Tank baffle spacing

[HankOnthewater]

I made quite a few tanks, or had alu tanks made (for my campervan). For boats I used mainly fiberglass, and fiberglass panels as baffles. I always used vinylesters as a resin. I have made a few of plywood covered in epoxy with woven glass fiber mats. As far as I know all these tanks still survive.

Generally I used maybe too many baffles, ie 300 mm or 1 ft spacing. Each baffle generally 6-8 mm thick with large openings each bottom corner ie 35-60 mm, and small openings at the top, either side, ie 5 to 10 mm. The bottom openings big enough and to push/pull through wire bottle-brush style cleaners. Ideally each baffled area to have an access hole in the top, but not always possible, hence the large openings in the bottom of the baffles.

My thoughts on the number of baffles was, and in no particular order :
- improves the rigidity of tank
- ability to stand/walk on tank, or put things on top
- reduces free surface effect

Although you did not mention how or where you are drawing your fuel from, I always (hmmmm, rather where possible) put a a small deeper section (ie 1 to 4 lt) where the water/diesel is drawn from. Therefore on a heeling boat, or a car on a incline, a near-empty fueltank still provides fluid to the suction point).

Secondly, this deeper section to have a drain (ideally with a metal flange/valve), so any crud/dirty water/fuel can be drained ie 1/2 liter each month. Not sure if such drain is legal in all countries.

[Emmalina]

I built some new 500L fuel tanks and put in 2 baffles Split it into 3 with a corner of each angle to allow flow probably 5% of the wall. Epoxy rather than steel as the old steel ones rusted up and leaked.

[GILow]

Originally Posted by Singularity

Your searching may have come across the following thread on a DIY diesel tank, but if not you might glean something from it: https://www.thehulltruth.com/boating...n-project.html

Very good article, had not come across that one in my travels so far.

Originally Posted by Singularity

Frankly the thought of using a core (wood or foam) in tank construction doesn't excite me...this is one case where I'd waste money and accept extra weight in making an all glass laminate. At the same time, the layup schedules we see are way strong for what they need to do. More important from my eye is the supporting structure allowing for zero movement/chafe potential...same with that about a bladder tank.

If the side/bottom of your water tank is the actual hull...I'm thinking that you have to be particularly concerned that your supporting structure has zero possible movement, lest you point load the heck out of the joint where the ~rest of your tank structure meets the hull.

I think I have to accept that the baffles should be solid fiberglass, but I am still happy using plywood to make the boxes themselves, at least for the fresh water tanks. Should be very easy to make them rigid this way, and at least I don't have to cater for any measurable hull flex.

[GILow]

Originally Posted by Karanga

I have 2 aluminium tanks that hold approximately 400 litres of water each, 1 tank in each hull. There are hull stringers, but no baffles. When they are about 85 to 100 % full, I get significant slapping.

Not good to hear, but thank you for the warning.

[GILow]

Originally Posted by Pete7

The baffles on our 30 Imp gallon water tank are only attached to the lid which makes the tank easier to clean when you take the lid off.

Interesting approach. I am hoping to straddle my baffles with two inspection ports on each tank, allowing me to install three baffles in total while still having full access for cleaning. (Long arms.)

[GILow]

Originally Posted by HankOnthewater

I made quite a few tanks, or had alu tanks made (for my campervan). For boats I used mainly fiberglass, and fiberglass panels as baffles. I always used vinylesters as a resin. I have made a few of plywood covered in epoxy with woven glass fiber mats. As far as I know all these tanks still survive.


Good to know. I am using vinylester over ply for the water tanks, and lining the keel area with vinylester for the diesel tank. For the keel tank I will make the top from solid fibreglass, the baffles are already in place, these are vinylester coated plywood, but they will get an extra three layers as part of the build.

Generally I used maybe too many baffles, ie 300 mm or 1 ft spacing. Each baffle generally 6-8 mm thick with large openings each bottom corner ie 35-60 mm, and small openings at the top, either side, ie 5 to 10 mm. The bottom openings big enough and to push/pull through wire bottle-brush style cleaners. Ideally each baffled area to have an access hole in the top, but not always possible, hence the large openings in the bottom of the baffles.

My thoughts on the number of baffles was, and in no particular order :
- improves the rigidity of tank
- ability to stand/walk on tank, or put things on top
- reduces free surface effect

See my previous remarks on baffles and inspection hatches, but I think I can make cleaning all of these tanks pretty simple. The diesel tank will be very deep, but easy to access.

Although you did not mention how or where you are drawing your fuel from, I always (hmmmm, rather where possible) put a a small deeper section (ie 1 to 4 lt) where the water/diesel is drawn from. Therefore on a heeling boat, or a car on a incline, a near-empty fueltank still provides fluid to the suction point).

Secondly, this deeper section to have a drain (ideally with a metal flange/valve), so any crud/dirty water/fuel can be drained ie 1/2 liter each month. Not sure if such drain is legal in all countries.

Fuel pickup will be from the bottom of the keel tank, so technically the top of the ballast. I may be able to fair in a bit of a V shape to the bottom before I line it with vinylester and CSM. I certainly need to do some fairing as it is quite lumpy and would be difficult to keep clean as it is.
The fuel tank is only for storage, I pump up to a 70 litre day tank for normal running.

The water tanks will have a lower corner brought about by the shape of the hull and how it meets the sides of the tank, my plan is to put the pickup tube in that corner. Hoping to avoid drains if I can, given they are a point of potential leakage, and would be very difficult to access. I may regret this, as you say, the ability to drain off crud is helpful. But the current tanks have remained very clean since I washed them out after the delivery trip, nearly seven years ago.

[JPA Cate]

Fwiw,

We had s/s tanks made for our previous boat in NZ. They were a little over 6 1/2 ft long, and each one had two baffles. I'm embarrassed to admit there were no cleaning ports.

I must say I like the idea of the removable lid with the baffles mounted to it. One rarely wants to clean the water tanks, but the ability to do it if needed is very appealing.

Our current tanks both have baffles, and cleaning ports.

[kapnd]

Here’s the design I’ve used to build many metal tanks, has worked well over the years, simple and cheap to make.