Keel bolts

[vesper1 2]

It's best if they are all tight carrying equal strain, you won't break a 19mm bolt, Put your shoulder into it on the end of a 3/4 inch drive ratchet or similar. Monel is the best totally unaffordable these days.

[TimB 5]

SAF2205 is a Duplex Stainless Steel. there are lots of them. They were developed for the oil industry in the 60's to prevent Stress corrosion cracking in high temperature heat exchanger tubes on oil rigs in the North Sea. Using seawater on the cooling side so hot wet and lots of  chlorides.

 

Much stronger than 316 but must be careful welding not to let the (inter-pass) temperature get too hot or the structure changes and it is no longer duplex. Duplex means the molecular structure is both austenitic and ferritic. 304 and 316 are austenitic.

 

An another interesting things is that its coefficient of expansion (with temperature) is almost identical to that of mild steel where as 304 and 316 are almost double.

 

I was involved in building two 30m by 5m diameter pressure vessels (10 bar pressure) for the pulp and paper industry back in the nineties. we saved about 30 tonnes per vessel by changing from 316 to 2205.

 

Tb

[Battleship 97]

We used 2205 on our rudder stock, lovely stuff they use it for hydraulic rams on big diggers, It allowed us to make the rudder much thinner and still be safely over spec. The engineer told me the 2205 had double the flex resistance of 316. And yes we had to get a welder who knows his stuff to weld the webs on.