Escapee-

In answer to your question. Depends on your boats weight, how far down it sits in the water, its angle of " V ". Is it a pump or prop, or is it a inboard or outboard. A general rule of thumb is about 5 foot or better. Reason is the 5 ft mark on the south fork of the Sultan on the USGS's site is what I used to gage for water height. I know I can make it almost all the way up to Goldbar although a little tricky. And all the way out in the sound going downriver.

My boat is pretty much flat, its gotta 10 degree " V ". thats it, not much. When its sitting idle in the water its in 8 inches with a load of fishermen and when its up on a plane, well its almost out of the water running full tilt. I also run a Merc 200 horse sportjet out the back so its actually higher up then the bottom of my boat.

Take all these things into consideration: get to know the river when its low and you'll find the fish. Be very careful about where you go upriver from Sultan, it can get hairy, sometimes dangerous. I don't know about you, but I took a course on how to run my boat in shallow water. I'm also taking USCG certification currently.

I would suggest if you have an outboard, 5.5 ft is a safe bet for a pump. For the most part there are a few tricky spots down below sultan. I wouldn't go hauln butt down the river in the dark from Sultan or when its foggy in the morn.

One more thing, when it comes to trailering your boat, you will find anything in the 5's and lower starting to get more difficult unloading and loading at Sultan. I launched once at 5.1, when I came back from my hole, it was 4.5. That was not fun gettn out! One other sled had to drop off his partner, go all the way down to high-bridge and pick-up there.

Anyways! goodluck and hope I helped out.
Tightlines!