Considering building a boat..

[Aeron99]

Hi all,
Im considering building a boat. My first homebuilt...
here's what Im trying to achieve with the design:

Im thinking of an open deck Catamaran, just under 40 feet in legnth...
maybe the maximum size that, when its taken apart(rarely) I can fit it in a standard 40 foot shipping container. Maybe 20 feet wide, Solid decks.
Im not sure about riging... I like the idea of a performance rig with maybe a jib and a gennaker on rollers... getting that mast in a shipping container represents hight issues, although I would prefer the simplicity of a single mast... I would prefer a boom thats more then 6 feet over the deck...
Im thinking of a an aluminum radar arch type arrangement...
I would also like to bow (as in 'take a') the mast to get it under low bridges, without a lot of work...
2 outboard engines- one on each hull. maybe 25 hp to start but rated to 50 or 60 hp.
shallow draft- 2 feet
skegs or keels or retracting keels, Im not sure yet

Hull- thick enough inside that each one is a long slim cabin with a toilet...

construction- Im thinking of making the hull out of thin sheets of 5000 series aluminum in the 1 mm range, and glued together using epoxy glue over the entire surfact. multiple, non overlaping sheets of aluminum, possibly in slightly different alloy's so the underbody is harder... This means the hulls are developable surfaces... Im told that aluminum sheets can be glued together using epoxy if the surface oxide is removed and its easy to do with a mild acid wash...Im hoping to prebuild frames, attach them with stringers/longitudinal ribs and then pull the hull sheet using it like a mold, then adding sheets.
I think this might lend itself to prebuilding frames at home, then a relavively quick and short glue up of the whole hull- like 1 or 2 weekends-

insulate the hull with poured closed cell foam between inner panels that are attached by small risers from the hull.

I need a foul wether blister in each hull...

steering is by tiller and crossbeam, with a good autopilot

Im still developing this idea. any ideas?
Im contemplating it as a world cruiser/explorer thats beachable and fast and has a ton of deck space...with a light weight, ~4500 pounds, it should really fly on sail, and achieve over 22 knots on the top engine config...
Any thoughts?

A

[Tim B]

that's a hell of a job you're taking on. The design itself would take a full time designer a fair while.
I like the concept of it fitting in to a 40 foot container, has a lot to be said for it.
The idea of going for tiller steering is not one that I'd personally like to try. Use hydraulics and put a wheel in, it will be easier.
I don't think I'd glue aluminium sheets together for a job like this. Use plates of the scantling thickness and weld them. The end result will be at least as strong and won't de-laminate.

There are a lot of good, interesting concepts, but it will take time. It is not a job to be rushed at,

Tim B.

[Seafarer24]

Check out www.sailingcatamarans.com .

How do you expect to "easily" raise and lower a 50-60' mast, and de-tension and re-tension the rig exactly the same each time? It sounds like a project for hydraulics to me, which will add weight and complexity. Weight is the bane of any catamaran- sending it's performance right down to the crappy levels of a monohull. Complexity is the bane of any sailor, and if a hydraulic system is responsible for holding the rig aloft, I wouldn't trust that rig to stay aloft! There would (obviously) have to be some sort of fail-safe in place to hold the rig up once the hydraulics have positioned and tensioned everything.

For the whole mast-stepping issue, a trimaran would simplify things greatly by giving you a place in-line with the stresses to mount the hydraulics. The base of the mast could be stepped on a track that runs forwards to the bow, allowing it to be slid forward to de-tension the rig and minimize how much of the mast overhangs the stern.

Aluminum and epoxy don't really mix. I second the above recomendation of single, thicker aluminum sheets. Alternatively a wood or foam core with your choice of outer and inner skins (kevlar, carbon, fiberglass). Check out the construction details of the Stilletto 23. A bigger, faster boat than the Reynolds 21 and less than half the weight.

I believe you could have a cool, complex boat- or a fast one. I doubt you can have both as complexity adds weight.

[Aeron99]

I was looking at a 36' macgregor westport as my inspiration- that design has the shroud wires connected to the hull crossbeam that the mast rests on. that is to say the shroud wires are in a verticle plane perpendicular to the center line, along the mast line. when the mast is 'bowed' the shroud wires maintain side to side tention. Im not sure how the rear is supported.. anyway it is just winched down by the rear shroud? support wire.

of course going with a single mast suggests that its longer then 40'... how detachable could the top 5 or 10 feet be?


