Preliminary Design Propulsion Efficiency

Hello everyone,

I am struggling with one question considering small power boat design (up to 24m, planing hull) in concept and preliminary stage. That is how to estimate total propulsion efficiency when working on new design? I have found some average values around the internet but I am not sure how correct they are. Please share your experience for following propulsion types:

- Inboard engine - direct drive
- Inboard engine - V drive
- Outboard Engine
- Jet propulsion
- Sterndrives (Inboard/Outboard)
- Surface drives
- IPS (pod drives)

Do you have any idea where to find this info in literature?

Thank you a lot.

Best,

Tom

 

For the fist two I'd be buying Gerrs propeller handbook, on a close couple zf style iv drive they could probably give a modifier to inline gearbox numbers. Guessing it's minimal and a wash in significant figures.

Outboards I'll defer to others as my use of outboards is very atypical and as such might be bad advice.

Jets are usually setup with manufacturer suppliers data. Although the quality of that data is up for a lively debate. Dinner last Tuesday with a bunch of jet users and we were trying to decide who hit the actual numbers from the mfg supplied data. Varied across the spectrum with Hamilton getting pretty close, and ultra jet being good across certain models but off on others.

A pair of jets for even a light 24m boat is going to range from 100-150k, while the jet companies want to sell you something they also want it to work and you be a happy customer. I'm my experience they were best source of sizing and Performance data as well as a source for a jet specializing n/a.

Would think the next three would have manufacturer specific data as well.

 

The Total propulsive efficiency, or PC, is made up of many variables.
The list you give below, is just one of the inputs.

Since it is made up of: appendage coefficients (if any), hull efficiency, propeller efficiency (in open water v Va), relative rotative efficiency and the shaft efficiency.

All these coefficients yeild a final PC.
Depending upon the vessel and speed, PCs can range from 0.25 - 0.75.
But as a starter, one can use 0.5, if a conventional hull form with a prop drive.

 

I would use 0.5-0.55 for fast craft, and 0.6 for some slow speed craft with propellers.