There is no 'equivalent' brushless motor for a brushed motor, there are equivalents in motor size (dimensions) tho....
As for you being led to believe that brushless motors draw less and give you more run time, I'm sorry to say that is an incorrect fact.
so here are the ACTUAL facts.
There are two types of brushless motors....
inrunners are the same style as a brushed motor and coming in a range of physical sizes. They are primarily for direct RPM and best suited for RC car & Fast electric boat applications such as the mono 1's hydroplanes etc.(surface drive props) they can also take water cooling jackets, or coils easily, which is required for both the motor and ESC or you will end up with a fire within moments.
outrunners are very different the internal armature dose not spin, the external can of the motor turns instead, these give excellent RpM for most boating applications other then super fast machines as they can accept larger props, they are primarily for Torque jobs, such as spinning an aircraft prop or for larger boating props anywhere from a 20mm up to the whopping 120mm prop (depending on the size of the motor)Outrunners tend to not require water cooling the motor and only the ESC needs to be water cooled.
Inrunner motors require the use of Lipos and cannot use any other type of battery and usually require ESc's ranging from 50 up to 220 amps depending on the size of the motor and its draw requirements.
Outrunners require smaller ESC's anywhere from 10 amp up to 80 amps depending again on size of the motor, on using a motor under 30 amps, you are able to use a NHMI battery instead of a lipo, but anything over 30 amps these motors require a lipo as its power source and cannot use any other types of battery.
Run times for an inrunner motor tends to be 8-12 mins, regardless of battery capacity, although there is a slight difference in larger battery capacitys but its to small to notice most of the time.
Run time for a outrunner can be between 20-35 mins depending on the battery capacity.
If your making a scale boat then I would suggest an outrunner motor. not only will you have the advantage of the cheaper cost but you will be able to use a motor to spin a range of props better.
heres the maths bit which will help....
Brushless motor KV rating X (times) V (voltage imput) = RPM..
most boats usually need an RPM around 7-9,000
faster scale speed boat types up to 10-12,000rpm
2s lipo = 7.4 v = equivilant of a 7.2v NhMI
3s lipo 11.1V = equivilant of a 12v Lead acid with shorter run time and weight reduction
( you probably wont need a 4s or bigger for a boat application so I have not included it here)
so heres the run down ... if you want a boat to do a reasonable speed.. start of with an outrunner motor ( inrunners are junk for anything but racing boats) so u want a motor that can do 9,000rpm and you want to run it on a 2S lipo (Mha dose not matter its just a capacity size) this set of equsions are based on a 2s lipo but can be swapped for a NHMI battery is the outrunner is using a 30 amp or less ESC...
1200 Kv motor x 7.4v = 8,880 RPM
1500KV motor x 7.4 = 10,800 RPM
Running a 3S lipo ..
1000 KV motor x 11.1V = 11,100 RPM
850 KV motor x 11.1v = 9,435 RPM
these show you what size motors you should be looking at for reasonable speeds for a fast boat.
If you want to go slower you just get a smaller KV motor.
There are many physical sizes of motors from 28mm up to whopping 60mm can sizes you will be looking for your boat projects motors in the 28 up to 35mm can sizes which a 28mm can sized motor is similar to a 400 sized brushed motor and a 35mm can sized brushless is the equivalent for a 540-600 sized brushed motor, remember this is a SIZE only not an RPM match.
Any question feel free to ask but that covers a lot of the basics.
if you want take a look at some of my personal build logs for other info on brushless setups.https://www.thercmodelboatforum.com/t876-aero-naut-classic
this one shows the use of a brushed 400 motor and swapping out to an equivalent sized brushless (28mm can) and running on a 7.2v NHMI batteryhttps://www.thercmodelboatforum.com/t1044-aero-naut-jenny
This is my current build and shows a direct build around a 35mm brushless motor and a 35amp esc running on a 3s lipo
you can also look around some of my other info on the forum at brushless info just use the search function.