Shell Construction

[floyd]

After a false start on another thread, I thought it would be interesting to start a thread dedicated to Shell Construction showing the similarities and differences across the spectrum of trailers represented in this forum.
My thought is to pick a brand for which you have good understanding of the shell production process and explain it here.
The purpose PLEASE, is to EXPLAIN the processes for better understanding of our beloved trailers of various makes, not to judge the respective merits.
I will start with the Scamp and invite others to fill in with comments and pictures, on this or other makes...



Scamp builds their shell in two main pieces (top and bottom)
I think there is a release agent sprayed into the mold.
This is followed by the gelcoat including the color which is sprayed to the desired thickness. Polyester resin is then sprayed into the mold along with fiberglass strands chopped and sprayed in as well.
This mix is smoothed into shape manually using rollers on long handles.
The two haves are manually fiberglassed together forming a one piece shell with a floor composed of Oriented Strand Board which is soaked in resin and fiberglassed to the bottom shell.
This structure is screwed to the steel frame using common self tapping or self drilling screws.
The furniture on the Standard Scamp is produced by the same mold process It is then installed with through the hull fasteners which are aluminum pop-rivets. The cabinets add essential structural rigidity.
The furniture on the Deluxe is constructed of wood and wood products including laminates in Scamp's Cabinet shop. They are fastened through the hull with wood screws instead of rivets and also add structural rigidity to the overall structure.
Who's next?

[k0wtz]

thanks Floyd very interesting!! I always wanted to see how they made those huge fiberglass yaughts.

bob

[floyd]

Escape? OLiver? anybody?

[TomK]

Floyd, it appears you're a tough act to follow.

Tom

[Donna D.]

Escape also builds the trailers in two halfs. Top and bottom. The difference between others and Escape manufacturing is how the two halfs are put together.

Escape places the top half over the bottom half before the top half is removed from the mold. A worker goes inside the trailer and forms the two halfs together thoroughly fiberglassing both into one piece. Then the trailer is removed from a mold as one complete piece.

[floyd]

Originally Posted by Donna D.

Escape also builds the trailers in two halfs. Top and bottom. The difference between others and Escape manufacturing is how the two halfs are put together.

Escape places the top half over the bottom half before the top half is removed from the mold. A worker goes inside the trailer and forms the two halfs together thoroughly fiberglassing both into one piece. Then the trailer is removed from a mold as one complete piece.

What about the process itself? Is it resin and chopper gun over gelcoat?

[John in Santa Cruz]

I thought the gelcoat on fiberglass was applied AFTER molding, like a paint?

[rbryan]

Originally Posted by John in Santa Cruz

I thought the gelcoat on fiberglass was applied AFTER molding, like a paint?

No, the gelcoat goes into the mold first. The inside surface of the mold is completely smooth. Usually there's a thin coat of wax or release agent that is applied to the inner surface of the mold prior to spraying with gelcoat, so that the piece can be removed easily from the mold once cured. The gelcoat is sprayed in, then the fiberglass and resin go in. Once cured and unmolded, you wind up with a shiny gelcoat on the outside, and the fiberglass on the inside. The gelcoat then is essentially a part of the fiberglass, and not a coating like paint.

There are other methods of fiberglass construction, but this is basically how it's done on most molded fiberglass trailers.

To answer Floyd's question though concerning Escapes, I believe they spray chop for the majority of it, along with matt in certain locations. The floor is plywood, encased in fiberglass and is inside the shell. The bottom of the shell is completely enclosed. Wood support structures are glassed in to the shell interior, and all cabinets/bulkheads are screwed into the supports. No rivets/caps pierce the shell in order to attach them. Like other fiberglass trailers, the interior cabinets and bulkheads add needed structural strength to the shell.

[Raspy]

Olivers are a double hull design. They have inner and outer hulls with insulation in between. The tanks, all piping and the heating ducts are in the area between the lower hulls so that there are no pipes visible or hanging down underneath. This means the tanks and waste piping cannot be damaged from road hazards.

The heating system ducts run between the lower hulls to keep the tanks and pipes from freezing. This, combined with the insulation, gives excellent freeze protection.

There is no wood in the floor. The bulkheads, counter top and other areas are cored construction for exceptional rigidity. The cabinets are molded into the upper/inner shell so there will never be any wood related failures or detachment from the hull.

The frame is box aluminum and heavily gusseted in the tongue area. The tongues are long to allow easy backing. The batteries are mounted in a compartment directly over the axles with an external door and rollout shelf for servicing them.

