Oceanis 430 (1988) keel bolt details

[Joli]

[QUOTE=sandy stone;3620388]I don't know if I can prove you wrong, but maybe convince you?

The people who manufacture threaded fasteners have gone to some trouble to determine what is needed for a secure, long-lived joint. Their intent is that a bolt will fail in tension before the threads strip out. After some decades of testing and experience, they determined that with steel, a thread engagement depth of 1 to 1-1/2 times the diameter of the bolt is sufficient. /QUOTE]

Ideally in cast iron it should be around 2.5 times the diameter of the fastener.

[GordMay]

[QUOTE=Joli;3621011]

Originally Posted by sandy stone

I don't know if I can prove you wrong, but maybe convince you?

The people who manufacture threaded fasteners have gone to some trouble to determine what is needed for a secure, long-lived joint. Their intent is that a bolt will fail in tension before the threads strip out. After some decades of testing and experience, they determined that with steel, a thread engagement depth of 1 to 1-1/2 times the diameter of the bolt is sufficient. /QUOTE]

Ideally in cast iron it should be around 2.5 times the diameter of the fastener.

It makes sense, that a softer threaded material, requires an increased thread engagement.

“Screw Thread Design” ~ Fastenal

”... It appears that one could theoretically increase the thread strength by increasing the length of engagement. However, as illustrated in the Load Distribution chart above, the first thread will be taking the majority of the applied load. For carbon steel fasteners (including tapped holes) the length of engagement would be limited to approximately one nominal diameter (approximately 1-1/2 times the diameter for aluminum). After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession...”

➥ https://www.fastenal.com/en/78/screw-thread-design

“Screw Stress Areas” ~ by Roy Beardmore

”... The following rules of thumb are suggested for arriving at reasonable lengths of thread for steel screws used with screwed holes in weaker materials.
For steel a length of thread engagement of at least 1 x Nominal dia's of the thread
For Cast Iron or brass or bronze the thread engagement should be at least 1,5 x Nominal dia's of the thread
For Aluminium , zinc or plastices the thread engagement should be at least 2 x Nominal dia's of the thread ...”

➥ https://roymech.org/Useful_Tables/Sc...ead_Calcs.html

“Thread engagement in a tapped hole” ~ Nord-Lock Group

"...However for a quality safe connection, when the tapped material has a significantly lower ultimate tensile strength than the screw material, - to ensure the screw will fail in tension before the female, it is preferable to use suitably rated nuts or engineered thread inserts ..."

➥ https://www.nord-lock.com/insights/b...a-tapped-hole/

Of course, aside from a very little extra cost, I see no harm in using over-long keel bolts.

[tkeithlu]

Good assembly of the information, Gord. Includng a good understanding of how bolts fail.