This Is How We Repaired Our Fiberglass Boat & What Tools and Materials We Used

Fun With Fiberglass Repairs!

As you have likely watched our latest episode on YouTube, you may have some more questions about how and why we made these fiberglass repairs to our sailboat. Here we will try to give you all of the dirty details.

What Caused The Fiberglass Damage?

In mid-November, during our sail from Tenerife, Canary Islands bound for Mar de Plata, Argentina, we struck an unidentified floating object (UFO) about 800 miles off the coast of Sierra Leone, Africa.

We were only moving at about 3.5 knots in very light air as we approached the doldrums. It was raining and there were intermittent squalls. Kate was on the helm, and I (Curtis) was sleeping off shift down below in the aft cabin.

There was a very loud set of bangs as the boat heeled and spun 180 degrees. Kate yelled that we had hit something, but she could not see anything. More about this in Episode 71 on YouTube.

We immediately made ready our life raft and ditch bags and commenced inspecting the boat for damage. That night, we could find none and the boat was able to continue sailing. We inspected the boat in the water when conditions allowed, also finding no damage.

Quite some time went on, and we sailed over 2000 miles since, dove on the hull with SCUBA gear twice, and even won a race, but we finally found damage from a small hole made by the aft edge of our rudder contacting and cracking the hull many months later while sailing the coast of Brazil, as evidenced by salt water entering through the laminate.

What We Did After Finding Damage

After docking in Itajai, where we knew from following the Volvo Ocean Race that there were good facilities and a travel lift available, we moved all of the weight forward to minimize water entry and sent a professional diver into the murky brackish water to do yet a 4th inspection. He also found nothing.

At this point, we knew we had to haul the boat out to find the cause. We also contacted the manufacturer, J-Boats, to gain a greater understanding of the fiberglass hull construction in the affected areas and enlisted the help of a local professional boatbuilder and naval architect at Magma Yachts to inspect and consult on the repair.

We determined that the UFO collision we had months ago was likely the cause. It had flexed the rudder shaft some, which allowed the rudder tip to contact the hull. We also learned that the rudder shaft was designed for this and that this is a common occurrence in boats with spade rudders. It was also determined that the boat should be hauled immediately and the rudder pulled to inspect the surrounding area and rudder bearings as well.

Planning For Fiberglass Repairs to Our Sailboat

We formulated a few plans to haul the boat, and even had a contingency plan to haul at a different location if need be, with the help of Gabriel @ Magma Yachts, whose help was instrumental throughout the repair process!

Despite his company producing his own brand of yachts (check out their 38’ racer/cruiser which IMO has fantastic build quality and awesome options like a lifting keel) he is also part of the J-Boat family, as he races J/70s in international competitions.

Lifting Our Sailboat & Removing the Rudder

Luckily we were able to schedule a haul out at Marina Itajai. We had to wait for almost a month at the dock though, to make room for us, as their boatyard can only accommodate a limited number of boats on the hard.

We were able to remove the rudder before setting the boat down onto its keel during the initial haul and blocking process. Before moving the boat to the travel lift, we had already removed the autopilot components, loosened the bolts for the steering quadrant, and had the tools at hand to complete the job. It is important to do this quickly to save from having to pay for an extra lift.

Inspection – Looking For Hidden Fiberglass Damage

With the rudder out of the boat we could finally inspect the hull, keel, rudder, and rudder shaft, visually and by tapping it out. We also inspected the rudder bearings, luckily finding no damage to our Jefa bearings which we replaced way back in Episode 12!

We did find delamination and a small, fingernail-sized hole in the outer laminate just above the aft tip of the rudder. This was a cored area, so we knew we would have to dig out and replace a substantial section of the core to make a proper repair.

The good news is, we could find no further damage to the boat except for a few scrapes in the paint.

Sourcing Project Materials – Where To Buy Fiberglass & Core?

If we were at home in the USA we can source almost everything we need online, included are some links to similar materials we have used on so you can easily obtain items similar to what we used to make these repairs.


Sourcing materials in Brazil can be difficult as we do not have a “CPF” number. Think of this as the Brazilian version of a social security number. It is required to make any large purchases or buy items online. It is possible to get a number as a tourist, but the process takes a few days. We tried to but weren’t able to complete the process.

Instead, a few excellent new friends in Brazil helped us out by allowing us to place the transactions using their information. Brazil actually has some excellent composite providers, one of which is E-Composites. We were able to arrange delivery through Gabriel. We purchased fiberglass, epoxy resin, core material, and vacuum bag materials. Gabriel loaned us his portable vacuum pump which was a huge help and cost saver!

