Now for something completely different

I'm not a boat builder (though if I live long enough, I might be); the project I'd like advice and help on is a marine plywood monocoque chassis for a vintage car. For those of you steeped in automotive arcana, the design is very much akin to the 1964 Marcos 1800 GT, which was a coupé whose chassis was built with marine plywood torsion box-and-sill construction, the corner joints glued-and-screwed, and reinforced with aircraft 1" x 1" spruce. The front suspension was attached to a wide-based tubular steel subframe (directly attached to the front plywood torsion box). The chassis was then bonded to the fiberglass body with epoxy resin along the lower sills and wheel wells, and the rear live-axle suspension was directly attached to the wooden monocoque with bolts and steel reinforcing plates.

My car will be almost identical in build -- except mine is an open car -- using MGB 1800 drivetrain components (the Marcos GT1800 originally used the same engine as in the Volvo P1800 -- same basic size, weight and power as the MGB engine), and the MGB front crossmember, which solves the front suspension problem, as the MGB front crossmember incorporates the Armstrong lever-arm front suspension, Girling disc brakes, and rack-and-pinion steering, and keeps everything aligned on the hollow steel structure of the crossmember. The rear suspension, like the Marcos GT, will have the MGB rear live-axle suspension directly attached to the wooden monocoque with Grade 8 bolts and steel reinforcing plates.

I have detailed pictures from the Marcos "assembly line," if anyone's interested.

Before I blather on like an idiot, is this an OK topic to discuss here? I really need some advice on bonding and reinforcing plywood. BTW, Marcos used marine ply to eliminate inter-laminate glue gaps, ensuring all joints are strong.

Thanks for your time!

Bart Brown

 

Go out and buy and old Morgan: English, wood, good looking, fast, & inflatable seats.

 

A good place to start. Many of the methods could be used for a car.
http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook 061205.pdf

 

Get it built in Thailand... there used to be a guy in Pattaya....

 

Welcome to the forum Bart. This forum is meant to be about boat building as the focus, but a post or two regarding a tangential build project is fine if you want to ask about common boatbuilding materials or how boatbuilding methods might apply.

 

Cool ride!
God's speed

 

Well, thanks, and I appreciate the suggestion...but:

A. Used Morgan 4/4s, Plus 4s, and even Moggie 3-wheelers average in the £18K ($US30K) to £30K ($US50K) range, and I'm retired and on a fixed income, and couldn't even afford the down-payment (or the hospital bills from my wife cracking my skull open)

B. I'm not a fan of sliding pillar suspension, and the way Morgan uses wood (solid ash) in their frame construction lends nothing to torsional stiffness, whereas the Marcos had one of the most torsionally rigid chassis per chassis weight -- almost triple that that of a steel chassis of equal weight -- of any car built before the advent of autoclaved carbon/Kevlar composites.

C. I already have a considerable investment in time, money, and storage space in a couple tons of MGB engines, spare blocks, transmissions, rear axles, front cross members, steering rack-and-pinion assemblies, wire wheels, windscreens, and stuff that will go on eBay, like the alloy bonnets and complete rear deck lids from the MGB-GTs, side-curtains, convertible bows, you name it... oh, and I already have the 6-section fiberglass body

D. A large part of the satisfaction (and unavoidable frustration) of this project is that I largely designed and will build the car myself (if I don't die first, which is an even-money bet). I suspect that's also a large part of the satisfaction (and unavoidable frustration) of designing and building your own boat

NB: On an historical note, the folks in the forum may (or may not) find it interesting that the name Marcos derives from the names of the builder (Jem MARsh) and designer (Frank COStin) — Frank Costin was an aerodynamicist at the de Havilland Aircraft Company, and was part of the design team that produced the very successful plywood monocoque DH.98 Mosquito, a front-line multi-role WWII combat aircraft which in the early 1940s was one of the fastest operational aircraft in the world. Its plywood construction made it one of the first “stealth” aircraft, practically invisible to the Luftwaffe’s “Freya” long-range early warning radar, as well as their short-range "Würzburg" anti-aircraft gun-laying radar

I thank you for the Morgan recommendation, but for the reasons above, I prefer my original plan

Thanks!