As for aluminum- I was watching a show on the history channel- I think it was on 'glue', they seemed to say that epoxy could be used to produce a bond that was good for life, and stronger then the material it was adhered too.
welding thicker sheets seems vastly more complicated....heat expansion, grinding welds, weld zone weakening...

[Tim B]

The problems with welding aluminium are far less than those of gluing it. Epoxy isn't anywhere near as strong as aluminium for starters. so you can't possibly have a joint that's as strong as the material it's glued to.

There are a lot of ways to raise and lower a mast, primarily, bolting the mast into the step (with one bolt to act as a pivot) then using the spinnaker pole between the forestay and the mast (braced sideways so it doesn't move initially) and then winching the whole lot up. It's not easy to do.

Now, as I remember, containers are typically 40ft by 8ft by 8ft or there abouts. to get the whole boat in there will be a struggle. Personally, with a 40 foot boat, I'd just sail it to where I wanted to go. that would make the design a bit easier and save totally removable cross-beams.

Tim B.

[Carlito's]

Hi,

Talking about catamarans chek www.volvoextreme40.com you could take a few performance ideas of it. The most that I'm impresive with is the main sheet it's hydraulic. They always run so full sheeted using the aparent that they don't have need for a long sheet. You have there a lot of information to design yours and look into the "simplisity", in racing thats the icon of the moment. Good luck

[Aeron99]

volvo extreme 40 hunh?

2 piece cabon fiber mast only weighs 100kg- about 220 pounds

total weight -1250kg or about 3000 pounds-

cost- astronomical...

nifty though-

Im thinking of ditching the trailer and possibly have the hulls sideways to allow most of 5 feet for the maximum width- possibly a little more with an inner, above waterline buldge..

[Carlito's]

Well Im not telling you to use carbon but there you have good specs information that with a equivalence formula you could work with a good own design. They'r great ha. They got a very impresive video. Cats are the future you are thinking good.

[marshmat]

Some interesting ideas tossed around here, for sure.

This project will take a long time. Much more than a few weekends. If you have a job other than this, and are building as a hobby, I'd book about two years for this boat.

We don't glue aluminum, no matter what the epoxy makers say. You just don't do that. It doesn't work. (Well, it works fine, until you get to the open sea.)

This will be a very challenging, very fun and very rewarding project. Best of luck to you.

I'll be back with more when I get a chance....

[Aeron99]

I gotta say Im throwing the whole glued aluminum idea out there to see if it leads to some solid answers... I mean, its not a conventional, or traditional, or whatever construction technique. Heck, even carbon fiber in an epoxy matrix is practically old fashioned by comparison.... and anyone would be a fool to risk their lives as well as their efforts on a hull that could delaminate...

frankly Im still really impressed by the demonstration where they said that the bond is for life and is stronger then the material. I guess Im really looking for an epoxy manufacturer to certify that if properly preped, it will hold for life...

no weld distortions, or weakening. no need to deal with thick 5 mm sheets that need special tools to form... the ability to create differing thickness in different areas by varying the number of laminate layers....

as for the couple of weekend comment of mine- I meant that I would prepare the framing members at home, and then only need a full size -40 feet long work area for those couple of weekends, having preped all the interior framing for assembly before hand working nights in my living room... with a pool of mild acid.....

Oh and geez that volvo 40 boat- Im picturing a quarter million dollar price tag. .. not that it isnt super wonderfull and all but geez, Im on a much smaller budget.

any idea how much can I expect to pay for 4000 pounds of a nice marine grade aluminum?

[cleblanc]

I like the 40 foot open deck catamaran, if the hulls are simple enough, these boat are faster to build but unfortunatly, the rigging is expensive.

About glueing aluminium, epoxy is not the best choice for "welding" aluminium. To put is simply, epoxy is a "stiff" glue and aluminium is a stiff material so there are going to be stress concentration at the gluing point and the glue will breake faster. You should use a "softer" glue like polyurethane glue and simply increase the contact surface to achieve the desired strength. This means that the aluminium would need to be overlapping.

About the cost of glue: You cannot glue aluminium with glue, you need an "adhesive system". If you take regular epoxy, the bond will not be strong and will breake. An adhesive system means that you need to use a process for glueing and you need to use: Brushing or sand blasting the area + acid wash + chomate solution + glue. This is an example but each system will have different process and you will need to use specific chemicals and tools to achieve the full strength of the bonding. These chemicals and the tooling are expensive and it takes alot of time to do it properly.

