Joining a fiberglass cabin to steel hull

[Tygafan]

I have a 44' steel hull and would like to remove the steel cabin by cutting it off just above the deck and replacing with a newly built fiberglass cabin. I am looking for suggestions on how to join the fiberglass to the steel. Bolting? Joining the fiberglass to the steel? ........
Also are there any issues with this? Is this a bad idea having fiberlglass mated to steel?

[FAST FRED]

I would simply weld SS angle iron to the deck , place a neoprene gasket between the GRP and SS steel and have at it with thru bolts..


FF

[GuestR01312011]

You can Laminate the fiberglass to the steel, here's a pretty basic article http://www.twi.co.uk/j32k/unprotecte.../ksfcs002.html
I know the French used a method similar to this kind of for their frigates, to reduce structural weight with a high CoG, ie the helicopter hangers were re-made of GFRP and bonded to the steel hulls.
This one if fairly in depth:
http://www.vtt.fi/inf/pdf/tiedotteet/1997/T1862.pdf

[clanning]

I would be concerned with differential expansion rates as well as the quality of the mechanical bond with a straight laminate -- didn't Chris Craft have fibreglass cabins on Roamer cruisers in the 60's? Alwest (like Alcan housecruisers -- same hull) did the same with aluminum hulls and FG cabins in the 70s.

(I have not reviewed the links provided by curridronan yet.)

I would be inclined to keep the vertical flange on the deck (as Fred is suggesting) and use mechanical fasteners. Mastic provides adhesive properties (vs. neoprene) but in either case the bottom edge of the fibreglass needs to be stiff enough to avoid local deformation (bows and wows) along the line of fasteners.

Cheers,

Chuck

[marshmat]

Laminating composite to metal is not impossible, but it is hard to get a reliable bond without a significantly increased corrosion risk. Note that the Comeld process mentioned bu curridronan uses an electron beam etching on the metal and a vacuum-bagging process, I don't think it would work on an existing hull.

I agree with Fred and Chuck here. Welding a bunch of steel angles around the perimeter of the superstructure (or keeping existing protruding steel), and through-bolting the superstructure to them with backing plates, would seem to be a good way to go. Neoprene or silicone gaskets could be used - then use a high-elongation silicone to seal the seam, tooling the joint properly and using compressible backer rods as necessary.

[Petros]

Boeing once in the late '60's attempted to use epoxy bonded joints to save weight and cost between aluminum skin panels, and between aluminum and fiberglass fairings. A few years latter they had to rework all of the skins of the aircraft delivered this way by installing conventional fasteners after the fact. It was only because of one stubborn engineer that insisted they put minimal mechanical fasteners through these joints that none of the aircraft came apart in the air.

They have never attempted bonding dissimilar materials this way again.

Mechanical fasteners between the fiberglass and metal would be the most reliable and simplest way to accomplish your goal. Any bonding agent or adhesive would add extra strength, but it must be flexible to allow differential expansion of the two materials. Or it will develope leaks.