Re: Force 70 hp Prop Question.
As with all prop changes, the maximun rpm you acheive at full throttle is important info to be used to determine prop changes.<br /><br />I have the same motor, same year, and a similar sized boat.<br />Spectrum Avenger 16.6' aluminum fish and sport, rated for 75hp, My rig weighs approx 1200 with boat motor batteries fuel and gear. I have two props, a Merc 48 73140 A40 15 pitch, and a similar Hustler 15pitch. Hole shot is acceptable and top speed is at 33-34mph (gps) at 5200 rpm.<br /><br />Suggested rpm for the motor is 4750 - 5250 rpm.<br />So if I drop the pitch to get a better hole shot, I would increase the rpm, well above the recommended range.<br /><br />So the question to you is, what are your full throttle rpm with just you in the boat??<br /><br />Here is a small post you can read.<br />
http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000015 <br /><br />Another thing to remember, is that this motor is fitted with a lower unit that was originally designed for a 40hp motor. It uses a relatively small diameter prop which effects the holeshot.<br />I would love to fit a 14" diameter prop on there, but that isn't gonna happen.<br /><br />If your rpm are close to 5000, then a lower pitch prop will only increase rpm's, and top speed should remain about the same.<br /><br />Post your rpm and we'll go from there.
