Transom Replacement with a plywood core
This tutorial will focus specifically on the most common type of transom job; how to replace/rebuild a plywood cored transom. We will show step by step the entire process using materials and techniques proven over many successful rebuilds. Following this guide will result in a rebuilt transom that is stronger and will last much longer than the original.
The boat featured in this rebuild is a 1984 Grady White. The boats owner is a local customer who purchased all his materials through our store and followed all of our technical advice, making this rebuild a great basis for the tutorial. The entire rebuild was documented by the owner at our message board. (This is a link to the rebuild thread). We provide technical help for all sorts of repair/rebuild projects through our forum. To receive the technical support for your project, please register and read this thread detailing what information we need to be able to help you. All materials in this rebuild were purchased through boatbuildercentral.com
Before beginning demolition: Take measurements of all the parts around the transom; fiberglass thickness of outside skin, plywood thickness, inside transom skin thickness, stringer location, string thickness, etc... You will want these measurements as a reference later. Before removing anything structural you must have the hull well supported. Removing stringers and/or a transom with out properly supporting the hull can result in a deformed or "oil canned" hull. The best support is a bunk trailer with additional blocks under the keel and transom. If you have questions on supporting the hull, please ask them on the forum.
In our example boat, you can see the transom core is soaked and it has lost nearly all of its stiffness.
The first step is to gain access to the transom. In the case of the example boat, there was a motor well bulkhead that made a natural place to cut through the liner/sole for access, but each boat will be a little different. The deck cap in this model did not need to be removed to be able to access the very top of the transom. If the boat had a single motor well and wide deck cap, a cut through the cap (or removal of cap) would have probably been necessary in order to reach the entire inside of the transom.
The next step in the rebuild is the removal of the old plywood core and inside fiberglass transom skin. You will need access to the entire transom plus at least 12" up the side and bottom of the boat. Depending on the boat's construction, you may be able to remove the deck cap, or you may need to make a cut through the deck and sole. If you post pictures at our forum we can advise you on the best places to make these cuts to avoid time consuming fairing work (hiding seams).
Now you must completely remove the old plywood core. A reciprocating demo saw, grinder, hammer and chisel are good to have. If you have an air compressor, a small air hammer is a good investment. Be careful to not inflict too much damage to the outside fiberglass skin. If you do damage the outside skin it is not a big deal, but you will want to reinforce it with a layer of fiberglass before the new core is installed (more on that later)
You can see in the pictures below that the liner is cut away and the old plywood has been removed. Any bonding putty in the corners should be ground out. The new core needs to be bonded directly to the old outside skin. NOTE: We recommend the last 8"-10" of the stringers be completely removed, in this case the stringer was not cut back far enough to be ideal.
Once the old plywood and putty are removed, make a template of the transom using cardboard or cheap plywood (or anything else handy). You will use this template to cut your transom core and also to draw/cut the wide fiberglass pieces that will make up the new inside transom skin.