Why is Rear Tube Splitting on Formosa 41?

[James Diego]

This weird! I have a PSS dripless system on a relatively new shaft on Formosa 41. I replaced my transmission 100 hours ago with a used identical model and noticed no new vibration or noises as I have gone to Catalina several times since with no problems since replacing the transmission and I thought my worries were over.
After returning from Catalina over Memorial Day, I heard water running and my bilge pump going off. I looked and the bellows on my PSS unit had slipped back an inch from the rotor face and sea water was coming in. Had I not tightened the stern of the bellows sufficiently when I relocated it to remove the transmission? Maybe, so I readjusted the bellows and tightened the hose clamps to stop the obvious leak at the rotor but the some water still continued to flow from a horizontal slit or crack in the stainless steel rear tube just outside the bellows! Wow? Where did that come from? I readjusted the position of the rotor and the bellows to enclose the slit but the slit kept creeping down the length of the tube and I ran out of adjustment room for the bellows and the rotor.
Fortunately, I was able to wrap some self sealing silicone tape around the rear tube crack to contain the water flow but I don't know how that slit or crack in the rear tube came to be and how to keep it from happening again! Does anyone have any thoughts? I have been living aboard 14 years and this problem has got me stumped!!

[MBWhite]

Do you think the tube is cracking from fatigue, metallurgy, or physical damage? How does the crack look? Is it a knife edged type of crack or if you look closely does it appear to be more "granular" at the crack edges?

When you mention the crack extending, were you running the engine or did you just retighten the clamps and the crack extended before your eyes? Could the prop shaft have gotten bent somehow? Did you replace the transmission or did a yard do it? (not knocking your work, just wondering about the other guys) Have you tried wiggling the transmission shaft to check for bearing wear?

Hopefully others will chime in with some more experienced advice, but I'd look closely at that crack and see what it can tell you.

[jimbunyard]

Sounds like someone used welded rather than seamless stainless steel tubing when they installed the shaft log.


Here's a scenario: Concentrated cell corrosion started under the seal bellows, and then followed the line of least resistance down the weld line of the tube, and was/is hidden due to the location. When you changed the gear, the work in the area aggravated a progressively deteriorating condition.


At any rate, it's bad news, for a proper fix, the shaft tube will have to be replaced.

If your boat is fiberglass, many prefer to use G10 epoxy tubing instead of stainless steel nowadays.


Concentrated cell corrosion:


This is an accelerated form of chemical attack in which the rate of corrosion is greater in some areas than others. It occurs when the corrosive environment penetrates the passivated film in only a few areas as opposed to the overall surface. As stated earlier, halogens will penetrate passivated stainless steel. Referring to the galvanic chart you'll note that passivated 316 stainless steel is located nine lines from the bottom and active 316 stainless steel is located thirteen lines from the top. Pit type corrosion is therefore simple galvanic corrosion, occuring as the small active area is being attacked by the large passivated area. This difference in relative areas accelerates the corrosion, causing the pits to penetrate deeper. The electrolyte fills the pits and prevents the oxygen from passivating the active metal so the problem gets even worse. This type of corrosion is often called "Concentrated cell corrosion". You'll also see it under rubber parts that keep oxygen away from the active metal parts, retarding the metal's ability to form the passivated layer.


Full article available here:
Corrosion, stainless steel


There's a thread addressing a very similar situation here:


http://www.cruisersforum.com/forums/...ml#post1624753

[Pirate999]

Metal fatigue. Fancy names for it but the bottom line is that it's old and needs to be replaced. The tube is constantly full of salt water and is subject to the elements as well as vibration and electrolysis over the past 40 years. You will not be able to repair, only replace. You can try the leaky teaks yahoo group to see if there are other solutions but I doubt you'll find any. Replace... Very soon.

[zeehag]

please seek assist from leaky teaky yacht club yahoo group. i know someone has experienced this.
our stern tubes are over 36 inches long and mine goes thru concrete to exit stern via shaft log, which is external. cutlass is in external shaft log, which is a cast bronze housing.
the shaft tube affixed to a beam, unless pss seal is in use, perhaps removal or mod of beam has been done which is moot. th etube shoulsd have been solid not welcded tube. mine is stainless most are bronze.
it is able to be lined with a pvc liner, as someone in san diego did, as theirs was lacework and leaking.
this is what sinks our boats. (oher than toilets)
be careful and have that damned tube replaced. my estimate in san diego was 8000 usd and made me gag hard.
please keep us posted as to progress. thankyou.
there was a member of ltyc in yahoo groups who had a mishap in midocean pacific on his way to guam. i was advised his boat sank.
i went into ltyc and found per his words, that he fixed while underway and the rumors of his boat's loss were not true.
many of us are interested in how you repair this one.

it is probably original equipment. that means needs replaced now. original equipment, aka taiwanese stainless, which probably came from usa, as 1970s usa still had some steel manufacturing and exporting, and taiwan was protected by usa for so long, as a territory. rumors of black steel are not all correct.
1970s anything is due to be replaced

[St. Elsewhere]

Stainless steel does not do well in stagnant saltwater. More information is here.

