ND filter adds an effect to your photos which you may or may not want.

ND filter will help to "slow" the water making it appear "silky". The darker the ND filter (more stops) the stronger the effect. You can make this silky effect extreme and even slow the clouds if you use a 9 or 10 stop ND filter. (Sometimes termed "black glass" because you will have to take it off to compose then mounted when ready to take the photo) The filter can also make the colours in your photo appear more saturated.

There are some disadvantages:

If the sun will be in your photo you will have to consider flare. The lens alone without any filter will produce flare that may be pleasing but adding extra glass will not make this better. Personally, I try to avoid flare when shooting with the ND filter but mine isn't a very good one. Get the best coated filter you can afford to minimize this problem

Colour cast - some ND filters produce colour cast, making your photo appear warmer or cooler or tinning it.

You can most certainly shoot without the filter and if you expose properly. The water and waves will appear sharp and aggressive. This is good if you want to stop motion. You can slow things down by controlling ISO and exposure time but if you really want to slow and calm things down then use the ND filter. Sunrise is the best time to take photos, the light is not as intense and direct so there should be no issues with blown out skies. (You might also consider taking the photo on a cloudy day which might work pretty well with the old boat. Better yet try HDR and you can make things look really intense and you will almost certainly not have to worry about clipping)

Sturdy tripod is a must!

Here is a good read on the usage of ND filter