Or could be that those who have them onboard legally simply have more sense than to shout about it on the internet? (but I wouldn't bet on it )
I wouldnt bet on it either.
On a serious note and why its difficult to give advice. Let me first say my information pertains to European countries.
I talk to port officals earlier this year in France
and the UK , re the situation regarding firearms aboard small non commercial
vessels ( ie typical cruiser, 40 foot etc). The officials were aware of the sometimes existence of firearms on large vessels, ( both private and commercial
, though most large yachts are commercially registers). These boats had agents, security
protocols, purpose built lockers, trained crew etc. They usually never had a problem and fireasrms remained on board.
But in both cases, both officials said it was extremely rare to handle this issue with small boats, in one case the official had never done it. They expressed a lot of harsh opinions as to why anyine would sail with a firearm. Their main concern was the security
of the firearm aboard a small vessel and also they were quite suspect as to the intentions of the person.
In addition both mentioned that this is an areas they are do not understand, as to whats exactly allowed or not. They both indicated that they regarded it as a police matter.
Hence in reality as to giving advice , its simply alomost impossible to do. One cruiser may have a certain experience and another a completely different one. What people ( especially North Americans) dont realise that in most "policed " socities, the presence of legal
firearms simply does not impinge on the general public. Where I grew up the vast majority of people have never seen a real firearm up close or even touched one. Hence the deep suspicion , that outside a bit of duck shooting, why do you have one. Its important to realise that claiming "personal protection" is NOT accepted in the vast majority of countries as acceptable and leads to seizure of the firearm.
Hence giving advice really is a non-starter, the issue is too complex, too open to local interpretaton , too based on the situation the cruisers finds himself in. to be in any way authoritive.
Sorry , but thats the problem