Can small cat hulls be made of ALUMINUM???

the sizzler is made out of alum, and no, I don't think you could make it as light as fiberglass.

I think you could make it very light out of aluminum if you didn't have to fill the whole thing with expandable foam to hold the shape, to give it structural strength, and to keep it from making a lot of noise. The prototype Sizzler with no foam in it was VERY light.

By the way, you don't know what wave-piercing bows are until you have seen a Sizzler -- like knives, top and bottom.

In theory you can make Al hulls as light as GRP hulls as the two materials have similar specific stiffness (stiffness to weight). However in practice the aluminium does become very thin and so difficult to work with, i.e. weld and easier to dent. Also GRP is easy to work into a very efficient sandwich structure, Al is more difficult. Aluminium is more suited to boats that are larger than the average beach cat.

That said there are lots of new ways of forming Al so while you might not get a weight advantage you could have a significant cost advantage if you could sell enough of them!

Gareth
www.fourhulls.com

I can see that aluminum would be a good material, but the joining of it could be a bit problematic. I have a lot of experience in the testing of metals, and know that a good water-tight, structual aluminum weld is often very difficult to make. I know that traditional wire-fed welds on material thin enough to give acceptable weights for catamarans are very, very tough, and the skill level required would be on the level of 1 welder vs 3 fiberglass mechanics. I give that as a ratio as welders working today with that skill level do not come cheap, and their numbers are declining.
I really think that to achieve a top quality product there will have to be the use of new technology such electon-beam welding for this. I've been around it and anything that can produce a flawless weld joining the foil of a cigeratte pack to a foil gum wrapper with no distortion....well, it's good. I know that the similar metalurgical techniques used in the manufacture of golf clubs today has potential elsewhere, just as a lot of it came over from the defense/areospace world in the 1980s.
Just my thoughts.

Rich

Alright, the SIZZLER... I like it. *Seems* seriously deficient in bow buoyancy, but that might be offset by the aforementioned "wave slicing" shape... and the shape is what I'd expect in sheet aluminum--basically 2-dimensional--easy to fabricate without expensive mold-tooling... yep, not very likely you're going to walk or belly crawl out on those bows. But it's ingenious in a way, at least from a cost of production standpoint.

Mary, great evolutionary insight (over in TheBeachcats.com) on how the constraints of shaping sheet Al influenced the G-cats. I believe the Darts and boardless NACRAs also utilize that narrow-hull w/ fin-keel approach...? Would love to know the dates each first appeared on the scene.

... I was thinking more of a 3-sided shape, with a flat deck. Instead of foam, much weight could be saved by semi-conformal air bladders... pop a pressure gauge on your tires, AND your catamaran, lol. Not sure how to do daggerboards, if needed.

Also excellent metallurgical info from someone in the field, with a real world perspective on the labor angle. Lets face it, once you get your female molds made, there's a lot of gelcoat and resin sprayers from the board and boat industries you can put to work cranking out GRP cats... less so with leading edge whiz-bang Al seam joining.

Sorry, I had planned to post the article here for you so that you wouldn't have to walk over to TheBeachcats.com, but I got sidetracked.

Here is the article I wrote for that website. (I worked for the company that made the Sizzler.)

Details on the Sizzler Catamarans from Mary Wells:
The Sizzler was one of various small cats that appeared in the 1970's and tried to ride the coattails of Hobie Cat's success. The name of the company was Great Lakes Manufacturing Co., located in a suburb of Cleveland, Ohio. It started in about 1974. The owners of the company were Ed Vlack and Art Bates. Bates was the one who ran the company. The designer of the Sizzler was Paul Swenson, an engineer who had built catamarans of his own in the past.

The Sizzler was unique in that it was made out of aluminum. And the process of making it was also unique -- the aluminum was stretch-formed to give it its shape. Each hull consisted of two pieces of aluminum that were fastened together all the way around, top and bottom. In order to give these two flat pieces of aluminum a boat-like shape, the two pieces of aluminum were first clamped together in a big jig, and compressed air was pumped in between the two aluminum pieces, forcing them into the desired shape.

Now that they had shape, the two halves of the hull were permanently secured together with a stainless steel U-strip that went all the way around, except for the stern. Castings were put into the sterns to create narrow transoms to hold the rudders.

The boat had a raised deck on pylons, just like the Hobie 16. The pylons were put in place, and then the hulls were filled with some kind of expanding foam that was supposed to fill the entire interior of the hulls. Supposedly, this foam could not absorb water, but it definitely did, and that was ultimately the downfall of the Sizzler. Not only did the foam itself absorb water, but the foam often had voids in it. Those would fill with water, and there was no way to get the water out. The boats kept getting heavier and heavier as time went on.

The tops and bottoms and bows of the hulls were very sharp because of the way the two aluminum halves were fastened together, so it had probably THE most wave-piercing bow of any catamaran ever invented. The bottom curved down, and its depth, coupled with its narrow profile, was what resisted leeway.

It was really a rather pretty boat. The first model was the Sizzler 16. It had the same sail area and mast height as the Hobie 16. But for some reason it did not seem to perform as well, despite its sleek lines. So they came out with the Super Sizzler with taller mast and more sail area. That boat seemed very well balanced and was much faster.

And then they came out with the Sizzler 18. That model had problems because the hulls were just too heavy, and they racked a lot under sail. (The Sizzler 18 was one of the catamarans in the movie Jaws 2.) There was also a powerboat model -- sort of a pontoon boat -- using the Sizzler 18-foot hulls.

One of its unique features, was its angled anti-pitchpole foil between the bows. The boat also had a roller-furling jib, which had a clever and simple furling system. It consisted of a plastic drum at the bottom, which was glued to a long PVC tube. The jib had a sleeve down the luff. So you slid the jib onto the PVC tube and secured it top and bottom with hose clamps. Then you ran the forestay down through the PVC tube and attached the forestay to the bridle. The furling string was wrapped around the drum. Swenson also invented a mast erector system for the Trailex trailers that we sold with our boats.

And he also was experimenting with little hydrofoils that he would clamp onto the U-ring on each hull, about halfway between the main beam and the bows.

We sold quite a few boats, but obviously not enough. The company owners spent a fortune on advertising and promotional materials. We went to regattas and to boat shows. Took a 16-footer and an 18-footer down to Miami for the Midwinter Multihull Championships. It was all for naught. Art Bates gave up after a few years of pouring money into the project.

One of our dealers in Florida was a man named Hans Geissler, who later designed the G-Cats based largely on the underwater shape of the Sizzler.

In case anyone wonders whether there were electrolysis problems in saltwater between the aluminum hulls and the stainless U-ring, yes, there were. So we put a strip of rubber all the way around, to separate the two metals.

Also, one practical problem with the design was that it was difficult to pull up on a beach because of it's very sharp hulls, which dig into the sand rather than sliding on it. It had an advantage on flat rock or launching ramps, because the stainless steel U-ring protected the bottom.

Mary Wells Catamaran Sailor Magazine http://www.Catsailor.com

Playstation (Cheyenne) was made of aluminum honeycomb sandwiched between carbon/epoxy, but this type of hull wall is a good solution for big cats only.