HDPE canal boat

[jim mitchell]

On 28/09/2024 at 13:11, IanD said:

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.

or 60mm on hull sides ?

 

so would using a mesh core of say 50mm x 50mm  and also around 50mm deep plus inner and outer 5mm skins, in which the voids are filled by expanded foam give a lightweight but rigid  structure with inbuilt insulation and without the expansion/contraction issues ?

 

maybe with twin side keels 150 deep and an open mesh similar to the old chinese rudders give lateral resistence to winds with only a modest resistence increase. ?

 

or for reduced draught with the use of electric drives ? - "props"  situated near the bow, housed within  tunnels along the boat floor with some form of adjustable side oulets to allow some of the fore / aft drive thrust to be used as side thrust in cross winds, even 'mutter mutter into my beard' in lieu of bow/stern thrusters for manoeuvring.

[Momac]

Just now, jim mitchell said:

 

so would using a mesh core of say 50mm x 50mm  and also around 50mm deep plus inner and outer 5mm skins, in which the voids are filled by expanded foam give a lightweight but rigid  structure with inbuilt insulation and without the expansion/contraction issues ?

 

The thermal expansion will potentially be the same except potential differential between the inner and outer skins.

Really not sure this is an issue in real life. GRP boats can be 80ft or more with no issues in far hotter climates than the UK.

GRP boats sometimes have wood cored parts. GRP hulls are also sometimes dark colours but always the decks and superstructure are white (possibly teak laid or plastic fake teak. Anything black or dark coloured  and a poor conductor of heat like GRP or even vinyl can become too hot to touch even in the UK on that rare hot sunny day. In very hot climates the fake teak can be too hot to walk on with bare feet while white GRP is okay.

[Mike Todd]

On 27/09/2024 at 15:04, 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

Tte canal water temperature is unlikely to reach such extremes if temperatures, even if the air does. I would be more concerned about the differential between hull and cab changes. 

[IanD]

3 hours ago, jim mitchell said:

or 60mm on hull sides ?

 

so would using a mesh core of say 50mm x 50mm  and also around 50mm deep plus inner and outer 5mm skins, in which the voids are filled by expanded foam give a lightweight but rigid  structure with inbuilt insulation and without the expansion/contraction issues ?

 

maybe with twin side keels 150 deep and an open mesh similar to the old chinese rudders give lateral resistence to winds with only a modest resistence increase. ?

 

or for reduced draught with the use of electric drives ? - "props"  situated near the bow, housed within  tunnels along the boat floor with some form of adjustable side oulets to allow some of the fore / aft drive thrust to be used as side thrust in cross winds, even 'mutter mutter into my beard' in lieu of bow/stern thrusters for manoeuvring.

Sandwich structures with foam cores are excellent structurally -- but you really want something much stiffer then HDPE as the skins, like glassfibre -- or carbon fibre, or even wood.

 

I did say that bow and maybe stern thrusters would help with the crosswind problems of a lightweight shallow draft hull, as would side keels -- almost anything would be better than doing a copy of a traditional steel boat in unsuitable material... 😞

[hughc]

Holt Abbot boats with an overall shallow water draught and a deep keel work very well indeed. In canal terms they are exceptionally fast with a small wake. With full standing headroom the air draught is below six feet and when we owned  'Moonbeam' we got her through Froghall tunnel. It looks as though some one is trying to re-invent the wheel 

[IanD]

2 hours ago, hughc said:

Holt Abbot boats with an overall shallow water draught and a deep keel work very well indeed. In canal terms they are exceptionally fast with a small wake. With full standing headroom the air draught is below six feet and when we owned  'Moonbeam' we got her through Froghall tunnel. It looks as though some one is trying to re-invent the wheel 

The problem is they're trying to reinvent the (perfectly successful, wooden or steel) wheel by making one that looks similar but is made from jelly... 😞 

Edited September 30, 2024 by IanD

[agg221]

8 hours ago, IanD said:

The problem is they're trying to reinvent the (perfectly successful, wooden or steel) wheel by making one that looks similar but is made from jelly... 😞 

I disagree. I think they are trying to do something really rather interesting, but not necessarily going about it the best way.

