Dear Jud:

Here I am providing you few translations of the verb as you have requested from Bengali, which is my mother tongue. I am providing you the first meaning as they are applied in our everyday conservation.

Dear Shibly,

Assalam u alikum! I am very appreciative of your kindness for spending so much of your valuable time on answering my questions so efficiently. It is acts of kindness like yours which make life worth living.

Shibly: 
Regarding your question of usage "to be" in the sentence, "the boat is sailing towards the island, " I would like to mention that in Bengali, usage of auxiliary verb such as "is" in your sentence, does not exist in Bengali in general. What happens in Bengali syntax, is the main verb contains the mood of action of the subject. For example, a translation of your sentence "The boat is sailing towards an island" in Bengali would be  "Naukati (Boat, I = a suffix for The article) Diper (to island) dikey (towards)  - Jaccheye (is going). " Here in this sentence, the last word,  "Jaccheye" is a present progressive tense and no use of auxiliary is   quired.

Jud: 
You have explained that to me very well indeed Shibly. Would you agree with me that the simple existence of the boat 'naukati' is introduced into the sentence simply by the mention of its name?  In other words, having said or written "Naukati = the boat" do you now accept for the purposes of the sentence, that the boat now exists and that we can now continue to describe the present continuous mode of existence of the boat which is: "Naukati = the boat"  "diper dikey jaccheye = towards island is going. "

Do you think that I have written a fair description of what goes on in the mind of a Bangla speaker either consciously or unconsciously when he says a sentence like that?

 What I mean is, do you think as I do, that no verb of existence is required in the sentence to establish the occurrence of the boat in the sentence, and that the main verb 'Jaccheye' [is sailing] contains within it [I say  'enshelled'] the sense of sailing towards the island as PART of its existence - a MODALITY of its existence in the world signalled by the present progressive tense?

 A good test to check if what I say is true, is to change the Bangla sentence to: "The boat WAS sailing towards an island. " If either you have to introduce the word 'chilo' [was] or if the verb 'jaccheye" has to change its morphology [shape] in any way [perhaps by altering its ending] to denote a different modality of existence, [the past] then that will prove that the word 'jaccheye' contains an 'enshelled' copula, which marks the present existential modality of the boat in the original sentence when translated into Bangla.

 Oh, dear, I hope in what I have just written that I have been able to explain what I mean sufficiently well for you to understand, for looking at the paragraph I've just written, it looks rather complicated even to me?

Shibly: 
I must say that I am not a linguist so cannot answer your question in details, since your question seems to refer to the realm of psycholinguistics.

Jud: 
You could have fooled me Shibly, for you have provided me with information in such a professional manner that I could be forgiven if I mistook you for a linguist.

Shibly: 
So far I know, professor William Radice, the Professor of Bengali at the SOAS may come some help to you. Meanwhile, I would look forward to get an e-mail address of an eminent linguist of Bengali. If you need further assistance, let me know. Wish you good luck with your pursuit of education.

Jud: 
Thanks for the tip regarding professor William Radice - I shall write to him to see what he thinks, in the meantime I would certainly be grateful for any contacts for any Bengali linguists that you may turn up.

Shibly: 
Note: In Bengali, we use group verb(s) to express an action, the mood of action and its relation to the subject, which is a complex discourse. I am not familiar with transliteration method of Bengali to English, so I used my common sense to invoke the sound of original Bengali words identically as it sounds in our conversation.

Jud: 
You did it very well indeed Shibly. It goes without saying that if there is anything I can do for you - any information that you require on any subject to will give me a chance to repay your kindness, just let me know. Looking forward to hearing from you when you have time.

Sincerely,

Jud Evans.

Dear Jud Evans: 
Thanks for your detail reply and I really feel happy that I have come to your help within my extent. Regarding your question about the sense of sailing the boat as a part of its existence-a modality of existence in the world signalled by present progressive tense, according to my understanding, is accurate, i. e., the sense does exist as a signal. I also employed your method converting the sentence in the past form and after much consideration came to the similar conclusion that you have made. And introducing the word, Naukati or the boat, we or should I say, I (?) accept the purpose of the sentence and now can proceed describing the forthcoming action of the boat.  Well, I do not see why do you feel to repay me. All I did is what I am supposed to do: to help you doing your research as much as I can. I am flattered to hear that you could have taken me almost as a linguistic by mistake. I wish I were, but I am an undergraduate student pursuing my major political science; however, I do read sporadically on sociolinguistics/language planning written for the laymen just for curiosity. 

Wish you a good luck.  Shibly Azad  Columbia University  NYC, USA.