I have a broken strut on my 356

Jan 5, 2017
143
Hunter 356 SF Bay / Delta
Heard a clunking sound Wednesday night during beer cans coming from the propshaft area. Motored as little as possible to get back into the harbor and had a friend dive under to investigate. Broken strut. From what he described, sounds like it broke off near the hull and has the "fin" part hanging down on the shaft.

I plan on ordering a new strut from SBO, what are the chances the propshaft will be damaged? Anything else to consider?
 
Feb 10, 2004
3,919
Hunter 40.5 Warwick, RI
Wow that sounds very unusual. No warning at all? Vibration? Noise? It just suddenly broke?

I never have experienced or heard of this happening, so I don't really have a clue. But I would definitely check the shaft for bends.
Check the stuffing box for damage. Basically check the entire drive train.

I would think you need to haul out to do all of this.

Finally, closely examine the broken strut. Is there any evidence of bad metal? have someone look at i who is very knowledgeable. I think it would be very important to learn why this happened.

Good luck.
 
Jan 5, 2017
143
Hunter 356 SF Bay / Delta
Everything was normal until we were motoring back in and the clunking suddenly started happening. It was a calm evening, didn't hit anything, etc. It wasn't even really that loud, the rest of the crew didn't pick up on it, but I could tell something sounded different.

I'm going to enlist a tow to the boat yard to have it hauled.
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
Almost always long term electrolysis damage to strut. not an easy one to replace because of the precise alignment necessary. As Rich says, shaft is most likely bent. A good machine shop can straighten it, or replace it and the coupling. Happened to me 10+ years ago on a 200 mile trip.. Had just retired so my buddy and I replaced it and carried on.. took a few days to get it shipped in so we did a bottom job while we waited.
 
Sep 11, 2015
147
Hunter 31 Marina del Rey
You will save yourself a lot of trouble down the road by replacing the shaft even if slightly bent and you would not know if it is (most likely it is). While you are at it, get a pss dripless seal as well. The whole procedure is not that difficult. I have done it twice:

Order shaft, strut and seal, prepare to haulout.
Mark the position of the engine and the bolts.
Haul out, remove the old strut, install the new strut losely.
Lift the engine and remove the shaft from below the engine.
Install the dripless seal, the new shaft, sliding below the engine, through the strut.
Connect shaft to the engine, leaving the engine bolts loose.
Add washers to the strut bolts to align the shaft in the center of the seal, tighten the bolts just a bit.
Run the engine at low rpm's for a couple of minutes. It will position itself nicely, check alignment again.
Tighten strut bolts and seal everything well, complete the pss seal.
Get the boat back in the water, you should have very little vibration, you can safely go back to the dock.
Wait for a couple of days for the hull to settle and finish the engine alignment, check that you have no vibration at high rpms.

You need half a day in the boat yard if you are organized. The trick is to let the engine align itself instead of the endless checking of clearances and tightening of bolts.

Good luck.
SV Pizzazz (H31)
 
Feb 21, 2013
4,638
Hunter 46 Point Richmond, CA
Could a bottom cleaning diver have identified the issue prior to failure and/or could this have occurred due to inadequate zincs? Based on this experience I will ask my diver to check the strut condition during each 3 month bottom cleaning and inspect it during each haul-out for bottom painting as preventative measures.
 

danm1

.
Oct 5, 2013
164
Hunter 356 Mamaroneck, NY
Just had this happen on my Hunter 34. Fouled a line which grabbed, broke the strut, bent the shaft. Also needed new PSS. I am not a do-it-yourselfer. Replacement strut looked identical, but was fractionally different and old holes had to be glassed and new ones drilled. One motor mount was too rusty to work with. Another was marginal. Replaced all. Forward mounts needed to be shimmed to new height due to the slight variation in strut. Wound up costing more than $8000. Lucky Geico insurance paid for the labor because of the accidental prop foul that triggered it all.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Reach out (PM) to @Ken Cross . Look up his experience posted here on the SBO forum. He broke his strut at the end of last season and was able to repair it without too much difficulty.
 
