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Showing results for tags '4-blade'.
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I've had the Response LX for about 5 years. It came with a 4 bladed stainless prop on it, and has the 330HP Mercruiser black scorpion direct drive. The Mercruiser has a rev limiter at 5180 RPM, or thereabouts (it stutters around 5180, maybe it's 5200). We're running pretty hard into the rev limiter, I think we can hit it on about 3/4 throttle. We get 72kph (45mph) at the rev limiter with 1 person aboard, about half fuel, not much spare weight in the boat. It feels like we're giving up quite a bit of top speed there. I've looked at the prop and it doesn't have any clear identifying marks for size. It has J1102 stamped on the side of the hub (where the blade merges in), and arguably it might be O J1102, but not sure why there'd be a gap between the O and the J if it was an OJ prop. So maybe the O is something different. On the end of the hub I can see CUP written clearly, then maybe the edges of some numbers. I'll probably have to take the nut off to see what else it might say on there. We mostly water ski, sometimes wakeboard (we have a wedge), we don't really ballast and the boat isn't big enough to carry a lot of passengers. We have more than enough hole shot - we seem to be able to pull as many tubes as we like (6+ at a time) with no real bogging, and basically nobody who we ski with is happy with full throttle starts. Probably the only use we have for all that hole shot at the moment is beach starts, in which we can idle to the end of the rope and then go (as opposed to the 3 coils of rope we took when I learned to beach start behind a 50HP Evinrude...). Seems pretty clear that we could do with more pitch. I don't have any actual problems with the boat, other than it feels like we could go faster. My brother's boat (when he comes visiting) does about 47mph, and those extra 2mph are annoying. Other than when he visits, I don't notice. I guess I might get a bit more fuel efficiency with more pitch. We like our current wake for slalom, we have an acquaintance with a very similar boat (early 2000s Response LX, Indmar powered I think) with a 3 blade, he reckons our wake is much softer (good thing). I haven't skied behind his boat to compare, he did ski behind ours. I see that the recommended prop would be an ACME 515 or similar, which is a 3 bladed 13 inch diameter, 12 inch pitch, with a little bit of cup. We're at maybe 1000' (300 metres) above sea level, lake use only in New Zealand. I have a lot of questions about 4 blade v's 3 blade. There seems to be a lot of hearsay about 3 blades being more efficient, 4 blades being more balanced, but my reading tells me that's not entirely accurate. Efficiency comes down to surface area, and 3 large blades have similar surface area to 4 small blades. The newer 3 bladed props seem to be pushing into more surface area, so that might not make much difference. Balance is probably comparing an older 4 bladed cast prop to a newer 3 bladed CNC prop, and I suspect there wouldn't be much in it. Wake shape is clearly different for every prop, and would be hard to tell without trying, I do feel like it should be related to surface area somehow, so the newer 3 bladed props might not be all that different to what we have. My options are: 1. Stay as we are. I don't have any actual problems other than a desire to tinker 2. Get my existing prop repitched. Apparently inexpensive and easy enough to do. For some reason that feels like the wrong answer to me, that it would end up with the prop a bit less balanced or it might fatigue the metal 3. Reprop to a 4 bladed newer prop with a bit more pitch. We'd get a bit more top end, perhaps similar wake and hole shot? It seems like you must have to give up some hole shot to get more top end, that's the basics of gearing, so I'm dubious, I think we'd lose a bit of hole shot. But we have plenty anyway 4. Reprop to a 3 bladed newer prop with a bit more pitch. As above, with maybe also some wake compromise? Is there any authoritative information on the impacts, or is this all really black magic and you talk to the prop experts then you try it and see? I guess I might need a spare prop anyway, so I could perhaps just buy a new one and try it. What are people's opinions?