For a lower unit finish, which is the fastest? Polished, gloss paint, or buffed primer? I kinda suspect the answer, but I want to hear what other people know (or think they know )

I guess a slightly rough lower unit. Going on the same theory as the sanded hull bottoms.

In theory, a slightly rough surface is better for reduced drag.

A smooth finish will allow [mostly]uninterupted laminar flow and induce direct water-to-solid friction. A slightly sanded or rough surface will 'hold' or grip some degree or water, a microscopic boundary layer, and create water-to-water friction -- the latter being less.

Yea, it was my understanding that the buffed primer was the fastest. The question is by how much?

So if you go with a slightly rough finish wouldn't you lose some prop efficiency ? You're introducing air to the prop/blade ?! I think it's going to be a very similar to nose coning a drive(you want to keep as much of an uninterrupted flow of water to the prop as you can) ?!

Actually, I believe the smooth polished surfaces are "sticky".

I think the differences would be so minor. Probably not even noticeable. Just like some prop shops will polish a prop and some won't both claim their way to be better ? Can they prove it ? Usually not. I think it's mostly just eye candy.

Now if you were going for a world record maybe a few tenths would be worth it.

On the nosecone issue, don't they usually want to smooth out the water before it gets to the prop ? With a rougher finish you'd be disturbing this water ? Which is correct ?!

Test is the only way and then it would have to be identical conditions(temps , water , fuel , weight etc.)

It's hard to say. I'm sure if you made calls to the manufacturers each would claim theirs to be faster ???

Here's a thought. What do speedmaster lowers look like.
If it's good enough for Merc, it's good enough for me.
Gary

Play along Gary, because I'm thinking gloss black.

I think gloss red is a lot faster than gloss black.
Gary