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Old 03-21-2023, 08:12 AM   #7
rslifkin
Guru
 
City: Rochester, NY
Vessel Name: Hour Glass
Vessel Model: Chris Craft 381 Catalina
Join Date: Aug 2019
Posts: 7,554
Quote:
Originally Posted by Portage_Bay View Post
I know of two cases where the fin holed the hull. In one case the fin was still attached to the shaft and had punched a hole in the hull. That was a KK42. I talked with the owner to find out how it happened. I didn't ask how they kept from sinking.

The KK42 was likely a refit and may not have been installed correctly. However I'm not sure the installation was the problem. They had run hard aground on a shallow rock which could have put much of the force on the shaft in a vertical vector. My understanding of the "break away" design of the shaft is the force needs to be a horizontal vector shearing the fin off. The fin was still embedded in the hull when I saw the boat.

The other was a Nordhaven with similar damage I saw loaded on a Sevenstar transport ship.

The Nordhaven fins were likely installed at build and probably installed correctly. The damage appeared similar to the KK42's damage. The owner was not around to talk with.

When having fins installed it is important that it be done correctly. On a delivery during a routine engine room check I noticed the internal block and hull around the block flexing. With the threat of the entire structure failing resulting in a large hole in the hull we secured the stabilizers. Better a rough ride than sinking.

This was an Ocean Alexander a well built boat. But the owner had tried to pinch pennies with a repower, stabilizer installation and electrical upgrades. There were so many serious problems with that boat I should have walked away when we made Morro Bay for the first round of repairs.

For the "drop fin on rock" scenario, I think I'd want to know the fin itself isn't too sturdy. Assuming the shaft doesn't go all the way down, something like a foam cored fiberglass fin should crush rather than getting shoved through the hull.
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