Standard side of a container is 8' wide x 8'6" high, remove about 4-5" to these dimensions for the door openings. The High cube container is 9'6"tallx8' wide. You should aim for shipping using two containers unless you want to have a triangular main section ;-)

About the aluminium, Anything under 3mm is difficult to weld. and anything under 2mm of thickness will need ALOT of strigners and of frames to meet the strength requirement for the hull. Also a catamaran has specific loads induced by the cross breams and the shrouds.

About the aluminium alloy, out of the current alloy available for amateur in thin sheets builders, the 5083-H32 is the best alloy for the strength after welding and the corrosion resistance. If you do not plan to weld, the 6061-T6 will have better strength but average corrosion resistance. The underbody should actually be softer. You want it to ding instead of shearing. when you condiser the allow, you need to look at the elongation%

One last thing about aluiminium thin sheets: you can have then in any length, ypu could order 5'x 45' and they will "unroll" it for you. This would allow you to build your boat with continuous longitudinal sheets

About the mast: the simplest solution is to use a vertical gaff rig but it is not going to ge a high performance; this would also solve your vertical clearance problem.

You should purchase some aluminum sheets and start doing some tests. Buy one tube of Sikaflex and use it as a reference system. BTW Sika is one of the companies doing an adhesice system for aluminium, Loctite is another.


> insulate the hull with poured closed cell foam between inner panels that are attached by small risers from the hull.

Actually if the foam bonds to the aluminium and to the inner pannels, it will help with the strength.


> steering is by tiller and crossbeam, with a good autopilot

This is the simplest system, like on a big beach catamaran. Look et the ARC-30 catamaran for some idead how to design it. You would need to have transom mounted rudders

>Im still developing this idea. any ideas?
>Im contemplating it as a world cruiser/explorer thats beachable and fast and has a ton of deck space...with a light weight, ~4500 pounds, it should really fly on sail, and achieve over 22 knots on the top engine config...

>Any thoughts?

If you take a backyard boatduilder attitude and simplify this project, it might give something interesting but you might reconsider the hull thickness because anything below 4.5mm doesn't strike me as a world cruiser. Also I believe that aluminium is the way of the futur for aluminium but you do not have the engineering departement of Boeing or Airbus to design and do the structural calculations for your project.

I have been looking at similar project iver the last year and I believe that there are some quick building methods for aluminium out there.

As far as the price of marine grade aluminium, I can have 5083-H32 for about 3$can/lb in Canada but it is not a marine grade, the cheapest marine grade is 5083-h116 but it is very difficult to get and it is not available in thin sheets. All of the other marine grade are even more difficult to get. Expect a few month of delivery time

[Aeron99]

Thanks Charles leblanc....

I already have a copy of Pollard's Boatbuilding with Aluminum... which discusses various aluminum alloys....
5052-h32 looks nice...
here's my thinking- Im narrowing the list to a 5000 series due to its higher ressitatnce to marine corrosion.. now looking at those 5000 series yields two classes of aluminum- the higher stregnth, high yield str. ones that have low elongation, and the lower yield ones that have a higher elongation %... frankly I was considering 5086-0 as it has high tesile stregth, 38k, medium yield 17k, and a higher elongation % at 22%...
Im noticing that the higher stregnth ones with the lower elongation % are rated only a B for forming ability... while the second group are all rated A for forming... all of the alluminum alloys are rated A for weldability...

As for your comment about the glue- Im talking about glueing over a the entire surface of the laminated layers- the aluminum will elongate or rip apart before the glud fails... (supposedly)....
Also Im did hear somthing about it needing only 10 minutes of the mild acid solution to prep the surface...

[Aeron99]

I was also thinking of building the mast myself using laminate layers- similar to the way wood laminate masts are built...

[marshmat]

Note that adhesives of any sort, regardless of how good their tensile strength is, will always fail readily under peel loading. You will have to ensure your structure is designed to have no peel, and minimal shear, loading on bonded components. 5086 is probably a nice fit for what you're planning; it's fairly common in marine use and is well proven in this application.

Also, watch out for the poured foams, some of the urethane ones turn highly corrosive when in contact with the oxide layer on the surface of the aluminum. Make sure whatever you use is rated for use in aluminum construction.

[John ilett]

I would also be concerned of committing to such a brave new method of construction.

I have come across this epoxy glue specific for bonding to alloys/metals.

Techniglue HP-R5

http://www.atlcomposites.com/product...ves/index.htm#

Personally composite boats are best, plastic cores (no balsa).