[floyd]

Shell construction?
I assume the the Oliver is chopper gun and polyester resin Like Scamp?
Lil' Snoozy uses a different approach, how about Nest? Parkliner, etc?

[Jake930]

This is a Scamp camper promo video, but the last half shows how they build them. I would imagine that it would be the same process with all molded Fiberglass trailers.

https://www.youtube.com/watch?v=LMg6YADmkfE

[Raspy]

Originally Posted by floyd

Shell construction?
I assume the the Oliver is chopper gun and polyester resin Like Scamp?
Lil' Snoozy uses a different approach, how about Nest? Parkliner, etc?

Oliver is mostly chopper gun glass with polyester over gel coat in the mold. But it also has various areas that are reinforced with hand laid over core material or hand laid over reinforcement pieces where brackets will go or stiffeners are needed.

There seems to be quite a bit of core construction in the roof, countertop, bukheads and other areas.

[Paul O.]

At one point Robert Johans described a vacuum assisted layup process used on the Nest prototypes, but who knows how Airstream modified that and other aspects....

[Cliff Hotchkiss]

The Escapes body are attached to frame with nuts and bolts not self tapping screws.

[Jim Bennett]

Originally Posted by Cliff Hotchkiss

The Escapes body are attached to frame with nuts and bolts not self tapping screws.

And now bolted through tabs welded to the frame, and not the frame itself, to protect the integrity of the frame.

Here is a cross section of a piece of the shell I cut out to add a hatch. The fibreglass is a minimum of 3/16" (near 1/4" in places), the foam backed vinyl 1/4" and the optional foam 1/2".

[Mikmay]

The HC1 s fg work is almost the exact same as the Oliver and I beileive the new Parkliner. The inner and outer top shell are 2 molds and the lower inner and outer are 4 molds with all the door, floor ,lower perimeter. Hatches etc and the Roto molded cubes bringing our total amount of molds to 22.for a 13 foot trailer.one of the other differences is most of our trailers use colored gel coat which can add $500 -$1000 to the cost unless you are using grey like the Nest as there is no difference in price between grey and white.double hull construction can add approximately 30% to the cost of a similar sized trailer since there is exactly twice the amount of fg.

[charlsara]

The LIL Snoozy hull is made like the others. Up to a point. After the gelcoat is sprayed into the mold, A layer of chop goes in. Then a layer of glass foam (I don't know the exact name for this) is hand layed in. An inner mold is then placed in and resin is vacuumed between the molds infusing the entire mixture. After both halves are molded the two halves are hand glassed together. The completed hull is bolted to the galvanized frame with sixteen stainless steel bolts. The floor is fiberglass and part of the lower half. The result is a hard shell similar to a fiberglass boat shell. It is self supporting and is 1/2 (bottom) to 3/8 (top) thick . The interior is then had sprayed with gelcoat. The cabinets are wood. They are fastened to the hull with stainless steel bolts through the belt line.The belly band strip goes over the bolts completely hiding them. There is one stainless steel bolt through the side of the upper hull. It stabilizes the upper cabinet.

[Raspy]

The Oliver frame/body system is more like a boat sitting on a trailer, than a frame offering rigidity to a flexible trailer body. As with a boat on a trailer, each are independent, but work together. The boat, in this example, is a complete rigid structure on it's own, the trailer supports it and tows it along. The strength the trailer offers is in towing and cradling the boat. Same idea in an Oliver. But since the Oliver body does not have to go on and off the trailer, as a boat would, the connection and reinforcement can be much better. There is no separate "floor" in the Oliver, it's all part of the same molded layup. The outer, lower, shell is what you see when you look underneath. It also holds the tanks inside and bolts to the frame. The inner, lower, shell is what provides a floor inside to walk on. It is above the tanks. The space between also provides room for wiring, plumbing, ducting and insulation.

Up front, in the tongue area, the aluminum frame is heavily gusseted to take the down load and cornering forces. Out back, behind the axles, it's much lighter. The two axles and springs are bolted to a small steel "truck", or subframe, that cradles the main frame and is cross bolted. Then the main frame cradles the body and is cross bolted to it. This distributes the load from the body to the aluminum main frame to the steel truck/subframe, to the suspension system. But again, the trailer body is already a strong unit, on it's own, like a boat. The frame adds to the strength, but doesn't solely provide the strength. The towing, stopping loads are sent through the main frame to the steel subframe to the wheels, via the suspension system which is a tandem axle, leaf spring system with equalizers and shocks.