 

There is a global shift at the moment in terms of energy. It really isn't clear how it is going to drop out eventually, but two factors which are pretty clear are a significant reduction in the use of oil as a fuel and an increase in the cost of energy. Those who have oil are therefore less likely to be selling it for fuel, but they will still be extracting it and that means selling it into the petrochemical and plastics industries instead. You can see the direction of travel here:

 

https://www.non-metallic.com/ (look at who the funders are if you want to see how serious they are about it)

 

Unsurprisingly, since the oil industry is involved, their first target is oil pipelines - cutting their own costs is the priority. However, the development work on thermoplastic composite materials which this is driving is significant. Production costs are dropping rapidly and performance is increasing.

 

You describe steel and wood as 'perfectly successful' and, to an extent, I agree. However, both materials have significant down-sides too. Just look at how many wooden boats remain/are being built to see how the drawbacks to wood are currently affecting its selection as a material (despite being sustainable etc). Cost, skilled labour hours and lack of durability are the main issues, together with the current absence of good preservatives to extend life. Steel isn't bad and ever-improving coating systems are extending life significantly, plus it can be recycled at end of life in a cradle to cradle loop, but it still has down-sides including the need for maintenance and, increasingly, the energy cost of manufacture will only go up. It's certainly an increasing concern.

 

In practice, current boat construction is already a composite sandwich to make it habitable - steel/insulation/lining. It's not that much of a stretch to consider composite panels being made. Thermoplastic composites are also much easier to form into complex shapes than steel - the sheet itself can be laid up in sections, formed and welded. This opens up more opportunities around design and cost-effective fabrication. The speed of fabrication is also notably higher - you can manually weld 6mm thick HDPE at over a metre a minute and at much lower energy input.

 

Exactly what design this drops out as, in what configuration, is entirely undetermined. It probably isn't a simple slab construction with an internal steel frame. However, just like cars which have progressed from steel to increasingly composite construction, as the materials become more available at lower cost it is inevitable that people will look for ways to use them. Personally, given the amount pit welding we are currently undergoing and the remedial action that will necessitate internally to the insulation, I rather like the idea of a HDPE boat which can be repaired at much lower temperatures, probably by me with the appropriate hot air tool!

 

Alec

 

 

[shaun15124]

Thank you for sharing your thoughts and engaging in this discussion. We're pleased to address some of the points you've raised about our HDPE narrowboat.

Firstly, we completely respect and appreciate the long history of steel in boatbuilding. Steel is indeed a recyclable material, and its durability has made it a go-to choice for narrowboats over the years. Our choice to work with HDPE (High-Density Polyethylene) was driven by a desire to explore new materials that offer unique benefits alongside traditional steel. HDPE is not only fully recyclable but also highly durable and resistant to corrosion, which can potentially reduce maintenance requirements for boaters.

Regarding the weight, you’re absolutely correct that a lighter hull material like HDPE requires proper ballasting, just as a steel boat would. We’ve carefully adjusted our design to ensure the necessary ballast is included, keeping the boat stable and performing well in water. Fuel efficiency is achieved through the lower weight of the material itself, but it’s balanced with ballast for optimal draft and stability.

We’re always open to feedback and would love for you and others interested to see the boat in person. We’ll be showcasing our latest 57ft HDPE narrowboat model at the Crick Boat Show in 2025. This will be a great opportunity to experience the craftsmanship firsthand and see the practical solutions we’ve developed.

Thanks again for your interest and comments. We look forward to showing you more at Crick!

Thank you for your input—it’s great to see so much engagement around our HDPE narrowboat. We’d be glad to clarify a few points in response to your feedback and everyone’s comments.

Our upcoming model, set to debut at the Crick Boat Show 2025, will be entirely free of steel. We’ve worked closely with Rodley Marina on this project and collaborated with Vetus to incorporate an electric propulsion system, optimizing the boat’s sustainability profile. We’ve taken all feedback seriously and are committed to refining our design based on both industry input and practical experience.

Our team brings over 30 years of experience working with HDPE, and our first boat was indeed a proof of concept. We’ve learned a lot through that process and have implemented several enhancements based on our findings and industry insights. We’re confident this new model will demonstrate the potential of HDPE in canal boating, not only as a durable and eco-friendly material but as one that meets the functional demands of waterways.

We genuinely appreciate the dialogue and invite everyone to see the progress we’ve made at Crick 2025. Your perspectives are valuable, and we look forward to sharing this journey with the community.

[IanD]

27 minutes ago, shaun15124 said:

Thank you for sharing your thoughts and engaging in this discussion. We're pleased to address some of the points you've raised about our HDPE narrowboat.

