What shutter speed balances motion and detail for long-exposure dusk seascapes?

[Donald.T]

I'm on a photography trip to the coast next week and want to finally master long exposure photography to capture smooth, dreamy seascapes and cloud movement. I have a sturdy tripod and ND filters, but my previous attempts have resulted in either overexposed highlights or images that lack sharpness despite the tripod, likely from mirror slap or wind. I'm unsure about the optimal shutter speed for moving water at dusk and the best camera settings to balance exposure time with maintaining detail in the waves.