Cracked composite (plastic) through-hulls are a fairly common problem, as a walk in pretty much any boatyard will bear out.  Ultraviolet light is the main culprit here and while different brands vary widely in their susceptibility to UV damage, some are so poorly made they can fail within a year.  Although manufacturers began adding inhibitors to second and third-generation fittings to make them more UV-resistant, the older ones are still around and it's almost impossible to tell one from the other (one reason I view all of them with suspicion).
Composite through-hulls typically fail where the body of the fitting joins the outer flange, resulting in a crack or total failure (both of which are shown in the accompanying picture).  Once the flange is sheared off, there's nothing left to keep the through-hull in place, meaning it'll be pulled inboard, leaving an open hole in the hull.  Such failures at or below the waterline can easily result in sinking, however even those well above the waterline can be just as bad - as in the case of a bilge pump discharge, which now just continues to pump water back into the vessel, meaning the waterline rises till it reaches the hole and then...well, you get the picture.

Plastic fittings should be inspected at least annually. If you find one fitting that's bad, play it safe and replace the remaining ones too; they're probably the same age and prone to failure as well.

Look closely at this one. It took me a few moments to figure out just what it was about this install that gave me willies. At first I though it was the gate valve (which I’m not overly fond of to begin with, especially in below the waterline applications such as this), then it hit me – there’s no hose clamps! The only thing holding all this together is a few pieces of PVC pipe insulation and a prayer.

Do you have any idea what the boat you are buying has been through?

Be wary of installations that employ short pieces of pipe between the seacock and through-hull (as in the below picture). Each section of pipe introduces a potential failure point within the hull that is not protected by the seacock and should be removed as soon as possible.

The builder has added bits of scrap iron, steel, and probably anything else he could get his hands on to add weight to the poured concrete ballast (concrete is not very heavy, particularly as compared to lead). Once water seeps into the ballast (from the bilge or possibly via hull damage) the metal scraps begin to rust and expand, causing the FRP of the hull to crack and rupture.  The voids in the concrete indicate where metal scraps were located.

Fractured floor to stringer joint

This is one of around a dozen such fractures found on a 1988 Wellcraft St. Tropez 32. This type of damage is typical where lightly built vessels are powered by large engines (in this case twin 454 XL Crusaders)

The caulking has hardened and fallen out along the entire joint.

Mechanical Problems

This is one of two cutless bearings on a 32 foot power vessel that were allowed to wear so severely that both shafts were damaged and had to be replaced. The seller had replaced both bearings the day before the survey, however both shafts still had significant play. When pulled, it was discovered both shafts had lost almost a quarter inch of their circumference.

Standing Oil in Engine Pan

Small boats and big engines often equate to major headaches from both a survey and upkeep standpoint. These twin 454 Crusaders were shoehorned in so tight an average-sized person could barely wedge himself in sidewise between them, let alone conduct preventative maintenance or repairs. It's also impossible to physically access the spaces forward and outboard of the engines. The owner commented that when he had to replace the battery charger (located on the bulkhead forward of the starboard engine) he hired a 7-year-old boy to squeeze into the space and unscrew the mounting bolts.

Damaged Exhaust Riser

Cracked and severely corroded exhaust riser for a small diesel auxiliary on a 30-foot sailboat. If it's this ba the outside, just imagine what the inside looks like. That corroded fuel shut-off control line resting against the of the riser isn't looking too good either.

Engine manifolds and exhaust risers should be periodically removed, pressure tested, and fully inspected for corrosion, and clogging, as failure here can easily cause catastrophic engine damage. This should be consi standard maintenance, particularly with systems operating in salt water. How often depends on vessel location and use, however at a minimum they should be removed every four years (more frequently depending on age).

Cracked Strut

 

The potential problems caused by any joint formed by clamping a larger sized hose on a smaller one are obvious, but it's particularly bad when done in the exhaust system. Not only does it create a potential source of CO leakage into the interior, but failure here also means the engine would be pumping water directly into the vessel.

