Before you mix the materials as you outlined, check how they move, both when a load is applied and when temperature changes. Expansion at different rates will put a stress on the joint.
If the glass fibre hull is just built inside the aluminium parts, such that they are only held together mechanically, they will move against each other and erode. If you want to bond them together, here is one source on what to do with the aluminium first:
A Beginner’s Guide to Using Aluminum Epoxy https://www.hotmelt.com/blogs/blog/a-beginner-s-guide-to-using-aluminum-epoxy
I have been a casual and infrequent lurker (reader, not member) for a decade or two and have some professional experience with aluminum in seawater.
Meter size FRP panels in an aluminum frame exposed to seawater, vibration and wracking loads: been there done that. If you can think of a way it could go wrong, it did, on much smaller scale. Something this size would be much more difficult to manage.
The beginners guide to epoxy looks to me like it was written by the marketing department by a beginner for using their adhesive in a dry environment. Someone in marketing read some obsolete literature and wrote up a brief summary. It isn't all bad, but not all good either. Replacing 'Step 3 Etch the surface' with 'apply a conversion coating' would be better. For a large structures, grit blast, then pretreat with a non-chromate conversion coating, which includes the rinse, then prime with a two part corrosion inhibiting epoxy primer. Much better to look for information from Henkel Loctite, 3M or anyone who sells non-chromate pretreatments. In salt water, without a conversion coating, the bond will eventually fail. The bond interface needs a corrosion inhibitor. Moisture will always work its way to the bond line, and without a pretreatment, corrosion will spread under the coating. As far as the interface is concerned, there is no difference between paints and adhesives. The plating advice is for small parts in protected environments. Far too much detail to go into here.
As for the overall concept, I can only say that I am reminded of
Phil Bolger's Rose on one end of the scale and any number of disasters near the bottom. Rose is about 38 m long. His description in 3
0-Odd Boats is worth reading here. The lines are in the book along with offsetts and some construction plans. It took Bolger, a professional NA, 6 months to produce 30 sheets of plans that did not fully detail the construction. Bolger preferred to call designs intended to mimic a historical vessels representations, not replicas because there are always unknowns and deliberate deviations. The main similarities are the size and appearance with an intended use that is very different from the historical vessels of similar appearance. The construction was traditional, so it does not apply here.
I got lost somewhere between massive FRP panels bonded to an aluminum frame and ferrocement. I think we are trending for all aluminum. Al should be certified to meet
ASTM D928 to avoid cracking problems, or give up some strength and look at Al5052. Ferrocemet as been done very well but only very rarely. I read about a company in Maine that researched ferrocement with the intent to build some boats back in the 70s. They evaluated various ratios of steel to concrete for any number of cost and performance parameters. The article said that when they graphed the data, every one pointed to 100% steel as the optimum ratio. They went into the steel boat business and never looked back.
