A photo of the Varunastra HWT from late 2021:
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A photo of Varunastra HWT from mid-2023:
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The 2021 photo shows 2 rows of 6-bladed contra-rotating open screw type propulsion set up. The newer photo shows a pumpjet propulsion set up. Finally, they have managed to make the transition towards a pumpjet. It seems the recent torpedo test was conducted to verify this propulsion set up.
DRDO's 1st HWT project was the Shakti thermal torpedo project which would have had a 400-500 KW power & would run at 55-60 knots.
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As with many ab-initio projects, DRDO at that time failed to meet the Navy's QRs & this project was killed. But the tech developed for that project lives on.
It was DRDO's 1st attempt at making pumpjets & thus we got to see a lot of different configurations in terms of no. of blades, size/position of blades, blade geometry etc.
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At that time this was the configuration that they eventually settled on.
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The Varunastra is an electric torpedo as opposed to the Shakti. The Navy has decided against thermal torpedoes as they are prone to inadvertent detonation & can cause catastrophic damage in case of an accident.
The downside of this decision is that making a 400-500 KW battery for a torpedo is not an easy task. The current Ag-O-Zn battery is rated 250 KW & is being upgraded to 300 KW. Even with a 300 KW battery, the 1.5-ton Varunastra HWT can't be propelled faster than 48-50 knots. It would be equivalent to the French F21 torpedo but still somewhat inferior to the Mark 48 torpedo.
Still there are advantages the pumpjet will bring. Reduced acoustic signature, higher range & speed, increased maximum operating depth. But to fully exploit the advantages of the pumpjet the battery has to be at least 400 KW. That would bring the Varunastra on par with the Mark 48 in performance.
Also good on the Navy for purchasing 130+ torpedoes before all the incremental improvements came about. The Navy wanted a F21 equivalent but settled for something inferior for the time being. This provided the DRDO time, funding & user feedback to continue development of the torpedo. This is how projects need to be run.