What is the purpose of the large through hull on the bottom of the boat at the notch in the transom (dead center)? The thru-hull attaches via hose to a water dump thru-hull on the STB side rear. Does this introduce air into the props on take off?

This is on a 06 35 Lightning Twin Step.

my 38 has the same thing and im not sure what its for???????

It is for factory a/c

i have the same thing on my 38 still not sure what for .....thinking something to do with a/c .....but then again i have no a/c

Seems odd to poke a hole in the bottom of the boat unless you would be installing that option. Unless the mold has that opening integrated, but I doubt it.

It is a BIG through hull with a meaty hose running through to the BIG through hull on the side. Seems overkill for an A/C condesation dump.

29 Fevers' have had the same thru-hull, too, for a long time. I've never seen a 29 with a/c. I was told it was to break suction at the notch and assist in getting the boat up on plane (airate the prop?).

I have the same thing on my 35. according to the Lords at
Fountain it is for the optional a/c sys

Also it may be for a gen-set. I agree it is BIG

Since I have neither A/C or the GenSet should I close the gate valve (currently open) to that thru-hull? I wonder if while under way I get a cool blast of water coming out of the side thru-hull? Maybe that is worth leaving open! My Fountain's fountain.....

I have never seen one with a gate valve. All of the one's I've seen have been direct plumbed from the thru-hull in the notch directly to the thru-hull on the side. The only thing I've seen with a gate valve is the Fountain version of freshwater flush and that is usually installed on the transom. That has 1 quarter turn valve and 1 gate valve. Don't remember which way the gate valve is plumbed, but if you open/close that gate valve you will open/close water flow from the outdrive to the seawater pump and that would be bad for the engine! Regarding the vent to the notch, I've never seen any water come out the side vent - it pulls air to the notch, not pushes water from the notch to the side thru-hull. Hope this helps.