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Hull Oil Canning

Jul 18, 2018
1
Catalina 30 Hotty Toddy Jackson Yacht Club
I own and sail a 1984 Catalina 30 in a large freshwater lake in MS. Because there are no facilities other than hiring a large and very expensive crane to pull boats, larger boats tend to stay in the water a long time between hauls. My boat has been in the water for 7 years. In preparation for pulling my boat next month I got under the hull to check it out. The hull feels fine except for the expected slime, but I did find an indention, approx. 14" round, in the starboard rear quarter of the hull. It feels to be maybe 3/4" deflection. I'm reading that this is called oil canning, and can be caused by poor placement of jack stands, or occasionally by sling placement when lifting.
It's been this way for 7 years with no problems. I had never noticed any problem in the boats interior. So my question; how serious is this, and can it be repaired?
 
Jan 11, 2014
4,155
Sabre 362 113 Fair Haven, NY
Jackstand placement comes to the top of the list of culprits. Ideally all of the boat's weight should be on the keel with jack stands simply keeping the boat from falling over. The keel should be blocked in 2 places at the fore and aft end of the keel. Jackstands should ideally be placed under bulkheads.

Once the boat is out of the water, sound the hull with a plastic hammer. If all is solid and has a nice sharp ring to it. I think you'll be good to go. If you get a dull sound, the hull may be delaminated where you feel the soft spot. That should be repaired.

Brownell are *the* jack stand people. They invented them. Here's what they say about putting boats on jack stands: http://boatstands.com/proper-use/
 
Jan 19, 2010
6,670
Hunter 26 Lake Martin AL
Can you get to the indentation from the interior? If so, the proper thing to do is to push it back out and then class in a "rib" or "stringer" to give it some stiffness. Commonly, the "stringer" is just a piece of foam and it is the fiberglass around the foam that adds the stiffness. I have done this job on a Coronado 23 in the past and I used a swim noodle that I had cut up long ways into strips. It is a quick job. Get some matted fiberglass cloth from Autozone and some resin. Wet the cloth in your shop or where ever and place the wet cloth on a piece of plastic sheeting. Put masking tape around the edges of the sheeting before you start. Then bring the plastic sheet with the whetted cloth into your boat, lay it over the foam stringer, tape down the edges of the plastic sheet and wait for it to cure. Done!

When you push out the indentation, it may not want to stay "pushed out" in which case you will need to brace it with a broom stick or other pole against the cabin top.
 
Jul 20, 2005
2,422
Whitby 55 Kemah, Tx
Interesting that it didn't go back to it's normal spot after the pressure was taken off. I had my Hunter hauled out in Tonga with one of those trailer lifts. The wing keel prohibited the boat to get into the proper spot so they just pulled it out of the water with most of the back weight on the side lifts. After it was out of the water I saw the hull was pushed in maybe 1/4" but as soon as they put it down and took the pressure off it, it evened out right and nothing seemed wrong. We tried different spots when putting it back in the water but same result. Even though a trailer worked fine in FP, I will never use a trailer again. It was too scary to me.
 
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SG

Feb 11, 2017
1,463
J/Boat J/160 Annapolis
The Catalina 30 has a (as I recall) a solid fiberglass (i.e., not cored) hull.

Oil canning is something that goes in- and -out. If you do have crushing of the fiberglass or a permanent "pushed-in" section, then i) I'd expect to see some sign on the inside of the hull in the form of distress and stinger separation, etc., ii) it's possible that you had some lay-up issue (but I think that's less likely...but)

It there is nothing showing on the inside or in the stringers in the vicinity, then I'd wait until you haul the boat. That assumes that the outside of the hull isn't obviously distressed in any way.

You then will need to determine if it was defect in the hull from the beginning of time or if its something more. If you're concerned further, just do a "short haul" and see what's what.