Lnking to give a latest start date

[DavidC]

I have a project with three interfacing contractors. One has plenty of
slack, but their last task (T1) must be complete x days before the start of
another contractors task (call it T2). The task T1 cannot limit the start of
T2 though. What I wnat the programme to do is show the latest date that the
T1 task can start and still finish x days before T2. If T2 slips because of
reasons of that contractors own making, then T1 can move as well.

 

[JulieD]

Hi David

If i'm understanding you correctly you should be able to achieve what you
want using a Start / Finish relationship between these two with T2 as the
predecessor and T1 as the successor and the number of days needed between
the two as a lead (i.e. in the predecessor tab of T1 the line would read
T2 start-to-finish (SF) -xd

Hope this helps
Cheers
JulieD

 

[DavidC]

Hi,

Sorry about the delay in responding. I had tried that method but it wasn't
giving me the result I needed. Basically I was hoping that there was an
automatic method of moving a task forward until it reached the point where
it's finish date was constrained by the next task. The way I have now
resolved this is to use the predecessor as a SS-xdays where x days is the
length of time between the start and finish of the sequence of activities. A
bit cumbersome, especially if the next task slips or firms up and I will need
to manually adjust the lag value rather than have project adjust it
automatically.

 

[Steve House [MVP]]

Why would you need to adjust the lag value? You said you wanted to T1 to
occur at the latest date that would have it finish Xd before T2 starts and
it was the date of T2 that controlled the process. You set the link to FS
with T2 as the predecessor and T1 as the successor with a lag of -Xd. That
link would be the only link to T1. If T2 moves forward or back, T1 moves in
synch. No further manual adjustment necessary.

 

[DavidC]

I guess it must be the overall complexity of the plan I am doing.

I have basically seven units each having the essentially the same activities
and logic with the units being sequential. There are three different
contractors working on a unit. One contrator's (c1) work is such that it can
start at the start of the outage or any time up to a period where if the work
starts any later it would not finish no later than 3 weeks before the start
of another contractor's (c2) work on that unit.

Using the method described, leaves the start activity for C1's work at the
earliest possible start time, but if I change it to sart as late as possible
it then works back from the end of the project which can be six units away
and the start of C1's work for a unit ends up years away from where it should
be. The activity needs to start as late as possible in respect only of that
unit not the whole project.

Hence the reason why I have installed a 3 week lag behind the start of the
relevant activity for c2 on the unit, plus the overall duration of c1's work
to give me the latest start date. Where I would then need to modify the lag
is if on subsequent units the durations drop through efficiencies and better
processes then the start date for c1 could change accordingly and I would
then need to re do the duration of c1's work. Basically I want the start of
C2's activity to 'push' the last activity of c1 back 3 weeks from it's start,
and then all the previous activities for c1 would then 'push' back to give
the latest start date.

I am sure I have done it in Projectview, and I certainly used to do it on
tracing paper back in the seventies.

It could be done using each unit as a project plan in it's own right and
then creating a master submaster plan, but have had difficulties with that
method where the plan is on the clients server, but then download it to my
laptop and work on the plan from elsewhere then try to replace the plan back
on the server. Or the client changes the directory for parts of the plan.
either way the links get lost and confused, so I have settled for one plan
for all the units.

As I understand the process of assigning "As late as possible" on a task it
calculates the start date from the end of the project date and not from the
next task.

It has me baffled still. I did try as you suggested and in the predecessor
for T1 put T2FS-21d but that did not shift T2 forward, but rather left it
some weeks prior to the start of T1.

Regards

DavidC

 

[Steve House [MVP]]

You aren't reading my suggestion in its entirety. I'm saying T2 is the
*predecessor*, T1 the *sucessor* -- think of "predecessor" as meaning
"controlling" and "sucessor" as meaning "controlled." Most importantly the
link type is Start-to-Finish. NOT the statndard Finish-to-Start that you
have said you've tried. Start-to-Finish means that the Start time of T2
will link to and control the Finish Time of T1.

Your note below says the links you've tried are: T2 FS-21d T1.
I'm saying try: T2 SF-21d T1 Note that the order of F and S are reversed
in what I suggest versus what you say you tried. Leave the constraint at
the default "As Soon As Possible" for task T1. This will place T1 starting
as late as it can to have it finish 21 days prior to the start of T2.

I have to wonder, though, is there some reason T2 has to be the controlling
factor? Why not schedule T1 to start when the outage starts -- since you
said it can start then, why wait? Then have T2 linked from T1 FS with a 21
day lag time so that it starts 21 days after T1 finishes? Isn't that what
will happen if T1 takes longer than expected somehow? Won't T2 be pushed
back in that circumstance? The start dates for tasks are not the ends of
date ranges where task could start if the resource wished. They're better
looked on as the dates you have determined where the tasks SHOULD begin so
the project finishes on time and in budget, proactive rather than passive.
You don't the contractor he can start anytime after 01 Dec as long as he's
done by 15 Dec. You tell him the site is ready for him at 10am on the 3rd
of December and you'd like him there at that time with a backhoe to begin
digging a trench that should take him 2 days to finish. <grin>
--
Steve House [MVP]
MS Project Trainer/Consultant
Visit http://www.mvps.org/project/faqs.htm for the FAQs

 

[DavidC]

Thanks a heap.

The situation is a little complex with three contractors on site and under
differing Conditions of Contract. One contractors work i effectively
dictating the critical path, the contractor in question has so much float
that he can start at any time up to a point. The thing is though that he
cannot start any later than a date which will allow him to complete
installation, commissioning and we want three weeks lead in time just in case
there are some problems with the work and we have to bring in replaement
material from overseas. It is specialist cable work at 220kV so not the sort
of thing that we can get from the local wholesaler. The critical date is
that the gernerators are back running by the date dictated by the contractor
on the critical path and not the cable contractor. What we need to know
though is at what point in the schedule do we start panicing if the cable
contractor does not seem to be starting work. Also some of his staff are
coming literally from the other side of the world so he needs some
flexibility in getting those people here. All in all not really the straight
forward type of situation generally found. Interesting though. I also now
need to identify how many resources on site in total to see if they will all
fit in the on site accommodation. Your see the working site is a one hour
boat trip from 'civilisation', and it is a working station.

Anyway thank you very much again. I had forgotten that SF variant. You are
right to often the majority of links are FS or SS that the SF option can be
overlooked and my paradigms set in.
Regards

DavidC