Advanced aluminium extrusions for boatbuilding?

[simon]

Most of the sources mention flat bars, L-, T- or bulb aluminium extrusions for the use of longitudinals. But are there other types of extrusions, for example like a D-shaped, that will distribute the load more evenly and will reduce the unsupported panel area, not being heavier, faster to build?

In shipbuilding new extrusions for decks have come up that simplify the construction process.

What is the potential for use of specialized aluminium extrusions in boatbuilding?

[kmorin]

simon,

In the NW new extrusions can be done several ways. One is to pay the die charge to design and machine the extrusion plate and also buy the minimum wt order - as 1000 lb of material. The second is to OWN or hold rights to the plate's output in addition to the above.

The latter method resembles a patent, or copyright but if the extrusion mill finds lots of customers for your shape-well you'd need some good prior agreement to defend your proprietary shape.

I've done this a few times over the last few decades- design an extrusion- my first was the 1/2 pipe now one of the most common shapes sold in 6061 for wrapping the gunwales without splitting whole pipe.

The second time was a much more complex shape- still very simple compared to 80/20's bar stock, but again if you don't have dialog with the extrusion company your idea becomes their property and they can sell it to whomever they'd like.

1000 at $2.50 to $3.00lb for the metal order and another 2- 5K for the plate seem to be about the likely costs. All these numbers could be off if the alloy was not 6061-T6 or something similar since that is what the example is based on.

If the framing members (extrusions) are larger than four inches in one direction(?) it would probably be more economic to bend sheered plate into tall "L's" rather than extrude.

Depending on the boat size and the orientation of the structural elements bending is extremely cost effective. Building open skiffs for commercial fishing I used to bend 1/8" 5086 into an 8" tall 8" wide U where the legs were not parallel but 15degs spread. This was fit to the bottom of the skiff transversely. The resulting fully welded box was an 8" x 8" hollow member holding a 3" convex camber in the bottom. These "rib's" were light, stiff and kept the load from shifting fore and aft so they did lots of 'work' in the overall design.

The folded sheet was much less expensive than an extrusion of a similar section.

An extrusion that is 2" x 3" x 1/4" of a similar cross section described above is available - I've only heard it referred to as "Hull Stiffener" I don't know the extrusion order number. I've used thousands of feet of this material to stiffen hull panels in lots of different boats.

Cheers,
kmorin

[FAST FRED]

I wonder if someone would be kind enough to publish current (JAN 08) per pound prices for aluminum for a common hull build .

say 1/4 , 3/16 plate and the price of appropriate T and L stock? 5083 ? or whatever would be a good choice.

Close $$$$ costs would be great , Thanks!

FF

[kmorin]

FAST FRED,
I just called the supplier in Kenai Alaska and 6061 extrusions are from $3.75 to $4.03 /lb depending on shape.
5052 is $3.88 to $4.10/lb. - larger sizes have a handling cost with crating to our location.
5086 is $4.70-$4.85 lb larger sizes carrying similar extra burden for handling and crating.

Costs can usually be reduced (5-15%) by buying >10k lb. in a single order and accepting delivery directly off the shipping flat instead of having local distributor handling material as inventory. Savings is in quantity break (volume), handling along the way (multiple crates vs one) , local loading and handling costs (who's employees move the goods) and bulk customers generally receive better (lower) distributor margins.

All of this material is shipped barge to Anchorage or Seward from Seattle- and trucked on to Kenai- so freight costs are very likely higher than in the contiguous states (the Old Country).

Cheers,
kmorin

[Seaboater]

You may want to look at the features page of the Duroboat website. It has a sketch of the extrusions they use to build aluminum boats without rivets or welds.
www.duroboat.com

[kmorin]

Seaboater,

It looks like the patented Duroboat extrusions wouldn't be available to the general market? Plus they look to require some hull panel edge treatment that might be out of scope for less than a manufacturing plant investment.

From their site; it seems the panel edges are 'wedged' into the extrusions in a jam fit with an extruded plastic gasket filler that locks into a precisely cut groove in the hull panels. It may work for them but I'm not confident a one-man shop could get this type of system to be effective?

I may not understand the joint's seal and lock method but that is what the site implies to me.

Cheers,
kmorin

[Thunderhead19]

There are a number of mills out there (the majority) that retain the dies when someone special orders an extrusion. Generally if the mill can sell more of the extrusion to other customers, they refund part of the die tooling cost to the original buyer. Check with some of the bigger mills and see if they have a catalogue, or a tool similar to what you want. Some of our local suppliers have contacts in Asia that charge next to nothing for tooling, and can crank out 500ft of specialty extrusion AND ship it to Vancouver or Seattle for less than what we can get it for domestically. Go figure.

[petereng]

Hello Simon,
You ask about advanced boatbuilding then discuss aluminium. Fiberglass construction will produce lighter and stronger boats then aluminium and you can make any shape you like on site. If you go to sandwich construction the boat will be significantly lighter then aluminium can can produce. I suggest you sidestep the aluminium path and go straight to composites. Military shipbuilders are going this path so must be OK.
Cheers Peter

[Thunderhead19]

Who wants to work with FRP...Stiiiinky poooo.
Just kidding...well, no not really.

