Uniflite gas tank capacity

[Takoradi]

I have an '84 Uniflite 42 with twin Crusaders. The factory manual says that she has 350 gallon fuel capacity in 3 tanks, aft, port, & starboard. After crawling around the engine room for a few hours yesterday and measuring the 2 main tanks, she appears to have a much larger capacity. Without even including the aft tank which is much smaller than the others, it appears I have 250 gallons in each side tank which puts me over 500 gallon capacity. They are aluminum and angled at the bottom to match the hull and I measured 3 times.

The outboard tanks are 60" long, 32" wide, 33" tall on the taller inboard side and 27" tall on the shorter outboard side. I calculated 57,600 cubic inches volume, divided that by 231 cubic inches per gallon of gas and got 249.4 gallons.

This boat was built to spec by the original owner I purchased from so perhaps he had larger tanks installed but I'd think that would be reflected in the hand written capacities in the manual.

Questions:

1 Would someone please check my volume calculations?

2 Do any other '80's Uniflite gasser owners have an accurate fuel tank capacity measurement and/or have gone thru the same exercise?

Thanks for the help,

Tak
Pics are the spec sheet and a couple of the tanks. Hard to see the angled bottom but they're there. All the pics but the bottom one are rotated 90 degrees counterclockwise.

 

[OldDan1943]

Do the tanks conform to the outboard hull shape?
That could make the calculations.
The best way is to empty one of the main tanks then, fill it at the pump, noting the # of gals. You will have determined the volume of the 2 tanks. Per the 3rd tank, tank, when you empty that tank refill it, noting the volume.
Do you have an some sort of tank minder?
OR
For the time being assume your calculations are reasonably correct.
1 gal = 231 cubic inches
1 gal = 6.3 pounds

 

[Takoradi]

Thanks Dan. The tanks were partially full when I bought the boat and just filled them so it’ll be a while before I can use that method unfortunately.

I can’t see if they conform to hull shape. Assuming they do not because if they did it would increase the capacity further.

Tak

 

[C lectric]

Which model, the aft cabin model or the sports fisherman.? May be different tankage between the two which did not show up in your info.

By your measurements I arrive at 249.35 gal per tank

I used 27H x 60L x 32W = 51,840 cu. in. for the main body less the angle at the bottom.

Then the angled bottom 6 x 60 x 32 / 2 = 5760 cu.in.

Then 51840 + 5760 = 57,600 cu. in.

Then 57,600 / 231 = 249.35 USG per tank


What might goof things up a bit is the outboard sides of the tank and the bottom do not maintain the width or the depth but taper where you cannot see or measure. I would not think though that would account for 150 gal.



As suggested best is to run one tank empty and then refill it. Could be done untill one engine stalls from lack of fuel assuming each engine is fed by one tank. THis method would need any crossover to be shut off or it won't work.

OR

By running down both tanks to less than half and then pump one tank into the other to empty. Then once one is empty go fill it.

Just be carefull with the last when pumping.

I have done that with my diesel tanks but gasoline would need far greater caution. And no I am not getting into the great debate, just being cautious.

 

[MYTraveler]

I allowed 1/4" for material thickness and came up with 240 gallons. It would really surprise me Uniflite made that boat with only 350 gallons total fuel capacity.

 

[tiltrider1]

I do not know what uniflite did for tanks in the 80’s. In the seventies they installed 2 outboard tanks each with a capacity of 200 gallons. In the stern, in the bilge space they would install 3 tanks that were connected that jointly had a 75 gallon capacity. The stern tanks had about a 15year life due to its poor location. When new these boats had a 475 gallon capacity.

 

[Comodave]

I would guess that the original owner had bigger tanks installed. Do they have a certificate of manufacture on them?

 

[C lectric]

I did not allow for wall thickness. Thought later I should have but I thought it really did not matter for this purpose.

 

[tiltrider1]

Uniflite tanks are made from 3/8 “ thick aluminum and fully baffled. After you account for this you end up in the neighborhood of 210 gallons which sounds about right. Out of the 210 capacity 200 is usable in normal operating trim.

 

[rslifkin]

Based on the math here, I'd say you've definitely got more than 350 gallons total, likely 400 - 500 in just the side tanks. Hard to say just how much without draining and filling a tank to confirm (and figuring out how big the 3rd tank is).

 

[OldDan1943]

Are all the tanks inter connected?
Can you isolate a tank?
Do you have a reasonably accurate 'tank minder'?

