Shaft advice

[cariedl]

Last summer while cruising at dusk I hit a submerged log. Did all the immediate checks once it happened. Pulled the boat the next day, did a visual inspection and saw that the starboard shaft had been "polished" but everything felt tight and not issues to struts/props. This winter when we pulled the boat I asked the marina to pull the shafts for further inspection and replace couplers, re-pitch props and check shaft alignment. Work was done and now the prop/shaft shop is saying the shafts need replaced.

I have Yanmar 230s and 1 3/8 shafts. The boat is on Lake Erie (fresh water) and will only ever see fresh water (as long as I own it). I read Pat's article about performance shafts and he says at Aq19 or Aq22 shafts are preferred. When the prop shop quoted me new shafts they said I would need to go with Aq22 or sign a waiver to absolve them of any liability of going with Aq19 shafts. The Aq22 are double the price of the 19s. Everything I've read online says the 19s should be more than sufficient for the application and freshwater.

Any input would be appreciated.

[cariedl]

update: I've tracked down the answer, but in effort to share with others who might search this topic in the future here is what I learned today.

The ABYC has a shaft safety rating for recreational boats with a minimum threshold for safe operation based upon a formula that accounts for engine HP, gear reduction, torsional strength of the shaft; that is a score of 3.

This calculator is super helpful: https://retmarine.com/propeler-shaft-size-calculator/

Western Branch Metals was extremely knowledgeable and explained that Aq19 and Aq22 shafts less than 1.5 inches in diameter share the same torsional strength of 70,000 psi. The only difference between the 19 and 22 at that size diameter is the corrosion resistance to saltwater. They have an in depth pdf that shares all the technical data and differences. https://wbmetals.com/wp-content/uploads ... uchure.pdf

When I plugged my info to the calculator linked above it offered a safety score just below 6, so the Aq19 is more than adequate for my needs and they cost about 50% less than the 22s. Hope this helps others in the future.

[Ironworker]

very interesting. Thanks for posting the links.

[Tony Meola]

One question I would have is if you ever sold the boat, would you need to make sure the buyer knows the shafts ar 19's and not 22's just in case it will get moved to Salt Water?

[Carl]

A22 is more corrosion-resistant than A19 with similar strength.

In saltwater A19 can hold up well, provided the boat is not left idle for long periods in still water, especially still warm water. In tight spots where water does not flow around the shaft, such as the cutless bearing, shaft seal, and packing gland the water stagnates losing oxygen. Oxygen is what gives SS its corrosion resistance so when it's gone, the shaft starts to corrode seen as pitting. Often the shaft will look fine till pulled. Once pulled the area that was inside the cutless and shaft seal can show pitting.

A19 may be very similar in strength till it starts to pit, pitting at the shaft seal creates leaks, and pitting at the cutless can also reduce bearing life. How much idle time and how fast does it take for pitting...I don't know, but would guess weeks of sitting and years before it becomes an issue.

Years ago when the price of A22 started to go up high, some unscrupulous shops started selling A19 in place of A22. Most people didn't know the difference. Almost impossible unless shaft is marked, starts to pit down the road or how we found out, by machining it. A19 machines like butter compared to A22 so a shaft needing to be cut down and re-keyed or a customer wanted shaft keeper keys machined in we had the misfortune of having to tell them their A22 shaft wasn't A22. We couldn't tell them what is was, just what it's not. Yeah, we made some enemies.

[Yannis]

Carl,

Thanks. I have no idea what 19 and 22 are, but you explain it damn well!

[Carl]

Carl,

Thanks. I have no idea what 19 and 22 are, but you explain it damn well!

Aquamet and Aqualoy are brand names from 2 companies that produce boat shafting, that's the "A" part of
A17
A19
A22


The A-17 is the strongest of the basic three and the least corrosion-resistant. Its basically 17-4PH and least $$

The A-19 is a step up in corrosion resistance. It basic recipe is 304 Stainless Steel with some special ingredients and hardening process.

A22 has the highest corrosion resistance of them all. Its basic mix is 316 Stainless Steel with proprietary ingredients and processes.

As a supreme choice, there is a step up to A22HS. This has all the corrosion resistance of regular A22 with the extra strength ( High Strength HS ) of A17. Not mentioned initially as it is only offered in shafting 2-1/4- 6" in dia


Now you know more than you wanted to know about boat shafting

[Yannis]

Carl, I can sell petfood like hotcakes, but about shafts? Clearly you are the authority!

[cariedl]

Thanks for adding in here Carl. I went with 19s, given the boat is in fresh water I couldn't justify the almost 2x price difference of the 22s.

If I ever sold the boat (not happening), I would be sure let the buyer know. I keep a very detailed log of any and all work done along with receipts. I believe in karma and not telling someone just feels like bad business.

In talking with Western Branch sales rep he said if you're in saltwater they would strongly advise to only go with 22s and to make sure you stay on top of zincs and close inspections when the boat is hauled out.

[Amberjack]

Last summer while cruising at dusk I hit a submerged log. Did all the immediate checks once it happened. Pulled the boat the next day, did a visual inspection and saw that the starboard shaft had been "polished"

The shafts seem to be where drift winds up. This is the second year I’ve found wood fibers jammed between the two zinc halves.

[Tony Meola]

Doug

I am thinking you hit something. I don't know how else that would get in there.

[Amberjack]

Yes, probably a small chunk of drift. I suspect it happens a lot more often than I'm aware. The zinc told the tale this time.

[Carl]

Yup, I've had bit of wood in the zincs as well. A little zinc floss will get it out.


Don't ask, cause I don't know as I made it up. The floss part that is, I had the wood fibers...

[Tony Meola]

It was probably small. otherwise you would have known. Would have made a heck of a noise going through the props.

[Marshall Mahoney]

I'm curious -- how did the shaft shop determine that the shafts needed to be replaced? As a side note, most of the shrimpers in Louisiana use Aquamet 19. Since they run their boats frequently, they don't have the crevice corrosion in at the cutless bearing that Carl mentions above.

[Carl]

I'm curious -- how did the shaft shop determine that the shafts needed to be replaced?



As a side note, most of the shrimpers in Louisiana use Aquamet 19. Since they run their boats frequently, they don't have the crevice corrosion in at the cutless bearing that Carl mentions above.

A19 is a good product, especially for commercial boats always on the move. It's often the recreational boaters who leave the boat sitting in the water for months on end that see issues with crevice corrosion. If the boat is run often, docked in moving water, pulled out after use, on a dock lift, or left in freshwater...A19 becomes a reasonably good option.


I can't speak for why his shop condemned the shafts, but often the reasons seen are:

Wear at the cutless area. Monofilament line can do a job on a shaft as can gritty dirty waters.
Wear at the packing area (stuffing box wear, often from packing too tight)
Bent badly
The coupling area worn...loose coupling banging away.
Corrosion, deep pits that can tear up the cutless, cause shaft seal not to seal or pitting to the point of possibly being too weak.

Lazy mechanic decides it's easier "for him" to cut the shaft than try to pull the coupling off.

[cariedl]

Carl once again is spot on, number 4 on his list of options was the reason my shafts were deemed to be in need of replacement. The coupler area was worn so replacing those too. There was too much play once the shafts were inspected and adjusted.