How good is the quality of the stainless steel used on flexshaft stubshafts?

[Old School]

Several days ago I test ran a boat in brackish water for about two minutes. On returning home I removed and cleaned the flexshaft but did not remove the brass propellor. Today, I removed it and was surprised that rust stains had formed on the stubshaft under where the prop was located. Now I know that there are differing grades of stainless including multiple grades of marine and medical metals but I was surprised because the shaft was relatively expensive and came from a reputable local supplier (not Model Hobbies Supplies) and was not one of the super cheap Chinese eBay sourced models.

Is it normal practice to remove the prop when servicing the flex after a run, if so the perhaps the dog drive should also come off?

[CraigP]

It’s the big problem with running in salt water. Anywhere water can be trapped is a problem. Makes it a PIA to clean up from running.

[Old School]

Ideally then the prop and dog drive should also be removed when servicing the shaft. Any trapped moisture would start electrolysis between the prop and shaft so I suppose that cleanliness is essential.

[Bp9145]

I used to submerged mine in a bucket of water and run it around in circles until I know it has completely washed the salt off. Then I refill the bucket with fresh water again and leave the whole shaft with the prop for about 5-10 min. Then I take it out and dry it completely with a dry cloth and then blow dry it. After that I grease it all up put the prop back on and I've never had any problems with rust. I know it sounds a lot of work but it's not really as it dries quickly then greasing it as usual.

[boredom.is.me]

There is a common misconception that stainless steel doesn't corrode/rust. The three common grades are 18-8, 304, and 316. 18-8 is the cheapest and has no resistance time corrosion. 304 has a very slight resistance, but not nearly enough to consider. 316 is the most expensive option and is very resistant, but do you think the overseas manufacturers are going to splurge on 316? Nah, stainless is stainless right? "Made from stainless steel" is all they state.

[rol243]

the staining on the shaft will come off easy with a rub.

[Old School]

I removed the stainless dog drive and as expected the shaft was also stained, so not just electrolysis causing the staining. Worse though was the cut threaded section leading me to believe that unless complete disassembly was carried out each time then it would not be long before a prop was lost.

[Old School]

the staining on the shaft will come off easy with a rub.

The staining required the use of a very fine wet 'n' dry abrasive sheet. Scotchbrite did nothing.

[martin]

Are you sure the stub is stainless, I have a number of boats where the stub is not stainless steel. Even aeromarine uses carbon steel on their stubs as they are hardened & ground to be able to run direct in needle bearings as well as the normal plain bearings.

[martin]

There is a common misconception that stainless steel doesn't corrode/rust. The three common grades are 18-8, 304, and 316. 18-8 is the cheapest and has no resistance time corrosion. 304 has a very slight resistance, but not nearly enough to consider. 316 is the most expensive option and is very resistant, but do you think the overseas manufacturers are going to splurge on 316? Nah, stainless is stainless right? "Made from stainless steel" is all they state.

Yes its the same for stainless screws & nuts these manufacturers use on rc boats, they us the cheaper A2 grade that will corrode rather than the more expensive A4 grade fixings.

[NativePaul]

Often the stainless used on stubs is crap.

Rust resistance is only one part of a stainless's quality, and for my use it is a low priority part although for you it is obviously a higher priority. H1 is the only stainless steel I know of that is truly rust free, but it is not commonly available here in the UK.

304 is known as one of the 18/8 alloys, although technically plain 304 is only 17.5% chrome and 8% Nickel, and it is not till you get to 304H that the chrome content actually hits 18%. Both 304 and 316 are machining grades, often chosen for the ease and speed that they can be machined which along with the quantities it is produced in makes the cost of manufacturing a stainless item much more economical than the higher grades. Neither can be heat treated.

431 and 630 are recommended shaft grades and have similar corrosion resistance to 304 but both have over three times the yield strength of 304 or 316 in their weakest condition, and can both be heat treated to 5 times that of 304/316, but I don't know of anyone using them as they are more expensive to buy and tougher to machine. 630 is a 17/4 stainless which I have just learned is what Prather props are made from.

All stainless's are more resistant to corrosion in a polished state, so you may want to rub some elbow grease into your existing parts to improve things a little for free.

[CraigP]

Excellent info! Thanks for writing it up...

[Old School]

Thankyou Paul. It would seem then that nothing is taken for granted and when running in brackish/salty water a full stripdown is necessary.

[rol243]

I used to do alot of running in salt water with both closed deck hulls and open deck hulls in my offshore r/c gas powerboat days, what i learnt from running in this water type is to do the preventive work first and then after. so what i mean is use a good quality anti rust spray such as the good old wd-40 before you run your boat and spray all alloy / metal hardware after each run and then when you get home remove the drive shaft etc and spray clean and oil these parts. never leave the drive shaft in the boats tube as it will attract rust very quick. we used to have a length of 2 inch diameter plastic pipe about 2 foot or so long which was used as a holding tank for all shafts, this was filled with a mixture of auto fluid and kerosene, this kept the shafts as new for long periods of storage . so a good spray etc etc etc and all is safe.

[Bp9145]

a holding tank for all shafts, this was filled with a mixture of auto fluid and kerosene, this kept the shafts as new for long periods of storage . so a good spray etc etc etc and all is safe.

Yes, I also treated everything with WD-40 as it's easy to apply and all the preventive measures mentioned above. But I've never tried auto fluid and kerosene. . .it's inexpensive and effective. I definitely will give it a try. Is there a mixture ratio? Nice to learn something new all the time. . .thanks Ronald.