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 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