The aft tank is the smallest? Draw down the aft tank, refill it from one of the outboard tanks. Make note on the outboard tank level when you fill up the aft tank.
You should have determined the aft tank capacity. Isolate the aft tank, for now.
Make note of the outboard tank you used to fill the aft tank.....
Now until you draw down both of the outboard tanks.... you can only guess.
When you get both outboard tanks down to 1/2.... start the calibration again, pumping the contents of one outboard tanks, filling the other totally. Refill the empty tank at a fuel dock, writing down the #of gallons it took to refill the tank.

 

[Takoradi]

Thanks C. Good to know my calculations make sense. That's what I got for capacity. 500 + the aft tank makes me much happier on range, the one thing I didn't like about the boat.

Tak

 

[Takoradi]

None that I could find Dave. Where would I find the certificate? Are they actually on the tank like GM used to do? They'd put the build sheet for the car on top of the gas tank and then install it, figuring the only people needing to see it were people rebuilding the car and taking out the tank!

There are some hand scribbles on the end of each tank but I can't decipher them.

Tak

 

[Takoradi]

Tanks are interconnected but no tank minder. Without an explosion proof pump of some sort I'm not sure how I'd go about moving fuel around.

Tak

 

[Takoradi]

C, I know you're diesel but did you use a manual pump? If I go that direction, I'm thinking I'd use a manual pump on the cockpit with hoses to the saddle tanks.

Tak

 

[Takoradi]

Tiltrider,

The aft tank is a single but pretty small. 8" wide by 26" long and I have to get under the aft cabin mattress to find the height. Interesting. Who would think 3 small separate tanks were a good idea? These tanks appear pristine with the exception of the port tank which looks in great shape but the sender is kaput and I don't do yoga well enough to replace it.

 

[Takoradi]

Tiltrider, I forgot all about the baffles!

 

[Takoradi]

Thank you everyone. That's the reality check I needed. Again.

Tak

 

[C lectric]

I really ran the tanks down going into the winter. I have a small fuel transfer pump, electric and used that.
THere are electric pumps that are rated for gasoline such as I think Conelec.

But a manual would definitely be safer.

With the calculations and Tiltrider's knowledge I suspect you would be good with what he suggested.
Even when I considered the tank wall I did not expect 3/8. And of course I didn't consider baffles. I doubt the baffles will account for much , maybe a gallon or two.
You could recalculate allowing for that and the baffles.

THen just run it down and then run untill one engine quits. Then refill and that should give you what you need.

 

[sbman]

None that I could find Dave. Where would I find the certificate? Are they actually on the tank like GM used to do? They'd put the build sheet for the car on top of the gas tank and then install it, figuring the only people needing to see it were people rebuilding the car and taking out the tank!

There are some hand scribbles on the end of each tank but I can't decipher them.

Tak

My Uniflite is a bit older and diesel, but the saddle tanks don't seem to have any build plate, just the sharpie written scribbles as you have found. Mine refer to the boat model the tank was made for. I've seen all sides of side tanks except the one against the hull and the bottom. There's nothing that I can find on the tops.

The aft tanks, if bilge mounted were known for leaking if you ever get any splashing of seawater around the bottom of the tank. My aft tank leaks and I'm decommissioning it for now.

My diesel three tank system has a transfer/prime pump to pump fuel around. I don't think it's hard to find explosion proof gasoline compatible pumps.

 

[Comodave]

None that I could find Dave. Where would I find the certificate? Are they actually on the tank like GM used to do? They'd put the build sheet for the car on top of the gas tank and then install it, figuring the only people needing to see it were people rebuilding the car and taking out the tank!

There are some hand scribbles on the end of each tank but I can't decipher them.

Tak

Maybe yours was built before the label for the certification was required. Not sure what the date for the labels was. The photo of the label didn’t copy with the text but you will get the idea. Even my diesel tanks from 1987 have the label.



Fuel Tank Labels: 33 CFR 183.514 Gasoline fuel tanks for boats must have a label certifying that they have been subjected to a Static Pressure Test (see Fuel Systems https://newboatbuilders.com/pages/fuel.html) The label looks like this:

Fuel Tank Label
It doesn't have to look exactly like this but must contain the information seen on this label. That required information is:

Manufacturers Name and address:

Month and Year of Manufacture

Capacity in US gallons

Material of Construction

Pressure the tank is designed to withstand without leaking

Model number is applicable

The statement: This tank has been tested under 33 CFR 183.510(a)

If the tank is tested under §183.584 at less than 25g vertical accelerations the statement, Must be installed aft of the boat's half length."