Bart Brown

 

Isn't that the beginning of an unprintable limerick:

There once was a guy from Pattaya... ?

Thanks!

Bart

 

Thanks, that was my intention. For example, I was wondering if a process I'd seen in a product magazine from the Gougeon Brothers/West Systems called "Epoxy Works" that showed how to secure plywood joints together with epoxy and a continuous wire stitch through pre-drilled holes might be of use in my project.

If you know of a forum concerning plywood construction that would be more appropriate for my needs -- and less annoying the boatdesign.net forum members -- please let me know.

I confess, I AM interested in a boat-building project -- in the late '50s through the '60s, there was a little fiberglass boat I always coveted: I think it was called a "Viper." It was very small, perhaps no more than a two seater, shallow-draft, with an outboard motor, a wrap-around plexi windscreen, bucket or wrap-around bench seat, and usually finished in a really large-flake metal flake -- very George Barris/Ed Roth-looking. Though I live on Connecticut's Fabulous Vacation Shoreline©, I've seen too many people go missing in Long Island Sound, and I don't need the hassle of salt-water, so this would be strictly a fresh-water boat. Do you know of a design like that?

Thanks again!

Bart

 

Thanks! I'm going to put up some pix on Photobucket of the fiberglass body I'm using, a splash of a 1959 Bill AMes/Dewey BROhaugh design called the "Ambro,", originally made to fit on a Triumph 2/3 chassis, but cleverly manufactured to accommodate wheelbases from 88" to 100", and a 52" to 55" front/rear track. I also have pix of the Marcos GT-1800 production floor, with all the marine ply and spruce reinforcement chassis elements laid out, and several construction steps illustrated, including the final glass and epoxy bonding of the fiberglass coupé body to the semi-monocoque chassis, which again nearly doubles the assembled car's chassis torsional rigidity.

If anyone's interested, I'll provide a link upon request.

Thanks again!

Bart

 

Thanks! I get West's Epoxy Works magazine and visit their site often. Being two miles from the largest State Beach Park in CT, and within a stone's throw of about a thousand marinas, we have a HUGE West Systems store just down the road.

Thanks again!

Bart

 

what a cool project. I want one! by the sounds of the construction you can even make it an amphibian, than you can ask any questions you want on this forum.

If it were me I would stay with the volvo engine, more common and more reliable than the MGB (I have owned and worked on both). I think buiding the original tube type front suspention might be a better choice than using the MGB suspention as well.

Epoxy is the way to go on wood construction. where are you getting that cool body? kit, or fabbing the panels your self?

 

The difficulty I see would be the glassing of the inside of box-like frames, meaning channel frames instead. Also, providing threaded holes for attachment of suspension, etc., etc., etc.. But that is your problem. Otherwise, besides heat from exhaust and engine, the monocoque frame would be a good idea, both light and rigid.
This is just normal epoxy and cloth with high strength filler to create fillets (coves) to allow taping or glassing after assembly. Your glassing schedule is an engineer's task and the question is, will you over-glass to compensate for lack of engineering and possibly lose some advantage of the method?

 

an optimized quality built wood structure can have the same strength to weight ratio as aluminum and steel tube truss space frame. And it is the only method that can use common hand tools, simple wood tooling to hold it all in place, and takes no special skills to form. The only draw back is you must keep it dry or it will eventually rot, but aluminum and steel will corrode or rust, so it just means you have to take careful precautions to encapsulate the all of the wood components. designing "hard points" to take suspension loads and engine mounts is not so difficult, no more complex than you would for thin sheet metal, you just have to spread the load out enough with reinforcement (wood or metal) to keep the loads within acceptable limits.

I thought of designing a laminated and varnished wood bicycle frame to prove the point, but than I discovered there was already several craftsman already doing it. both aircraft and boats were made of wood or wood/compostie, no reason a car can not be done too.

