

 

Those temperature ranges are pretty large for a narrowboat in the UK -- but to be honest, thermal expansion is probably not the biggest of their problems, there are so many other issues with what they've built... 😞 

 

Don't forget there's also an internal steel frame, this is much stiffer than the HDPE shell so will fix the length/width -- at least, at floor level... 😉

 

Joining materials together with different CTE can cause all sorts of problems, try a silicon chip and a copper/aluminium heatspreader and see what can go expensively wrong.

 

Luckily in this case HDPE is much *much* softer than steel so steel will win every time, but the challenge will be to fasten the HDPE to it so that it doesn't buckle (sproing!) or pull apart (glug!) over temperature changes.

 

The alternative is to use flexible joints which allow them to expand/move differently, but I'm sure I don't need to point out how badly this could go wrong on a 70' long boat... 😉 

Edited September 27 by IanD

[Peugeot 106]

And your toes may hang out of the end of the (wood) bed in winter

[nbfiresprite]

 

1 hour ago, IanD said:

 

Those temperature ranges are pretty large for a narrowboat in the UK -- but to be honest, thermal expansion is probably not the biggest of their problems, there are so many other issues with what they've built... 😞 

 

 

For the ambient outside air temperature, the range is about right. Last winter we had nights of -11 -12 and this summer daytime temperatures of 30. In direct sunlight, steel can reach temperatures that are too hot to touch. I would be concerned with people walk on a roof made of HDPE in hot weather due to the low melting point of: 135°C (275°F), the  maximum working  temperature for HDPE pipes is between 60C and 70C depending on the brand.

[Peugeot 106]

3 minutes ago, nbfiresprite said:

 

For the ambient outside air temperature, the range is about right. Last winter we had nights of -11 -12 and this summer daytime temperatures of 30. In direct sunlight, steel can reach temperatures that are too hot to touch. I would be concerned with people walk on a roof made of HDPE in hot weather due to the low melting point of: 135°C (275°F), the  maximum working  temperature for HDPE pipes is between 60C and 70C depending on the brand.

I assume  there are HDPE  boats, sailing boats and canoes  in places like Greece at the sailing schools. I’ve never been to Greece  myself but we used them year round at our sailing club in the UK without issue 

[Momac]

2 hours ago, nbfiresprite said:

One thing that no one has taken account of is the high thermal expansion of HDPE as regards to both licensing and fitting the canal gauge.

For example Densetec HDPE expands 1.5mm per linear metre for every 10 degrees C, approximately that means a 2.4m strip of this material can expand and contract 10.8mm between a temperature range of 0 and 30 degrees C

 

Take a Narrowboat with a length of 17m and a width of 2.1m using a temperature range of 40 degrees -10 to +30.

 

a = ΔL / (L0 * ΔT)

1. a is coefficient of linear thermal expansion per degree Celsius.
2. ΔL is change in length/Width of test specimen due to heating or to cooling.
3. L0 is the original length/Width of specimen at room temperature.
4. ΔT is temperature change, °C,

Material: Steel CTE 13 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.00884m

Final Length (L + ΔL): 17.00884m

Change in Width (ΔL): 0.001092m

Final Width (L + ΔL): 2.101092m

 

HDPE typically exhibits a linear expansion behavior, with its coefficient of thermal expansion ranging from approximately 100 to 200 x10^-6/°C.  So have used the mid range value of 150

 

Material: HDPE CTE 150 x 10^-6/°C

Change in Temperature range -10 to +30 (40)

Change in Length (ΔL): 0.102m

Final Length (L + ΔL): 17.102m

Change in Width (ΔL): 0.0126m

Final Width   (L + ΔL): 2.1126m

 

While there is little expansion in steel beween Winter and Summer temperatures. With HDPE there is enough expansion to cause problems passing through narrow beam locks if the boat has been built in winter and then there the problems with inside the cabin with gaps opening up due to the thermal expansion. Fitting standard boat windows could also be a problem.

 

 

How does this compare with GRP with regard to thermal movement?

 

Do you you really think 12mm of expansion is likely to occur in practice and even if it did occur would it really be a problem.with regard to locks?

If so the simple solution is to allow for the 12mm in the design and fabrication of the boat.

 

[IanD]

2 minutes ago, Momac said:

 

How does this compare with GRP with regard to thermal movement?

 

Do you you really think 12mm of expansion is likely to occur in practice and even if it did occur would it really be a problem.with regard to locks?

