Deck-Hull joint

[Simon]

Not sure if this inquiry belongs in boatbuilding techniques or Q+A, so I'm puting it in both.
I am the new owner of an old Lapworth Gladiator (hull32). Like many boats its age, it has an aluminium trim at the deck/hull joint, which in this case seems to be rivetted or screwed right through the deck-hull joint, with glass over the protruding ends of the screws on the interior. The alu trim is badly pitted with green slime growing in the gaps between the trim and deck. I want to rip it off and replace, or just sand and fill. I have several questions:
1. Are the screws/rivets structural? (ie If I remove the alu extrusion, and don't replace it, should I replace the scews/rivets?)
2. Are the deck and hull bonded?
3. Having removed the alu trim, how should I clean the joint before filling/sealing etc?
4. What should I fill/seal with?
5. any other suggestions?
thanks
Simon

[heartofgold]

Simon,
I can address some of your issues generically--I am not specifically familiar with the Lapworth Gladiator, but many boats of that era were built in a similar fashion.

To answer your second question first, are the hull and deck bonded, probably not. If you can inspect the joint from the inside, you may be able to assertain whether or not these two pieces are bonded. And if they are not, then yes, your machine screws and nuts are "structural."

As for your green slime, I would spray the infected area with an ammonia and water solution, Be sure to flush the area well with acetone the following day (give the ammonia a chance to kill whatever is present).

3M 5200 would be my top choice to seal this joint. It is durable, flexible and down right indestructible. 3M 4200 or polysulfyde would suffice if you were looking for something a little less permanent.

I can relate to your undertaking this project, as it was the removal of my aluminum rubrail which led to my entire rebuilding. Once I had the rubrail removed, I found considerable "dry rot," as much of the edge of the hull had not been fully wetted with resin at the factory. I ended up grinding out all the loose edges, and in addition to sealing the joint with 5200, I lapped 2 layers of cloth and resin. When I added the mahogany rub rail several months later, I placed screws through this joint from the inside back into the rub rail (which was also secured across the outside of the joint with more 5200). It would take a hurricane to separate the deck from the hull. No, wait, it did survive a hurricane. Let's just say that the two will never part company again.

If you want a more detailed description with accompanying pictures of how I preformed this on my boat, feel free to read the restoration logs on my site; January, 2004 is when I worked on that project.

Good Luck.

[Tim]

Simon,

Knowing more about the character of the joint would be helpful. For instance, can you tell if you have mating flanges between the deck and hull? These are usually fairly obvious. A mating flange, along with the other construction details of your toerail, would usually suggest that at least some sort of bonding exists between the flanges. In many cases, wet mat was used here; in other cases, some sort of flexible sealant/adhesive was used. Both methods are designed to provide some watertight integrity to the joint, as well as secure the parts together.

In this type construction, bolts or rivets holding a toerail on are structural at least in the sense that they were probably used to secure the joint during construction, until the bedding inside the joint cured. Exactly how structural these fasteners are depends, but generally in a flanged hull-deck joint, consider the fasteners to be an important part of the structure.

You might also have more of a shoebox joint, where the deck overlaps the hull edge a bit, like the top of a shoebox. These sorts of joints are usually (not always) glassed over from inside, as it sounds like yours is. In this case, the fasteners on your toerail are not likely to be structural; the joint is held together mechanically by the fiberglass inside, and perhaps some sealant where the deck mates over the hull.

If you can't tell right off, grind some of the glass off around the fasteners on the inside. The fact that your toerail fasteners are glassed over after installation suggests to me that the toerail was bolted (or riveted) to the deck before it was installed on the hull, and then the whole area was glassed over to secure the joint.

Once you figure out exactly what the mechanics of your joint are, we might be able to give you a better idea how to properly rebuild things.