S1 Duty vs S2 Duty Motor

If the customer is sure the duty cycle requirement will never change, then the S2 will meet revised spec, but a written document noting the change in motor spec must be signed by the recipient accepting the limited use as acceptable...

If I specified an S1 motor in a request for proposal, and the successful low price offerer supplied (or proposed to supply) an S2 motor I would:

1) Issue a Certificate of Non-compliance with specification, accepting the substitute. This will be considered if the dollar amount of price deduction for accepting the non-compliant motor is deemed sufficient.

2) Reject the non-compliant motor. Provide as specified or default your purchase agreement.

Too late to edit.

A specification is a minimum acceptable standard. A proposed substitution of a higher standard will seldom be rejected; a proposal to supply a lower standard item will generally be rejected unless accompanied by a very good reason why it should be accepted.

...which is why some sort of document accepting the change should be obtained prior to purchase and filed with the rest of the project documentation.

If the crane operates for less than half an hour once every five hours: is it worth asking the question "Why did the original S1 engine fail?"

S2 is for short time duty. The run time is so short that the motor would not have reached its equilibrium temperature and the rest period following the stop is so long that the motor will cool down to ambient temperature.

I don't thing crane duty fits in above definition for short time duty. It is appropriate to insist compliance with the specification, I suppose.

Just to understand S2 duty better, the following listed applications from Google:

• Applications S2 duty motors are used in applications such as operating lock gates, sirens, windlasses, and capstans.

If I was the buyer in this case, I would be asking myself why is the supplier not offering the specified S1 Motor in the first place ?
Why is he offering a lower class Motor that does not meet the required Specification??
Also the specs require a motor rated for S1 continuous duty. So what would happen if the Davit Crane needed to operate for a number of hours instead of a short time frame?
And why was a S1 motor specified if a S2 is able to do the work required ? Over- engineered or is a S1 needed ?