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It can be a jungle under there

From too little resin to cheaply made hose clamps, pretty boats sometimes can hide ugly problems

You remember that scene from the old jungle movies, where the guy is treading carefully through the dense foliage when suddenly he disappears from the screen - drops off the bottom of it. The camera pans down and he's in a deep hole. He'd walked over an innocent-looking bed of leaves and grass that in reality was a disguised cover for a pit of doom.

The hull of a newer boat showing voids, blisters and weak spots being repaired.

Maybe he's impaled on stakes. Maybe he's peering anxiously at a tiger lurking in a corner. Maybe someone's gleefully pouring cooking seasoning on him from above. Whatever, it's not good. I've seen this theme in various boats through the years. Nobody dug a hole and nobody was out to get anybody, but lurking beneath innocent, sometimes even beautiful surfaces there might be traps.

About 10 years ago, I was walking the docks of a prominent marina in Fort Lauderdale, Fla., and admiring a particularly shippy-looking yacht. The builder was well-known and this was a boat to admire and desire. Then I saw where, in some high tide somewhere, the majestic flared bow had come down on a piling that had punched through the gelcoat.

It shouldn't have been a big deal. This thing happens more frequently than you'd like to think. But wait. There's more. The piling had also punched through the fiberglass hull under the gelcoat. Must have been some blow, I thought, until I reached up and touched the strange-looking hole. There was fiberglass, all right, but no resin.

During construction, for one reason or another, the resin had drained from the area or had been inadequately infused into the glass. The strands were soft and flexible with very little strength. The beautiful gelcoat had been covering up the problem. I shuddered at the thought of having paid maybe a million bucks or more for a boat that looked as if it could handle the roughest of seas, only to learn that a construction flaw had rendered at least part of it extremely weak. For all I knew, much of the hull could have been compromised.

Since then, I've seen more of this. I've seen far too much of it while looking at junked boats in salvage yards after hurricanes. I realize that with enough impact a good fiberglass hull will shatter, the shards separating, but I'm talking about shards that weren't well-bonded by resin in the first place.

More recently, we were walking on another dock and saw the same thing. Unlike the first boat, this one wasn't intended for crossing oceans. It was what some consider to be a "price boat" - more affordable than many comparably sized boats but nevertheless a good deal for coastal and tributary cruising. But its hull laminate, where it had impacted with a piling, had very little resin under the gelcoat. You could see all the way through.

A number of things can cause this. Poor wetting out of the glass as a result of poor technique or sloppy work is one. Resin settling downward in the hull before it cures is another. A poor environment for curing, improperly mixed resin, improper application of the resin and other issues also could cause the problem. I don't profess to be an expert at building fiberglass hulls, but I do know that the consequences of an inadequate resin and glass laminate can be disastrous.

Rust streaks down any part of the underbody are a telltale sign of problems.

I also know that one of the characteristics of fiberglass construction is that you can (inadvertently or not) make something look very rugged by using sculptured lines, which elicit the aura of toughness and durability, and cover weaknesses with a good-looking gelcoat. For example, we all know how tough a North Sea fishing trawler looks. But this "look" can be accomplished without achieving the substance of the real thing by making a boat's lines similar to that of the rugged workboat, although the hull itself might be quite thin.

So if you're buying a boat, how do you know? There are ways to tell, including, obviously, hiring a good surveyor. There are also good, reputable builders who'll help you know what you're getting. In some boats, the pitfalls lie just beneath the gelcoat. In others, the traps are elsewhere - some more serious than others but none are desired.

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After the shortcomings of balsa coring became known, builders turned to various synthetic foam cores or took greater care to ensure the integrity of the bonds between the balsa and the fiberglass skins. I'm not going to get into the merits of one core or another because I'm not qualified to do so and failures were often the result not of a particular material but of the way it was used or bonded. However, I've seen some older hulls cored with synthetic material that were filled with water and mushy "plastic" between the outer and inner skins of some hull sections. This came from stressing, during which the outer and inner skins of fiberglass pushed in and out with enough intensity and/or frequency to break up the core inside, pulverizing it.

When water enters cracks in the now poorly supported skin, mush results. With freezing or further working, this can spread. Causes can include poor structural support within the hull, poor adhesion between coring and skin, impact or simply the daily working of the hull in the merciless sea.

More modern coring material does much to prevent this situation, but there are some older boats out there in which the problem exists. The technique of balsa coring improved greatly through the years, to the point where it has become a very successful process if done well. But with older boats in particular, water seeping through the hull skin and into the balsa via improperly bedded hardware or some other means turned good balsa into mush.

