Carl Schwamberger wrote: ↑
20 Feb 2021 03:40
I failed to see anything about cavitation in the linked article. Did you link the item you intended?
My mistake, an earlier article in that series mentions Iowa's propeller cavitation if spun up to 70k HP per shaft. http://www.navweaps.com/index_tech/tech-029.php
That's still far short of the 82.5k HP/shaft for the fast Montana's designs at 4 shafts. Even at five shafts (were that possible on 13 feet more beam - Iowa's props were on average 17.6ft diameter), that's 64k HP/shaft.
As the originally-linked article notes, the previous article far overstates the Iowa's speed capabilities. I.e. it's likely that cavitation was already taking a big bite from effective HP as the ship exceeded 31 knots at the 55.6k tons average trial displacement.
As the more recent article notes, extrapolating BB62's speed and HP cubically from its 1985 trial max HP to its listed max HP of 225k HP would yield 31.95kn.
If we look at the HP/Speed curves for that trial, however, we can see that New Jersey was already far exceeding cubic escalation of HP with speed to get to 31kn.
The curve only gets steeper as speed-length ratio increases; it's unlikely that Iowas could get much above 31kn at 225k HP.
There's other support
for Iowa's hitting a cavitation wall:
Early on in the pursuit of speed, it became apparent that propeller cavitation (7) was the
single-most important consideration at speeds in excess of 30 knots. Propeller design, therefore,
took on new meaning and importance if speed was going to be sought after. When cavitation
occurs, the propeller efficiency falls off drastically and propeller damage could result. Model
tests proved ineffective in the prediction of high speed propeller cavitation (Raven, Feiler, and
Sorry about the misrecalled link... Anyway, it seems impossible to have designed a fast Montana under the design's specifications even with 5 props.