Interior lining alum cat

[Gandolph63]

Hi all. I am looking to bank on the experience on this forum to maybe help with some ideas. I have an aluminium catamaran that has been spray foamed inside which has been trimmed back ready for interior lining. This is the dilemma. What to line it with? Fairly convinced the deckhead will be vinyl with a foam layer. I have access to gelcoated fibreglass panels ranging from 1.6 mm to 3.5 mm which unfortunately are only available in a bright white gloss. This may be the way to go but am unsure how to join corners and joins well to make it appear seamless. Can anyone help with a process here?

 

[bajansailor]

Welcome to the Forum Gandolph.
Your aluminium cat sounds interesting - will she be a power cat or a sailing cat?
What design is she? Could you post some photos of her please?

Re covering the joints of the fibreglass panels, you could perhaps fit varnished timber battens over the joints - these would provide a nice contrast?

 

[Rumars]

Very nice job of trimming the foam. There are several ways depending on how you want it to look. A simple way is a textile glued directly to the foam. Another way is a ceiling of thin plywood, fiberglass, pvc, etc. It can be glued in place or screwed ower furring strips. Seamless joints depend on the material, but mainly you would scarf it, then sand the line and if necessary veneer, paint or gelcoat it. Corners can be rounded from the sheet (you bend the sheet around the corner), filleted, formed from a separate strip, etc. It all depends on how you want it to look.
The traditional way is a solid wood ceiling screwed over furring strips. Joints would receive either some form of shadow gap or molded trim.

 

[Barry]

As Rumars suggested, foam backed vinyl glued to ply is one of the ways that aluminum boat builders use to hold vinyl against deck works and sides. Over time though the ply may delaminate and/or rot with the moisture, we had an old
fiberglass Silverton that did that though the boat was old. The last high end aluminum we owned used a different product as the sheet and I do not know what it was. With screws to hold the sheets in place, a person can always repair wiring and access spaces. (backing areas of cleats or new add ons in the future)
I did not see any pipe ways in the foam. Normally aluminum boat builders who foam will run 2 inch pvc pipe and cut the odd hole to act as a drop out for wires etc. Then this is foamed in place, a fish wire, or pull through is left in place in case
you want to add more electronics etc

 

[Gandolph63]

Thanks everyone for your replies so far. She is a Tim Mumby designed sailing cat 48 ft. I have some photos somewhere. Historically these cats were fitted out with seamless fibreglass interiors and we are leaning that way but need help with the process. Are the joins normally scarfed, then taped and bogged, then perhaps flowcoated? How to get the brush marks from flowcoat? Just lots of sanding I suppose? Pretty naive when it comes to fibreglass work I'm afraid. A lot of the wiring was incorporated into the foam on the builders advice. Perhaps not the best scenario but it is done now. Has anyone tried putting peel ply over gelcoat to get a seamless smooth finish on a join after bogging I wonder?

 

[fallguy]

Man, lots of work and lots of weight added.

the lightest thing I have seen is vinyl wrapped and spray glued on formica and velcroed; your foam work looks pretty good; if the foam was dense enough; another thin piece over the aluminum and you could bog the foam seams with an epoxy bog and paint it; if it was a bit soft you could maybe laminate 1.4 oz in place; test a piece of 1.4 oz spray glued and wet over top and see if it is a hard enough wall that way. It would only add about 3-4 ounces per yard of wall; you would probably want to peelply it on the wall to avoid runs; more testing required, but peelply would provide a really uniform sirface then a minimal sanding and bog work at the seams

I have a similar hull shape and have decided to do nothing in my foam boat, but not an option for you..as she'd be pretty wet down there (hehe).

Try ultralight glass. Maybe someone on the forum can even reply on the weight of the glass. I just have a feeling 1.4 would work..

Also, if the foam wasn't glued in; you could laminate the panels on a table

 

[Rumars]

Seamless fiberglass interiors are usually done as a one piece molded liner, and is a series production thing. If you want that there are two options, pregelcoated fiberglass sheets that you glue, then grind and gelcoat the joints, or directly laminating fiberglass over the foam, then fair and paint. Flowcoat is just gelcoat with added wax, the brushmarks are removed by sanding and polishing. Google "gelcoat repair", the process is the same as repairing scratches from fiberglass hulls.
One material I did not mention is rigid PVC foam, as used in bathrooms. Comes in a range of colours (including different shades of white), and can be thermoformed into complex shapes with a heatgun. The joints can be hidden by clever design or trim, it's much less work then fiberglass and has the same shiny smooth appearance.

 

[Barry]

Just a couple of other things to consider;

On a couple of previous threads, some of the contributors have introduced the possibility of corrosion of aluminum hulls that begins between the aluminum hull and the foam. We have owned a spray in foam aluminum boat and
know that many of the aluminum boat manufacturers in the Pacific North West spray foam against the hull for heat and sound insulation. I have not seen any corrosion in this area. But others evidently have and
may want to provide some information on actual cases.

I would be concerned though with creating relatively sealed and stagnant areas that this may create areas for mould/mold growth, As you cannot absolutely guarantee a 100% sealed volumes, moisture will be present in between the two
barriers, the aluminum hull, foam and the liner. Again, maybe some other contributors may add their expertise. I recently noticed in our RV which is a fibreglass outside shell, with about 1 1/2 inches of foam, in any lockers, they have added
a 1 inch diameter push in insert with a venting grid to allow ventilation.