We're all familiar with that, and with the thousands of pages of magazine and book articles describing barrier coats and the proper way to seal hardware and fasteners so this doesn't happen, and how you deal with the problem when it does. But, as always with boats, there are a few twists.

I surveyed a very large, expensive motorsailer with a balsa-cored hull some years back. This one broke all the rules in that the coring didn't stop at the waterline but went all the way down to the keel. And the outer skin had some blisters - a trait not unusual in that particular boat. But the previous owners had done much to make sure the skins were sealed well. I found the problem not by tapping or drilling but by walking around the deck, admiring the hefty cleats and other hardware. I love high coamings around a deck. This boat had them, with heavy stainless chocks giving dock lines a fair lead through. But the chocks were inserted from each side into the coamings. This meant there had to be a seam in the middle, and because of the usage, the seam would have suffered from much stress. Getting down on my knees, I saw the seams had cracked apart so water could enter any time the boat took a sea.

This older sportfishing yacht grounded on a sandbar on the starboard side, and the impact pulled the rudder right through the bottom of the boat.

I went below and tracked the hull down in the area beneath these chocks. I found a through-hull that had been carefully added the correct way. The inner skin had been removed, the old balsa had been scooped out, and solid laminate and skin were applied to keep the hull tight and give the through hull good support. But foul water was oozing from the edges of that scooped cavity and coming not from outside the hull but from within. For years it had been making its way from the split seams down the balsa, causing rot in its path all the way to the bottom.

I can't leave this subject without mentioning another very different type of core problem. I call it the Boston Whaler phenomenon. I first noticed it with old Whalers in the Bahamas. It was the result not of poor construction but of construction that was, in one sense, too good.

The company advertised that the boats were unsinkable. Photos showed the boats cut in half, each half floating with occupants. In the Bahamas, many islanders took this a bit too far. It was commonplace for them to run these old Whalers up on beaches or rocky bars. Not even the best boat can take this for long, and soon these boats would develop tears in the fiberglass of the bottom skin. The islanders would just dig up some epoxy and glass and patch over them, returning the boats to the same kind of very rough service.

On more than one occasion, I've known of people flying across the water in these boats and suddenly hearing a bumping noise underneath, even though they were in deep water. Then something would hit the lower unit of the outboard and disappear astern. The boat would begin to behave very differently, but usually the folks got safely (and very slowly) back to the pier.

It was there they found that the bottom skin had torn completely off, peeled back by water rushing into flaws in the repairs. It's always wise if you rent an old Whaler in the Bahamas or the Caribbean to take advantage of those clear waters and dive in and inspect the bottom before you take off.

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I've also seen quite a few hidden disasters that weren't caused by coring but by the construction technique of relying on bulkheads, grids, stringers, seats and other internal structures for basic hull stiffness rather than thickness of the hull. There's nothing wrong with this technique if done well, and it's hardly new. I've always marveled at old steel ships with plates that have been hammered into slightly concave shapes by the waves but that are still serving well because of the interior support.

On a poorly constructed fiberglass boat this can result in problems such as holes in the hull, leaks between the decking and the hull, and the hull moving and flexing to the extent that it begins to self-destruct. The problem increased as some manufacturers, who perhaps didn't have the necessary engineering and fabricating skills or quality control, built lighter boats with thinner skins to reduce weight and costs. You need to know what you're doing to build light, strong and safe.

My 1975 motorsailer has no coring and a fiberglass hull so thick I have difficulty finding through-hull fittings long enough to go through the hull. But I've seen many hulls built since then that, to my old-fashioned view, were far too thin. A hull - whether for offshore or inshore use, power or sail, inboard or outboard - must be capable of handling incredible stresses. The problems are usually associated with insufficient utilization of interior structure, poor placement of the stringers and support for the stresses involved, and methods of attachment of that support to the hull.

This problem might first manifest as crazing or gelcoat cracks. This can be misleading because it is not unusual for the best of boats to develop this to some extent, particularly as the boat ages. But if the cracks are concentrated around bulkheads or other internal structures, beware. I've also seen bulges in the hull where the inner structure appears to be trying to push through.

Mysterious working sounds while under way or leaks above the waterline (such as the hull deck joint) give additional warning. And sometimes the supporting interior bulkheads or other structures actually separate from the hull, leaving inadequate support for a particularly thin hull.

