Preventing aluminium corrosion in saltwater environment?

[Dogone]

So aslong as i use epoxy in mounting holes and plenty of stikaflex theoretically it will work?

In my humble view it will be ok.

 

[noelex]

Brilliant thank you, wish i had your knowledge man!!

To save on all that do you think a 18mm marine grade ply board, fibreglassed and flowcoated do the same job and be as strong?

If it is a fibreglass boat, your idea of ply is potentially a good solution. It will integrate and become part of the structure better than aluminium.

I would cut a thin ply sheet extending the full width of the transom to the hull. It does not need much extra thickness to add a lot of extra stiffness. Weight is a consideration. Somewhere around 5-6mm would be good choice. Bond this to the inside of the transom with thickened epoxy. Then create a fillet of thickened epoxy between the ply and the hull to round the 90° transition. Cover the whole thing in a couple of layers of fibreglass extending the fibreglass several inches onto the hull to tab and bond the transom securely into the hull sides and floor.

Paint this as epoxy has poor UV resistance.

The only problem is the outboard will tend to crush the ply and potentially let water in creating rot. I would therefore fashion an additional aluminium plate a little larger than where the outbound contacts the transom to spread the load. Round the edges to prevent stress concentration. The outboard will fundamentally hold this plate in place, but a sealant such as Sikaflex 291 will prevent water between the plate and transom, and without any extra bolts the sealant should hold the plate in the correct position when the outboard is removed.

The final problem is the dissimilar metal between the outboard clamping bracket and the aluminium plate. Some washers cut from thin (2-3 mm) plastic chopping board would be fine, but better still, when laying the fibreglass spread a little extra on a flat plastic sheet and when cured cut the washers from this material.

Finally try and move as much weight in the boat as far forward as possible to compensate for the extra weight and thrust of the larger outboard. It may be appropriate to consider relocating the tank and/or battery further forward if possible.

Please keep in mind that is only one solution and I have not seen or are even familiar your particular model of boat. Hopefully it should at least give you some ideas.

 

[MystyBlue2]

If it is a fibreglass boat, your idea of ply is potentially a good solution. It will integrate and become part of the structure better than aluminium.

I would cut a thin ply sheet extending the full width of the transom to the hull. It does not need much extra thickness to add a lot of extra stiffness. Weight is a consideration. Somewhere around 5-6mm would be good choice. Bond this to the inside of the transom with thickened epoxy. Then create a fillet of thickened epoxy between the ply and the hull to round the 90° transition. Cover the whole thing in a couple of layers of fibreglass extending the fibreglass several inches onto the hull to tab and bond the transom securely into the hull sides and floor.

Paint this as epoxy has poor UV resistance.

The only problem is the outboard will tend to crush the ply and potentially let water in creating rot. I would therefore fashion an additional aluminium plate a little larger than where the outbound contacts the transom to spread the load. Round the edges to prevent stress concentration. The outboard will fundamentally hold this plate in place, but a sealant such as Sikaflex 291 will prevent water between the plate and transom, and without any extra bolts the sealant should hold the plate in the correct position when the outboard is removed.

The final problem is the dissimilar metal between the outboard clamping bracket and the aluminium plate. Some washers cut from thin (2-3 mm) plastic chopping board would be fine, but better still, when laying the fibreglass spread a little extra on a flat plastic sheet and when cured cut the washers from this material.

Finally try and move as much weight in the boat as far forward as possible to compensate for the extra weight and thrust of the larger outboard. It may be appropriate to consider relocating the tank and/or battery further forward if possible.

Please keep in mind that is only one solution and I have not seen or are even familiar your particular model of boat. Hopefully it should at least give you some ideas.

That is fantastic mate thank you very much that semms like a fab plan, i will gather up all my materials and get this started with hopefully spring being the time to do all the work and having some safe fun fishing!

Thanks again mate ?