Firstly, we completely respect and appreciate the long history of steel in boatbuilding. Steel is indeed a recyclable material, and its durability has made it a go-to choice for narrowboats over the years. Our choice to work with HDPE (High-Density Polyethylene) was driven by a desire to explore new materials that offer unique benefits alongside traditional steel. HDPE is not only fully recyclable but also highly durable and resistant to corrosion, which can potentially reduce maintenance requirements for boaters.

Regarding the weight, you’re absolutely correct that a lighter hull material like HDPE requires proper ballasting, just as a steel boat would. We’ve carefully adjusted our design to ensure the necessary ballast is included, keeping the boat stable and performing well in water. Fuel efficiency is achieved through the lower weight of the material itself, but it’s balanced with ballast for optimal draft and stability.

We’re always open to feedback and would love for you and others interested to see the boat in person. We’ll be showcasing our latest 57ft HDPE narrowboat model at the Crick Boat Show in 2025. This will be a great opportunity to experience the craftsmanship firsthand and see the practical solutions we’ve developed.

Thanks again for your interest and comments. We look forward to showing you more at Crick!

Thank you for your input—it’s great to see so much engagement around our HDPE narrowboat. We’d be glad to clarify a few points in response to your feedback and everyone’s comments.

Our upcoming model, set to debut at the Crick Boat Show 2025, will be entirely free of steel. We’ve worked closely with Rodley Marina on this project and collaborated with Vetus to incorporate an electric propulsion system, optimizing the boat’s sustainability profile. We’ve taken all feedback seriously and are committed to refining our design based on both industry input and practical experience.

Our team brings over 30 years of experience working with HDPE, and our first boat was indeed a proof of concept. We’ve learned a lot through that process and have implemented several enhancements based on our findings and industry insights. We’re confident this new model will demonstrate the potential of HDPE in canal boating, not only as a durable and eco-friendly material but as one that meets the functional demands of waterways.

We genuinely appreciate the dialogue and invite everyone to see the progress we’ve made at Crick 2025. Your perspectives are valuable, and we look forward to sharing this journey with the community.

 

Given my comments above about the structural properties of HDPE, I'd be genuinely interested to know how you've built a sufficiently rigid/stiff narrowboat out of just HDPE with no steel frame, because the numbers suggest this is somewhere between difficult and impossible without either very thick HDPE or internal braces so deep they would severely compromise internal space -- unless you use foam-core sandwich panels, which only want to be flat, and would have to be very thick given the properties of HDPE... 😉 

 

I've been involved in the past in designing and building various things using materials including sandwich composites, and though HDPE has some durability/corrosion/recycling advantages it doesn't seem to me to be a good structural material as it stands for building something like a long thin narrowboat which needs decent rigidity, including in torsion -- its Young's Modulus is simply too low, especially compared to its density... 😞 

Edited November 4, 2024 by IanD

[shaun15124]

Thank you again for your thoughtful comments. We appreciate your technical perspective, and we’d like to share more about how we’ve addressed these challenges in our HDPE narrowboat design.

We’ve partnered closely with naval architects who specialize in HDPE, leveraging their expertise to create a structurally sound design without a steel frame. Their experience with HDPE has been instrumental in developing a hull structure that achieves the necessary rigidity and torsional strength while maintaining interior space.

These specialists helped us design a layout with optimized bulkheads and compartments, allowing the hull to withstand typical canal stresses without excessive thickness or intrusive braces. The architects’ familiarity with HDPE’s unique properties, combined with advanced engineering tools, enabled us to maximize the material’s strengths and address its limitations effectively.

We’d love for you to see the result at Crick 2025 and welcome more insights from knowledgeable voices like yours.

[David Mack]

I still don't see why this is more efficient due to the lower material weight. If you ballast it down to the same depth as a steel boat, then the total weight is the same - just that there is more ballast and less shell weight. If you go for a lower draft, then that reduces the energy required to propel the craft, but also requires use of a less efficient smaller higher speed propeller. Or else you have a prop descending below the general baseplate level, which is then much more vulnerable to damage in a canal environment. And a reduced draft either means reduced internal headroom, which users won't like, or increased air draft, which will mean more problems with low bridges.

[magnetman]

Hull skin friction is interesting .

 

Rotomoulded polypropylene canoes are hard work compared with GRP and gelcoat. Lots of friction..

 

How does this get dealt with with HDPE? 

 

 

 

It will be interesting to watch the massive increase in oil-based plastic products being produced as people move to electric cars. 

 

Surely by now people have worked out that plastics are not the correct way to achieve construction of useful articles. 

