Re: Prop Diameter help
Limestone<br />Only way I know to find right prop is to run wide open and check your rpms. If your rpm range should be 4400 to 4800 rpms and you are in that range then prop should be ok.<br /><br />My boat came with a aluminum prop 13 1/4 by 17 by 3. My RPM ringe is 4200 to 4600. With the aluminum prop boat ran 4600 rpms at a speed of 33 mph. I bent the prop a little but got it fixed but also got a Stainless Steel prop. Stainless Steel prop is 13 3/8 by 17 by 3 but also double cupped, it still turned very close to 4600 rpms with a top speed of 35 mph. Later I got another Stainless Steel prop, this one is 13 by 19 by 3 double cupped. It top RPM is 4200 rpms with a top speed of 38 mph. The 17 pitch has a better hole shot and gets on plane faster but top speed is 3 mph slower and engine turn max rpms. The 19 pitch takes longer to get on plane is 3 mph faster and gets beter fuel mileage, engine still in wot rpm range at 4200 rpms. I use the 19 pitch in ocean where we do not start and stop much and do a lot more cruseing at lower speed and much longer distance. I use the 17 pitch in rivers and lakes where alway starting and stoping for other boats or marineas, also usually much shorter distance.<br /><br />I no expert but small change in diameter I think has very small change in rpms. The bigger size will push a little more water and turn a little slower. A smaller diameter should turn a little faster. Stainless steel props usually cupped and has thinner blades, cupping means prop gets a little better bite. A 1 inch change in pitch will equal 200 rpm change. 2 inches = 400 rpm change. In general terms boat from manufacture should come with best aluminum prop. Large heavy boats normaly have bigger diameter and lower pitch, Smaller lighter boats have smaller diameter and higher pitch.<br /><br />Best prop will be one that at full throttle will be in the recomended rpm range for your boat. Any prop that is in that range should not hurt your motor. A higher pitch will be slower to get up on plane have a little better top speed and get better fuel mileage, but if does reach at least the low end of your rpm range then is lugging the engine and can cause dammage. A lower pitch will jump up on plane quicker have a slower top speed, get lower gas mileage and if it go over the max rpm can also cause damage engine.<br /><br />When picking a prop many dealers will work with you to get the right one and let you exchange if does not meet your rpm range.
