Please help with prop size

[dirtninja]

I'm in need of some advice if you would please. I own a 2000 bayliner 16' bowrider (1400lbs) with a classic 90hp 2stroke outboard. The prop on it now is a 12.75 diameter x 19 pitch and at WOT on stock guages, the tach reads 4600 rpm's trimmed up for a max speed of 40mph on gps. The load entails an extra 500lbs to bring the total weight to approximately 1900lbs. I ordered a 15'' pitch prop thinking i needed to get the max wot up to the rated 5500 rpm. After reading alot of post on the forum, im thinking the 15 might be too much and a 17 might be in order?? Thanks in advanced for any help that you may have to offer.

 

[coolbri70]

if you already ordered the 15, it cant hurt to give it a try, keep an eye on your tach

 

[jestor68]

A 2.33 gear ratio turning a 19 pitch prop using a 10% slip at 40 mph works out to about 5698 rpm.

Check your tach. It's not working right if it's only showing 4600 rpm; if the speed is accurate.

Is the speed by GPS?

 

[dirtninja]

Thanks for chiming in Jestor as you were the person i was looking for. Yes, i used a garmin automotive gps. Other person, i plan on canceling / returning the prop if it is deemed to be incorrect. I figured some of you guys are experts and would know common speeds for certain motors with certain set ups. Thanks again guys.

 

[SkiDad]

that 19 seems right for that combo - if you can get out of the hole in about 4-5 seconds you are propped good for most things - maybe a 17 if you pull heavy slalom skiers - but 15 would definitely over-rev big time.