Posts: 3514
Location: Elk River, Minnesota | Hi,
Depending on where your RPM's are now, you may have the correct prop in hand. When switching from Aluminum to stainless, there is usually a drop in RPM's when you stay with the same pitch and diameter. The reason for this is due to a significantly less amount of blade flex as the prop turns in the water. In some cases, though ( and this is general and not a hard and fast rule here), the RPMs may not change due to the design of the prop. For example, the Yamaha aluminum prop and it's standard stock steel prop. They are identical except for their materials, so what one mainly gains from going to the steel equivalent is durability. Because the design is the same, the overall performance characteristics will be similar.
When you switch to an aftermarket prop, there are many other variables that come into the picture. Blade design, thickness, pitch, and diameter are different than what you have from the stock aluminum, and each characteristic will do different things for the rig. No matter what, there is a compromise in anything you do, but in many cases that compromise is minimal as compared to the gains you will see in other areas.
Because you are swtitching away from your standard prop and going to the cabelas prop, you are right in choosing a lower pitched prop. In most cases, going from stock to an aftermarket prop in the same pitch and diameter usually means a drop in RPM around 200 - 300 RPM (due to the lack of flex in steel and the extra cupping on the blades trailing edge) So...to get the equivalent RPMs to what you have currently, going down in pitch will be the correct move. The most common switch is to go down 2 inches in pitch when you switch from aluminum to steel. (again, not a hard and fast rule, but generally the norm)
Now..in your case, going down to a 15 pitch you will see the following: Increased hole shot...your boat will most likely jump up on plane much quicker than with your stock 17 pitch. You will also probably feel the boat being lifted a little more out of the water in the stern due to the cupping on the trailing edge of the prop. That increases lift overall, so you may also have to trim the motor up less for your desired setting. In turning, the prop will not "let loose" on a moderate turn as well.
What you may see as a compromise is a touch of top speed lost, but with less flex that could be negligible...all depends on what the prop does for you.. If your RPMs are a little low (like 250 or more) when you try the prop out, you can move the motor up a mounting hole and try again. you can gain some RPMs back in that manner, and with a switch to steel, the prop will usually keep a bite on the water well. That is the real difference in steel....it allows you to move your motor up to get more RPMs without much loss in handling...but it does have a limiting factor as well. It is also a test-and-see situation.
Now..if you decide you want to try more props, there are plenty out there that may even make the boat perform even better. But..that is a test, test, test again situation, and some don't like to do that...due to time, or just don't care for the 'putziness' of it. If you get the urge to do so, I have found the michigan ballistic to peform very well on different rigs with yamaha engines. I have a 90 2 stroke yamaha and turn a 17 pitch ballistic. It has the same RPM's as my stock aluminum 17 pitch (same as yours) but I saw increases in every area. I'm running a multispecies rig (alumacraft navigator console) and have the motor mounted in the highest possible bolt-hole position...and it still hooks up well. Top speed is just a touch below 40mph with my normal load.
Good luck and report back on how the change-over went..
Steve |
