Boat­yard Tip

Power & Motor Yacht - - IN THIS ISSUE - By Capt. Bill Pike

Dried or cracked bed­ding com­pound un­der a boat’s deck­ing can cause leaks; this “dough­nut” so­lu­tion is the per­fect fix.

If your boat is more than a few years old, you’ll even­tu­ally need to re­new the bed­ding com­pound un­der at least some of her deck hard­ware. This chore is im­por­tant, es­pe­cially on boats with balsa-cored decks, teak-planked decks and fuel tanks lo­cated di­rectly be­low the fuel fills. Wa­ter in­tru­sion un­der such cir­cum­stances can cause rot, cor­ro­sion and other dire de­vel­op­ments long be­fore ob­vi­ous warn­ing signs man­i­fest. Prob­a­bly the gloomi­est (read: most ex­pen­sive) prob­lems arise in a fu­eltank-di­rectly-be­low-the-fuel-fill sce­nario. If the bed­ding com­pound in­volved is dried out and cracked, wa­ter is un­doubt­edly slip­ping through, dam­ag­ing the sur­round­ing cor­ing ma­te­rial (if the deck is in fact cored) and eat­ing away at the top of any fuel tank that hap­pens to be blan­keted with a mois­ture-trap­ping, crevice-cor­ro­sion-caus­ing ma­te­rial, like sound in­su­la­tion, ply­wood sheath­ing or plain ol’ fiber­glass. Steel tanks are no­to­ri­ous for this kind of thing, but modern alu­minum tanks are not im­mune either.

How do you deal with the is­sue? Cre­at­ing a thick, evenly com­pressed, gas­ket-like “dough­nut” of poly­sul­fide com­pound ma­te­rial un­der the leaky fuel fill or fills is the an­swer. And, to guar­an­tee the suc­cess, I sug­gest avoid­ing the use of sim­ple screws when se­cur­ing the fill once the new poly­sul­fide is in place. In­stead, opt for bolts, a back­ing plate fit­ted from be­neath the deck (3/8-inch star­board works well, with a large, cen­tral open­ing cut with a hole saw), stain­less-steel fen­der wash­ers and avi­a­tion-style lock­nuts.

Does this belt-and-sus­penders ap­proach add dif­fi­culty to what might oth­er­wise be con­sid­ered a rou­tine task? Ab­so­lutely. But it also makes for a much more pos­i­tive, wa­ter­tight, long-last­ing con­nec­tion be­tween your boat’s deck and the deck fill that pen­e­trates it. More­over, the use of bolts, nuts and a star­board back­ing plate—as op­posed to three or four sep­a­rate, wholly in­de­pen­dent screws—cre­ates a stronger, more evenly dis­trib­uted, unified bond be­tween all the sur­faces in­volved.

And don’t for­get: At first, only lightly tighten the avi­a­tion-style nuts un­der the deck. Over­tight­en­ing be­fore the poly­sul­fide has cured and hard­ened will squish too much of the stuff away, thereby elim­i­nat­ing or at least abat­ing the gas­ket ef­fect you were shoot­ing for in the first place. Once the com­pound has set, how­ever, go ahead and tighten things up with a ro­bust tug.

Find­ing a per­fect re­place­ment is not of­ten easy.

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