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So I just bought this 1990 boston whaler 25 walkaround wide body with whaler drive(actually have 2 of them now)Has twin 1997 yamaha 225 ox66 that run perfect. They have 4 blade 14x19p props on it. Top speed was 37 mph at 5100 rpms. Lots of cavitation with these props. Can't trim up because of cavitation. Cavitates when trying to plane too. Previous owner said he bought it new and only used it to putt up and down the river with his grandchildren. Never ran it over 25 mph. I can believe that cause the boat was setup for low speed cruising sort of. trim tabs stuck in full down position, and huge whale tails bolted to the lower units. Was able to get the trim tabs up and removed whale tails before test.
There was a boat test article back in 1989 for this exact boat. But they were running 200hp yamahas said the boat easily broke the 50 knot barrier. I find that hard to believe for such a big heavy boat.
There was a boat test article back in 1989 for this exact boat. But they were running 200hp Yamahas said the boat easily broke the 50 knot barrier.
That is total baloney. There is no way a 25 Walkaround can run 50 knots (57.5 MPH) with only 200s. I would expect no more than 45-46 MPH with those motors.
With twin Yamaha OX66 225s, i'd expect a top speed of about 48 MPH (42 knots) if everything were in good tune and the motor were set up well with good props.
What 14" x 19" four blade propeller are on there now? If they are Mercury Offshore/VenSuras, that is your problem right there. They are TERRIBLE for applications like this.
I'd try a pair of 14-5/8" x 19" Mercury Revolution4s and see what it really does.
That is interesting. When I seatrialed my 1989 Whaler 27 FC up in Wisconsin before I bought it and moved it here to TX, I actually saw on the GPS 44mph. This huge boat had those 1989 Yamaha 200's on it with 3-blade Yamaha Saltwater series 2, (I think), props
. After repowering the boat due to the existing engines age alone, (they were still performing perfectly), with the new Yamaha 300 four strokes, and using Mercury Revolution 4 props, I can't get over 50 mph with the increase of 100 hp on each engine. That's a total of 200 hp increase in power netting me only 6mph!
I don't know what Yamaha had going on with those old 200 hp 2-strokes, but those engines were beasts! I would not immediately discount that article you remember, I would try putting 3-blade Yamaha saltwater series 2, 17 pitch props on those engines to find out what they can REALLY do. This is from actual experience, not calculations.
I would definitely use a 17 pitch prop, not a 19 pitch. The one you are using now is not allowing that engine to turn enough rpm's, and it is a 19 pitch.
I don't think you will hit 50 knots either, but you just might hit 50 mph!
Both the original props are pictured on my personal page, last 2 pics.
I don't know what kind of props they are. Just know they are 4 blades. Will look when I get off work. My other 25 walkaround(identical boat) has twin 175 evinrudes that have 14.50x17p 3 blade props. Have not had that boat in the water yet. Have loads of Fiberglass work and electrical work to do on it. But if that boat can run 17's I would think the 225's could turn a 3 blade 19.