[petereng]

Haven't you heard of Infusion or VARTM. No fumes, can take as long as you like to lay dry fibre, then you get excellent engineering properties, lightweight super strength (much much stronger then aluminium) no corrosion, easy to repair (no welding), can make any shape yopu want... the list goes on.

Peter

[Jratte]

I gotta say after spending nearly the last year and a half building aluminum ships, I certainly wish we used fiberglass for certain pieces, especially lately. Some of the complex curves they have designed would be much better suited to glass, especially since many of them don't serve a structural purpose.

[Thunderhead19]

Infusion works great except for the cosmetic part. I'm sure someone has this figured out already, but the last time I was involved with infusion, we had to lay down our cosmetic layer and some mat and a print barrier before we were even ready to set up the infusion equipment...and it was stinky. Okay...I'm just bitter because my first day on the job I slipped and fell into a mass of uncured FRP.

[petereng]

To get good cosmetics from styrenated resins you need to use a "finishmat" type product or you can use CSM for the outer layers. If an oven (or heated mould) is available the part can be post cured in the mould and the cosmetics will be perfect. Print through with epoxy is not a problem as it dosn't shrink as much. Since the resin consumption in infusion is well down compared to conventional processes and since this thread was "kicked off" by "advanced boatbuilding" I'd be using epoxy for various reasons anyway so all of your concerns would be covered.

The best practice is as follows;

1) Gel coat (0.5-0.75mm)
2) Barrier coat (0.5 - 0.75mm)
3) felt mat of suitable thickness (laid dry) infused thickness can be from 0.3mm for lantor finishmat up to 1.0mm for other products behind heavy laminates
4) 200gsm layer of needle punched CSM (laid dry)
5) structural laminate
6) Infuse, let exotherm peak under vacuum
7) Post cure on the mould under vacuum, to resin suppliers spec

If the laminate is very light use epoxy.

Cheers
Petereng

[simon]

OK, we are back to fundamental discussions and are writing about laminates in the metal construction area.

So you cracks, give me a solution to my wish. I want a low maintenance surface, no fairing, no painting. I sometimes bump into things and my fender is not where it should be, or other boats are hugging mine, like recently a catamaran that had it's laminate ( on the water level, so reapairs are quite difficult without drying out) beaten down to the core while my (5mm)aluminium hull has some scratches.

I hit big iceblocks and broke through solid ice surface for hundreds of meters.
Tell me how you are going to do this with your shiny, awlgripped topsides?

I might be a bit sloppy about paint maintenance, I do not want to spend any sweat on fearing for my precious paint job.

I want a construction that will not need hundreds and thousands of hours of sanding.


Any suggestions about using a prefabricated top layer (any material) that will bring these qualities.

Anyone has seen aluminium used as a top layer on a cored hull. How can I combine the best of both worlds?

So you composite cracks, lets see your answers

[SeaSpark]

The bond between aluminum and any adhering material requires a careful preparation of the alu surface.

http://www.google.com/search?hl=en&q=site%3Aboatdesign.net++etch+aluminium&btnG=Google+Search

http://www.boatdesign.net/forums/showthread.php?t=12408

http://www.boatdesign.net/forums/showthread.php?t=2629

http://www.boatdesign.net/wiki/MaterialsForBoatbuilding#Painting_.2F_Surface_Preparation_for_aluminum

Riveted/bonded/ Rivalike http://www.silvestris-aquamotive.com/aquamotive/
Skip the first minute:
http://www.youtube.com/watch?v=6Q7mrVPZfVM

http://www.google.com/search?hl=en&safe=off&q=amorphous+metals&btnG=Search

Please let me know of any other options.

[simon]

Seaspark,

thanks for the links.

Did you follow your idea with the barrier coat any further?

How thick should the metal barrier be, so that it can withstand the abuse of daily use?

Would it be better to have a thin metalic layer without structural purpose or making it thicker to take on some load, or even just use metal as the outer shell of the sandwich structure?

Would the epoxy bonding of aluminium withstand structural loads? What about the product that West System is selling called G/flex Epoxy.

http://www.epoxyworks.com/25/pdf/G-flex_Epoxy.pdf

I can think of two ways to easily construct a hull:
- hard-chined hull
- something like the tortured plywood, or the cylinder mold approach.

This way the panels can be fully or partly prepared with vaccum bagging or infusion and asembled afterwards. How join the panels so that the metal is connected throughout the hull?

Any good input? This theme bugs me for a long time and would be interested in seeing a realistic ideas.

Simon

[SeaSpark]

Have not found a metal yet that bonds easily with epoxy or polyester in a marine environment.

[SeaSpark]

Somekind of lapstrake construction with aluminum extrusions and non structural goo between the strakes has my interest.

[SeaSpark]

Simon:
Did you follow your idea with the barrier coat any further?

Seaspark:

Have not found a metal yet that bonds easily with epoxy or polyester in a marine environment.

