The Rot Doctor


Subject: Tug (resealing hull)
Date: Tue, 13 Aug 2002

I just bought a 37' wooden tug. It was built in 1936. It has quite a history. It was the first mail boat to run to Mackinac Island and was seized twice during prohibition for rum running. The boat is in very good shape for the age. The hull is made of cypress and sealed between the planks with cotton and tar. I am researching the best (and most economical) way to reseal the hull. Would you recommend epoxy to install splining strips? You recently sent me an information packet. I am very impressed with your CPES and plan to use it. I am also debating weather to spray the inside of some of the hull planking. How much stronger will this method leave weak spots? Any advice will be a great help. I have watched friends go through hell with wood boats and said I would never own one. Well here I am but I do hope to avoid such headaches.

Thank You,



Your question is appropriate because we have gone through the exact same analysis vis-à-vis our old 50' 1889 tug. You (and us, too) really have three choices:

1) Reef the seams and re-caulk. This is not "permanent", and it involves yard costs plus the cost of a professional caulker. I've done enough caulking myself to know that it is a job best done by professionals. This method also assumes good planks and frames and good fasteners, otherwise she will not take the new caulking well.

2) Take the hull down to wood, and, as you suggest, rout the seams to bare wood and epoxy-spline (we'd use our Tropical Hardwood Epoxy adhesive) with a soft wood, such as pine or western red cedar. Saturate the exterior with CPES, and then epoxy-sheathe with glass cloth and epoxy resin. Paint. This type of work has been done, and it will work if the hull is dry. The main downside is that epoxy/glass is not very flexible, and so some strain is produced as the wood attempts to expand and contract under different atmospheric conditions. It will produce a watertight hull if done correctly.

3) Follow the same procedure as above, except instead of using epoxy/glass as the final coating, use two coats of our ELASTUFF 120 Polyurethane coating followed by two coats of our Elasta-Tuff™ 6000-AL-HS Polyurethane. This produces an absolutely watertight coating, and the Elasta-Tuff™ 6000-AL-HS being totally UV resistant also produces the matte-gloss final finish. The big advantage of the poly coatings is that they always retain some flexibility, which reduces stresses on the hull as the wood expands/contracts.

After a few years of testing the polyurethane's, we have elected to use alternative #3 for our tug. She is now sitting inside a steel barn drying out, and we will begin removing all miscellaneous wood and paint down to the bare hull probably within the next 6 months. We are confident that this will produce a totally watertight final seal that will be good for 20++ years. It is a process that is also easily repaired, which epoxy resin in glass is not.

There is not such thing as "economical" in these kinds of matters. To do it right it costs what it costs.

To answer your question about spraying the inside of the hull with CPES, I would say this is necessary only if there is evidence of overall wood softening. This being true, then yes, the CPES will harden the surface, but more importantly it will stop the softening process. If there is more specific deteriorated wood inside, then certainly CPES is indicated to put a stop to the rotting process. Whether this in itself is sufficient depends entirely on the degree of the rot. We have often followed the CPES with our Layup & Laminating Resin to restore structural strength.

I hope this is of some help, and please feel free to come back if you have further questions.