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As for propulsion that was and is most definitely a major issue and more likely than not would of had to be imported. So what?
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Question:
Am I wrong or it was the great difficulties in importing the French high-power diesel engines and gearboxes that greatly postponed the completion of the works at Jamaran 76, Damavand 77 and probably also at Dena 75 (this remained for even longer in the shipyard) , and for these reasons later we opted for a scheme with 4 diesel engines but with lower unit power, as they are more easily available abroad (see the Caterpillar installed on the Sahand 74) and with the expectation of implementing Iranian design.
Precisely the absence or difficulty in finding high-powered diesel engines or adequate gas turbines, which certainly postponed the construction of heavy destroyers.
Therefore I think that making the hull and equipping it with all the electronic and armament systems was not and is not a problem for Iran, but if you do not already have an adequate engine system available you would risk putting a lame elephant into the sea, therefore it would be it is useless to start building it, also because the experience in the nautical sector, the innovation in systems and armaments make great strides quickly
Therefore it would not be profitable to build a ship with the intention of completing it when and if I have the adequate engine equipment at home, it would risk becoming obsolete even before entering the fleet.
Such the Dena 75, a ship begun to be built before the Sahand 74 but completed later and which evidently shows an old conception of the superstructures and probably in the realization of some internal compartments of the hull.
The class of these frigates cannot be considered unique, but each ship is a prototype that implements improvements deriving from the experience accumulated in the construction method, from the experience gained in the operational use of the ships built, from the nefarious results from the loss of Damavand, from testing different electronic systems and where and how to install some weapon systems and finally the implementation of the new 30mm CIWS or future VLS.
Therefore I think that the practice of small steps is correct, since all these experiences, have certainly led to significant changes to the heavy destroyer project and future naval units.