Boat Transom Replacement
The transom is a major structural area on your boat. It has to withstand the rough water and power that run through it. The old saying that “an ounce of prevention is worth a pound of cure” rings true for this area.
One way to access this area is to cut away the exterior fiberglass skin. You can then pull out the rotted wood and treat the remaining wood with CPES and a resin mix. Read the article below to learn more about Boat Transom Replacement.
The boat transom is an important structural component of any vessel, whether a sailboat or a powerboat. The purpose of a transom is to disperse engine power throughout the greater hull structure safely and effectively. However, the durability of the transom is dependent on how well it is maintained. This is why it is so important to thoroughly inspect a transom before buying or selling any used watercraft.
A rotten or soft transom is not just unsightly, but it can cause serious problems with the rest of the boat. The boat’s engine is bolted to the transom, and the force of the motor can push and pull on the fiberglass skin of the transom. Over time, these forces can lead to cracks and delamination of the skin. If the cracks are not repaired, the transom can eventually rot or collapse, and it must be replaced.
In some cases, a boat transom can be repaired with spot repair methods, but this is typically only a temporary fix. In order to completely repair a transom, it is important to take the time to remove any deteriorated sections of the skin and core. Once the damaged wood has been removed, it is important to sand and re-prime the entire area before refinishing or repairing the skin and core.
Once moisture enters a timber-cored transom, it can move between the layers of the wood and create hydraulic erosion that can shred the timber core, leading to further areas of delamination and irreversible damage. Moisture can also penetrate the transom skin at hardware fasteners, drain holes, and I/O cutouts.
The best way to prevent this is to keep the water in the bilge and out of the transom. This can be accomplished by installing a bilge pump and checking the pump regularly. Additionally, it is recommended to use a quality waterproofing product to protect the hull from moisture and rot. This can be found at your local marine hardware store and is an inexpensive solution that will last a long time. By following these simple steps, you can help prevent transom rot and keep your boat safe for years to come.
Git-Rot is a unique two-part liquid epoxy that saturates and restores the strength of dry-rotted wood by capillary action. This system can be used on transoms, stringers, and balsa core decking. Dry-rotted wood must be thoroughly cleaned and dried as much as possible prior to application. Soaking with acetone will assist in the drying process. The optimum temperature for use is around 50 °F. For complete saturation and ultimate strength, it is recommended that the volume of “GIT”-ROT be equal to half the volume of the rotted wood.
To apply the epoxy, mix 1 part “B” to 3 parts “A” and shake vigorously for a full minute. This will initiate a thermal reaction. The epoxy is then injected into the wood via capillary action; be sure to inject into the end grain whenever possible to prevent trapping air pockets. Once applied, the epoxy will penetrate the rotted wood and solidify overnight into a tough, resilient mass.
Repairing dry rot
When dry rot is allowed to spread, it can delaminate the fiberglass skin and damage the plywood core. This can lead to further rot and the eventual loss of the entire transom. Moisture can also penetrate the transom skin at hardware fasteners, drain holes, and I/O cutouts. This will cause the transom to flex and eventually fail.
It can be challenging to get at a transom for a repair without removing the outdrives or through-hull units. but it is doable. A good reciprocating saw, grinder, hammer, and flat prybar will help. The first step is to carefully cut away the exterior transom fiberglass skin, being careful not to damage it in the process. Once the old plywood core is removed, it can be replaced with new marine-grade plywood. The new plywood can be bonded to the existing fiberglass using a thickened epoxy/406 mixture. Make sure all contact surfaces are clean, dry, and sanded before bonding.
If you are going to replace the old core, it is a good idea to use 1708 biaxial fiberglass tape to reinforce the edges and bottom of the new transom. This is stronger and easier to work with than traditional woven fiberglass tape. The core can be sanded to a smooth finish and then sealed with polyurethane caulking.
Depending on the size of your boat, you may need to make an additional hole in the fiberglass for access to the rudder control and outdrive trim tabs. If so, be sure to cover the hole with a sacrificial plate that will protect the caulking and give you a solid surface to bond a new fiberglass transom skin to.
The sacrificial plates can be made from plywood or fiberglass. If you choose to use plywood, it is a good idea to have it CPES (Chip Proof, Eternal Seal) treated. You can then cut, glue, and CPES treat the new wood to fit the space in the transom, epoxy-glue it to the existing fiberglass, and fill in the area with either our Fill-It or our putty-mix Layup & Laminating Epoxy Resin ™.
Choosing a New Transom
As with any boat repair, when choosing a new transom, you want to be sure it is a good-quality product. If you want your new transom to be as durable as the original, make sure it is laminated from multiple layers of 1/2″ or 5/8″ plywood. The plywood should be thicker on the outside than it is on the inside, and there should be no gaps or voids in the laminate. Before you install your new transom, be sure to wax it thoroughly and tape up old bolt holes, sterndrive or anode holes, etc. It is also a good idea to use some marine-grade epoxy to fill any cracks or voids on the transom surface.
When installing your new transom, remember to take careful measurements to ensure it will fit the boat. It is not uncommon to have to oversize a transom if the boat is older or has had a number of modifications done over its life. You also want to check that the new transom is the correct height for the engine mounts (not all manufacturers believe in the same standards for “short shaft” motors; one may think short means 15 inches, another may use 17 inches, and some even have an XS extra-small shaft option).
After the transom has been installed, it is a good idea to do a spot check for any areas that are still wet. Moisture in the timber core of a boat transom is a very bad thing, and any areas of wetness should be core filled, re-glassed, and painted immediately. Moisture in a timber-cored transom will eventually track down into the floor and stringers of your boat and can compromise their integrity as well.
The bottom line is that the transom, floors, and stringers are three of the most important parts of a vessel’s construction. Compromising any of these components puts the safety and lives of everyone on board in serious jeopardy. Regularly checking a boat’s transom for cracks and signs of rot is the best way to avoid a costly repair in the future.