Leak Near Aft Bilge

[Paul Samiljan]

Hello Alajuela Forum,

On San Picaro (38 Mk2) we have a new leak around the area of the stern tube that occurs during engine operation (1.5 - 2 gallons every 12 hours). We discovered a crack on the top surface of the filled and bonded area of fiberglass that is located between the dripless shaft seal and the out end of the stern tube. This is an intensely difficult area to reach on our boats, but I was able to make contact with the top surface using a boat hook. When I press down with only trivial effort, water weeps out of the crack and flows down into the aft bilge. Until now this area has been bone dry for all the years we've owned her (we installed a dripless shaft seal early on). We are going to have the boat hauled and inspected, dried out, whatever it takes. Any ideas what to look for? What's inside that bonded area on the Alajuela? Is it solid? That would have to be a deep crack if so, and what could cause a crack of that size? Bent shaft? We did run over our mooring pennant last summer, wrapped it badly, had to call a diver to cut it free, and even then remnants of fused braided nylon remained. Stupid as it sounds, we didn't think to check the aft bilge at the time, things seemed to be running fine.

I found an old post from Rod Jermain (9/24/2011) that had a description of the stern tube factory installation. I've attached a screenshot of a diagram from that post with an annotation showing the location of the crack. I've also attached a photo of the area and visible crack (outlined in red).

Thanks, 

-Paul and Jim Samiljan

[Douglas Wertz]

Appreciate the information: I did a wrap a couple years ago but somehow escaped this particular failure.  I did strip the set screws on the external side of the shaft protrusion.  I still have the stuffing tube type of seal. Fingers crossed!  And yes, quite the limited access point!

[Chris]

The drawing posted of the shaft tube is spot on. The tube was fitted through a slightly oversized hole in the "stern post" and aligned using a dummy shaft and jig bolted to the engine bed. A plywood dam was glassed in as shown and the void filled with what was referred to in the industry as mish-mash. This  was a commonly used filler made from polyester resin and asbestos powder. Yup, we had 50# bags of it all over the place. Once the mish-mash had kicked off the whole area was glassed over with mat and roving. The outside seam was given a fillet of filler and then gel coated. It's possible that the filler has cracked and is allowing water ingress. Normally the mish-mash would bond directly to the hull but if it was mixed too hot it could have cracked or not bonded correctly. I suspect this could be the case.

If you open this area for repair, take every precaution and use proper PPE. The mish-mash is brittle and can but chiseled out which is far better than grinding and creating dust. Chances are the plywood will be rotten and have to be replaced. I would suggest grinding the outside seam and wrapping the area with strands of glass cloth or roving to get the best seal.

Here are some notes on the stern tube itself. The set screws were #10-24 x 3/8" cup point in Monel. The tube was from Skypole in Costa Mesa and was a special order with polyester resin. They made pole vaulting poles. There were some issues with the threads stripping over time so Jim Edwards and I came up with a bronze sleeve that fit over the outside of the fiberglass tube and allowed the use of 1/4"-20 set screws and solved the stripping problem. I left the company around this time  (hull 71?) so I don't know if they put the sleeves on after that.

I hope this is of some use to the group.

Chris Welton

[James Samiljan]

Chris, thank you so much for sharing with me and my son Paul all that valuable information about the construction of the dam and the stern tube. I still do not fully understand how the water is leaking into the dam. Would it be through the stern tube if it were damaged? If, as you suggest,  the mish mash filler might not have fully adhered to the hull, then there would be a void in that area. Removing the mish mash filler is a daunting task and sounds very expensive. Once we determine the cause and entry point of the leak, would it be possible to open up the dam during winter storage on the hard to let the mish mash dry out and then fill in the void with some other type of filler material and epoxy, seal up the dam, and glass over the whole thing?

Jim Samiljan 

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[chris welton]

Hi Jim,

Opening up the area is the only way to be sure of where the water is coming from so cutting away the laminate over the filler is the first step. I would recommend drawing the shaft and inspecting the bore of the tube as well. I doubt that the tube is the problem but everything is on the table until you find the leak. You could also try building a temporary cofferdam  above the area and fill it with water to see where it leaks out. Once the leak is located, repair as needed and let everything dry out before sealing it back up. 

Mish mash could be tricky to work with and the biggest issues were weather (temperature) and catalyzing the resin. Too cold or not enough catalyst and it wouldn't kick. Too hot or too  much catalyst and it would go off in the bucket, smoke, burn whoever was unlucky enough to be working with it and crack once it was set. 

My gut feeling is that the interface between the hull and the stern tube has been compromised and that you might have had a "hot batch" that cracked.

I'll be interested in hearing what you find.

Chris

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