 

Its a wonder material but basically dodgy. Humans are far more clever than this. 

 

 

 

 

[IanD]

1 hour ago, magnetman said:

Hull skin friction is interesting .

 

Rotomoulded polypropylene canoes are hard work compared with GRP and gelcoat. Lots of friction..

 

How does this get dealt with with HDPE? 

 

It will be interesting to watch the massive increase in oil-based plastic products being produced as people move to electric cars. 

 

Surely by now people have worked out that plastics are not the correct way to achieve construction of useful articles. 

 

Its a wonder material but basically dodgy. Humans are far more clever than this. 

 

 

Hull skin friction is negligible on canals at canal speeds, drag due to water displacement (narrow/shallow channel) is far bigger, wave/wake drag is next, skin drag is the smallest component.

 

1 hour ago, David Mack said:

I still don't see why this is more efficient due to the lower material weight. If you ballast it down to the same depth as a steel boat, then the total weight is the same - just that there is more ballast and less shell weight. If you go for a lower draft, then that reduces the energy required to propel the craft, but also requires use of a less efficient smaller higher speed propeller. Or else you have a prop descending below the general baseplate level, which is then much more vulnerable to damage in a canal environment. And a reduced draft either means reduced internal headroom, which users won't like, or increased air draft, which will mean more problems with low bridges.

This was discussed earlier in the thread, along with problems with susceptibility to cross-winds in a light shallow-draft boat -- which could be dealt with by the equivalent of fin keels at each side.

 

A boat with half the draft/displacement would also need about a third the power to propel it at canal speeds, meaning a smaller prop as well as 3x the electric range and making it much ore likely that solar power would be enough for propulsion. If dual props were used -- easy and cheap with electric drive -- then these could easily fit in a 1' draft boat while still having low enough rpm to be quiet and efficient.

 

This would mean a foot more air draft for the same headroom inside, but that would be OK in most cases so long as you don't cover the roof with lots of junk or tall chimneys -- which hopefully an HDPE eco-boat wouldn't need.

 

1 hour ago, shaun15124 said:

Thank you again for your thoughtful comments. We appreciate your technical perspective, and we’d like to share more about how we’ve addressed these challenges in our HDPE narrowboat design.

We’ve partnered closely with naval architects who specialize in HDPE, leveraging their expertise to create a structurally sound design without a steel frame. Their experience with HDPE has been instrumental in developing a hull structure that achieves the necessary rigidity and torsional strength while maintaining interior space.

These specialists helped us design a layout with optimized bulkheads and compartments, allowing the hull to withstand typical canal stresses without excessive thickness or intrusive braces. The architects’ familiarity with HDPE’s unique properties, combined with advanced engineering tools, enabled us to maximize the material’s strengths and address its limitations effectively.

We’d love for you to see the result at Crick 2025 and welcome more insights from knowledgeable voices like yours.

 

It sounds like you're using structural cross-bulkheads to provide torsional stiffness by turning the hull into a cellular beam structure, presumably together with the cabin/roof?

 

If so, how does this work when you cut door apertures through them, since this normally destroys the overall stiffness?

 

The other problem with this approach is that the bulkheads have to be built as part of the hull not added at fitout, which means a lot more planning is needed and it's then impossible to change/move the bulkhead structures, which means the internal boat layout (room sizes/positions) is also fixed.

 

That would work for a build where hull and fitout are designed together from the start (like mine was), but not so well for the more traditional build process where the hull is standard and internal fitout can be decided on afterwards.

Edited November 4, 2024 by IanD

[Momac]

33 minutes ago, IanD said:

 

It sounds like you're using structural cross-bulkheads to provide torsional stiffness by turning the hull into a cellular beam structure, presumably together with the cabin/roof?

It is possible to design a diaphragm with openings.

I would have thought the internal stiffening more like ribs and stringers which is normal for timber and GRP boats.

Okay this might need to be designed according to fit out but why does fit out have to be totally flexible? Most factory fully built boats come with maybe a couple or three layout options decided when ordered by the customer so why not a narrowboat?

[IanD]

12 minutes ago, Momac said:

It is possible to design a diaphragm with openings.

I would have thought the internal stiffening more like ribs and stringers which is normal for timber and GRP boats.

Okay this might need to be designed according to fit out but why does fit out have to be totally flexible? Most factory fully built boats come with maybe a couple or three layout options decided when ordered by the customer so why not a narrowboat?

