Ask your vendors.

BB are usually multi stage major pumps of probably 250kW or more and high pressure high flow units.

Each vendor will have different model ranges which have different ranges of flow and pressure.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

I would request proposals from a couple of different manufacturers. They may be incentivized to offer overhung options in order to be the low cost bid. I might go back and request proposals for between bearing double suction based on the NPSH margin (< 5 feet), Suction Specific Speed (>13,000) or Suction Energy (>240 x 10⁶). A large, low rpm, between bearings pump would improve all three of those parameters. Then I would balance the higher installation cost and higher energy costs against better reliability and availability.

Johnny Pellin

Low maintenance is nice when offshore.
Otherwise you don't give much information to decide between them.
Do you have a specific application in mind, or are you trying to frame a general rule of thumb?

What does your company guideline for selecting off-shore pumps tell you ?

You, know .... the one that your company developed at its own expense to guide newbie engineers like yourself...

I am sure that you do not have to rely upon tribal knowledge or vague memories of things "that an older engineer once told me years ago"

What ???... !!! No in-house guideline ? .... Are you relying on old CHEVRON or EXXON guides that you found on the internet

More details please ....

There are many other choices to be made when specifying pumps

What is your pumped liquid, Design temperatures and Pressures etc....????

MJCronin
Sr. Process Engineer

I'm trying to do a general rule and maybe a general spreedsheet

Bearing configuration is selected by the pump designer to limit the effects of deflection and critical speed of the shaft and impeller. As the details of that subject are well above my pay grade, these links will better explain what you need to know than can I. Bearings on both ends of the shaft are far superior to controlling maximum deflection on the longer shaft pumps and that configuration must be selected when deflections of an overhanging impeller are too large, which might cause impeller contact with the casing.

https://roymech.org/Useful_Tables/Drive/Shaft_Crit...

http://sandv.com/downloads/0505swan.pdf

It's horses for courses, what flowrates and heads are required, 10 gpm at 50 ft or 1000gpm 250ft. There is no rule of thumb, it's always (or should be) a considered engineering review,

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)