Fastest means of organising preflood from surfaced condition?
 

Hi,

Not that it's a manoeuvre I care for much, but some skippers like to proceed on the surface in a preflooded condition (13m3 in forward ballast, 5m3 in aft ballast). I've been practicing various methods to strike the right balance between speed of attaining the pre-flood, and accuracy in terms of nailing the required values.

I've found that blowing the negative ballast to 2m3, then opening forward MBT, and moving to close the valve as it passes 10m3 seems fine, with a very slight blow required of the forward MBT if one over-shoots the 13m3. The aft MBT valve is opened and closed for 1 second to achieve 5m3. (with practice). The negative tank is then fully blown.

I try to do the preflood using the e-motor and then readopt the diesels to prevent accidental flooding of the diesels.

Has anyone found an easier/better or more rapid method? There's so many possible permutations possible. It's not a manoeuvre I like because it's awkward, (from surfaced) risks making noise, uses air etc. On the plus side you sink like a stone if a crash dive or PD is required.

1.Open front MBT (recommend already flooded negative)
2.keep it open so you flood around ~20m3
3. Blow out forward MBT water until 18.5m3
4. blow out negative tank to 0m3
5.replenish compressed air.

Many thanks indeed, I'll give that a go!

Did that in the Frost game tonight and it worked well. The only aspect I need to practice is not greatly overshooting the 18.5m3, so getting the instant when you need to move to the forward MBT valve seems pretty critical. I'll practice that over the coming days. It does seem a little inefficient as you still need to reflood the negative. Pre-flooding to 14.0 max on the forward MBT and keeping the negative tank flooded, would mean you can go straight on the 'planes instead of having to reflood the negative. I suspect that it'll be a touch faster?

if you choose to use 14.0m3 in the front MBT and keep the negative it will add unneeded steps when diving and consume a bit of compressed air.

As you have to, blow out the negative once submerged forcing you away from the dive planes, and you need th use compressed air to blow out the negative.

Easier to put all 18.5m3 in the front only. if you overflood, it is fine, just clear it to the appropriate level with the air vent, as described in the list above.

if you already are submerged, you dont need to blow all air out, just blow both tanks to 9.25m3 as that makes 18.5 if you add it up. It cost less air to blow it to 9.25 instead of blowing them both to 0.0m3

just to be clear. it is not critical to shut the forward MBT exact, intentionally get it more, and then use the MBT air valve for the fine adjustment to 18.5

you only need to do this in the first pre-flood of the game. when the negative is already flooded. then purge it once the ballast is at 18.5. do not keep the negative flooded and then 18.5 unless you want the boat to loose speed

Here's how I do it:

-With the neg flooded, open the rear MBT until it reaches 5m^3 then close it. Blow down the rear MBT if needed so that the tank is at 5^3

-Blow out the neg until it is empty.

-Open the forward MBT and watch the gauge until it reaches 10m^3 then close it.

-Top off your air supply.

The end result should be 15m^3 in the forward MBT, 5m^3 in the rear MBT and 0 in the neg.

There is no effect to the boat's top speed or acceleration as long as the combined total of all tanks(MTBs/Trim/Neg) and bilge are under 27m^3

When a dive is called for, open the forward MBT, set the front dive plane full down, leave the rear at 0, then open the rear MBT. Return to the dive planes and arrest the dive by setting both dive planes to 0.

You'll sink like a rock and use 0 air in the process, but make sure your engines have kicked over to electric first though, otherwise you'll flood the engines.

That's more or less how I'd been taught to do it to start with, but have been playing with other permutations. Thanks to you both for the views

Will give this a go :-)
However you are referring once to 10m3 in forward MBT and then 15m3 in forward MBT.
Typo or I'm confused somehow?..


Cheers,
Lost

It's not a typo. Wait until the gauge reads 10m^3, then go close it. By the time you walk over and close the forward MBT vents, you will end up with 15m^3 in the tank

Oh, I see !
Thx for the clarification.

Cheers,
Lost

I've been testing this a lot, and it's a neat and easy solution, and more importantly performs well. How viable it is when hull-valves come into play remains to be seen. I'd be interested to hear tester's views on this aspect?

For now, I'd advise moving to close the forward MBT valve at 9m3 rather than ten, as I find myself at typical trim values, having to slightly blow the MBT's in order for the boat to maintain 18kts. Not that am I ever thrilled to be asked to do it.

Thanks to all who contributed!