Best method to attach gunnels?

[keithbehrend]

I am quickly approaching the stage where I will be attaching the gunnels on my 16' Prospector. I am using red oak for the gunnels, and have used white pine for the planking. I would appreciate any comments on the advantages and disadvantages of attaching them solely with epoxy vs. attaching them using a mechanical connection, such as through-bolts. Any thoughts are appreciated.

[Dean in Eureka, CA]

A mechanical anchor will make it easier to replace them later on.

[Todd Bradshaw]

Red oak is one of the more difficult woods to get a good bond with using epoxy resin. It also tends to be more prone to rot than most other oaks and similar woods. Buy a box of bronze screws and save yourself a major hassle later.

[John Michne]

From time to time there is a thread about gunwales, their installation, and replacement. A while back I wrote a few paragraphs about gunwales that are repeated below. In addition, a few other thoughts come to mind.

For lack of space, I store my boats outside. They only get paddled or rowed a few times a year, if that. One has never even been in the water. The point here is your boats will spend a lot more time in storage than on the water. What consideration must be given the gunwales when the boat is not in the water?

Boats are usually stored upside down. The joint between the hull and the underside of the outwale is a water trap. If the outwale is installed dry, with no epoxy on the mounting surface, you virtually guarantee the need to replace them after a few years of outdoor storage. If the outwales are installed with at least an epoxy seal on the mounting surface, you will delay the need to replace them or, barring any physical damage, may never have to. I imagine replacing epoxied outwales would a job, but not impossible. I just never had to do it.

For more info about gunwales, see my web site, http://michneboat.com. Click on Builder’s Corner, then scroll down to Gunwales.

Now here is what I wrote earlier:

I have been following the gunwale discussion here for a few days, and offer some thoughts. The question revolves around whether to epoxy the gunwales on, screw them on, or use both. There was also some concern about gunwales staying on the boat after driving at highway speeds with the boat on top of the car if they are merely epoxied on. I have driven my boats at 65+ mph for over a hundred miles many times, and the epoxy-only gunwales show no ill effects. If well-made gunwales were to come off under those conditions, what would happen to the rest of the boat?

The question of ease of replacing the gunwales should be a non-issue. If the gunwales are simply screwed on, you are virtually assured of the need to replace them at some point. The problem here will be water damage. No matter how well they are sealed with paint or varnish, there is a joint that will get wet – from rain, paddling, or condensation, like fog or dew. Wood that is not sealed and gets wet will rot – count on it.

Replacing a gunwale is not something that needs doing every season. Mechanical damage may require repair, but that is the unusual circumstance that hopefully is never needed. If you insist on fastening the gunwales with screws only, then I recommend strongly that the inner surface be given a couple of coats of epoxy before mounting. This will seal them, preventing (or delaying) water damage for years, and make eventual removal a lot easier. If you opt for gluing them on with epoxy, make sure the inner surface is roughed up with coarse sandpaper and soaked with unthickened epoxy before gluing.

Some builders also leave the screws in, even though epoxy was used to glue them on. No problem with this, although if you are sensitive about added weight, the screws do add a few ounces. An alternative here is to leave a few screws in at the ends only.

Hope this has been useful.

John

[JimND]

I would suggest that you seriously reconsider your choice of red oak for gunwales. Red oak is not rot resistant whereas white oak is fairly rot resistant. After a year, I doubt anyone could tell which one was used. But if you use red oak, almost certainly you will be replacing them within a couple years.

[Todd Bradshaw]

John's post about water intrusion with screwed-on gunwales brings up an interesting point. Canoe builders (including most of the major manufacturers of traditional wood/canvas canoes) have been screwing bare wooden gunwales to hulls and then varnishing over the tops for better than 100 years. They have been able to get away with this because of the limited amount of use and weathering that the average canoe gets. As far as standard wooden boatbuilding practices go however, this technique is not considered sound boatbuilding. Gunwales, decks (breasthooks) and similarly installed hunks of wood or wood-to-wood joints are SUPPOSED to be bedded with bedding compound.

If you haven't seen or used it, this stuff is a thick, paste or a soft putty-like substance which is designed to stay that way. It isn't an adhesive and isn't particularly sticky. You butter the mating surfaces of the wood piece before mechanically attaching it to the boat. The excess squeezes out when you tighten the joint and you scrape it off. It fills any tiny gaps and keeps water out of the joint, preventing deterioration of those hidden surfaces. It works quite well and usually lasts for many years, yet should you need to remove the wooden piece for refinishing, etc. it is easily removed and the piece can then be re-bedded when you're ready to screw it back on. I have rebuilt old boats where the only thing still in good shape and not in need of major work were the bedding compound and the surfaces it was there to protect. It seems to be much better long term protection for these areas than the vast majority of the modern goo-in-a-tube marine sealants and in my experience will do as good a job as epoxy sealers without glueing the piece to the boat and making it hard to remove or replace later.

The canoe industry has for the most part ignored the availability of this extra level of protection over the years with the exception of bedding wooden keel installations, brass stem bands and the laps of the canvas at the ends off wood/canvas canoes - most likely due to the cost and time savings of leaving it out and since they can get away with it seeing that the majority of wooden canoes aren't left out in the weather.

As I've said before, I do not epoxy my gunwales to the hull and don't like anything about the idea of it, but those inner surfaces will certainly benefit from some form of protection. At a minimum, this would be several coats of varnish. Three coats of epoxy resin as a sealer (sanded smooth so you're not trying to attach a lumpy surface to a smooth hull) would be better. Bedding compound seems to be about as good as resin as far as I've been able to tell and still allows easily removing the gunwale if ever needed. Once you've had to remove a properly bedded, 50 year-old rubrail from an old boat and seen how easily it comes off and how well it protected the wood in the joint, it's hard not to become a believer in good bedding compound.

It should probably also be pointed out that for outside storage of strip canoes U.V. damage to the resin covering the entire hull is easily as big of a danger as water lifting the finish on the trim. U.V. absorbers in varnish get used up as they do their job and need to be replenished on a regular basis. Failure to do so will eventually turn epoxy/fiberglass into a yellow, crumbling mess. So by all means seal the hidden surfaces on gunwale installations, but if you plan to store the canoe outside, don't forget to look at the whole scenario and it's potential to do damage.

[Alan from Wisconsin]

After installing gunwales dry with screws, you can remove them and paint with epoxy all surfaces including the insides of the screw holes in the outwales, hull, and inwales. A thin epoxy like system 3 clear coat soaks in well to provide protection without a thick coat. After light sanding, the gunwales can be installed and varnished. This prevents moisture access to wood. If you use steel screws the first time, and brass (or bronze, or stainless steel) the second, you minimize the risk of shearing a screw.