Specific Gravity Test (Flooded batteries only)


1. Do not add water at this time.

2. Fill and drain the hydrometer 2 to 4 times before pulling out a sample.

3. There should be enough sample electrolyte in the hydrometer to completely support the float.

4. Take a reading, record it, and return the electrolyte back to the cell.

5. To check another cell, repeat the 3 steps above.

6. Check all cells in the battery.

7. Replace the vent caps and wipe off any electrolyte that might have been spilled.

8. Correct the readings to 80o F:

  • Add .004 to readings for every 10o above 80o F
  • Subtract .004 for every 10o below 80o F.

9. Compare the readings.

10. Check the state of charge using Table 1.

The readings should be at or above the factory specification of 1.277 ± .007. If any specific gravity readings register low, then follow the steps below.

1. Check and record voltage level(s).

2. Put battery(s) on a complete charge.

3. Take specific gravity readings again.

If any specific gravity readings still register low then follow the steps below.

1. Check voltage level(s).

2. Perform equalization charge. Refer to the Equalizing section for the proper procedure.

3. Take specific gravity readings again.

If any specific gravity reading still registers lower than the factory specification of 1.277 ± .007 then one or more of the following conditions may exist:

1. The battery is old and approaching the end of its life.

2. The battery was left in a state of discharge too long.

3. Electrolyte was lost due to spillage or overflow.

4. A weak or bad cell is developing.

5. Battery was watered excessively previous to testing.

Batteries in conditions 1 – 4 should be taken to a specialist for further evaluation or retired from service.

II. Open-Circuit Voltage Test
For accurate voltage readings, batteries must remain idle (no charging, no discharging) for at least 6 hrs, preferably 24 hrs.

1. Disconnect all loads from the batteries.

2. Measure the voltage using a DC voltmeter.

3. Check the state of charge with Table 1.

4. Charge the battery if it registers 0% to 70% charged.

If battery registers below the Table 1 values, the following conditions may exist:

1. The battery was left in a state of discharge too long.

2. The battery has a bad cell.

Batteries in these conditions should be taken to a specialist for further evaluation or retired from service.

TABLE 1. State of charge as related to specific gravity and
open circuit voltage


Percentage of Charge Specific Gravity Corrected to
80o F
Open-Circuit Voltage
6V 8V 12V 24V 36V 48V
100 1.277 6.37 8.49 12.73 25.46 38.20 50.93
90 1.258 6.31 8.41 12.62 25.24 37.85 50.47
80 1.238 6.25 8.33 12.50 25.00 37.49 49.99
70 1.217 6.19 8.25 12.37 24.74 37.12 49.49
60 1.195 6.12 8.16 12.24 24.48 36.72 48.96
50 1.172 6.05 8.07 12.10 24.20 36.31 48.41
40 1.148 5.98 7.97 11.96 23.92 35.87 47.83
30 1.124 5.91 7.88 11.81 23.63 35.44 47.26
20 1.098 5.83 7.77 11.66 23.32 34.97 46.63
10 1.073 5.75 7.67 11.51 23.02 34.52 46.03




By Paul Graham

There are two ways to transit the Whale.  You can go around the east side of Whale Cay or you can go though the Whale using the Don’t Rock Passage. The one thing “you must have” before coming to Abaco, Bahamas is the “Guide to Abaco Bahamas” by Steve Dodge. Steve Dodge has excellent directions for going around the Whale, so this article will focus on the Don’t Rock Passage (DRP). In this article, the guide is referred to as SDCG (Steve Dodge’s Cruising Guide).

It is important for you to know that either of the Whale Cay Passages can be more dangerous and has caused more deaths/accidents than all other areas in The Bahamas combined.


On the other hand it’s just like going through Hell’s Gate in New York at slack tide.

A non-event. But just like Hell’s Gate the Whale (either the outside route or the DRP route) must be approached with the same planning.

Over time, 20 mph winds from the North, Northeast or East can produce swells that make the Whale dangerous. Once the winds have been blowing for a day or two from any of those directions and then abate, it can still take a day or so for the wave action to settle. This is called a “Rage”. From a distance, using binoculars, a Rage looks like elephants dancing on the horizon.  A Rage is not a good time to cross the Whale – either passage, east or DRP.

In the winter season 75% of the time the wind and waves are favorable to go around the east side of Whale Cay as shown on page 68 in SDCG. Also in the winter season, 80 % of the time conditions are favorable to transit DRP which is also located on page 68 of the SDCG.

Once you have determined favorable weather conditions for the DRP Whale Cay Passage, the next step is to check the tides (2009 page 202 SDCG). For 2010 tides you will need a 2010 SDCG.

Special Note: We cannot stress enough that you CAN RELY on the SDCG for tide information; but not always from other sources. Earlier this year, we heard an employee of a marina giving the incorrect tide information for a different inlet (not Whale Cay). The tide information given was almost reversed hi and low, and ultimately caused a boat to go AGROUND for 10 hours with extensive damage to the boat.

Normally we (GH37 Odyssey) are comfortable transiting the DRP up to 3 hours before or 3 hours after high tide. Using this guide, we have never seen less than 3 feet under our boat.  The very best time to transit the DRP is on a rising tide about an hour before high tide which allow for boats with 5-6 ft drafts transit then. Note: If conditions are less than favorable this becomes even more important. However, on a calm day it doesn’t matter, it can even be low tide.

Traveling south, you will arrive at WHLSW way point. From this way point, you will have a visual on the Sand Bank Cay (page 68), but if you want a way point to go to I recommend WHLDR1 (Whale Don’t Rock 1) at 26 41.670N and 077 15.714 W which puts you at the passages North entrance with the Sand Bank Cay on your starboard.

At this point you will also have a visual on Don’t Rock. If you want a way point to go to I use WHLDR2 at 26 41.098 N and 077 14.850 W which take you right to the Don’t Rock’s rock. You can transit either side of the rock. We have transited the East side more often than the West side but have transited both sides comfortably.  Keep in mind that:

  • You can go safely to the East of DRP route even a hundred plus yards. The bottom is only sand.
  • Be careful not to drift to the West as it shallows up quickly.
  • Great Harbour Trawler auto pilots do not like shallow water so I usually end up hand steering at some point.
  • DRP is shorter and usually a lot smoother.