Designing a 25-30ft boat with a HDPE hull

[mattosmond]

Hi guys and girls,
I have been reading some of the posts on here and have been really inspired with the use of recycled HDPE (plastic milk jugs) and am thinking of desiging a multi-use hull that can be manufactured from this material. This is for a design proposal for one of my final year design projects at uni. I would like to have a 25-30ft hull made that could be sold to many small craft manufacturers to build their own uppers on so that fibre glassing could be phased out a bit, by using a recycled material. where with cars you get many different tyoes using the same chassis, i like htis principal and think that it could possibly cut some costs for small to medium size boat builders. The general jist is that you would have say 1 manufacturer of the hulls in the uk to supply lots of companies at a reasonable cost and save them having to build the hull themselves, thus cutting down production times and hopefully costs, therefore making more revenue for these businesses. Do you think this is a good proposal or just dead in the water? Please give your valued opinions..
Many thanks,
matt

[Figgy]

Well, your first obstacle would be to design a hull that enough people want, to justify production. Frankly, thats what most designers are after anyways. Then shipping, what if I want ten, and I live in Maine, can you get them to me? What about one hundred? UK only? My point is, at what point is it less of a hassle to just "splash" one of yours, and produce my own from your proven design?
It's a good idea, if you can sort out the logistics.
-Figgy

[mattosmond]

this is a problem, but i was thinking more along the lines of uk based only at first, then if it were in theory to take off, then different countries can adopt similar principles. Thanks for your speedy reply, this is a very conceptual idea, but with some real ideas in it..... The hull design would be key...... And would probably be the real sticking point. Do you think the strength of HDPE would be enough..... Maybe mixed with another material or with a spine...

[Figgy]

Well, looking at this site, I'd say probably not. Mabe too flexable, but I dont know alot about the product. You might be able to make it work tho'.
I'll have to do some reading up on it. I know there are a few other members on here more versed on this subject than me. They will chime in soon...

[mattosmond]

cheers Figgy

[catmando2]

There are quite a few of these things in Australia polycraft being one,placa or plaka boats being another. Seem to have good reports as far as ride and longevity is concerned, but have a weight issue compared to other building methods eg: light alloy or composite,not sure compared to solid glass.

I am looking at a "polycraft tough tender" 3m as my tender on my current project. I was impressed by the picture of 3 blokes standing on the gunall on one side.

Dave

[marshmat]

Sounds interesting to be sure.
I'm not sure how manufacturers would take to the one-hull, outfit-it-yourself business model. The hull's a significant but not horrendously large part of the total cost, and it's also one of the few things marketing departments can differentiate themselves on (even if all 22' cuddies are pretty similar in reality).
HDPE is pretty flexible, its elastic modulus is only 0.7 to 1.0 GPa. Plus its maximum service temperature is only around 45 C (50 C tops if crosslinked), above that it loses its structural properties pretty quickly. You'd need quite a lot of it to get the same strength as a fibreglass hull, and if it's anything other than gloss white it wouldn't take too well to the tropical sun.

[antonfourie]

So how much do you think that the water cooled machined injection die is going to cost for a 30 foot HDPE mould, considering that you would have to have a male and female mould and be able to move them apart. On top of that machining a monster like that is going to take years not months.

Sorry to burst your bubble but the logistics are scary, also what if there is a fault with the design and you have to create a new set of moulds ...

[mattosmond]

thanks for the input, this is really what i needed. antonfourie: sure this would be mamouth, but i was thinking of the long term.. Are there any other good ways of making a strong hull from a recycled material? This is the main point of my concept.

The boat is going to have a wave piercing hull and be a 30 ft cabin cruiser.... Just to try a different type of hull in this ferocious market!! What do you think or am i being unrealistic? matt

[hansp77]

Hey Matt,
I like your passion, and your acceptance of critisism.

I love the idea of basing your design around recycling. In my opinion there is not nearly enough of this done in modern boat building.

I seem to be an instinctual collector, salvager and thinker along these lines. (however most of my thoughts end up impossible or already achieved)

From my limited knowledge on getting moulds made (for glass and plastic bottles not boats) it is a VERY expensive process.

For the size that you are talking about, and the design, I think I agree with Anton.
Very Scary!

Maybe you could look at dramatically downsizing your project to something more universally desired- such as a tender. I don't know.

For the amount of investment that would be required, and the sales required to reach a profit, your project just may never get off the ground.

I don't wanto burst your bubble either...
I'll keep my mind on it, and maybe soon start offering some ridiculous and unlikely alternative recycling materials or methods.

Good luck.

Hans.

[mattosmond]

Cheers Hans, if you see my last project in the student design gallery then you'll see i like to think of the off beat concepts (this was my 1st boat deisgn so it is a bit rough around the edges)

[MarshallT]

You could make a boat using HDPE but since it is a thermoplastic material it will require heat to form the shape and that means expensive tooling. Rotomolded kayaks is a good example. At 20-30 ft you would need a big oven and metal tooling that could be rotated and rocked back and forth. In your design you would have to add bulheads and stringers to make up for the lack of stiffness (compared with FRP). Maybe a nice soft hull would make for a smoother ride

[mattosmond]

Thanks MarshallT that sounds like a good idea. i will investigate this channel.

[Richard Hillsid]

Boat buyers want shine and more reflections 2 things most thermoplastics can’t offer. After this has been solved fibber reinforced thermoplastics could rule.

[mattosmond]

Richard Hillsid: that's a fair point, but if someone did make one look really slick, then people would jump on the bandwagon i'm sure....