 

The potential problems caused by any joint formed by clamping a larger sized hose on a smaller one are obvious, but it's particularly bad when done in the exhaust system. Not only does it create a potential source of CO leakage into the interior, but failure here also means the engine would be pumping water directly into the vessel.

 

Fuel System Problems

This picture shows chafing of an outboard motor fuel line that was draped across the tiller while the vessel was moored.

Corroded Fuel Fill Hose Clamps

Fuel fill hose clamps aboard a 45 foot ketch constructed in the orient during the early eighties. They crumbled to dust for the most part during replacement

More Vice Grip® gate valve handles, these in the fuel return system.

Faulty Fuel Tank Shutoff Valve

The valve handle of this fuel shutoff has completely corroded away, leaving the valve inoperable.

Like oil and water, only a lot more flammable.

Does it get any worse?  What you have here is your basic leaky fuel valve.  Can't have it leaking into the bilge, so let's just set a bucket under it until we can figure this thing out (never mind the A/C electrical connection soaking in it).

Electrical System Problems

Like oil and water, only a lot more flammable.

Does it get any worse?  What you have here is your basic leaky fuel valve.  Can't have it leaking into the bilge, so let's just set a bucket under it until we can figure this thing out (never mind the A/C electrical connection soaking in it).

The majority of onboard fires can be traced to faulty or improperly installed electrical systems. The below photo proves no weekend project is too complicated when the services of JD & P. Lopez, esq., are employed. Problems with this homegrown AC installation included the use of cut extension cords for wiring, no circuit breakers, no GFCI (Ground Fault Circuit Interrupt) outlets, and no way to secure power other than unplugging the cord at the dock receptacle.

Can you feel the frustration of the poor technician tasked with trouble shooting an electrical problem in this mess? Also note the lack of chafe protection where wires penetrate the bulkhead, as well as the evil "electrical tape joints," which will eventually fall off, leaving exposed conductors.

Although once common, use of wooden boxes to house AC outlets is considered a fire hazard (due to possible arching plug terminals) and no longer acceptable.

Below is a picture of an AC generator cut-over switch, another one that gave me that "something isn't quite right here, but I can't put my finger on it" feeling. It took me about thirty seconds to realize those three nice, shiny, hurky fuses where in fact pieces of copper pipe cut to fit into the fuse holders.

The construction seams of these batteries where bulging outward after minimal use. They were deemed defective and replaced by the manufacturer. 

Electrical system upgrades are a good thing, but only when done correctly. The installation below should have used a bigger panel or a backing plate behind the smaller new panel.

This engine room exhaust fan and motor was covered with grease and muck, representing a substantial fire hazard.

How many connections can you tie to one battery post?

Charred shore tie connectors are a leading cause of AC related boat fires.  The charring is a result of resistance build up (due to dirty contacts, poor connections, etc,) which generates heat and the potential for fire.  The problem is especially prevalent among livaboards who tend to continually run high energy loads such as hot water heaters and air conditioning (you know who you are). 

Do yourself a favor - get out there and check the plugs and connectors at both ends of your power cord today and at least every couple of months thereafter.

The pride and professionalism employed during an installation is often evident by the simple things...adherence to industry standard wiring practices, for example.

Jethro's patented sure-fire elec-tronical wire connector

Boaters are an creative lot when it comes to solving problems afloat.  Not only is this homegrown connector / junction in the positive DC wiring non-standard to say the least, it also leaves an energized bolt to arc and spark while bouncing around the engine compartment.   

AC Power Feed Splice

After years of additions, removals, abuse, and misguided McGyverisms, no system on board harbors greater potential for starting a fire than your vessel's electrical system.  Here's a good example of what we're talking about - a splice in the main AC power feed (between deck receptacle and main panel) made by simply twisting the wires together and covering it with electrical tape (more is better, right?).  Splices are not recommended here and if they were, you'd at least want to utilize proper, marine grade connections.  The wiring is also not properly supported and secured, meaning it could easily bounce into, say, the spinning propeller shaft to the left.

