plastic diesel tanks in mobos, where is the outlet best located

[simonfraser]

lowest point to remove any water, asap ?

if higher up, would it make sense to have a second take off point to remove any water / crud ?

 

[Tranona]

ost common now is to have the take off from the top mounted in a removable inspection hatch which you can remove to clean the tank. See the Tek Tanks or Vetus sites for examples. Bottom take offs are not now common because tanks are usually mounted close to the hull bottom and there is no room for any type of removable drain. Much more important to have a good filter system and access for cleaning from the top.

 

[NormanS]

An ideal tank is shaped so that the area of its bottom is quite small. That way, any dirt or water accumulates in a small area, and is not stirred up by the movement of the boat. It is greatly improved if there is also a small sump incorporated in the base of the tank, ideally with a means of draining off any dirt or water.

Unfortunately, many installation make this drain impracticable. The next best is to still have the shaped tank and the sump, but access it from an inspection hatch on the top.

I am told that connections on plastic tanks are less reliable than on metal tanks, so you probably are better with the second option if your tank is plastic.

 

[gordmac]

ost common now is to have the take off from the top mounted in a removable inspection hatch which you can remove to clean the tank. See the Tek Tanks or Vetus sites for examples. Bottom take offs are not now common because tanks are usually mounted close to the hull bottom and there is no room for any type of removable drain. Much more important to have a good filter system and access for cleaning from the top.

That is the way mine are.

 

[GrahamHR]

That is the way mine are.

A simple question. Not meant to ignite any fierce discussions about petrol vs diesel etc

How does water get into motorboat diesel tanks, but i t doesn't get into motorboat petrol fuel tanks ?

 

[superheat6k]

A simple question. Not meant to ignite any fierce discussions about petrol vs diesel etc

How does water get into motorboat diesel tanks, but i t doesn't get into motorboat petrol fuel tanks ?

The most common point of entry is from poor quality O ring seals around deck fillers. Keep the threads well greased, and the O rings fresh. Condensation within part filled tanks has been thoroughly de-bunked as allowing any more than at most a couple of teaspoonfuls over a winter.

 

[gordmac]

A simple question. Not meant to ignite any fierce discussions about petrol vs diesel etc

How does water get into motorboat diesel tanks, but i t doesn't get into motorboat petrol fuel tanks ?

I would think it gets in to petrol tanks as much as diesel tanks. Petrol (or petrol engines) is probably a bit more tolerant of water and I suspect petrol vs diesel consumption means the fuel is used so the tank is cycled more if you like.

 

[NormanS]

A simple question. Not meant to ignite any fierce discussions about petrol vs diesel etc

How does water get into motorboat diesel tanks, but i t doesn't get into motorboat petrol fuel tanks ?

I have large tanks, and don't need to fill very often, but I do notice that every time I unscrew the flush deck caps, there is condensation on them. A possible source?

 

[GrahamHR]

I have large tanks, and don't need to fill very often, but I do notice that every time I unscrew the flush deck caps, there is condensation on them. A possible source?

Thanks for the insights re water ingress into diesel tanks. Maybe a simple self indicating silica gel or molecular sieve drier on the filler/ tank vent would prevent water getting in ?

 

[Billy Blue]

The most common point of entry is from poor quality O ring seals around deck fillers. Keep the threads well greased, and the O rings fresh. Condensation within part filled tanks has been thoroughly de-bunked as allowing any more than at most a couple of teaspoonfuls over a winter.

That's very interesting about condensation, I wasn't aware of that. Were tests done and if so, is there a report somewhere to read? Is it considered so minimal that you don't need to bother about keeping tanks full or is it still a good policy?