Bob, there will be a number associated with the ignition module. The number indicates the advance that the module provides.
It will not include BASE advance.
When strobing the timing marks, the actual curve/limit seen by the timing light, can't help but include BASE.
It's while looking at these curves, and doing the math where it can be confusing.
The important advance, IMO, will be at/neat 3.2k rpm or so.
At 3.2k rpm, this curve below shows approx 22*.
Add a BASE of 6* (for example) and the actual advance is 28* @ 3.2k rpm.
The TA (total advance) occurs where the diagonal line becomes horizontal.
The TB V tends to continue the advance further than some others.
Example:
Take a look at the 26* @ 3.8k rpm.... this equates to 32* @ 3.8k rpm, if a BASE of 6* were to be used.
This equates to 34* @ 3.8k rpm, if a BASE of 8* were to be used.
These are still somewhat conservative numbers due to the non-quench style combustion chambers of Merc's SBC engines.
This came up under a search for the TB V.... so verify this for yourself.
It should be found in the Merc Service manuals.
http://www.boatfix.com/merc/Techbk/95/95HGB4.PDF
http://www.boatfix.com/merc/Bullet/95/95_11.pdf
Also be careful that specs for smaller ski boats are NOT used for Cruiser Boat engines.
These systems bring the advance on much earlier than for our cruiser engines.
Apples/Oranges.
FYI, while searching for an advance curve image, I came upon many forum threads where information is either lacking, or is incorrect, and/or both.
Please use caution when viewing some of these forums and the information provided.
Example:
We'll often see an advance number being thrown out there on a forum, such as 30* or 32* or 34*.
Since Ignition advance is progressive,
advance numbers are meaningless without an associated RPM.
IOW, we can not suggest a TA of 28* or 30* without accompanying this number with an RPM.
This is just too dang important to fool around with.
So use caution.
.