3.5m HDPE jetboat

welding bow section up

http://www.youtube.com/watch?v=fYYORrm2L2c&feature=youtu.be

 

It sure works out good when you have the right tools and some help.

I'm thinking of a home-made welder of a Stainless Foot heated by Propane torch. I will try to duct some Hot Air to the Weld site with some kind of Focused air supply.
I wish there was something like that going on around here so I'd have a visual and some more options.

 

welding shoe is PTFE, if you are going to make a boat it would pay to use the right tools, they are digitally controlled as well

 

Nothing as elaborate as a Boat. You are correct in your guess that I do not know enough about the different poly's to be making anything that complex.

I'm just interested in using some of these old Poly Buckets n' stuff for something.

 

Yea could worth a go, you never know, you might stumble across something great

 

When I looked at this last week I came across these pretty cheap welding setups (OK for those of you in the US): http://www.harborfreight.com/plastic-welding-kit-with-adjustable-temperature-96464.html and http://www.harborfreight.com/plasti...r-motor-and-temperature-adjustment-96712.html

Not very sophisticated and probably not ideal for critical welds, but might be OK for experimenting with.

 

As I thought, the stuff has a pretty high density (and a very low Young's Modulus of just 0.8GPa) which makes for a fairly heavy boat. Not a problem in this application, I'm sure, as the advantages of robustness and abrasion resistance probably more than make up for the weight penalty.

Ordinary hand laid glass composite (not CF or anything exotic) would be around 20 times stiffer, and maybe 10 or 12 times stronger, for a given thickness, but it probably wouldn't bounce off rocks too well!

 

HDPE kayaks seem to weight about 20% more.

 

i dont think they make too many fiber glass white water kayaks

this boat is built for adventure boating in the back country of New Zealand where a hole in the boat could end in a chopper ride.

this is some of the boating i hope to get up to: http://www.youtube.com/watch?v=C1IyMMrWKfQ

this is not me but its these videos that inspired me to make such a hull.

i have another alloy boat but this is the first one i have designed and built and to my knowledge no one else is making a Jet Boat of this type and size in their garage, during their spare time.

 

most if not all jet boats are now alloy, i think the SG of alloy is 2.7 compared to HDPE @ .96 so if the boat is build three times thicker than alloy for the same weight i think i may be onto a winner.

Alloy dints, is very grabby, if you hit a sand bar you will almost stop on a dime

where as HDPE has excellent memory and very good wear resistance and also VERY slippery making it an idea material to build boat of this nature with

 

I agree that the wear resistance and low surface friction properties of HDPE make it very good for a boat like this, but generally boat scantlings tend to be dominated by material stiffness (i.e. the Youngs Modulus of the material) rather than by ultimate strength or even density (hence the reason steel is pretty good for making bigger boats).

Aluminium alloy may well be around 3 times heavier than HDPE for a given thickness of material, but the same thickness of aluminium alloy would also be around 86 times stiffer and around 7 or 8 times stronger. For a "normal" boat this means that you could use alloy that is a lot thinner than the HDPE for the strength and stiffness requirements, and so get a hull maybe half the weight. The big snag is that, for your application, such an alloy boat would undoubtedly be at much greater risk of being holed on rocks.

 

Hobie addresses the weight/stiffness issues with a foam layer in their PE boats.

http://2010.archive.hobiecat.com/sailing/sailboat_spotlight_roto.html

 

Its very good having ppl comment on things they know about, a lot of forums ppl just comment for the sake of it, cheers for taking your time and explaining the pros and cons of different materials.

 

great video clips there Jetboat, looks like a blast.

One way to keep the weight down on an HDPE hull that is not stiff enough is to use stringers and lots of frames or ribs to support the hull skin to keep it from buckling. Soft materirals suffer from buckling failures, so if you can stiffen the hull by secondary means the hull skin does not have to be as heavy.

 

had a little time in garage today