pitch of prop for my 90hp Rude?

[Oscar^Boy]

Hello everyone, first off I would like to say, "Yes, this is my first post and I am a newbie". Ok now thats out of the way here is my question; I have a 1987 15ft challenger bass with a 1987 90hp evinrude with a 13x19 pitch prop. With this set up I run about 54mph @ 5600 rpm's with just me in the boat. I just purchased a jack plate and want to purchase a prop that will get me over the 60mph barrier. (my buddy had same motor on a 16ft skeeter and he ran 62 with jack and ss prop...so i know its possible) I was wondering if any of you boat and motor gurus out there could help me. Does cupping a prop help? I have seen all shapes and sizes and I have no clue what to purchase to satisfy my need for speed, thanks for any replies I might recieve!

 

[blueboat1]

Re: pitch of prop for my 90hp Rude?

from what i have read here for every pitch you go up in the prop you should drop 200 rpms. (say from a 13X13 you run 5400 then go to a 13X15 to run 5000rpm's and of couse there is a balance point of no more power or two little prop) I would say at the rpms you are running you are about where you want to be on rpm's. Dont go act on this info without checking around. I am somewhat new to this also. my 2 cents is also that aluminum props are good for two things. cheaper to buy and if you whack a rock you kill the prop not your lower unit gears. last time i looked a lower unit is about 1200-1400 for your motor. good luck.<br />scott

 

[roscoe]

Re: pitch of prop for my 90hp Rude?

You got what you got. If it ain't broke, don't go doing something that will break it. If you want to go a lot faster, its cheaper to sell the boat, add $10,000, and buy a faster boat.

 

[Boatin Bob]

Re: pitch of prop for my 90hp Rude?

You could try a 21 or 23 in pitch or go to a cupped prop if yours isn't, all of these will reduce your WOT RPM's which maybe you should do anyway since your up at 5600, should give you a few more mph but it will also have a somewhat negative affect on your hole shot, take a little longer to get up, as with everything else in boating it's a compromise!

 

[Dhadley]

Re: pitch of prop for my 90hp Rude?

Just install the jackplate (manual or hydraulic?) and test. Make ONE change at a time. You are a tad low on rpm now so a little work with the X dimension should help that. You have a pretty good baseline now. You might want to add the water pressure reading to that data.<br /><br />Once the plate is on test, record data, make a height adjustment and retest. Once you have the best set up for that prop we can calculate slip %. From that we can determine where to go as far as props go.<br /><br />When looking at props you have to consider inches of pitch, prop diameter, progressive pitch, rake angle, ammount and length of cup.<br /><br />Post your results and we'll go from there.<br /><br />Good luck!

 

[Oscar^Boy]

Re: pitch of prop for my 90hp Rude?

Hey thanks for that info, I had no idea that a prop had so many variables with it. I will post a new topic when I get the data because it will be awhile. You said something about prop slippage, what is that? The prop I have now is ss teflon coated prop, it has amazing hole shot. I could pull my step mother out the water on a salomn ski! (j/k in case she reads this.. ) I saw a prop on iboats for under $300, it was a 131/4 X 21, I was considering buying, the name of the prop was "Express" has anyone had any luck with those?<br /><br />Oh and roscoe, I am from Louisiana. Down here we dont spend $10k on a boat...its to demorilizing when some redneck in a flat boat with a bored out 40 yamaha passes like you are standing still, anyways thanks for all the posts!

 

[Dhadley]

Re: pitch of prop for my 90hp Rude?

Thats only some of the aspects of props. Dont go blindly throwing money at a "pretty" prop. Lets do the testing first.<br /><br />Pitch (19" in your case) is the theoretical distance a prop will travel forward in one revolution. Slip refers to the % of that travel that is lost in a given set up. 0% slip is not possible - yet! Most pleasure boats with a decent set up will have 12 to 15% slip. The higher the slip %, the poorer the set up and or prop (technology wise).<br /><br />Pitch is always measured in inches. Some folks think it is referd to in degrees. That comes from the thinking that the "degree" is the angle of the blade in relation to the hub. Thats rake angle. That has to do with how much lift the prop will produce. The overall shape of the blades (chopper/round ear, cleaver, cleeper or "pig ear") will also determine bow lift, stern lift or overall lift.<br /><br />Then you have to deal with number of blades - 2, 3, 4, 5, or 6. They all have their useful place in the boating world.<br /><br />Start with the jackplate (smart move) and we'll go from there.<br /><br />Keep us informed!

 

[moderator1]

Re: pitch of prop for my 90hp Rude?

Moving to Outboards.