Oct 24, 2010
2,405
Hunter 30 Everett, WA
Yep I ordered the new strut from here (SBO) and found that my shaft wasn't bent. Replaced the strut, new bottom paint and back in the water.
The problem turned out to be stress over a long period of time. (Someone did a metallurgical analysis for me).

Ken
 
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Feb 26, 2011
1,428
Achilles SD-130 Alameda, CA
Could a bottom cleaning diver have identified the issue prior to failure
Possibly. However, if the strut had been painted, that might hide a pre-existing condition.

...or could this have occurred due to inadequate zincs?
Most struts do not have an anode attached and do not suffer from corrosion issues. That said, there was clearly a problem with this one.
 
Jan 5, 2017
143
Hunter 356 SF Bay / Delta
Possibly. However, if the strut had been painted, that might hide a pre-existing condition.
It was painted. About a year and a half ago I had the local yard (KKMI) install a new cutlass bearing, so it at least held up through that. Our diver did indicate that another boat on the same row as us lost their strut recently. I asked him about it being a hot harbor and he didn't seem to think it was hotter than usual. Alternatively, after thinking about other possibilities, we did bump a deadhead last year, it's possible it hit the strut before popping up the back and just took this long to manifest.

I attached some pictures provided by the diver.
 

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Oct 24, 2010
2,405
Hunter 30 Everett, WA
It looks just like ours did. After ours broke, another skipper down the dock with the same make and model said same happened to his a year earlier.

Ken
 
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Mar 20, 2004
1,729
Hunter 356 and 216 Portland, ME
It looks like a fracture from a hit..... Struts should never be painted with a copper based paint because the copper will leach the zinc from the bronze - if the bronze looks pinkish, that's what's happening. I lost my strut because of dealer incompetence; the boat was delivered with a strut that was cracked completely around and the dealer painted completely over it. He also used the wrong color paint (blue) and since that original coat Escape has always had black bottom paint. When the strut broke, there was blue paint inside the break! My shaft wasn't bent so the replacement was fairly straightforward.
 
Feb 26, 2011
1,428
Achilles SD-130 Alameda, CA
Struts should never be painted with a copper based paint because the copper will leach the zinc from the bronze - if the bronze looks pinkish, that's what's happening.
While bronze props, shafts or struts that have developed a pinkish hue have done so because of dezincification (the loss of the zinc component of the bronze alloy), it is likely due to another source of electrolytic corrosion, not because the part in question has been painted with a copper-based anti fouling paint.
 

dLj

.
Mar 23, 2017
3,374
Belliure 41 Sailing back to the Chesapeake
From what I've seen, these struts don't look like they are made from bronze, but rather more likely a leaded yellow brass casting alloy. It's hard to really say what the alloy is unless I were to spend quite a few $'s to have a complete wet chemistry performed on a strut to get the specific chemistry identified. This family of brasses is frequently used in plumbing fixtures so there is a "logical support" in the original selection. They are typically less expensive to cast than the navel bronzes. They are also not particularly strong tensile strength wise.

Most of the bronzes have a more significant amount of tin in them than zinc, but the bronzes really are all over the place as far as chemistry. The general rule that brasses are copper-zinc and bronzes are copper-tin alloys is a gross generalization, but is generally indicative...

It's kind of hard to complain about a strut that runs for a few decades and then fails... At least hard to complain in any formal way - e.g. legal action.

The photos taken by your diver are remarkably well done for underwater photography. I'd guess your strut broke in fatigue in a back and forth bending motion due to the action of your propeller, likely happening over a significant amount of time - e.g. - the life of your boat. The surface cracks that would have developed over time would have been nearly invisible under visual inspection. You would probably have to go to a dye penetrant type inspection and I don't think most folk would even think to worry about that on a strut that has been doing just fine for a number of years. Also, if you bottom paint over it, you won't see them.

There are no visual indications, that I can see in the limited information you have there, that there is anything wrong with your harbor being "hot".

Just my 2 cents worth.

dj