DuPont granite sealant products last much longer. Our house based countertops are approaching 6 years and still impervious.
We have Quartz in the house and on the boat, Corian in the Motorhome and a Granite kitchen table at home. Side by side granite and quartz at home, but the granite is now over 10 yrs old and I haven't had to go to the store for sealant yet as it is very much "new" condition still.
The base for the table top supports it only in the inner 30" of a 48" radius. Other than refraining from sitting on the edge, no special cautions against cracking. It is 3 cm thick, so the same as heavier countertops. On your boat, if you place it over your existing laminate, you can use a thinner slab.
The look of the Quartz and of the granite beside is very similar, so there is little advantage in one over the other. Both are far superior to Corian.
The reputation of granite for cracking comes from the difficulty of getting a huge slab in place for a large kitchen island. Unless you are equipping a true superyacht you won't have that concern.
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