If so the simple solution is to allow for the 12mm in the design and fabrication of the boat.

 

 

The absolute length change is not the big issue here -- the issue is that the HDPE cabin/hull wants to change in length (high TCE) but the steel base-frame doesn't (low TCE), and they're fastened together. So you get a lot of stress where the two are joined (which could break the fixings, or cause a lot of stress), and the differential expansion tries to bend the boat into a banana... 😞 

[Momac]

In the narrowboat are the steel and HDE fastened  together or is there provision for movement ?

It looks like the steel sits on the HDE baseplate and HDPE ribs fit between the steels. The ribs and the floor to follow will then to keep the steel in position within the hull. If so  this would cater for differential thermal movement.  It would be interesting to understand the designers intent regarding the steels. 

 

 

[IanD]

21 minutes ago, Momac said:

In the narrowboat are the steel and HDE fastened  together or is there provision for movement ?

It looks like the steel sits on the HDE baseplate and HDPE ribs fit between the steels. The ribs and the floor to follow will then to keep the steel in position within the hull. If so  this would cater for differential thermal movement.  It would be interesting to understand the designers intent regarding the steels. 

 

 

 

Those HDPE ribs (glued/welded to the HDPE baseplate) are cut to fit tightly between the steels, so I don't see how the HDPE and steel can move relative to each other -- cue plenty of stress due to different TCE. If they're not fixed together there will be quite a lot of movement with temperature changes, like Concorde (grew longer when flying, things moved relative to the fuselage inside) or the SR-71 Blackbird (leaked fuel like a sieve on the ground when cold, they took off and flew till it heayed up and then filled the tanks in the air).

 

The problem is that there's 2m of HDPE hull sides/gunwales/cabin above this and bonded to the HDPE baseplate, and all this desperately wants to grow in length as it gets hotter. So you'll get  lot of compressive stress especially in the roof, which might buckle, or this might cause the whole boat to bend down at then ends. The reverse will happen when it gets cold, the roof will be under tension so try to pull any joints apart.

 

All the kind of stuff that structural engineers know how to analyse -- including the stress levels and amount of any movement or bending -- but which I rather doubt that the builders of this boat have done. They're probably relying on that massive steel frame to keep the bottom plate flat, and hoping that the rest of the HDPE hull/cabin will be kept in check by this and do as it's told and not buckle when hot or fall to bits when cold.. Maybe they're right, or maybe not.

 

There's a very good reason that designers who understand all this stuff deliberately avoid using materials with widely differing TCE to build things, unless they're *very* sure that everything is so tightly joined together that nothing is going to break or move -- and if they do go this way, they try and keep the structure reasonably well balanced, for example with low-TCE skins firmly bonded on both sides of a high-TCE core, or vice versa. Having a very asymmetric structure like this boat is a recipe for all sorts of bendy trouble... 😞

 

BTW did you know that trees grow as prestressed structures to make them stronger? Wood is stronger in tension than compression, so trees grow with the larger inner core (heartwood) in compression and the thinner outer section (sapwood) in tension, so when the wind hits they can bend further without breaking? All designed by nature without a structural engineer or equation anywhere in sight... 😉 

Edited September 27 by IanD

[Momac]

51 minutes ago, IanD said:

 

Those HDPE ribs (glued/welded to the HDPE baseplate) are cut to fit tightly between the steels, so I don't see how the HDPE and steel can move relative to each other --

I don't think the HDPE ribs are going to do anything to restrain the steels . If the HDE  ribs and the baseplate are not physically fixed to the steels this will cater for differential thermal movement . In any case the baseplate and steel will not see a 40 degree temperature range in the UK , especially so for a boat in the water.

 

The roof expanding /contracting relative to the baseplate is a more interesting  consideration.. 

 

 

[Peugeot 106]

Father in Law worked for carpet manufacturer and they made special stretchy carpet for Concorde so passengers didn’t notice it climbing up the walls!

[Peanut]

I measured the skin temperature of my lumpy glass reinforced plastic boat when in the water.  The immersed skin remained at around 4°C when it was freezing outside. Likewise, in the summer, it is cool on the bottom, while dark-coloured steel canal boats have a very hot roof. The HDPE boat is dark green, which I believe is a mistake.

[IanD]

12 hours ago, Momac said:

I don't think the HDPE ribs are going to do anything to restrain the steels . If the HDE  ribs and the baseplate are not physically fixed to the steels this will cater for differential thermal movement . In any case the baseplate and steel will not see a 40 degree temperature range in the UK , especially so for a boat in the water.