Fiberglass Repair Steps

It was now time to make the fiberglass repair. Here are the steps we used to complete it.

Step 1 – Grinding

Step one is the removal of all of the bad material. To get to the bad core, we would first need to remove the skins on either side. We started from outside the boat and drilled a hole using a cordless drill and standard drill bit through the punctured area. This gave us a good location on the inside to start.

Next, we started cutting, grinding, and peeling away anything on the inside laminate that was at all questionable, cracked, or delaminated from the core itself. This turned out to be approximately a 1.5-square-foot area.

We used an orbital saw and grinder with sanding pads for most of this part of the process. Sanding disks mounted in a grinder or drill were also helpful. The key takeaway here is to grind away anything that is compromised, delaminated, cracked, or unattached.


Step 2 – Core Removal

Now that we have access to the core itself, we can start to determine what parts of the core have been affected by the damage. There are two parts to the core damage. The first is impact damage and crushing of the core from the collision itself. The second is damage to the core from water intrusion, which softens the core and if left alone will rot the balsa core in our boat.

Just a note, there are many types of core. Depending on the way your boat is constructed you could have solid fiberglass with no core, wood or plywood core, end grain balsa core, foam core (of which there are several types and uses), or other composites like a honeycomb.

Any damaged core, either by impact or water needs to be removed. We do this by carefully using a hammer and chisel, as well as our orbital saw to remove it. You can also grind out the core, but we find in large areas such as this it is easier and less messy to extract with a sharp edge.

The key here is to make sure to remove all core that is compromised and keep digging until everything is dry and firmly attached. This may be a mentally painful step, tearing into your beautiful and loved boat, but it must be done to make the repair like new later.


Step 3 – Prep for New Glass & Scarf

Now that we have ground away all of the damaged fiberglass and removed all of the questionable core material, it is time to finally begin the actual repair steps.

Because we are going to be applying new epoxy and fiberglass to the old, there will be no chemical bond, only a mechanical bond. It is important to give the new repair a large area to grab onto, so to speak. The technical term for this is called “scarf area” or “scarfing.”

Scarfing means sanding or grinding an angle in the old fiberglass to which the new fiberglass is attached. The normal scarf angle is about 12:1, or for every 1 unit of thickness of the repair, you need to sand away at an angle from it 12 units. Another way to think of this: if your fiberglass is 1” thick, you need to grind or sand away an angle 12” from the hole.

Since our fiberglass outer skin is only a few thousandths of an inch thick we only need to scarf a little more than 2”. After this is done the area should be cleaned of dust and wiped down with acetone. This step is perhaps one of the most important to achieve a strong bond for your repair.

Step 4 – Repairing Outer Layer

Because our hull is cored, we have to repair 3 different layers, making the repair much more complex. We could repair all three layers at once, but we find it easier to repair the outer later in this case first.


Epoxy is mixed in the proper ratio, and cloth is wetted out in layers to cover the scarfed area. A few tips here:

  • Pre-Measure, mark, and cut your cloth before mixing your epoxy.
  • Use the same cloth and thicknesses as the original layup if possible to maintain the designed structural strength.
  • Stack your repair layers in a pyramid shape, the largest in the first layer touching the old fiberglass and the smallest as the last layer.
  • Wet out your cloth and the scarfed area before applying if possible.
  • Use peel-ply cloth to smooth out the repair and remove any air bubbles.
  • A vacuum bag is not needed, but using it will increase the strength of the repair.
  • Repair from both inside and outside if possible.

Step 5 – Inserting New Core

After we completed the repair to the external skin we moved on to the rest of the repair, of which the most important part is the insertion of the core material.

The core material gives the laminate most of its strength. In our case the core in our boat is made from balsa wood, cut, dried, and arranged on a backing material in an end-grain fashion, increasing its stiffness and strength when laid up properly. The core material on our boat in this area is 5/8″ end grain balsa core.

The core needs good adhesion to both the outer skin and inner skin. It is important to sand the repair to the outer skin smooth and use structural epoxy and filler to aid in its attachment. In our case we also filled the core sections with epoxy to mimic the original SCRIMP construction done by J-Boats as we found it was beneficial to the original structure.

Step 6 – Apply Fiberglass for Inner Skin & Using Vacuum Bag

Vacuum bagging our fiberglass repairs was probably not a requirement in this case, but to us, we felt it was needed to obtain the greatest strength and contact between laminate layers. Using the vacuum bag technique does add a level of complexity, but once learned it can make repairs stronger and less messy.

