Not sure if you're answering your post or someone elses. But if you read good guides of advice from marine pros like in Practical Sailor, they almost always conclude that it is not worth the increased drag of the additional blade & angle resistance of a 3 blade prop, compared to the marginal improvement in torque you might gain. The 3 blade does offer better power in reverse, not so much in forward. Only if you can afford a folding prop is it a good investment on a sailboat. But some of those props cost thousands, & are questionable when they are priced to 25% of the boats value! Your 25 Xp engine was the most powerful model that Catalina used. Even the early 36 footers used them. Remember that after all you're sailing a yacht, not a power boat. The engine was really designed to get her out & back from the marina, not motor all day. I have an engine half the size of yours on my C 30 that does just fine in most instances, with a 2 blade prop. Adding the extra blade also increases resistance on the old trans & engine, reduces the efficiency of the engine by effecting the optimal RPM range that its designed to run at, etc. These are the reasons for why I never changed my 2 blader. At the end of the day its a waste of money. That one extra blade could also cost you a knot of speed under sail. Not worth it in my opinion.
Easy to say in Virginia... Not every locations is a "get you out an into the marina"... In Maine or Seattle with the tides, currents and fickle winds it is not unheard of to put 100-120 hours on the iron genny in a season. Anyone who says a three blade does not make a marked improvement, well, I want what they are smoking...
On our own boats we have had four opportunities to physically compare two to three bladed props in the tides, currents and rivers of Maine. NO COMPARISON.....
We had a Cape Dory 27 the two blade prop was as useless as tits on a bull. Prop was sized correctly but still had very, very poor performance when needed. Switched to a three blade and could actually motor up a river against a tide. We could also back down on our anchor to set it. The three bladed prop made all the difference in the world.
We owned a Catalina 30 with Universal M3-20B. it had a two blade Martec. Again, in Maine, that prop was as useless at tits on a bull and vibrated like I had a jack hammer under the boat. She had less than what I would even consider "safe" powering ability with the Martec. I might as well have had a trolling motor pushing that 30 footer... Switched to a three blade Michigan Sailor and it was smooth as silk, had GOBS more power and the loss in sailing speed was barely noticeable. The pluses vastly outweighed riding in a vibrator and the lack of ability to move against a current when needed.
We owned a Catalina 36. It had the M-25 and the factory installed two blade. It SUCKED under power and we could barely make way against a tidal current. Would have been fine going into and out of a marina, but in Maine that is often not the case. Switched to a three blade and the boat was perfectly fine with the M-25 and, WOW, not under powered at all. Once again the three blade prop made a HUGE difference in powering performance and had minimal impact on sailing speeds..
We owned a brand new Catalina 310 and I was smart enough to order it from the factory with the three blade.
We now own a CS-36 and last season put on a brand new Flex-O-Fold two blade prop. Doh' what was I thinking......... IT SUCKED!!!!
We lost nearly all our backing power, forward speed was ok in flat water but could not compete it in any current. It vibrated so badly my WIFE made us get rid of it.... Went back to the three bladed Campbell Sailor and the boat powers, backs and is as smooth as silk with ZERO vibration. Again the speed differences under sail are barely noticeable, except when ghosting in very light winds.....
I'll take the hit of a three blade in Maine anyday of the week. Course I've already tried the two blade route, FOUR TIMES...... Some never learn
...Doh''''''
