a boat consider if you’re willing to take on the type of
work needed to maintain and repair the hull.
Repairing the hull considerations
The ability to repair different hull materials is often a matter
of the type of work one is willing to tackle. For some grinding
a fiberglass hull is pure agony, while, For others cutting steel
with a hot torch can be a torturous experience. In this article
were going to discuss the basics owning and repairing three of
the major hull types-
Let’s start by considering some repair advantages and disadvantages
of each hull material.
• Resin and fiberglass are available the world over
• It’s a very basic technology known in the most outback
• Repairs are relatively cheap
• Very few power tools are needed
• Often the DIY can make his own repairs
• Repairs available in the most remote locations
• Needs only the most basic of welding machines
• The constant paint maintenance can overwhelm a yachting
• Steel boats have about a 30 year life span due to interior
• Steel produces high “sweat equity” return
on effort invested due to the low cost of materials
• Difficult to find repair facilities in remote locations
• Specialized welding equipment is needed
• Low, low maintenance. No rust. No paint above the waterline
or in the bilge.
• Highly susceptible to electrical corrosion
• The “right” aluminum must be used in each
• The hulls are loud and easily transmit engine and equipment
noise along with waterline noise
• Difficult of effectively insulate
• Reacts poorly with wood
Let’s consider an overview of repairing each type of hull
material from an owner’s perspective.
Fiberglass is a strong, and almost inert material. It’s
possible to own a boat for years without ever having to repair
the hull except for a hull polish.
The four most common reasons for needed hull repair are-
• Poor workmanship
• Fastener failure
Impact from striking a reef, another boat, or even cosmetic damage
from normal wear and tear are all repairs within the scope of
most DIY boaties.
The repair typically starts with the use of a grinder, followed
• Gelcoat removal till fresh, clean fiberglass is reached
• New glass cloth is laid over the damaged area
• Resin is painted over and into the cloth
• The repair is left to cure and then ground smooth
• Paint or gelcoat is applied to provide a finished look
This type repair is not typically considered difficult, but the
grinding of fiberglass can be an itchy, uncomfortable job. The
trick is to start the work by gearing up with proper protective
gear such as-
• A Tyvex suit
• Safety glasses
Tip-Too often we see the DIY grinding fiberglass in shorts, tee-shirt,
thongs. If you find you started a job in this manner and now are
paying the price late in the day by itching and scratching try
a cold shower and vinegar rinse. The cold shower prevents your
pours from opening allowing the ground glass to rinse away without
further penetrating your skin while the vinegar can break the
bond of the polyester or epoxy resin allowing the sticky remains
to be rinsed off without the use of harsh chemicals.
Often fiberglass boat owners will comment on how they can maintain
much of their boat with a few simple tools. The list often starts
with a small 100mm angle grinder coupled to a 36-40 grit grinding
disk with a hard rubber back. This inexpensive grinder and interchangeable
heads is available at hardware stores the world over and allow
basic repairs to the hull.
When making a repair the DIY will have a choice between polyester
or epoxy resin. Polyester is less expensive and often what the
boat was originally built from. Epoxy has a higher price tag and
can only be over coated with more epoxy, but its adhesion properties
are much higher. Short of other knowledge to make a decision on
it’s often best to make a repair with epoxy.
Osmosis, or the “pox” is considered a major downfall
of fiberglass boats. Blisters often show up on haul out and can
mean a high priced repair. The long, challenging fix often revolves
around stripping the complete gelcoat from the bottom of the hull
using an electric planer like device. The boat is left to dry
while the moisture content of the remaining hull is checked. Once
the hull is considered dry enough a new layer of epoxy and glass
is laid over the complete bottom followed by gelcoat.
Repairing the “pox” can tax the DIY. One method to
make the job easier is to hire out the initial stripping of the
bottom. This gives the DIY a starting point to start the labor
Oil-caning, or the hull skin flexing between the ribs often happens
in thin production glass boats. The owner might first notice gelcoat
cracks running parallel and near to the ribs. Left to their own
devices the hull will eventually begin to form a crack.
The standard repair is to add longitudinal stiffeners to the
inside of the hull. The project can be as simple as ripping a
piece of PVC pipe lengthwise to lay against the hull and use as
a mold to add a few layers of fiberglass cloth. The difficult
part of this job is removing the interior of the yacht to reach
the hull inside of the hull.
Note-Boats built pre 1970’s did not tend to oilcan as the
hulls were made thicker.
Fiberglass hull tend to have nice clean edges, radiused curves,
and fast water drains. This is because one of the big advantages
of building a boat in a mold is these delicacies can be thought
out and built into the mold ahead of time so each successive boat
has some elegant features.
Glass boats, especially older production boats can be a great
bargain costing much less than a “one off” version.
Production boats also tend to have a known history and value.
A quick Internet search will show the basic selling price and
the boats reputation such as typical speed, best point of sail
and even know design flaws.
Glass boats are often thought of as a low maintenance boat owning
experience. A simple polish and waxing is often all that is need.
