Don’t fall into the “theoretical hull speed” trap. Under power, and for the long haul, boats hardly ever achieve that. For example, my boat is 34 feet (29 foot waterline) with a 35 HP engine and under wide open throttle, my max speed is 7 Kts vs. the 7.3 Kt THS. I use 5 ½ kts for planning purposes when doing a long trip such as the one you’re contemplating. An older boat, unknown bottom condition and an older outboard and a water line somewhere around 20 feet – you should be using 4.5 – 5 kts max as a planning number. You will also want to bring along a couple of extra jerry cans as you will be running WOT for about 18 hours.
Go to West Marine and buy their Northern California Chart Book. It has the multiple charts for the Delta which you will be using for your future adventures anyways. There are also a lot of free guides for Delta cruising that will help you on the bridges. If you are going to the Isleton/Brannan Island area – can’t you do that from the Sacramento River? There are no bridges requiring an opening AFAIK
on that route. (except for Hwy 160 and Rio Vista?) Do any of these boats that you are considering have a working depth sounder? The good news is they are all relatively shallow draft (no more than 4.5 ft?) But you will still have to avoid the shoal areas. Here is a little “local knowledge” (my boat draws 6 feet). Oyster Point – stay in the channel until the junction with the main ship channel, then head north. San Bruno shoal will be on your right but shouldn’t be a problem unless the tide is low. You can go on either side of Treasure Island – let the currents be your guide. Favorable current – take the City side and sail to Red #2, then South Hampton Shoal. If tide is against you, take the Oakland side and follow either the 15 or 20 foot contour to South Hampton. Call ahead for a temporary berth at Marina Bay in Richmond.
Next Day: Leave early! Try to make the flood! If you have a Flood, pass to the Right of Red Rock and the Brothers. Past the Brothers there is a day shape channel marker – Pass well to left of it as it is badly silted in and even your boat will run aground there. If you are fighting an ebb, it’s best to pass to the left of Red Rock and stay in shallow water up to Quarry Point then proceed into San Pablo Bay. Transiting San Pablo Bay – Once you safely get past the shallow area near the day shape at Pt. San Pablo, you can follow the 20 foot contour up past Pt. Pinole and then onto Vallejo. There really isn’t a good way to get past the Napa River and the narrows area without some previous experience (you will need to hug the northern shore very closely). Halfway up the straits, the Benica Marina is a good stopping off point for your second night.
Last Day: You will want to pass the Martinez Bridge on the right hand side (refinery side) to stay in the river channel. If you blunder up into Suisun Bay and the Mothball Fleet, you will have to back track as the center part of Suisun Bay is a mudflat at low tide. You really need to stay in the marked channel from this point on. You may deviate to the right while passing Port Chicago unless there is a ship docked (the nice guys with guns will be there to remind you to keep clear.) The northern edge of this channel (Middle Ground) is ground at low tide. As you get towards Pittsburgh, stay in the main Sacramento River Channel and do not go down New York Slough. Eventually, there will be a split in the river where the Deep Water Channel junctions off of the northern side. Do not take it. Stay in the old river channel and stay between the marker buoys until you get to Isleton or where ever you’re going. Up to this point you do not have any draw bridges to worry about (except Rio Vista and Hwy 160?)
Are you going to Seven Mile Slough? If so, you will want to take New York Slough past Pittsburgh and Antioch. You will then be in the San Joaquin River system. Stay between the channel markers until you get to confluence of Seven Mile Slough.
This is a long trip, split it into several days and enjoy the ride!