Thread: "Plastic" hulls.
02-26-2014, 08:58 AM #1
Found this old article discussing "plastic" hulls back in '97 or so.
THE FUTURE IS PLASTIC
A line from the movie "The Graduate" had stuck in my brain. Dustin Hoffman's character is lying on an inflatable raft in a swimming pool as his father offers this advice: "Ben, I'm going to offer you one word of advice, just one word: plastic."
The line is still stuck in my brain and I offer it again, this time with a personal watercraft twist. I've got one word of advice for any of you who think about the future of watercraft. One word, just one word: plastic.
I came to this conclusion after a visit to the western Georgia town of Carrolton. All it took was a short ride on a rather non-descript watercraft. I was excited by the performance of the craft, though not for the usual reasons. Truth be told, its performance was run-of-the-mill, about what you'd expect of a craft built three or four years ago.
Actually, what excited me about the craft was the way it was made. After all, the watercraft underneath me was made of plastic, not the typical fiberglass or SMC (sheet-molded compound) construction found on virtually every popular watercraft model available to today.
This particular model, the creation of Superior International Industries, bore a striking resemblance to a non-current model produced by one of the largest manufacturers in the market. That was because SII used a 1993 craft as the mold for its prototype watercraft.
Bob Stevens, SII's director of design, engineering and product development, kidded that he built the prototype simply because he wanted a watercraft and didn't want to pay for it, but don't believe him. The prototype is being used to demonstrate the potential of plastic hulls in the manufacture of personal watercraft to all of the major manufacturers in the personal watercraft market. The technology represented in the hull and deck material of the prototype is of great interest to the manufacturers for a number of reasons, not the least of which is manufacturing cost.
The idea of a plastic hull is nothing new in the marine industry. For years, boat builders have been toying with the idea, experimenting with different processes and materials in an effort to be the first to bring a full-fledged plastic hull to the market. So far, no one has yet been able to bring a plastic boat to the market, at least in any discernible numbers.
They've all been hindered by the same problems: They can't get the plastic rigid enough without making it too brittle, or the complicated manufacturing process becomes cost-prohibitive or the final finish is considered too rough for a market that equates quality with the smooth finish of gelcoat.
Still, the lure of plastic remains great, largely because plastic has the promise of being not only less expensive than fiberglass or SMC, but also cleaner and more environmentally friendly. There are other draws as well, including durability and ease of maintenance.
And that's why SII is so excited about its new process of roto-molding polyethylene (or plastic) hulls.
"Our process answers all of the concerns about plastic hulls," Stevens said. "We've come up with a way to sandwich a layer of foam between two plastic skins. This process allows us to mold the hull and deck as internal parts and gives us enough strength and rigidity without making the hulls brittle."
The process has its roots in playground equipment. SII is one of about 250 companies in the United States roto-molding plastic products, but it is also one of the biggest and best known for its playground equipment, the kind often found in fast-food restaurants.
Bryan Dunne, SII's manager of product and process development, said the company was first introduced to the skin-foam-skin method of roto-molding plastic in Europe.
"Very few companies in this country are experimenting with new techniques," Dunne said. "With most companies, their product needs are so narrow that it doesn't make financial sense.
"We're one of the few that companies that have been aggressively pursuing new products and techniques."
The new skin-foam-skin technique is an example. The process begins in a similar way to most roto-molded products. Polyethylene pellets - about the same size and consistency as sand - are placed inside a mold which is in turn rotated inside a giant oven. When the pellets come into contact with the heated walls of the mold, they form a hardened skin. With each rotation, more and more of the pellets melt into the skin, increasing the thickness.
With standard roto-molding techniques, once the heating is stopped and the mold is opened, any unmelted polyethylene simply falls out of the mold, leaving a space between the "inner" liner and the "outer" skin.
However, with the skin-foam-skin technique, another element is added to the mold at a specific point which turns the remaining polyethylene pellets into a layer of foam. This part of SII's roto-molding technique is proprietary and what makes it unique. It is also what makes it suitable for the personal watercraft market, giving SII's plastic hulls the stiffness and strength needed without making them too brittle. In fact, Stevens said the process offers more overall strength than fiberglass or SMC.
Another boon is the relatively light weight. Stevens said the skin-foam-skin process can result in a weight savings of up to 40 percent compared to identical hulls made with fiberglass and even more when compared to SMC.
"The key here," Stevens said, "is how much strength you want to build into the hull. Right now, we're building in more strength than we probably need."
Stronger and lighter. That is an incredibly attractive combination for any manufacturer, but when you factor in the relatively low cost of the process, you've got a potentially winning trifecta. The cost savings come from a number of factors, including the relatively low cost of the material and machinery. The polyethylene pellets are relatively cheap, and considering they come in a variety of colors, manufacturers can save on the cost of paint. The molds, ovens and rotational equipment can all be acquired for a fraction of the cost of similar FRP or SMC tooling and machinery, and since the technique is "green" or environmentally friendly, no expensive environmental safeguards are needed. Any leftover material can simply be swept up and used in the next cycle.