 

Thanks to all who responded! I’d like to clear up some inadvertent misinterpretations I may have created:

Petros wrote: “If it were me I would stay with the Volvo engine, more common and more reliable than the MGB (I have owned and worked on both). I think building the original tube type front suspension might be a better choice than using the MGB suspension as well.”

I’ve never owned a Marcos GT 1800 (very low production, even lower numbers of Marcos GTs imported to the US —couldn’t afford one then or now), so I have neither the Volvo engine nor the tubular steel subframe for the front suspension. The use of MGB components was largely decided upon because of the great rigidity and accuracy of kingpin inclination and other suspension and steering parameters of the incredible torsional stiffness of the crossmember, which is a hollow steel weldment monocoque in its own right. On the production MGBs, everything that has to do with front suspension, steering, and braking has their base data points on the crossmember, which is held to the MGB’s pressed steel unit body by 4 bolts. The crossmember will be even more rigidly mounted on the “torsion box” monocoque (and far more rigidly mounted than the original Marcos suspension subframe, which was also difficult to repair). The plywood monocoque is based on a Herb Adams steel chassis design for a much heavier and more powerful all-out race car — the plywood monocoque has considerably greater torsional rigidity than even the steel Adams design, and is vastly lighter.

“Epoxy is the way to go on wood construction. where are you getting that cool body? kit, or fabbing the panels your self?”

The body is a modern splash, by Bill Bonadio of Oklahoma City, of the 1959 Bill AMes/Dewey BROhaugh “Ambro.” Bill Bonadio sells the body under the name “Dio.”

Alan White wrote: “The difficulty I see would be the glassing of the inside of box-like frames…”

Marcos found glassing the inside of the box frames unnecessary — all the boxes and sills were mutually supporting, and bonding the coupé body to the plywood monocoque, as I said, made it at least twice as strong. Though the Ambro is an open car, the plywood monocoque chassis all by itself has such great torsional stiffness it would be perfectly tractable with no body at all (it would look pretty strange, though!)

“Also, providing threaded holes for attachment of suspension, etc., etc., etc..”

Steel tabs and bracketry backed up on both sides of the wood panels by steel load-spreading plates

“the question is, will you over-glass to compensate for lack of engineering and possibly lose some advantage of the method?”

No doubt I will “over-glass to compensate for lack of engineering!” As this is strictly a street car, weight is not a critical problem. Plus, glass will be used only in certain areas, mostly to create semi-enclosed bulkheads and load-bearing cowlings. Not quite sure if I should glass the entire bottom of the car, which will be a single sheet platform of marine ply upon which all the load-bearing sills, bulkheads, and torsion boxes will be tied. When I loft up some pix to photobucket showing the Marcos GT assembly process, the method (of my madness) will become clear

Petros wrote: “an optimized quality built wood structure can have the same strength to weight ratio as aluminum and steel tube truss space frame. And it is the only method that can use common hand tools, simple wood tooling to hold it all in place, and takes no special skills to form. The only draw back is you must keep it dry or it will eventually rot, but aluminum and steel will corrode or rust, so it just means you have to take careful precautions to encapsulate the all of the wood components. designing "hard points" to take suspension loads and engine mounts is not so difficult, no more complex than you would for thin sheet metal, you just have to spread the load out enough with reinforcement (wood or metal) to keep the loads within acceptable limits.

“I thought of designing a laminated and varnished wood bicycle frame to prove the point, but than I discovered there was already several craftsman already doing it. both aircraft and boats were made of wood or wood/compostie, no reason a car can not be done too.”

Indeed, there are many people making beautiful, strong, light, and functional works of art — mobile and otherwise — with composites of all kinds. It always knocks me out when I check out what’s new on the West Systems’ site.

So, I’ll take up no more forum space with questions that are non-building-related, but when I get my head together, I’ll post pertinent drawings and photographs to photobucket, and provide links for those who are interested

Thanks again!

Bart