After we had our core in place, we wetted out and applied our inner skin layers. Now we apply our vacuum bag tape to allow the area to seal when the other layers are applied, in a pinch one can also use butyl tape, or even duct tape (this does not work as well and is just a field patch). After this we applied a layer of peel ply, then breather material, then absorbent material.


The peel ply is a non-stick layer, that also allows the epoxy to cure without “blush” on the surface, this means that you can add another layer after it dries without sanding and washing. There are different types of peel ply to accomplish different goals, but the standard stuff should work just fine for normal fiberglass repairs.

The breather material allows the air and excess epoxy to flow to the vacuum. Spreading out the area of suction amongst the entire repaired area. It also acts as an absorbent material sucks up any excess epoxy drawn out by the vacuum. It is important to remember that the fiberglass is what gives the structure strength, extra epoxy beyond what can be absorbed by the fiberglass actually weakens the repair. This is where vacuum bagging has a great advantage over conventional wet layup repairs.


Last, the vacuum bag itself is placed over the top of everything and sealed to the boats hull with butyl tape. The vacuum pump is not your normal vacuum, and fairly specific to this task, but they can be sourced easily. The repair needs to stay under vacuum for the duration of the epoxy cure time, sometimes up to 24 hours. It is important to use a vacuum pump designed for this, otherwise their can be a risk that the pump will fail and you will need to start your repairs over.

Step 7 – Fiberglass Finishing and Painting

The last step in the progress is finishing the repair to make it pretty. This can be as simple as removing the peel ply and moving on with your day, or more steps of sanding, fairing, sanding, priming, sanding, and painting to achieve a show quality perfect gloss finish. In our case, we finished the outside portion of the repair nicely, but left the inside repair bare epoxy. This way we could monitor the repair (the dried epoxy is clear), and we could paint it later to match the rest of our bilge.

Balsa Core vs Foam Core

Many people have asked us, why not use foam core instead of balsa core? This is an excellent question. Before we answer it, we need to give you a little background on core materials.

Balsa sometimes has a bad wrap. This is because many boatbuilders have taken shortcuts in construction using this core material. When balsa gets wet, it rots. That is well known. If it is sealed in epoxy and fiberglass, it will last almost forever, and it is stiffer than its foam cousins.

Most people don’t realize that foam cores can also get wet and delaminate, so choosing foam as a core material does not necessarily isolate you from the problems caused by poor construction and water intrusion, it usually only delays the damage. For the most part, any core when damaged and infiltrated with water will eventually begin to delaminate and lose its strength.

Because foam has a different density than balsa core, it is also used in different thicknesses in layups. For us to achieve the same stiffness, we would need to use a thicker foam core. This would change the internal shape of the hull and make for a more complex repair. We could use the same thickness of foam as the original balsa, but that would also mean our repair would not have the same strength as the original hull in this area.

We firmly believe that a balsa core that is well taken care of is just as good, if not better than foam. In our case, using the same size core, and restoring the boat to its original design and layup specifications was the best course of action.

Professional opinions may vary on this. Many fiberglass repair persons will just fill the area with epoxy rather than re-core or may fill in with foam, wood, or whatever is “on hand.” This happens in boat yards around the world and most consumers or yacht owners would never know the difference. It is much cheaper and faster, and some of these repairs are OK depending on the use of the boat, for example, if she will be a dock queen, appearance may be of more value than strength.

Basically, there are many ways to accomplish a good fiberglass repair, so discuss these options with your repair person if not doing it DIY. We prefer to take an engineering-based approach rather than a patch repair approach and like to do things the right way one time, even if it takes more time and costs a bit more.

Tools Used For Our Fiberglass Repair

Orbital Saw
Cordless Drill
Shop Vac
Vacuum Pump

Materials Used For Our Fiberglass Repair

Tyvek Suit
Masking Tape
Duct Tape
Plastic Sheet
Fiberglass Cloth
Grinding Disks
Grinding Pads
Drill Disks
Peel Ply
Breather Cloth
Butyl Tape
Vacuum Bag

  • Linda Woodall
    Posted at 22:53h, 25 October

    Thank you for the detailed explanation.. I also thought your “collision note” logbook entry was very good information. I have written that out and put it in the front cover of our log book. Hope we never have to use it, of course! Safe travels. Give Roxy a hug :D.

    • sweetruca
      Posted at 23:17h, 25 October

      Thank you Linda, we are glad you enjoyed it! Safe sailing!!!

  • Michael Van Winkle
    Posted at 00:17h, 26 October

    Very good job Curtis! Hope the new repair lasts the life of the boat!

    • sweetruca
      Posted at 18:08h, 26 August

      Thank you!