Bom Dia JC and welcome to Cruiser's Forum.
Not necessary to apologize. I am certain that your English
is much better than my Portuguese.
I think you are asking about a hot water heater or calentador in Spanish. I think Portuguese for this may be aquecedor de água?
In the USA these are available from marine
supply stores. There are models that heat water by propane
gas, electricity or from the cooling
water system. Some models will work with engine
and gas or engine
They come in many sizes, starting around 5 gallons and go as large as you would want.
Here is a link for some. I apologize if I misunderstand and you are asking for something different. If I am wrong perhaps post a photograph.
Defender.com Search Results: hot water heater