Scantlings for welded HDPE boat construction

Not just rotomolded kayaks
Yacht Tenders, Utility Boats, Dinghies - Rigid Aluminum Hull Boats http://www.bullfrogboats.com/

Though not 100% poly, these guys build to 17 feet

 

6-metre poly boat.......

 

Sorry for the tangent, but can anyone tell me what equipment is used to "weld" PE material?
I keep thinking about modifying a plastic trimaran to hold an actual centerboard.

 

I wonder how stick-on registration numbers stay on these boats ! Painted would fare no better.

 

They typically use hot air extrusion welders which are rather expensive which would make it difficult to build a one off. You can stick to it with proper prep. It may be possible to buy the sheets pre treated, I don't know. I'm wondering if the material supplier would rent a welder.

 

At what temperature does the material soften to the point some nice ridges or clinker pattern could be rolled in to it ? Seems a good way to save lots of weight and work.

 

If u watch the hdpe pipe fusion welding on youtube you will see:
the temp, 204~Celsius, also there are approximant heat soak times as about 1 to 2mins, and the two surfaces mating 1+/-mm tolerance, and then pressed at 50daN~=100lbs of force.

I am sure you can find technical manuals on hdpe pipe fusion welding to confirm.

 

one should think disadvantages of this material before designing and thinking its advantages ;
Very low emodulus,
Lower stiffness at higher +ve temperatures.
Very high thermal expansion coefficient, hard to consolidate with different materials.
Fast aging at temperatures over 45 Celsius.

Low surface hardness, easy to scratch
Very hard to paint, very hard to coating and hard to get aesthetic view
Low UV resistance except black color,
High labor cost and needs skilled person to build

 

It is stretchy material, I installed a couple of 1000 gallon tanks under the house, a tight fit between some galv piers......About a half inch or so clearance, when the tanks filled, that half inch disappeared.

 

The data sheets show HDpe, high density pe has similar properties to marine plywood of the same thickness. Except moduals elasticity, hdpe simply does not shatter like wood, it takes a load to some point where it will deform permantly.
Thick plastic cutting boards are usally made of hdpe, it's pretty damn unflexible as proof.
As to UV aging yes carbon black is the best Resistance(more than 30 years) idk bout u but i'll be old in 30 years so who cares? not I. But not my alot compared to other additives.
Besides white is boring.

 

We manufacture HDPE workboats up to 11m for welde sheets, 15/20mm

 

Hi Bruno, it was actually your boats that got me thinking that HDPE would be a great material for a workboat style shallow draft cruiser for areas such as sections of Americas great loop. Unlike other more common boatbuilding materials though it seems like it would be out of the scope of folks wanting to build their own one off boat due to the cost of the extrusion welder. I suppose one could front up the money and then recoup some of the cost by selling when you are done with it. One of the biggest problems I see for the DIY builder would be coming up with the scantlings since the material lacks stiffness which is of course of prime importance in a boatbuilding material.

Steve.

 

Steve, this material is not suitable for leisure use. HDPE scratches easy and is only available in black. We only use it to make workboats... DIY is not an option, the welding is too difficult for amateurs

 

I don't know your location.
Harbour Freight in US sell 3 models of plastic welders with p.e. sticks for $20-75.

 

Black would be murder in a hot climate, there are plenty of moulded poly boats around, and the most common colour I see is green, but obviously what is available in large sheets is another matter.