Hulls made of HDPE

[icetreader]

Originally Posted by grob

With us weight is a big issue...Our hulls are a sandwich construction and the thickness varies throughout, they weigh 10.5kg or 42kg for 4. When we were getting quotes for the hull, we were finding that rotomoulded came out about twice the weight to get equivalent stiffness. Gareth

Gareth,

Weight is a big issue for everybody -Nobody likes to haul, carry, paddle or sail heavy boats.
Rotational molding gives you a pretty good control over the wall thickness in different parts of the hull.
It's possible to mold a polyethylene part (e.g. hull) with some walls that are thin and other walls that are many times thicker.
This is achieved by combining local insulation of the mold with different levels of local exposure to heat, and a careful setting of the way the machine is rotating the mold on different axes and thus distributing the PE resin inside it.

Looking at the size and shape of your boat's hulls I think it may be possible for you to stay within a similar weight range if and when you decide to upscale production to bigger numbers.
That would probably require only little re-design work when creating the roto-mold since the hulls as they are now look perfect for rotomolding.

Yoav

[mackid068]

What's the sandwich constructed of? Tuna and mustard? Seriously, of HDPE and foam?

[grob]

The Sandwich construction is Twintex and balsa.

[mackid068]

Balsa for buoyancy?

[Packeteer]

Originally Posted by grob

The Sandwich construction is Twintex and balsa.

why balsa instead of foam?

[John ilett]

Why not nida core, it's polypropylene honeycomb!

[grob]

We tried a couple of different core materials, remember that it has to be able to withstand the high forming temperatures, balsa worked out best, as its relatively inexpensive easy to source, and bonds well to the twintex.

Not sure if we tried Nida core I will have a look.

Have you used Twintex John?

Thanks

Gareth

[mackid068]

Polyprolene honeycomb sounds promising. Clearly, it'll resist the temperatures...as it needs them as well for forming.

[ersyncar]

Originally Posted by Baldur

....
One of the only boat manufacturers using HDPE:
http://www.boulderboatworks.com/bbw_home.html

only one? nooo there are many boat manufacturers . one of them is www.master-boat.com or www.orfimarine.com

[rasorinc]

Can fiberglass panals CF65 be changed out for HDPE panals? Would the thickness have to be the same?

[Fanie]

Sorry I came in a bit late to this thread.

PE has some advantages, it is quite abrasive and impact resistive. If it's yellow it remains yellow, you cannot paint it (forget it !). It is very difficult to repair, so if you do finally succeed to hole it you're in for a time to repair it well.

There are more boats made from PE than what we are aware of. The best process is probably a roto mould process where the whole construction is formed (melted) in one go. The advantage of this process is it is a mass production process so you can produce volumes which helps to bring costs down.

Nothing glues to PE. If you fasten anything to the hull it is usually above the water line and it gets pop rivited or bolted in place. PE is quite heavy, if you want it to compete with fiberglass you may not make strength.

I saw some 10m boats made from PE, but I have my doubts about them for keeping their integrity in such huge forms - or be very heavy. I would still for larger boats prefer good old fiberglass. Small canoes and sail boats, great. You can drag it over the stones and gravel, it will last for years.

PE doesn't like heat, but doesn't produce poisonois gasses if it burns. Doesn't mean it won't be friggin hot though PE is the only material suitable for containers / tanks in the food industry. PE absorbs almost zero water, and is a good engineering plastic.

[jonr]

My understanding is that PE can be bonded with the right glue and pre-oxidation.

[Fanie]

Oxidation in plastic ? Never heard of it, and our PE suppliers tell you there is no glue that sticks to it. You can ultrasonic weld it, a specialized process in which the two pieces melts and flows into one another, but I am doubtfull if such a joint will be full strength.

[ersyncar]

Originally Posted by Fanie

Sorry I came in a bit late to this thread.

PE has some advantages, it is quite abrasive and impact resistive. If it's yellow it remains yellow, you cannot paint it (forget it !). It is very difficult to repair, so if you do finally succeed to hole it you're in for a time to repair it well.

you r right PE has advantages and disadvantages but we can paint it its very new technology but enable. also its not difficult to repair , also its easier then aluminium or steel
http://www.ersinkar.com/model_big11.jpg this boat is made of hdpe(black). but can you see black color?

[ersyncar]

Originally Posted by Fanie

I saw some 10m boats made from PE, but I have my doubts about them for keeping their integrity in such huge forms - or be very heavy. I would still for larger boats prefer good old fiberglass. Small canoes and sail boats, great. You can drag it over the stones and gravel, it will last for years.

PE doesn't like heat, but doesn't produce poisonois gasses if it burns. Doesn't mean it won't be friggin hot though PE is the only material suitable for containers / tanks in the food industry. PE absorbs almost zero water, and is a good engineering plastic.

pe is a good metarial for boats until 17m LOA. longer then 17 meters are critical for strength. and they dont seem nice as much as fiber boats but stronger then fibers. thats why they are suitable for workboats

For heat , they better then fiber or wooden boats because with some additions it can be fireproof. also we made some boats (14m LOA) working in s.arabia in 50'C degrees. they have no problem with hot weather

we made some test with HDPE boats. for example we hit the boat to the scaffold by 18 knot speed and boat has no damage except some scratchs

we measure draft at bow and back. then hold it up by tieing from bow and back. after 2 hours we put it in water and measured the drafts again and there was no changing in dimensions.

these test has been done by a 12 m length boat.