I disassembled the bow foil of my N5.5 with the expectation of cleaning the interface and riveting again. But the aluminum was way more corroded than expected...
https://www.thebeachcats.…ictures?g2_itemId=134137
Anybody has been there? Any advice will be greatly appreciated. Thanks!
Corroded bow foil
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Posted: Dec 22, 2020 - 06:46 AM
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Posted: Dec 22, 2020 - 09:38 AM
My preliminary thoughts:
- The surface is corroded unevenly, it looks ugly but most of the holes seem to still have some strength.
- The load is taken mostly by the cable so I'm not too concerned that the rivets will come off.
- If possible I would recover the surface with epoxy and fiber. I don't expect that it adds significant strength but it is important to have a smooth and even surface.
- I will rivet most of the holes again but for a couple of them, or additional ones, I will put bolts through the foil with washer and nut on the other side, making sure not to press too much.
- I would add a sacrifice anode to avoid further corrosion, I understand that zinc will protect aluminum, right?
Edited by Andinista on Dec 22, 2020 - 09:39 AM. -
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Posted: Dec 22, 2020 - 09:43 AM
The anode won't help unless the corroded parts are submerged all the time. What you see is crevice corrosion, which is usually not helped by anodes even if the parts are submerged.
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Chuck Miles
1978 Hobie 16
1991 Hunter 23.5
TsaLaGi Yacht Club, Jackson Bay Marina
Fort Gibson Lake, OK
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Posted: Dec 22, 2020 - 12:14 PM
I assume we are looking at 30 years of corrosion here, and periodic disassembly or use of a corrosion inhibitor coating may have helped. That is galvanic corrosion between the aluminum and stainless, so whether it occurred submerged or in a crevice is immaterial. Your proposal to use glass fiber reinforced epoxy amounts to the equivalent of a "glass reinforced epoxy (GRE) gasket" and is a common solution for galvanic corrosion in pipe flanges. If you can use a cut-to-fit GRE gasket or laminate your own, and fit it between the aluminum and stainless part, then combine that with a coating of CRC 06026 Heavy Duty Corrosion Inhibitor, especially in the riveting holes, I think you will have a good long-lasting solution. It may not be maintenance free.
Considering what you found on the foil, it would be a good idea to check the rest of the connectors on the crossbars and mast.
Edited by tominpa on Dec 22, 2020 - 01:35 PM.
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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Posted: Dec 22, 2020 - 12:30 PM
Let me start with a disclaimer - all of my aluminum corrosion experience is with aircraft. That includes restoring a 1946 Cessna 140 (lots of corrosion experience there!), plus building airplanes for fun and working at a helicopter company. So if this is not applicable you can dismiss it and my feelings won't be hurt.
The best option would be to replace that part. I realize that can be a challenge, both financially and even to find the parts.
Assuming that was not an option, I'd at least patch the area. I'd have a patch that was bigger than the bad spot, maybe 2X the overall area. The material should be the same type and thickness of the original, which I assume is 6061. You can probably find 6061 at your local metal supply area. Here we have Metal Supermarkets and they are pretty awesome. I did discover that if I call the local office directly the cost is about half as compared to the internet price. Otherwise you could mail order from an aircraft supply company. I would not buy anything from Lowe's Depot.
https://www.aircraftspruc…ges/alumsheet_6061t6.php
The easiest thing would be an external patch. Not sure if that would give you issues with the rigging length. If you cut out the bad area you might be able to put the doubler inside the tube, but that would be a lot harder. If it was my boat I was rescuing I'd go external.
With 6061 you have the option to weld. It may be easier to use Cherry Max rivets. The 1/8" ones, and even the 5/32" ones can be set with a normal hand rivet gun. Note the proper hole size for rivets is a #30.
https://www.aircraftspruc…g/hapages/cherrymax2.php
For corrosion proofing, I'd use an Alodine conversion coating like this. It forms a chemical conversion coating which protects against corrosion, and also makes for great paint adhesion.
https://www.aircraftspruc…e1001.php?clickkey=11999
Having paint in between those parts would be awesome. Some sort of epoxy primer would be the best, or whatever is favored in the boat world. For this area I think anything is better than nothing.
https://www.aircraftspruc…rwhite.php?clickkey=5223
If you want to read more about aircraft aluminum corrosion and repair stuff, AC43.13 is the FAA guide. Page 4-11 for repairs and page 6-25 for corrosion stuff.
https://www.faa.gov/docum…r/AC_43.13-1B_w-chg1.pdf
Good luck!
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Bryan in Poplar Grove, IL
Supercat 17, unknown year. Future project
Hobie 16, 1977 - died a spectacular death https://youtu.be/Y7O22bp2MVA
Hobie 16, 1978 - current boat
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Posted: Dec 22, 2020 - 12:44 PM
The other thought I had was to re-make the steel part, and make the plate section 2X bigger in area. Looks like an easy part to make. That corroded aluminum doesn't have any strength left.