Sometimes the bulkhead, bunk or other structure is simply abutted directly against the hull and secured with fiberglass. However, normally the bonding should allow for some flex, with the stress transferred from hull to support along a wide area. On my boat (I have to brag about the boat I love) the hull is so thick and tough that it is less reliant on internal support grids. But most boats aren't built like that today - not because they are inferior but because of differences in building technology.

Cracks in areas of high stress, such as the outside edges of a transom sporting a powerful outboard or the hull section to which an external keel is attached, should also be carefully watched. The stresses inherent in both situations can be enormous. It's easy to check a transom but not the area of a keel attachment, except when the boat is hauled. Checking inside the hull helps.

This keel joint shows rust from the steel keel and keel bolts, a catastrophe waiting to happen.

A telltale sign of serious trouble would be any moisture seepage in the area. Even if the fiberglass is totally sound, keel bolts, if used, can be an issue. Some older boats had mild steel keel bolts rather than stainless. It's only a matter of time before these fail. I've also seen sailboats in which plywood was used for the bolted-on keel's "backup" area inside the hull. It's only a matter of time before this compresses to uselessness and/or rots.

Even high-grade stainless-steel keel bolts are eventually suspect because they aren't invulnerable to crevice corrosion, and this occurs when the stainless is in a wet area in which water (and, therefore, oxygen) is not freely flowing. The joint between keel and hull can make a perfect breeding environment for crevice corrosion, which can render the keel bolts useless.

If you don't know what type of keel bolts you have, it's not a bad idea to swallow the expense and have the keel dropped as the boat ages so your bolts can be inspected, replaced if needed, and the joint cleaned and resealed. If a keel breaks loose while you're sailing, typically the result is an immediate capsize, affording little or no opportunity for the people aboard to save themselves.

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Moving to one of the less massive but equally destructive hidden horrors, let's take a look at the hose clamp. Aside from the fact that they draw more blood than a vampire at a sleepover party and can strip you naked on just about any job in the engine room as they tear up your Dickies, they are capable of much more harm - even sinking the boat.

Most hose clamps I see on the market are not all stainless (usually the barrel or screw is not) and are perforated at the band, which may be the only stainless part. These perforations can cut into hoses and weaken the clamp. When corrosion from the salt-water environment begins, as it will, it doesn't take much for the band to break. As we know, there are different grades of stainless, and cheaper hose clamps seldom use the better grades.

I prefer to use AWAB hose clamps (, which are 316 stainless, non-perforated, have rounded band edges to avoid cutting the hose, and are said to be designed so the clamping surface extends 360 degrees around, rather than the raised section under the barrel found in some less-expensive brands. Beware of cheap imitations.

Many hose clamps, particularly where the hose is clamped to a through-hull, are out of sight and out of mind. But there's one application that's more out of sight than most and very likely to create big trouble. It's where the rubber hose connects the stuffing box to the fiberglass shaft log on many boats.

An exhaust hose that's cracked on the outside is probably compromised far worse on the inside.

If you have the traditional waxed-fiber type of stuffing box (as I do and much prefer) you'll normally have a fine spray of water around the box when your shaft is turning. This will probably wet the clamps holding the stuffing box into the hose. This hose normally vibrates whenever you're running. (The dampening effect it offers is one of the reasons I believe this to be a good arrangement.)

But the constant salt spray will quickly deteriorate an inexpensive clamp to the point that it separates completely. The next step in the process could be spinning the stuffing box out of the hose and/or burning up the end of the hose, with ensuing rapid flooding.

Hoses, even when secured well, can conceal serious problems. Many hoses found on boats have wire inserted within the hose wall. This method has been used for many years to keep the hose from collapsing and to keep it rigid enough to do its job well. But as a hose ages, cracks can develop in the inner wall, which, of course, you won't be able to see.

As this happens, water can leach into the wall and reach the wire insert, causing the wire to rust and perhaps eventually break. Now we have rusty sharp wire ends tearing into the wall as the hose vibrates or moves slightly under normal use. The process can speed up as time goes on and result in serious leakage. It can also result in ballooning of the inner wall of the hose, causing an obstruction you can't see.

The inside of your exhaust hose can be particularly vulnerable to other attacks. If your engine's raw water cooling supply is ever impaired, the exhaust traveling through that hose can become so hot it'll damage the hose or even destroy it.

Usually we know something's wrong before an exhaust hose completely burns through. Alarms will go off, as will, perhaps, the engine itself. But the typical scenario is far more subtle. It isn't unusual for one or more impeller blades to break in the engine's raw-water pump, causing a gradual increase in exhaust temperature. Also, it isn't unusual for debris to clog the strainer with a similar result.