Use a buffing machine with rubbing compound followed by an application
of wax during the yearly maintenance can keep an old boat looking
Glass boat pitfalls
Deck leaks, fitting maintenance and lightening strikes are often
considered the big three pitfalls of a fiberglass hull.
While not really a hull repair, fiberglass boats are notorious
for deck leaks and dealing with them is part of living on a fiberglass
boat. Water finds it way into one of the many bolt holes securing
a hatch, sailing track, or deck fitting only to migrate through
the overhead to drip in some inconvenient place.
Some tricks used to find the source of deck leaks are-
• On a hot sunny day blast water at individual deck fittings.
The idea is to limit the places water could have entered the boat
• Try to get to the underside of the leaking fittings. Dry
the areas as much as possible then use toilet paper laid over
the fittings to identify the “wetspot” showing the
individual leaking bolt.
Fiberglass boats are held together by fittings. These are the
nuts and bolts that secure the chain plates to the hull, the bolts
that secure sailing track to the deck etc. Each bolt is a source
of corrosion and possible leak. Metal boats don’t have this
problem and it’s often one of the prime advantages of a
metal boat over glass.
Fiberglass boats are susceptible to lightening strikes. While
New Zealand in itself is not often thought of as a lightening
prone area, if the boat is taken cruising lightening zones will
be encountered. Metal boats are almost completely immune from
lightening strikes. A glass boat can suffer thousands of dollars
in damage after a severe strike.
Aluminum hull repair
Repairing an aluminum hull is relatively simple. The work is
clean and the welding easily learned. The challenge revolves around
finding the right equipment. Let’s look at a few basics
of aluminum repair.
Cutting aluminum is most often done with a powerful circular
saw and a carbide tip blade. Amazingly a good carbide blade will
cut right through a sheet of aluminum leaving a near perfect cut.
Be sure to wear hearing and eye protection. The flying aluminum
chips are notorious for their sharpness.
Tip-Blade noise can be reduced by first cutting into a block
of beeswax followed by the aluminum cut.
Welding aluminum is fast and easy, but it takes a lot of power
to maintain the molten welding “puddle”. The power
source must be clean and consistent thus a large generator or
good shore power is needed.
The welding kit
Let’s look at a typical aluminum welding kit. In the welders
hand is a spool gun. A spool gun is a welding lead that can be
held in one hand with a small spool of aluminum contained in the
handle. The spool gun is powered by a power source, most often
a DC inverter welder powered by a 6KW or larger power lead. The
welding arc itself must be covered with an inert gas, most often
Argon. This means a metal cylinder of gas and a regulator must
be included in the welding package.
While all this gear has dramatically shrunk in size over the
last few years the welding kit bulk is still outside what most
boats would carry aboard. This means when a repair is needed the
first step is the yacht must find a competent shop. Inside New
Zealand this is relatively easy. On the cruising circuit finding
a good welder willing to come to the boat can be a challenge.
Aluminum boat factoides
• The welding process for aluminum is faster than steel.
This means it costs less labor time to lay the same amount of
weld in aluminum.
• Aluminum is less expensive to work than steel since the
cuts are made with a circular saw rather than a “gas ax”.
This means no buying expensive gasses and less fire hazard from
flying cutting sparks.
• Aluminum does not need to be treated when the weld is
complete. This translates to considerable cost savings when compared
to a steel weld. Steel requires cleaning (sandblasting) and five
coats of paint to prevent rust.
• Aluminum has no life span. A steel boat lasts about 30
years till the cost of maintenance begins to overwhelm the budget.
An aluminum boat that has been taken care of will still be “good
as new” in the same time period.
• Copper and mercury are big killers of aluminum. One drop
of mercury (from a broken bilge pump float switch or thermometer)
will eat through the hull in just weeks. Copper dust from bottom
paint tracked onto shoes from walking through boatyards can leave
a groove in an aluminum deck.
Insulating an aluminum hull
Aluminum hulls are difficult to heat and cool. Often we hear
“just insulate it”, but this is not really an appropriate
answer. Our personal sailing yacht for over twenty years has a
steel hull and aluminum cabins. This means I live in a world comprised
of half aluminum and half steel. The steel has one inch of laid
in insulation while the aluminum has two inches of blown in insulation
with a half inch of wood over the top.
Standing inside the boat on a cold day it is readily apparent
the cabin tops are “sucking” the heat from my body.
In cold climates the effect is even more dramatic. Screws into
aluminum with exposed heads form icicles inside the boat while
exposed steel simply condensates.
In Alaska areas of exposed aluminum built up ice over a half
inch thick with the diesel heater is set to maximum. Meanwhile
the steel may be chilly, but it has yet to form ice on the inside
of the cabin. This might explain why aluminum makes such good
Steel is often considered “easy” to repair, but it
should also be considered “dirty” to repair. Every
aspect of the job leaves a mess. Weather its grinding dust left
on the deck, burned ash in your lungs, or steel dust in the air
that covers surrounding boats with rust streaks, steel messy to
Most often steel hull repairs are needed after an impact, or
a rust hole has opened up under the water line. Typically the
repair steps are-
• Decide on the amount of plate to be changed by use of
ultrasound or visual inspection
• Mark the edges of the cut
• Cut the straight sections with a cutting disk or plasma
• Cut the curved corners with a hole saw, gas ax, or plasma
• Cut a new piece of plate and hold it into location
• Tack the plate to hold its position.
