Through hull fittings on Aluminium sailboat

[Wideocean7]

Mine is going to be DIY job and I don’t have the tools or cash to spend on cutting/holing thick aluminium plate, which I’d also need to form to the hull shape. Trudesign “recommends” that the hull thickness is a minimum of 20mm. My hull is 6mm aluminium so a backing plate will need to be 14mm min. That’s a lot to machine.

Michael- I’ve read all the Trudesign stuff and have to double check again if the load bearing collar circumvents the need for a 14mm backing plate. Good news if not but I need to confirm.

[Fuss]

Originally Posted by Wideocean7

Mine is going to be DIY job and I don’t have the tools or cash to spend on cutting/holing thick aluminium plate, which I’d also need to form to the hull shape. Trudesign “recommends” that the hull thickness is a minimum of 20mm. My hull is 6mm aluminium so a backing plate will need to be 14mm min. That’s a lot to machine.



Michael- I’ve read all the Trudesign stuff and have to double check again if the load bearing collar circumvents the need for a 14mm backing plate. Good news if not but I need to confirm.

a backing plate in alu is never a bad idea however more important is that there is a max of 1mm tolerance for the through hull fitting and if it’s not then you could make 2, 3mm thick oversized washers for either side. this would add some strength and ensure the the right hole size tolerance. the alu used has to be the right grade alm 4.5 is one of them. this method works fine for 6 mm alu ...
1 mm hole tolerance
3m 4200
trudesign with load bearing collar

as i said before... you are not refitting an expedition boat. so trudesign is perfect for you.

[double u]

...to go for out-&-out strength in the through-hulls while having a saildrive with it's giant hole covered by a rubber membrane......do only I detect the irony?

[Wideocean7]

I’ve opted for a 15.9mm thick panel of GPO3 for the backing plates and have a nice piece delivered today. For those who’ve machined such a thick piece before, any suggestions how to cut and hole it? Apparently it eats bits and blades so I’m expecting to have to buy something with a carbide or diamond edge. (I have looked and looked on the internet to no avail). Thanks again.

[stormalong]

Shouldn't be any worse than cutting through a fiberglass hull. Bi-metalic hole saw and cut slowly. Should be able to do many holes with one saw.

[Wideocean7]

Thanks Stormalong. I’ll check those out.

[DeValency]

Originally Posted by Wideocean7

I’ve opted for a 15.9mm thick panel of GPO3 for the backing plates and have a nice piece delivered today. For those who’ve machined such a thick piece before, any suggestions how to cut and hole it? Apparently it eats bits and blades so I’m expecting to have to buy something with a carbide or diamond edge. (I have looked and looked on the internet to no avail). Thanks again.

I used b-metal hole saws for fiberglass but you can get even a carbide cutter at a very reasonable price - multiple diameters available:
https://www.amazon.com/Rannb-Cutting...3978234&sr=8-8