Stainless steel vs zinc plated bolts for kicker mount in salt water

[Skidude17]

I'm about to install the kicker mount for my 1979's Honda BF100 (10hp) on my 19' Glasply. It has a thick transom (about 3") so I don't plan on beefing it up any more (the 500+ lb cast iron AQ150 has been hanging on it for almost 50 years without a problem).

My my question is what kind of bolts should I use for bolting the kicker mount through the tronsom? My initial thought was stainless steel for the corrosion resistance, but I understand it isn't as strong as zinc plated steel. I'll mainly use the boat for fishing and crabbing in the Puget Sound or Hood Canal.

If there are other materials that are even better, I'm open to suggestions.

Thanks for for your help.

 

[Scott Danforth]

the zinc coated bolts will be stronger, however the salt will oxidize them quickly.

look into fluorokoted bolts or armor-coated bolts if you want a strong bolt that will last a bit longer. they will eventually still rust. however once you install them, apply a thin coating of 3M 4000 UV over them to seal them and they will last nearly forever.

https://www.metcoat.com/fluorokote-coating-process.htm

https://www.mcmaster.com/#armor-coated-hex-head-cap-screws/=1bc3roc
https://www.mcmaster.com/#ultra-coated-washers/=1bc3s2y
https://www.mcmaster.com/#armor-coated-hex-nuts/=1bc3sdq

 

[dingbat]

Zinc hardware goes plop, plop, fizz, fizz in saltwater.

Use passivated (no Home Depot) 316 stainless hardware and don’t look back.

 

[Scott Danforth]

problem is 316 bolts are a one-time use, they are softer than grade 2 hardware.

 

[dingbat]

problem is 316 bolts are a one-time use, they are softer than grade 2 hardware.

ASTM F593 - 316 stainless hardware, tensile strength of 100,000 to 150,000 PSI and a min. yield strength of 65,000 PSI.

We're not building a bridge....we're bolting an outboard motor to a transom.

A 1/2" SS bolt with a 60% load factor is good for 7.5 tons (3.9 t shear). A 3/8" SS bolt is good for 4.3 tons (2.1 t shear)...If that isn't enough you can get strain hardened grade 80 stainless (grade 5). Really in vein considering it's physical impossible to torque the bolts anywhere near capacity without crushing the core of the transom. Double or Ny-loc nuts are required to secure the connection.

The 20 yro 5/8" Stainless hardware used to bolt my 200 HP to the transom still looks and functions as new. The connection has been dissembled at least 3 times that I know of.

 

[Bondo]

Ayuh,... SSteel bolts will be Plenty strong enough to hold that little motor,....