Its me the OP. Here is what I have been able to figure out.
1. If the owner was marketing the boat on their own as a courtesy they should have informed the broker of what they were doing as they went along for the precise reason to avoid what happened me.
You are taking this business too personally. Even if one retains a Broker to sell ones yacht, if one really wants to move the boat one is a fool if one doesn't continue to market the boat oneself as well. The Brokerage Agreement--regardless of type--is not an anti-alienation agreement. It merely ensures that, even of an owner does locate a buyer, the owner will still be obligated to pay the broker some, if not all, of the commission that the Broker would otherwise earn as consideration for his/her efforts to arrange a sale of the boat. Listing and marketing boats/houses/cars/et al
isn't inexpensive and consumes time that a disenfranchised Broker might have used otherwise to better advantage.
2. The broker should never have promised me my offer would be the only one presented when the broker does not have control over other people making offers to the owner bypassing the broker.
I suspect that the Broker meant that yours would be the only offer presented by him/her. He/she could have no way of ensuring that yours would have been the only offer at all, although by your carrying on, it sounds like you were hoping so in order that you would be the only game in town for the Seller and could somewhat dictate terms. Free markets don't work that way.
3. If the broker had a high level of ethics she should have severed her relationship with the seller the moment she realized what the seller had done going behind her back marketing the boat. The commission was more important than the ethics.
That's a pretty ignorant opinion (see note one above in re: commissions). Severing the relationship with the Seller would only have benefited the Seller had he/she managed a sale absent the Broker's participation/assistence. Your take on the "ethics" is warped to suit your own self interest/disappointment. The Broker isn't in business to spend time and effort to loose money. Moreover, the Broker is the Seller's (contract) employee and hence his/her interest, and in fact fiduciary obligation, is aligned with and to the Seller.
Buck up. There's never a last great deal, or boat, and in the long run more people have been happy that their earlier offers were not accepted then were.