David,
If memory serves, the 90 foot reefs are at ten miles, and at 16 miles it's 300 feet. Twenty miles or a little more (where we did lots of tile fish studies) it's 700 feet. Thirty-five to forty miles out is the center of the Gulf Stream, which runs 1200 to 2000 (ish). Sixty miles and a little bit due east puts you just off the northern Bahama Banks. 3000 feet to the north, stepping up (and they are BIG steps) toward the Bahamas. It's about a hundred and some miles to the eastern side of the Bahamas and the abyssal Atlantic plain. The water depth there goes from 40 to 140 feet right off the eastern beaches, then over the next three miles or so drops away to 12,000 feet, give or take. In other words, however good your nerve is, we got the water!!!
As to the bottom composition locally, there are reef ledges running north and south between hard swatches of sand. You find the ledges in 15 feet, 35 feet, 60 or so and 90. Then it gets pretty sparse from there on out. Mostly sand. North of here off Vero Beach is the horseshoe reef structure in 120' (so-called because it is horseshoe shaped and roughly 2 miles across).
The 35' reefs that Jay is thinking of are the first line where we could dive, although it will have to be early on a good summer day. Wave motion is distinctive to about 50 feet. Considering the size subs we are dealing with, this will be something to consider in planning overall. A 3 foot chop is common, and that's probably enough to shove a K-sized boat around some. Near the bottom, this can be interesting, although probably not particularly dangerous.
The real issue is the Gulf Stream. I've worked a ROV at 3000 feet off Canaveral and the ship was making turns for over 6 knots headed south, just to stay above the work site. The currents are much closer to the beach south of here. If you look at the map, Jupiter is a sort of point sticking out from the eastern seaboard. Underwater it is deep and rocky, with precipitous ledges. That shoves the main current way out, relatively speaking. I'm here to tell you, it is definitely an issue down south of us. Diving off Palm Beach can be quite an adventure, going hand over hand down an anchor line and streaming out like flags in a high wind.
Even here in Ft. Pierce, the summer currents can be fierce. We did a lot of research on the Occulina Reefs (now protected from the peons). They are in the western edge of the stream, and we often had to vent 1/4 to 1/2 mile south in order to make bottom on target in 265 feet of water.
Vance
-----Original Message-----
From: David Bartsch <dbartsch2236@hotmail.com>
To: personal_submersibles@psubs.org
Sent: Sun, Feb 21, 2010 5:12 pm
Subject: [PSUBS-MAILIST] local seabed conditions
Jay,
Just out of curiosity, what is the seafloor like in Fort Pearce?
In the Gulf of Mexico, the depth gradually increases even when very far offshore.
Is this the case here as well? How far out would we need to venture to have deep enough water...say 100'?
Is the sand deep or does it cover rock or sandstone?
David Bartsch
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