Eventually you'll probably notice the problem because of the temperature gauge and alarm and perhaps because of the different sound produced by the exhaust as water flow diminishes. But in the meantime, the exhaust might be overheating the inside of the hose, damaging the material where you can't see it. This can result in water reaching the hose wire and also structural compromise of the hose directly. Close attention to water supply components, gauges and an exhaust elbow alarm will help.

I've also known of instances in which, for one reason or another, hose wire inserts became a conduit for electricity, causing a wide range of problems. There are numerous possible causes for this. One occurs when the insulation on an electrical wire wears through as it vibrates against or rubs on a hose clamp, with the current ultimately finding its way to the hose wiring via cuts in the hose caused by the cheap clamp. Another cause could have the hose wire energized by a lightning strike, resulting in severe flooding and other dangers.

Although it's difficult to protect against the last example, there are simple things we can do to avoid other causes of sabotage by hose wire. The first is to replace hoses regularly. Another is to inspect hoses regularly, looking for cracks in the outer skin that will indicate there probably are cracks in the inner skin, even though it may be of a different material.

Also, look for chafing, electrical wires not properly secured and hose clamps that are unprotected and of poor quality. You can buy hose clamp covers for the end of the band that protrudes from the barrel. These save skin and clothing and also lessen the risk of the clamp abrading an electrical wire that may have worked its way loose and onto the clamp between your inspections.

I also often cover the clamp with Rescue Tape. I'm amazed at the versatility of this product. Although most people probably use it to mend leaks in hoses and pipes, I've found that it'll do much more. In this application it will cover the protruding band and barrel without tearing from the sharp edges, as electric tape will, and without easily slipping off, as do some of the ready-made band end covers. Of course, you can't see the hose clamp to inspect it, but it's simple to remove and reapply the Rescue Tape periodically.

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Having discussed doom and gloom for so long, let's turn to a more subtle type of torture. I've seen many fine yachts that appeared flawless - until bedtime. And I'm not talking about the mattress or bed linens; I'm talking about what's underneath. Some boatbuilders (presumably those that have never slept on their boats) have insisted on installing one or more types of pumps under the bed.

I was on a fine yacht a few years ago where the bed in question was the majestic owner's bed in the majestic owner's stateroom. Under this bed was the vacuum pump, which serviced all of the vacuum-type heads on the boat. Any time anyone flushed, the pump would start thumping away under the blissfully sleeping owners.

No problem, you might say. Just threaten to execute any guest who flushes while you're sleeping. But this wasn't good enough because one of the heads had a slight deformity in its seal. This produced a slight vacuum leak, which caused the pump to cycle on and off all night. Depowering the pump was the only solution that worked, but this, as you might suspect, caused other unwanted results, especially when there were guests aboard.

Other boats have freshwater delivery pumps under a bed. Any time someone gets a drink of water at night or any time a faucet drips, dreams are disrupted. Even more insidious are tanks under a bed. Water tanks slosh about enough to keep you awake, even though they are baffled. But much more fun are the holding tanks that, again, some builders that have never slept aboard their boats insist on installing under a bed.

Yes, there is indeed the sloshing issue, but this is just the beginning. I don't care who says what, holding tanks stink. And I've never seen one (and I've seen and smelled plenty) that failed to allow a significant degree of that stink to escape inside the cabin, no matter how well the tank was ventilated and no matter what high-tech special concoction of chemicals had been added. Unfortunately, I have no suggestions for remedying this problem that are practical.

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You may be feeling that the boat you own or the boat you're thinking about buying is not merely a hole in the water into which you pour money, but also a hole ready to eat you alive. I've had boats for more than 50 years, and I don't even know how many boats it's been. I still love them and love messing about on them. I'm even now thinking about selling my current boat to buy another - to downsize. And I'm no masochist.

I've learned to infinitely respect what the marine environment can do to the devices we construct to survive there. And I've learned that the glitzy aura of a boat show or dealer show room doesn't well portray what's going to be happening to that boat on the water. But when you know something about the telltale signs of that jungle floor on the path ahead, you're less likely to fall into the pit and better able to deal with the tiger if you do.

Tom Neale is technical editor for Soundings and lives aboard a Gulfstar 53 motorsailer. You can buy his book, "All in the Same Boat," and his two-disk DVD "Cruising the East Coast With Tom Neale" at

This article originally appeared in the March 2011 issue.