• Weld the outside of the plate back-stepping to prevent
• Grind the weld from the inside and re-weld. Finish with
another weld from the outside.
• Wire brush or sandblast and paint on five coats of epoxy.
Some tricks to making steel repairs-
• Use high quality electrodes. Low quality electrodes produce
low quality welds that tend to crack on cooling or worse during
• Pay particular attention to the grinding out of bad spots
on a weld. Much time is saved by grinding deeper to clean out
the impurity and thus produce a good second weld.
• Don’t rush the welds. Be sure to take time to let
the weld cool. Distortion, weld cracks, and rusting welds often
come from overheated welds.
Look at a piece of raw steel and you’ll notice the surface
will either shiny, lightly rusted, or black. Black is the left
over mill scale remaining from the production process. Mill scale
MUST be removed prior to welding or painting. This is because
mill scale is not really bonded to the steel so it will eventually
lift off ruining the best paint job.
Worse, mill scale is located on the galvanic action chart slightly
higher than steel, thus the mill scale will cause the steel to
rust in a marine environment. Ever see steel repair that has simply
rotted away in a matter of years, or in some cases months? This
is most often caused by the thin layer of mil scale that was not
removed during the repair process.
Removing mill scale
Mill scale is difficult to remove. It is harder than steel and
thus difficult to grind. To remove mill scale before a repair
• Buying steel plate that specifically had the mill scale
• Leave the plate exposed to the elements for a short time
to allow the surface rust to form thus weakening the mill scale
• Grind or sandblast the surface of the plate
• Acid soak the steel plate to lift the mill scale
Steel welding gear needed
Welding gear for steel is cheap and getting cheaper. Modern welding
machines are solid state, weighing about three kilos and can be
fit under a single arm. The basic machine can be purchased as
stick welder, or for a few hundred extra dollars the tig option
can be added allowing welding of special metals such as stainless
steel, bronze, brass etc. A modern welder can easily be carried
on the smallest of vessels for repairs in remote locations. Steel
does not require the high current of aluminum to weld, thus a
much smaller generator can be used.
A plasma cutter is a special machine that cuts metal by using
compressed air and electricity. This makes them specially suited
for boats where tanks of special gas can be difficult to come
by. The compressed air can be supplied by a small onboard compressor,
or even the low pressure side of a SCUBA regulator. Expect to
use at least a 4KW genset to power the newer smaller machines.
Note-In New Zealand machines can be purchased that are a four
in one. Stick welder/Tig/Mig (power source)/plasma cutter. While
a little larger than a single welder these new welding machines
give almost any boat complete shop facilities in one package.
While there is no perfect hull material choosing “your”
material is often a matter of forethought and what “devil”
your willing to live with. By taking the time now to decide on
the work you’re willing to perform you can narrow you search
in purchasing a new boat.
Note-Much of the background information for this article was
taken from Scott’s new book, “Metal Boat Maintenance
and Repair” available at Yachtwork.com.
The answer to last month’s question about the two types
of load a breaker is designed to protect against is- A breaker
must protect against long slow overload and a direct short. The
long slow overload is often regulated by temperature build up
through a bimetal strip. During a direct short the load must be
released immediately or the wires will burst into flames. The
breaker does not have time to heat up and release, therefore a
second “bullet” breaker is built into a breaker. A
bullet breaker looks like a bullet and has a few wraps of wire
around it producing enough magnetic force to “shoot”
the bullet from its seat instantly disconnecting the load incase
of a direct short.
Q-We all know if you want to cool a piece of hot steel you put
it into a bucket of water, but what is the ratio of heat holding
ability of water to steel. In other words if a kilo of steel at
100C were dropped into a bucket containing a kilo of water at
0C what will the approximate final temperature of the water and
steel be? (Ignore heat lost due to outside forces such as air
the right hull material for your skills
Glassing the bow of a fiberglass cat
Laying the glass on in layers.
No matter what type of work you perform take the time to protect
Mystery crack in the bow of this cat.
Repairs to fiberglass
Aluminum hulls needs special welding gear. Mig machines and Argon
Deep pitting in aluminum can mean changing plate.
This pitting was caused by poor radio grounds.
Repairs to most hulls can be made in the water
Look at the lack of material inside the hull
Just a gaping hole in the glass. No wonder it cracked.
A plasma cutter can make cutting metal plate a breeze.
Steel welds need to be protected. Spray is an easy way to apply
a good thick paint covering.
Removing mill scale from steel before a boat repair.
Steel plate being changed. View from the inside.
Steel plate change. This simple work can double the life of a
The old plate does not come out easy. See the parts that had to
be cut to bits.
Welded and repaired steel hull waiting for paint.
A fiberglass cat still needs welding on the metal bits.
following photos are from the article on corrosion that can be
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How to repair a steel boat without sandblasting. Special report.
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