In about 2ft high waves I had high trim, right on the limit and at 58mph suddenly the speedboat turn to the left with a radius of about 100ft. There was no way to do anything, it was as if the drive had failed. It wasn't dangerous, it was surprising, but if it happened at a higher speed it wouldn't end well. I've had the same thing happen twice, both times under 60 mph and both times to the left, never in calm water.

Speedboat is 30 ft long, empty and with out of fuel weight 5.000 lbs, LS376/480 engine, ZF63A-1.58:1 transmission and Signature LS-5 LH propeller. Drive it is MSA Marine Systems 300 SXR.
The speedboat has a 1.2 ft wide pad keel.

Does anyone have an idea what could be the possible reason for this phenomenon?

If the wheel didnt move but the drive did Id say you have air in the steering system...full hydro ?

It is heavy hydraulic Saurer system. Drive did not move. It felt like the boat and drive was in the air, but I know it didn't jump. The steering didn't work at all until I slowed down.
Is something like this possible due to too much trim? I am really exaggerate with trim for fun to made rooster tail.

I think you are the problem................over trimming a boat at speed is dangerous

You're right. I never played with the trim above 60 mph.
But it seems strange to me that the speedboat "drift" to the left like on the air pilow.
It was really too much trim, but the propeller still kept the bow in the air.
Please explanation why this happens in such a case.

The leg of the drive below the keel is what keeps the boat going straight like a rudder, if its all jacked up out of position the boat looses steering, Im out good luck and dont crash

My brother and I came to the same conclusion when we were looking for reasons, but since we are greenhorns, I preferred to ask on this forum.
Thank you!!!

These are not toys. Don't kill anyone and learn to responsibly drive the boat.

^^^This^^^

You are all right and thank you so much for those words!
At the time of the first incident I was of the opinion that the combination of waves and wind was guilt, but after the second incident I trimmed much less and kept the speed below 45 mph. Until I become like one with the boat, it will remain so.

But I still don't understand something:
I have over 20 years experience with a faster small 14ft speedboat. I am trim up until the speed increased. When it stopped with acceleration I put the trim back a little and it went over the chine walk without any problems. I never had such isues.
I tried the same thing in this case. Even with this high trim, the speed was still slowly increasing, but I had a strange feeling and didn't go any higher. It feels like the skeg is gave way much faster than the propeller. Is it possible that the skeg is too small? There are two fotos with problematic trim angle.
In the future, I will definitely use smaller trim angle, but it would still be good to know this round skeg, and if it is to small, I have no problem lengthening it. A boat uses almost the same amount of fuel liter/mile from 35 to 50 mph, and these are almost the the speed limits for future. It is intended for longer routes and not for quick jumps around the bay. Anyway, I'm asking for an opinion about skeg.

https://i.postimg.cc/hGvr9Wd0/IMG-20240815-082236.jpg
https://i.postimg.cc/zG07bXVB/IMG-20240815-082247.jpg