4 blade props

[kthurm]

Anyone have experience with 4 blade props?<br />What are the advantages or drawbacks?<br />Will it cause more bow lift?<br />Do you go plus or minue pitch degrees, i.e.<br />standard 17 do you go to 15 or to 19 degrees when going to 4 blades? What are effects on top end with 4 blades over 3?

 

[ivar]

Re: 4 blade props

see this link -iboats prop help. 3 blades or 4

 

[Silvertip]

Re: 4 blade props

The numbers 17 and 19 are "inches" not degrees. Theoretically, these props would move 17 inches and 19 inches respectively in one revolution. But since they operate in a liquid, some slippage is encountered. The effects of switching from 3 to 4 blades depends on the amount of power available and the size, weight and design of the hull. To complicate things even more, one four blade prop may not be as efficient as another. Then there is aluminum vs stainless. You really need to experiment with the setup you have now to maximize it. Work with engine height to get the most out of the combination. Then think carefully about any issues you want to correct.

 

[Drybo]

Re: 4 blade props

Lost about 3mph with 4 blade but gained much greater stability turning, better holeshot, less blowout. Only advantage of 3 blade was top speed<br />with a 115 merc on 17ft runabout, I changed stock merc prop to a 4 blade comp prop and I don't even think about changing back. plus the comp prop is less than $100. Just my 2 cents, I used same size 13x19 in the 4 blade.

 

[ron7000]

Re: 4 blade props

have a 285hp v-8 in a 1976 24' deep-v formula, merc alpha drive with 1.5 ratio. The standard 14x19 3-blade is what I used to run, boat would do around 45mph wot. I have a stilleto 4-blade 14.25x20 prop, which gets me about 4400-4500 rpm at around 45mph. I ended up buying 2 props, a 14x18 and a 14x20, trying both and returning one. It was a huge difference, the 18" prop would take off great but at 3000 rpm my cruise speed was 25mph or less. With the 20" prop, not as great acceleration but cruise was much more comfortable at 30mph at 3000 rpm.<br /><br />4 blades always get more bite, so you can hopefully expect a little better cruise speed when heavily loaded. Top speed can suffer a little but it's so little you won't notice, not like you run full throttle all the time. They are also smoother, less vibration, at least on mine vs a 3-blade aluminum.

 

[Dhadley]

Re: 4 blade props

The advantage is you can run a higher X dimension, generally speaking, with a good 4 blade prop. The disadvantage of that is that with a stern drive (I/O) that dimension isn't easily raised.<br /><br />However, some manufacturers like Turbo make a 4 blade specifically for stern drives.<br /><br />The biggest disadvantage to any given 4 blade on an outboard is that folks are reluctlant to raise the motor. With really good 4 blade props, like the large diameter 4 blade Turbos, a jackplate is pretty much a must. Thats why its common to hear folks say they tried a 4 blade and it wasnt as fast as the 3 blade. They used a 4 blade on a 3 blade set up.<br /><br />Another common trait is that they tend to lift the tail or stern. Thats why they are such great props on air entrapment hulls. <br /><br />Not all 4 blade props are created equal. Just like a 3 blade, buy one thats suited for your rig, set up and intended use.