I hade the big bob the one jeremy referes to it worked great it alto qutie big. I just bot the moma for ny new/old 16 In my opinon the mama is pleny of floatation for the 18. from an intermediate stand point. Regaurless of what is avilable the mounting of eithe the moma ot the large bob on to an 18 will encounter some rivits. I'm nor sure but if you have an old non comp tip h-18 i bet the mamae will bolt up "not sure tho" its the aftermaket / comptip that requres thew rivvets. In my humble opinon the mama is perfect for the 18, you can figue out the mounting. athe big bob is nice for the huge safty factor .those are my 2 cents. H-18 if you know whats up I whould go with mamas, larger safty factor go with bob.