The biggest 'bottom' problem is blisters...
and, as Don said, you won't be able to judge whether the boat has a blister problem without hauling it. Along with looking for blisters, the surveyor will be checking the hull for previous damage (most boats have been grounded), how well the keel is attached (very important, for obvious reasons!), the condition of the thru-hulls, bottom paint, prop shaft and cutless bearing, and the rudder. Very important to haul the boat and have a professional examine it. Blisters occur (mostly on boats built between 1975 and 1995) because of many different manufacturing problems - the most common: the fiberglass is put up in layers, and if the liquid resin doesn't flow properly, there are voids between the layers - compounded by the unfortunate fact that the outer layer of gel-coat isn't completely waterproof. It seems that if there are voids inside the fiberglass, water will penetrate to them and react with the acid left over from the resin, causing pressure that pushes the gel-coat outwards. Most blisters are in the outer layers next to the gel-coat - deeper blisters are a much more serious problem and you should stay away from any boat that has deep blisters. Interestingly, it isn't just 'cheap' boats that developed blister problems - plenty of high-end boats also came down with blister problems. Newer boats are usually built using various techniques that prevent blisters, such as 'vacuum-bagging' in which the mold for the hull (with the glass mat in place) is inserted in a GREAT BIG plastic bag and all the air is sucked out, then the resin is introduced and literally sucked into the glass mat. Very effective! Now, here's the wierd part: a boat that 'has blisters' isn't necessarily a bad buy. Blisters by themselves have never sunk a boat, and in most cases will never be a serious problem, or require a huge fix job. (the way to 'cure' blisters is to pull the boat and literally PEEL the gel-coat and outer layer of fiberglass off the hull. Then you put the boat where it will be warm - like in a tent- and blow hot, dry air on it for about 6 months. After the hull is thoroughly dry, you put the outer coat back on, usually with some expensive (and VERY waterproof) epoxy. Cost for a 30' boat is probably about $10,000. So please do yourself a favor: don't buy ANY boat without a professional survey. BE THERE, even if the surveyor won't let you follow him/her around. At least you can discuss the findings with him/her and learn a lot. And if the survey says ANYTHING about blisters, do 2 things: investigate further to see if they are bad enough to require the 'big fix', and, if you decide to buy the boat, USE the blisters to get the price down...... very few people understand blisters, and most will freak out at the mention of the word. ;D Cheers, Bob s/v X SAIL R 8 p.s.... I've always wondered just HOW LONG a fiberglass boat hull will REALLY last.... the oldest fiberglass boats were built in the '50s, so they are about 50 years old. Will they fall apart at 75 years? 50 years? Also, the reason why blister problems started in the mid-70s - like so many other problems - is the Arab oil embargo. The price of the resin shot up, and boat makers, who previously made boats with heavy, thick, solid hulls started cutting down on how much resin they used. One last thought: this is my understanding of blisters... you'll probably hear other explanations, because it isn't a particularly clear, concise subject.
