Also, remember the tongue weight is going to drop the ass end of the truck a bit, depending on the boat and trailer, plus, 17" would be the minimum height of the typical trailer. It changes due to (most typically) tire size and spring height (on the trailer). I assume you have a class III hitch, 2" receiver. Most boat trailers take a 2" ball, btw.
The beauty of my suggestion that you go by the truck toy place to buy your drop is that they would 99% let you exhange it on the spot if you wound up not dead level after actually getting the boat vs. just living with a deviation or going through the hassle of an online exchange.
Don't forget to get the pin for the drop down, and don't forget to get the adapter if you have a 7pin trailer wiring slot. (about a 2 and half inch circle with a slot at the top with a cover)
If you have a 4 or 5 pin flat connector, you don't need that. The difference between a 4 and a 5 is that a 5 will light up your reverse lights on the trailer. The 7 pin is for a trailer that has trailer brakes and you have a trailer brake box in the cab of your pickup.
I'm telling you all this crap so that you can actually leave the boat dealer with the friggin boat after plunking down the cash 😆