Any where there is a hint of a chance of water possibly coming into contact with wood,seal it........and I mean back to front.Finishing resin thinned with denatured alcohol(rubbing alcohol) works best for this application.It will actually soak partially into the wood and seal it.I've built around 7 different flying boat models over the years and let me tell you, irregardless of how well sealed you may think you have your plane,water will still find a way of getting in.The wing seal is the biggest culprit of water penetration on a flying boat usually.Make sure you seal the wing saddle area well by making a silicone gasket using the silicone /saran wrap method.The saran wrap prevents the wing from permanently sticking to the fuselage and acts like a mould release.Jusy make sure the silicone is well cured before trying to separate or peel off the saran wrap.You will be rewarded with a very water tight seal when you are done.
I've seen flying boats literally fall out of the sky because of a altered C of G due to water wicking into the wooden structure at the back of the airplane.If you have open bulkheads which lead to the rear of the plane ,this is a definite possibility.Even if they are not,you can still have a small pin hole somewhere in the covering(built up structure) which water can migrate into.If water gets into the rear of the plane whether it's sealed or not,it will change your C of G very drastically.The difference being,if it is sealed,the wooden structure will not soak up the water like a sponge and you will visually see the water puddling inside the hull upon inspection.The plane can be easily mopped and dried out and no chance of warping to the structure.If it is left unsealed,the water will simply soak into all of the wood.This increases the weight of the plane,throws off the CG,raises the grain of all exposed balsa,and you run the risk of having a warped structure when and if it ever dries out again.This will lead to weakened glue joints eventually also.I wouldn't just limit the bottom part of the model to sealing either.Unless you never plan on flying inverted or performing any aileron rolls,water can reach just about any where inside the hull,up or down.
When flying off water,inspect the inside of your model very frequently to check for early signs of water penetrtation.This is especially true when flying a new model for the first time,but it is a good habit to get into any time you are flying off of water..It may save your plane from a disasterous ending.I've seen this ugly scenario play out many a time over the years and most could have been prevented if they had only periodically checked there models for signs of water penetration. Corrective action could have been taken to rectify the problem and prevent the inevitable crash.
I have done a lot of water flying both with float planes and flying boats(the latter being my favorite) over my 30 years in this hobby and these observations,recommendations are based on my own personal experiences.I have never lost a plane due to water getting in.Brain fade and arsing around?............Well that's a whole other story!
Hope this helps you some.Always glad to share ideas with a fellow modeler.