Deck Problems

Incorrect Swivel Installation

Swivels are installed between anchor and rode to prevent twisting (particularly when chain is used), however many boaters are unaware they can be installed incorrectly, as in the photo below. Ensure the jaw fitting of the swivel is attached to the chain, not the anchor shank – the swivel eye will be attached to the anchor shank with an anchor shackle – to prevent binding and possible failure as the vessel sheers at anchor. The swivel itself should be drop forged (not screwed, riveted, or welded together) and the largest size that fits the chain link without binding.

Improper Shackle Mousing

Mousing shackle pins with stainless steel wire to keep them from unscrewing is always a good idea, however it needs to be done correctly. Contrary to the photo below, the mousing wire should pass through the pin and around the shackle itself, not through the chain (which will work and eventually break the wire).

We Don't Need No Stinking Backing Plates!
Underside view of an anchor cleat for a mid-sized power boat. The mounting hardware washers are woefully inadequate, verging on ridiculous for a cleat expected to support the strain associated with anchoring. Larger washers, or better yet a backing plate, is called for here.

Rotten to the core

"Mounting hardware directly through cored decking without taking the proper precautions is just asking for trouble. Here a leaky lifeline stanchion has caused the coring beneath its base to rot. The mounting nuts are drawn up so tight they're crushing the panel, no doubt an attempt by the owner to not only keep the stanchion from wiggling, but probably to try and stop the leak as well (note the inadequately sized washers and lack of a backing plate).

Anytime you screw or drill through a cored panel, the first rule is properly sealing the core against moisture entry. There are a number of ways to do this, but the best one is to avoid breaching the core material in the first place. In a perfect world, your boat's manufacturer has anticipated where all deck penetrations are necessary (stanchion bases, cleats, etc) and has "de-cored" these areas by reverting to solid fiberglass, allowing you to mount hardware without drilling into the core. But, in the case of new installations (particularly if you're lucks like mine) your chances are slim-to-none that any of these areas will coincide with whatever aftermarket doo-dad you want to mount, meaning you're going to have to do it the hard way. The good new is the hard way is fairly easy, as long as you have access to the underside of the deck where you're doing the mounting.

What you're going to do is a little de-coring of your own. The easiest way to remove coring is with a hole saw and a little caution. Let's say you want to mount a new cleat on your foredeck, but the entire area is cored. First step is marking and drilling the appropriate sized bolt holes. Then, take a 2 inch hole saw (or larger, depending on the size of your backing washers) and remove the coring from the underside of the deck where each bolt is to be installed, being careful NOT to drill through or damage the upper layer of fiberglass (you also have the option of removing a single section of coring large enough to encompass both bolts). I find it works best to drill almost through the coring, but leave the last 1/4" or so to be removed by hand (to avoid any chance of damaging that outer fiberglass layer).

Once the cutout and coring is removed, seal the exposed edges of the coring in the holes with thickened epoxy paste. Now all you have to do is mount the cleat using properly sized backing washers and a good bedding compound (under both cleat and washers) and Whaa-la! You've got a properly mounted cleat that won't leak and has no chance of letting water into the core.

I like the above method of dealing with mounting holes in cored panels, but it's not the only way to address the problem. An excellent reference for this and just about any other type of fiberglass repair or maintenance issue is "Fiberglass Boat Repair And Maintenance" published by Gougeon Brothers, Inc. (517) 684-7286. It's a good how to booklet and well worth space on any vessel's bookshelf.

Deck-Stepped Mast Failure

The cored deck beneath this stepped mast is failing, a problem typically associated with deteriorated coring caused by water intrusion.  Note the deck depression and cracks in the fiberglass around the base of the mast.

Quick-connect links

Anchors should be attached to rodes using a proper anchor shackle.  Anchor shackles are "C" shaped to provide greater freedom of movement, as opposed to chain shackles (which are more U shaped) or quick-connect chain links, such as the one shown.  Quick-connect links are used to join chain only, and should be considered a temporary measure at that - they're weaker and offer less freedom of movement than anchor shackles.