Well, yes and yes, but...
Perhaps, first l must point out that l am writing about cruising boats, my reflections got nothing to do with racing craft or cats of any sort.
If one is sailing on a sea-cow where sails are almost just for decor the difference could be less indeed, compared to a yare boat where sailing performance is more important than speed and performance under engine power.
I remember sailing on a friends boat, a sea-cow, with full keel and keel-hung rudder, which was impossible to drive into a pen against the prop walk with a folding prop. After changing the prop, the three blade solid prop was able to do the job, just, but still, not against current or wind. It had to be driven into the pen from the opposite side using the boat's characteristics to one's advantage. The boat's sailing performance was not much to write home about but stronger the wind blew the old tub came more and more to life. Please, do not miss my point, l am not bagging boats with hulls like a dutch herringbuss, just trying to make the differences obvious.
On my Adams 28 which is a yare boat with fin keel and transom hung rudder with skeg, the twin folding prop does the job amicably all the time, every time.
As the prop walk is minimal and the skeg and rudder combination helps the twin Gori prop perform very well.
The difference between folded and open prop was approx. .2-.3 knots on calm waters in 12 knots wind. The clean hull also helped the performance.
On the other hand, the R27 which we sail the shoal draught keel and solid three blade prop works just fine in marinas considering a slight prop walk. The vessels age and sailing performance does not warrant a prop change. It would do marginally better with a three blade folding Gori or such, but the costs would not be acceptable.
It is sailing l am writing about and so, l am not considering fuel consumption at all. As l usually sail off and on to my mooring and l start the engine just as a back-up fuel consumption is negigable and not in the picture. It would be around 1,2L/hour for the 7.8Kw twin cylinder Vetus.
The verdict is open, the jury is still considering, however, if only the best would do, in my opinion, the least desirable is the solid two or three blade option while the three blade folding option is the most versatile available for a cruiser.
