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if you guys would join the Atlantik Pirat forums you would find probably the best of the information on the planet covering the Schnellbooten, units, personell and the Boots plus bases, etc. we are a pretty tight bunch over there and known experience is pretty intensive and high. Truly there was nothing close to these Boots in speed and agility and yes overall size was such with larger engines and arms/crew.
The SGBs ended up being fairly useful despite their being very vulnerable to gunfire. What I found interesting is that one, SGB9(Grey Goose) of may be still afloat, as a houseboat near Hoo St Werburgh (although that datum is from wikipedia, so I'm taking it was a few grains of salt)
Acceleration may have changed with the armor. I wonder if they were very quite?
The Blockade runners used Diesel engines, which gave much trouble.
I have seriously my doubts, that such an engine could be developed out of the blue and have not seen till now, any equal allied high speed (rpm) diesel engine from this timeline (WWII).
More important a diesel engine with this power to weight ratio and compactness.
.I think this engine is one of the main reasons of the success of the S-Boats
I think the largest and most advanced advantage of the S-Boats, next to the Lürssen effect and their high speed at rough seas, were the engines of the S-Boats.
The MB 501/518 diesel engines were developed out of the Luftschiffmotors LOF 6/DB 602 engine of the Zeppelin Hindenburg beginning of the 1930 years and were action ready 1935. This engine class was State of the Art till 1965 and was the cutting edge over 30 years. The last german S-Boat class with this original further developed MB 518 engine was the Zobel class from 1962/63 which were in service till 1983/84.
I think this engine is one of the main reasons of the success of the S-Boats.
Also this engine was exported in over 35 countrys after the war and even the USA bought this engine.