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Bryan in Poplar Grove, IL
Supercat 17, unknown year. Future project
Hobie 16, 1977 - died a spectacular death https://youtu.be/Y7O22bp2MVA
Hobie 16, 1978 - current boat
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Posted: Dec 22, 2020 - 02:41 PM
Thanks for all the advice, I’ll read carefully.. -
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Posted: Dec 22, 2020 - 02:47 PM
For replacement parts, one possible source might be pbegle call 909-800-5237
He seems to have more used parts for Nacra and Prindle than anyone I know.
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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Posted: Dec 22, 2020 - 03:06 PM
A cheaper and simpler solution could be to remove the bow foil and put double bridles, a higher pair to take the load and a lower one to hold the jib tack... That’s how many current boats are made right?
Edited by Andinista on Dec 22, 2020 - 03:19 PM. -
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Posted: Dec 22, 2020 - 04:30 PM
I'd keep it simple; use a corrosion inhibiter to keep it from degrading further. Possibly use a thin layer of material (UMHW "slick tape"?) to act as an isolator and reattach with rivets (also using inhibitor in the holes).
Yes and no, to match the current lateral load, you would need to determine and match the angle of the short wires that attach the bridle to the bows. More modern boats use a conventional split forestay, but add a solid extension below the split that attaches to the spinnaker pole. Having owned a 6.0, I suspect that the angle of the wires would make the split in the forestay much higher than a conventional modern forestay. -
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Posted: Dec 22, 2020 - 04:37 PM
I just realized that I can turn the foil around and rivet the piece at the other side... and invert the end caps. That makes more sense.
Will check the suggestions about corrosion protection now -
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Posted: Dec 22, 2020 - 05:24 PM
Andinista, I mentioned the CRC 06026 Heavy Duty Corrosion Inhibitor earlier. It is intended for marine use like this. If you are going to turn the foil to a new surface, then on top of the inhibitor, add a strip of Marine Butyl Rubber Tape https://shop.marinehowto.com/products/bed-it-tape This is the same material we use to bed and waterproof fixtures on monohulls. It will totally exclude any water from under the fixture. It is extruded very thin and is compressible. If you run it around the edge of the stainless part and where rivets penetrate, and press it into place it will stay pliable and keep out water for many years. Without the water, and placed on a corrosion barrier, this will not happen again.
Edited by tominpa on Dec 22, 2020 - 06:25 PM.
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Tom
NACRA 5.7 (1984 Sail 181)
Pennsylvania
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Posted: Dec 22, 2020 - 05:54 PM
Thank you Tom! and all! I will report when done, i suspect
I’ll have to import some of that stuff so it may take some time. -
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Posted: Dec 22, 2020 - 06:05 PM
Yes, leaving the jib zipper a bit too high perhaps, that was a concern I anticipated too, I was going to measure and estimate how much higher but now i’ll try to recover the foil turning it around, so I removed the end caps already. :) -
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Posted: Dec 22, 2020 - 09:07 PM
Did not know you were out of the U.S.
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Tom
NACRA 5.7 (1984 Sail 181)
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Posted: Dec 23, 2020 - 04:08 AM
Chile
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Posted: Dec 23, 2020 - 05:45 AM
Hi Andinista,
Sweden
Remember we had a discussion a few years back about bridle angles? It gave me a lot!
After that I rebuilt and widened my 5.5 to get rid of the clumsy, heavy and also heavily corroded bow foil. Also replaced the rig with a F18 complete with spin. The arrangement with the spinpole was totally overworked with the striker thing under the pole. Will go to the normal style with lines to each bow next year. Note my compression tube is quite long as the F18 jib sits lower than the 5.5.
Took a random image from the internet to show how I would do today, w and w/o spinnaker, if I hadn´t widened my 5.5. The "real" bridle lines are 4mm DM20, the others 3mm DM20 and the compression tube is a flattened 16mm stainless. This involves shortening the forestay and a simple modification of the jib zipper.
Will also save a quite a few kg of boatweight as this arrangement is just a few hundred grams.
Edited by revintage on Dec 23, 2020 - 06:54 AM.
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Brgds
Lars
Frankentri 5.8/5.5/Inter20
Aerow trimaran foiler
https://www.facebook.com/groups/1192604934176635
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Posted: Dec 23, 2020 - 10:13 AM
PRO tip here - thanks! -
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Posted: Dec 23, 2020 - 10:23 AM
YES!!!!
what is this you are holding ? some anti fouling or silicone or something? can't be aluminum oxide is it? (looks thicker than the foil metal to me)
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Posted: Dec 23, 2020 - 10:51 AM
I was assuming aluminum oxide. It's pretty ugly looking!
Clever idea to turn the foil around. Will you patch the other side?
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Bryan in Poplar Grove, IL
Supercat 17, unknown year. Future project
Hobie 16, 1977 - died a spectacular death https://youtu.be/Y7O22bp2MVA
Hobie 16, 1978 - current boat
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