[James Diego]

Leaky teaky's is a great idea! I will check with other Formosa owners to get their thoughts! Thank you all for your great suggestions! I will contribute my share when some one asks a question that I can answer. Thx again

[zeehag]

james diego---what is name history of that boat... isnt sunset gal by any chance is it or was it??

[James Diego]

Zeehag,
I saw your site and noticed that your Formosa is only 2 years older than mine so you know how great these boats are.
I have comfortably lived aboard mine 14 years and have no plans to jump ship, although she tries my patience at times, like now.
As far as I know Michelle has always been the name of the vessel because a) it is a great name b) I am to lazy to do the carpentry work to change the name besides I might get lucky and find a first mate named Michelle.
Do you still have a stuffing box? I don't remember if the box was on the bulkhead or on a tube. Could you get back to me at svmichelle1@hotmail.com and let me know? I would appreciate it.
Thx

[zeehag]

tube thru a beam. pm me for pjx. they in peecasa, some fb.
some had stern tube issues.
sounds as if the year of your boats creation may have been stern tube issue year. i keep checking mine. it is a disconcerting issue.
i have heard of modding stern tube with a pvc liner. consult a good reliable boat butt person. more than 1.
the other alternative is remove n replace which was 8000 usd TO START at 1 yard, knight n carver, in 2011, and 9000 usd in koehlers yard. there is a buncha concrete thru which mine passes.......just before hull exit n shaft log.

life is an adventure meant to be LIVED!!!

[Bruadar]

We had ours split about 90 miles offshore of Georgia while in the Gulf Stream. Sealed it up with butyl tape and duct tape until we were able to make proper repairs. On our Formosa 51 the SS tube was threaded and screwed into the shaft log housing and packing gland on each end. When we hauled out the boat at a later date I was able to make repairs without removing the rudder. Pulled the prop, shaft coupler and shaft. Then I cut the tube in half so the portion with the split could be removed from inside the boat with the packing gland. The external shaft log housing was unbolted and the tube just slid out. I do remember having to unscrew the shaft log housing so it would clear the rudder but that was easy enough to do with the prop and shaft removed.

After you get the tube out any good welding shop should be able to duplicate the tube for you and even thread it....

We took this opportunity to convert our boat to a PSS Drip-less Seal. No problems so far and the repair is now 9 years old.

Fair Winds,

Captain Dan

[barnakiel]

If the tube was SS and if it cracked it just probably corroded.

This is not easy to replace. Replace with bronze, IMHO.

Our tube is ... grp. Many ways to skin a cat.

b.

[zeehag]

with old style shaft tubes, please always carry a few pipe repair kits for emergency life saving measures.
i want to either slide a pvc tube into my shaft tube or glass it, but , as it passes thru concrete, it will be very pricey to do that--i think many of us have the option of sliding the inner pvc then re -doing cutlass bearing and shaft logs accordingly. hopefully without too many mods to keep water out from between pvc and original tube....
i donot have pix yet for this, and i am not certain if any leaky teaky members had it done, but it was reported to me by the yard manager what occurred and how it was repaired, as he knew i had same kind of boat.
check out that option. there should be no friction inside shaft tube by shaft, and there is plenty of room in it to add that pvc, as i was advised-- have not yet checked that out, but it makes sense as the least pricey option.

[Schooner Chandlery]

Zeehag, what makes it so difficult to remove the old tube? We have a similarly long bronze tube that goes through the deadwood of our 1931 schooner. We replaced it "just because" when we were doing the rebuild of the boat between 2007-2009. We made a tool to press/pound it out and it was difficult but certainly only a couple days of work to get it out and the new one in. Ours screws into the outer stern tube (bronze) and inner stuffing box (also bronze) and we hope it will last another 70-some years. Bronze is good

[zeehag]

Originally Posted by Schooner Chandlery

Zeehag, what makes it so difficult to remove the old tube? We have a similarly long bronze tube that goes through the deadwood of our 1931 schooner. We replaced it "just because" when we were doing the rebuild of the boat between 2007-2009. We made a tool to press/pound it out and it was difficult but certainly only a couple days of work to get it out and the new one in. Ours screws into the outer stern tube (bronze) and inner stuffing box (also bronze) and we hope it will last another 70-some years. Bronze is good

ours pass thru concrete in stern. that concrete needs to be drilled out then new tube installed and re packed into place or modified appropriately....was estimated in kohlers in sd at 8000 usd to begin the work. is why i have yet to do this. cf estimated below knight and carver and shelter island boat yard. is a LOT of work for one lil tube....that is why folks have been sliding pvc into the existing shaft tube and considering othe rsimilar mods. this is the only design flaw in boat, and i believe is not a design flaw but a mfg glitch.