Capt. JG wrote:.

8 or 5? I believe 5 is what signals a danger alarm.

5 or more short blasts is what the rules state.

Rule 34:
When vessels in sight of one another are approaching each
other and from any cause either vessel fails to understand
the intentions or actions of the other, or is in doubt whether
sufficient action is being taken by the other to avoid collision,
the vessel in doubt shall immediately indicate such doubt by
giving at least five short and rapid blasts on the whistle.
[Such / This] signal may be supplemented by at least five short
and rapid flashes.

More is better right? Never use a fly swatter if you have
a nuke.