 

The roof expanding /contracting relative to the baseplate is a more interesting  consideration.. 

 

If the ribs fit tightly between the steels as in the photo they can't move relative to each other, they'd have to slide past each other to do this -- and by a couple of inches at the bow and stern.

[blackrose]

On 25/09/2024 at 16:47, booke23 said:

 I'm not sure it will have the required abrasion resistance for canals.

 

 

 

Yes I don't think the abrasion resistance of HDPE will have changed since this topic came up on the forum several years ago. It would need to be well fendered all the way around, ideally low down near the waterline with large the D section rubber they put on aluminium boats like Sea Otters.

[BoatinglifeupNorth]

 I passed this boat at Rodley last week and never even noticed it, so it must fit in quite well, but when talking to a guy while doing the “Rodley bridge from hell” he mentioned it as the “boat made from recycled bottles” so it’s obviously a bit of a talking point up there, not as much as the bridge though👹

Edited September 28 by BoatinglifeupNorth

[booke23]

2 hours ago, blackrose said:

It would need to be well fendered all the way around, ideally low down near the waterline with large the D section rubber they put on aluminium boats like Sea Otters.

 

It would. Even then with it’s 15mm thick hull sides and 10 tonne+ weight, I think it would still be possible to hole the hull in certain circumstances…..like hitting a protruding bit of masonry in a bridge hole etc.

[Tony Brooks]

12 minutes ago, booke23 said:

 

It would. Even then with it’s 15mm thick hull sides and 10 tonne+ weight, I think it would still be possible to hole the hull in certain circumstances…..like hitting a protruding bit of masonry in a bridge hole etc.

 

Or one of CaRT's protruding bolts/tie bars, in fact the small contact area would probably make the likelihood of puncture greater.

[IanD]

The problem with HDPE is that it's a lousy structural material if you want to build anything rigid like a boat hull/cabin, never mind stop it being punctured by bolts etc. Anyone who doesn't like numbers should skip to the end***** right now... 😉 

 

To compare HDPE with wood and steel, let's start from something familar -- 20mm thick wood. Stiffness varies with thickness^2, steel is about 25x stiffer than wood but also 10x heavier -- so 4mm steel is the same weight as 20mm wood but half as stiff, for the same stiffness you need 5.5mm steel which is 40% heavier.

 

HDPE is about the same density as wood but also about 9x less stiff, so for the same stiffness as 20mm wood it needs to be 60mm thick and will weigh 3x as much as wood -- or more than 2x as much as steel. To be as stiff as 4mm steel -- typical cabin sides -- it would need to be about 40mm thick.

 

When building hulls or cabins you don't rely on flat panels, they're always stiffened with ribs much deeper than the skin thickness -- maybe 4" or more for wood, maybe 2" or more for steel. Because steel sections/tubes are mostly air and wood is solid, by the time you crunch all the numbers you end with similar overall weights for building from either wood or steel -- the steel will typically use more and smaller ribs and relatively thin skins e.g. 4mm cabin sides.

 

All this means that to be used on its own to build a hull/cabin -- as can be done with wood or steel, obviously -- HDPE needs to be enormously thick, and the result would be a lot heavier than either. If the skin was made thin enough to be light, it will need a large number of deep closely-spaced ribs or beams to be stiff enough, maybe 12" or so deep -- which is impractical since it steals loads of internal space.

 

If used as a sensible thickness skin (e.g. like wood) to keep the weight down then it needs an internal frame, for which steel is the obvious choice as here. But if this is only along the bottom of the hull, the hull and cabin sides and top will be far weaker and more flexible than either wood or steel -- the 10mm HDPE they used for the cabin is only about as stiff as 1mm steel. So I'm pretty sure it'll need a complete internal steel frame extending up the hull/cabin sides and across the roof, if it isn't all going to be ridiculously floppy. I suspect fastening the HDPE to this without movement or buckling or leaks is going to be a pig... 😞 

 

***** Once you've done that, what you've built is a steel-framed boat with an external HDPE skin which has to be firmly attached to it so it doesn't move over temperature or spring leaks, probably doesn't weigh much less than an all-steel or all-wood boat, is more prone to damage, and is going to be a pig to build -- just to avoid having to black the outside. Doesn't seem like a good idea to me... 😉 

Edited September 28 by IanD