Is using silicone under the rubber gasket a good idea?
Ouch! That is like swearing in a church! Never ever use silicone on a boat! Its rubbish. Use Polyurethane (PU) or MS polymer instead. The best known product is Sikaflex but it is expensive. I tend to use the cheaper alternatives available in most DIY shops.
Here is how I did it on a few boats:
With the boat on its side on a lawn or something else that is soft and can’t damage your boat, and a tote of Grolsch on the mast top to prevent the boat from righting. (It is important to use Grolsch because everything on a wayfarer must have two uses. You’ll need Grolsch beer to seal the CB bolt. But that is another story 😉 ).
– Make a hole slightly larger than the bailers require so the caulking has somewhere to go.
– Counter sink the bolts from the outside and have them well below (above?) the outer hull level. Again this is to avoid having a too thin layer of caulking that would otherwise not stay in its place.
– Cut the bolts if need be to size and use cap-nuts which are better on the fingers then the thread of the bolts when using normal nuts. (Some use caulking on the bolts and nuts to protect their fingers).
– Use some or all of the rubber rings that came with the bailers, if need be complemented by some home made fillers, to mount the bailer perfectly flush with the bottom of the boat. With a pair of scissors I cut some extra rubbers from a blown inner tire of one of my trolley wheels, using the original rubber as a template.
– Tighten the bolts and check if the bailer is still flush with the hull. If need be repeat the previous step. The rubber should provide adequate sealing.
– Now thoroughly clean and degrease the outside of the hull, the bailers and the bolt heads with paper towels and thinner.
– On the outside of the hull, finish the bolt heads and the groove between the bailer and the hull with PU or MS caulking. Use paper towels and thinner to model the caulking flush with the hull.
This way the hull will be perfectly flush again and there will be nothing slowing down your boat while the bailers are closed. When the caulking is sufficiently thick it will not tear due to mechanical stress caused by opening and closing the bailers. In my case the groove between the bailers and the hull was about 3 to 4 mm and the bolt heads were 2 to 3 mm below (above?) the hull surface. Don’t try to make the caulking too perfect you can always sand it after has set.
PU and MS polymer are actually two pot products. The secondary component, the catalyst, is water. Usually that is water vapor from the air but it will also set under water. However, it may be slower to set due to a lower temperature. Basically this means you don’t need to wait until the caulking has set before putting her back in the water. But be careful not to damage your work when the boat is put upright on a lawn while the caulking is still soft. On a flat surface the keel will protect your work from touching the floor. Perhaps it is best to leave the boat overnight, upright with some plywood under the keel to protect the caulking while it sets.