Stevens also said the process can offer the manufacturers increased flexibility, especially those that use SMC.
"That might be the biggest advantage to some of them," Stevens said. "Right now, I can build a prototype mold for around $1500, compared to the $60,000 to $70,000 they're spending for prototype molds now. Once they got all the bugs out of the design, the finished mold would cost more, but they can do a lot of tinkering and experimenting for that price."
As we mentioned above, the prototype we rode was built using a 1993 model as the mold, giving it an eerily familiar look. In fact, had we not known the boat was made of plastic, we wouldn't have given it a second look. On closer inspection, however, it was readily apparent that the boat was something new. Or at least different.
The most obvious difference was the color. Both the hull and deck were yellow, something that was accomplished without the help of paint or gelcoat. The polyethylene pellets come in a variety of colors, and the color is carried all the way through the hull. The benefit is that scratches are less noticeable.
Another difference was the finish, which was much rougher than what you would find on a late-model watercraft. Stevens, however, said they can get a finish which approaches gelcoat by lining the final mold with chrome.
"The finish is a product of how smooth the mold is," Stevens said, showing us a sample piece of polyethylene with a smooth, shiny finish. "To get this, we add chrome to the inside of the mold. It drives up the cost of the mold, but the final cost (for the mold) is still nowhere near what you would pay for a final SMC mold."
On the water, the differences between the plastic watercraft and similar fiberglass models were more subtle. The first thing we noticed was the quieter ride.
"The foam itself is a great sound dampener," Stevens said. "In fact, on some of the test models we have working down in Florida, we've been able to reduce sound output by up to 12 db, just by changing materials."
Much of the decrease in sound comes from the dampening effect of the foam, which also reduces the amount of vibration you feel through the hull. However, some of the reduction is due to reduced "hull slap."
In terms of handling and the quality of the ride, you'd be hard-pressed to notice any difference. We were familiar enough with the model the prototype was based upon to know what to expect in terms of handling and ride, and we found nothing dramatic that was different from the plastic version. You needed the same severe outside lean to get the hull to stick in tight turns, but as with the original, the technique worked on the plastic hull. Speed and acceleration also seemed about the same, though we didn't have a radar gun available to prove that.
"We've found that most models are about the same," Stevens said. "If a fiberglass model goes 43-44 mph, then a plastic one will go 43-44 mph. You might be able to make some gains with weight reduction, but the surface quality appears to be about even."
More than anything, it was the similarities in performance and ride that caught our attention. If, as Stevens suggests, manufacturers can reduced the cost of a unit without sacrificing any performance or handling, that's good news to the consumers.
So far, this technique is still in the prototype stage, though Stevens said he expects at least one plastic model to make it to the market within two years. "There's a pretty good chance you could see one next year," he said, "but for sure there'll be at least one within two years."
02-26-2014, 11:25 AM #2
Well there you have it. The answer is "Spark", but after seeing what happens with a simple collision ... the plastic BREAKS ! It will be interesting to see if more of these type issues show up this year. I had a Saturn, made of plastic .... when a side fender got hit a big chunk of plastic material cracked and soon fell of ... boy was that ugly. For my $$$ the jury is still out. Even @ < $5K, I think I will pass for now.
02-26-2014, 02:27 PM #3
02-26-2014, 02:58 PM #4
02-26-2014, 03:00 PM #5
Nothing will ever beat the durability of fiberglass
02-26-2014, 04:11 PM #6
02-26-2014, 04:16 PM #7
OK, I now understand ... I thought maybe you got a spark and was convinced of it's durability.
02-26-2014, 04:54 PM #8
No, absolutely not. Just passing it along !
02-26-2014, 05:05 PM #9
First I scratched the rear right hand said of my spark by scraping it on the loading ramp, but I love the ingenuity of Sea Doo BRP - I can just buy that piece and replace it! Wow I love it. It's screwed on, and so easily replaceable.
Also aren't some kayaks built purely of hard plastic? I think some are made extremely strong, very hard to bend or brake.
Also, after reading about Yamahas SMC, seems some people can't fix them with some Fiberglas repair, because it's not real fiberglass? I read somewhere where it's heated epoxy resin?
My Sea Doo Speedster Boat is fiberglass and it is very strong, and I believe that Fiberglass is the best material for boats, BUT FOR PWC's?
After riding my Spark, I believe that material is the future, either being a little stronger, with some foam backing.. But I believe that's the new road of PWC's. I'm very happy I didn't spend a fortune on a ski.. I couLd just replace the parts I break! Love it!
02-26-2014, 08:52 PM #10
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