Yes you can design in openings, but if these are big compared to the bulkhead size -- like a narrowboat door -- and extend close to the edges of the bulkhead -- like a narrowboat door -- then they greatly reduce the stiffening effect of the bulkhead.

 

Ribs and stringers would need to be much deeper than wood or steel because HDPE has a Youngs modulus many times smaller, I gave some numbers in an earlier post in the thread.

 

I didn't say it had to be totally flexible, but the room sizes would have to be fixed at hull build and couldn't be changed, which is not how narrowboats are built today. Even if you think the bulkhead positions are fixed they can end up being moved a bit during fitout to match with required internal space and fittings, mine were. It would also mean you couldn't have a long open-plan section without bulkheads since this would be too flexible (low torsional stiffness).

 

This is all basic structural theory, there's nothing new about it... 😉 

Edited November 4, 2024 by IanD

[Momac]

Just now, IanD said:

 

 

I didn't say it had to be totally flexible, but the room sizes would have to be fixed at hull build and couldn't be changed, which is not how narrowboats are built today. 

Almost all lumpy water GRP boats come with limited fit out options so why not apply that to a narrowboat?

[IanD]

1 minute ago, Momac said:

Almost all lumpy water GRP boats come with limited fit out options so why not apply that to a narrowboat?

You could do, but it's not how builds are usually done today. GRP boats are much shorter and it's a lot harder to have radically different interior layouts, where this is very common in narrowboats.

 

There's another possible practical problem, which is that given the width of narrowboats door openings, if the bulkheads are installed as part of hull build it would make it a lot more difficult to get things in during fitout.

Edited November 4, 2024 by IanD

[Momac]

Just now, IanD said:

 GRP boats are much shorter 

Not true.

[IanD]

2 minutes ago, Momac said:

Not true.

<sigh> go on then, show me a 72' GRP boat that will fit onto a UK canal and doesn't cost millions... 😉 

 

P.S. I think you know exactly what I meant and are arguing for the sake of it...

Edited November 4, 2024 by IanD

[magnetman]

GRP should be banned as a Boat building material. 

 

Plastic is terrible and once it gets to the end of its useful life it is a nuisance to dispose of. 

 

Aluminium and steel are much better as it is a basically useful material. And wood because you can just burn it .

 

Obviously plastic does end up being burned but it is still a bit naff to allow all of these things which everyone knows are going to result in negative outcomes to be produced. 

 

There is a basic driver behind all this. 

 

 

Just now, IanD said:

<sigh> go on then, show me a 72' GRP boat that will fit onto a UK canal and doesn't cost millions... 😉 

 

I think you know exactly what I meant and are arguing for the sake of it...

 

A 71ft9in narrow Boat made of FRP would, as you suggested, be an interesting thing to see. 

 

 

Oh no. It was 72ft. 

[IanD]

Just now, magnetman said:

GRP should be banned as a Boat building material. 

 

Plastic is terrible and once it gets to the end of its useful life it is a nuisance to dispose of. 

 

Aluminium and steel are much better as it is a basically useful material. And wood because you can just burn it .

 

Obviously plastic does end up being burned but it is still a bit naff to allow all of these things which everyone knows are going to result in negative outcomes to be produced. 

 

There is a basic driver behind all this. 

 

 

However at least GRP is a perfectly good structural material for building boats from (good stiffness-to-weight ratio), just like HDPE isn't... 😉 

[magnetman]

 

Just now, IanD said:

 

However at least GRP is a perfectly good structural material for building boats from (good stiffness-to-weight ratio), just like HDPE isn't... 😉 

 

Its a great material to make Boats. I have 4 GRP vessels (all small Boats with no accommodation) but at the end of the day it needs to be taken out as it is entirely non sustainable and just causes problems later. 

[Momac]

12 minutes ago, IanD said:

<sigh> go on then, show me a 72' GRP boat that will fit onto a UK canal and doesn't cost millions... 😉 

 

P.S. I think you know exactly what I meant and are arguing for the sake of it...

 

You didn't say anything earlier about canals or cost.

Edited November 4, 2024 by Momac

[magnetman]

 

To be fair the word 'canal' is in the title and people who own canal Boats are notoriously tight*

 

*there will be exceptions. 

[Momac]

4 minutes ago, IanD said:

 

However at least GRP is a perfectly good structural material for building boats from (good stiffness-to-weight ratio), just like HDPE isn't... 😉 

Well it looks like HDPE boats have been been built including one narrowboat.