To explain a little further, i think the required etching before bonding will eat away to much of a thin alu film and is impractical on a large surface. The idea as a whole has many impracticalities involved and the problem of moister ingress in a good epoxy laminate is mostly a theoretical one.

[petereng]

Hello Simon,
1) To go back to your original question - You can have nearly any shape you want custom extruded in aluminium and use conventional welding to build your boat. It comes down to the shapes you want to realise.
2) The problem with metal is acheiving compound curves. A company in australia built 35 foot sailing boat hulls using explosive forming. They had a concrete mould (in the ground) the shape of the hull. They welded flat pieces together that fitted into the mould roughly. They then filled the hull with water and couple of sticks of explosive and "BANG" the aluminium is formed to the mould shape. Then they fitted out the hull in the normal manner. This is advanced boat building in aluminium
3) If you choose to build in fibreglass flat panel, you require thermoplastic flat panels with pigmented resin. So no painting required. You bond it with plexus, no preparation required.
4) If you choose to build in fibreglass in a mould to get the shape you want then use pigmented resin (no painting required) use a high elongation epoxy (like they use in wind turbine blades for great impact performance) and use plexus to join it (no preparation required)
5) You can mix and match aluminium with fibreglass or carbon or steel but I'd try to live in one world. Its much easier.
6) I've been involved with thermoplastic/glass panels in trucks that outperform aluminium in impact and abuse. For floors and side walls, they get loaded and unloaded every day, scuffed by forklifts etc etc.

Cheers Peter

[simon]

Peter,

thanks for the interesting input.

I would like to know more about the use of thermoplastics in boatbuilding. I have not heard of it before.
- How does the thermoplastics's surface toughness compare to aluminium?
- How would you suggest to setup a sandwich structure with thermoplastics? i.e. Thickness of the thermoplastics.
- What would be the weight of such a laminate?
- Do you have any experience with Plexus's products? Their website tells that they have got approval by Loyds.

Simon

[petereng]

Thermoplastics toughness is greater then aluminium. Consider how tough a PETE bottle is vs the same thickness bottle in aluminium or a polyethylene canoe. The thickness and weight would be the same as conventional thermosetting resins. The processing temp is from 150 to 300degsC, depends on the plastic used. For flat sandwich construction I'd build the skins then secondary bond them to the core. If the core had a suitable processing temp then it can be done in one shot which is preferred. Plexus produceses bonds which are stronger then the laminate. Many boat builders are now joining their stiffeners and bulkheads using this. Advantages are no preparation required and no taping over the join. Saves considerable time. Curing time is 15mins so very fast in production situation. Plexus fulfils survey requirements so must be OK.

Peter

[simon]

Hello Peter,

sounds interesting. Could you give me some hints where to start reading to understand more about the handling of thermoplastics.
What are the size limits for panels and what is the procedure to produce large panels in a backyard workshop, or is this out of scope?
After a quick glimpse at Wikipedia, I see that there are more than 40 types of plastics. What do you recommend for the use in marine environment?

Thanks for your input

Simon

[petereng]

Size comes down to the size of your oven. Oven temp comes down to what plastics you want to do. An oven with 250degs is OK, same as your kitchen oven, fan forced but the size of the object you want to do.

http://www.twintex.com/products/tw_product.html

Here are some premade products and info as a primer.

Peter

[simon]

Hello Peter,

So if I want to build large panels like made for Kelsall or Hughes cats, I will need an oven of same length and width as the panels. This will be a huge oven or there any easier ways to produce them? Are there any ready sheets of large dimensions?

Thanks

Simon

[petereng]

You make the biggest oven that you can and then join the panels/parts together.

Peter

[simon]

Peter,

I have found a website describing large thermoplastic panels with fiberglass reinforcement and sandwiching with core material, like honeycomb and foam.
The sheets can be produced in width up to 2.69 m and lengths up to ~150m.

http://www.cranecomposites.com/zenicon.asp
http://www.azobuild.com/news.asp?newsID=1655

Panels for kits could be prepared in one part. So it would be possible to make kits for chined hulls with thermoplastics outer skins.

What do you think about this?

Simon

[petereng]

Hi Simon,
Looked at the site, very informative. The skins have good engineering properties typical of high quality vacuum bagged or infused laminates. The plastic is polypropylene which is very tough, tougher then epoxy or vinylester resins and PP is less dense so they would be lighter overall as well. Bond with plexus or equivalent and it would be bombproff!! Nearly
Peter

[simon]

Hello Peter,

I would like to continue this interesting thread, but think that it should belong to the composite department. Shouldn't we start a new thread over there?

I have tried to contact Crane Composites without reply.

- Do you know of any other producers of similar products?
- Are there economical ways to produce large Continuous Fiber Reinforced Thermoplastic Composites Panels?
- Would it be sufficient to glue thermoplastic laminates directly to both sides of the core?
- How could panels be structually joined and still have a continuous surface?


Simon

[petereng]

Simon,
I have strated a Thermoplastic Construction thread in the boatbuilding area. I have answered your questions there.
Cheers Peter