Lower Unit Casing Failure

[LSaupe]

Unfortunately, I lost my lower unit on the last run of the year this past Fall. My fin struck an obtacle at about 40 MPH and the engine lifted. What appears odd is that the fin held solid but the lower section of the case broke off (pics below). Anyone seen this happen before?

I would have expected the fin to break before the lower unit case. This was a Titus mod and a great running case prior to this (V-6 OMC CrossFlow). No visible cracks or leaks prior (looked like new actually). It did break through the middle of the drain plug hole so that may have been a weak point.

Any thoughts?

[ccrick]

Wow! That sucks. I would have thought the skeg would have broke off too but the planets may have been aligned just right, or wrong. You got insurance? Must of scared the daylights outa ya!

[LSaupe]

Actually, it wasnt that bad. I felt the bump/pop then shut it right down, the boat stayed stright the whole time (luckily I wasn't up at a higher speed). Unfortunately no insurance. I was quite surprised though when I raised the engine and saw the window in the casing.

[havingfun2]

I’m trying to look at that damage from an energy point of view.
The damage to the skeg from “impact” looks rather minor compared to basically ripping the carrier housing apart.
Perhaps the impact was actually higher, deformed the case enough to jam the gear set etc?
Any chance that skeg damage was secondary?

If still attached..what did the prop look like?

[LSaupe]

Actually the rest of the case was spotless as is the prop. No sign of impact on any part of the case or prop (not even a scratch anywhere). The lower unit would still shift and run smoothly afterwards.

I agree with ya on the energy needed to cause the damage, Something just doesnt seem to add up for some reason.

This is what it looked like just prior.

[77viper]

That is a odd break. I have seen it when the impact on the skeg will push up and cause the case to be out of round and the skeg will only be bent.

[havingfun2]

I’m sure there is an answer for the damaged caused…or it would not have happened!

While under the load that props and drives and gear sets would be at almost any speed that energy needs to go somewhere.

Not as sever ( or not all shown up yet)
Last summer running the 4 ton cruiser with twin 350’s, I felt a bump, then noticed a slight vibration.
Lifted the drives and inspected.
(both drives have aluminium 4 blade props)
One blade on 1 prop is sheared about an inch from the hub. I could not see nor feel any other damage.
(pulling it this fall.. still did not see anything)

Then I was thinking..and still do..
How in the logical world can only 1 out 4 blades shear by hitting some thing.

[LSaupe]

Wow, that sounds more bizzare than mine.

I posted this as well on S&F. Looks like I may have not been the only one with a similar failure.

http://forums.screamandfly.com/forums/showthread.php?p=1859837#post1859837

[ccrick]

Then I was thinking..and still do..
How in the logical world can only 1 out 4 blades shear by hitting some thing.

It's Lake St. Clair and that planet alignment thing. I've hit stuff so hard and not even a ding or sratch. But then again, just bump something a idle and all the blades are gone!

Larry, you got a lead on a new case yet? It's to bad, that looked like a nice case.

Rick..

[LSaupe]

Hi Rick:

Yep new case is on the way. Hopefully will be ready to go by Spring.