We were at the Delta yesterday near Bullfrog Marina and hit something submerged really hard. I've been up and down this slough many times in the past and never hit anything before. This felt way bigger and more fixed to the bottom than a log. Unfortunately the boat now has a pretty bad vibration. Limped back to Orwood at under 5MPH hoping not to do any more damage. No visible damage to the prop, which really surprised me, so I'm guessing its the shaft. I'm taking it in next Monday to have it looked at.
Here is a link to the spot. Might want to watch out if you are in the area.
I'll take some pics and post and see if anyone sees anything obvious.