Think I need a new Prop???

[Gasper Master]

I have a Cape Horn 17 with a 90hp Mercury. Loaded down, she takes a good while to get on plane and only tops out at about 4800 rpms. I am pretty sure I have the right numbers off of the prop, but they are quite hard to see. The numbers on the prop show 18 77346 405 19P. I am guessing this is a 19 pitch? I read somewhere where the Merc two strokes should run about 5500 rpms. What prop would you guys suggest i go to?

[fishinpox]

Call powertech tell them problems ect they will set u up propper, if it's close to what u have u might consider getting the existing prop re worked

[msu-tfrancois]

Originally Posted by fishinpox

Call powertech tell them problems ect they will set u up propper, if it's close to what u have u might consider getting the existing prop re worked

19 pitch prop is pretty low....I wouldn't think you would need to pitch it any lower...and sounds like your rpms aren't quite right..not sure if changing ur pitch would help that many rpm's.....my last boat i was having trouble with the rpm's not going over 4500 and had a lost of power...come to find out i just needed to rekit the carburator...that may help you out

[Dink]

Tlyou need a large diameter 17in prop. You can use mine as a test

[Gasper Master]

Originally Posted by Dink

Tlyou need a large diameter 17in prop. You can use mine as a test

Is that what u have on your 19?

[Dink]

I had a small diameter 19p. Could t get over 4900. Got a large diameter 17p and my boat now handles like a sports car!!! The difference is amazing!! Boat is way up out of the water now.....

[msu-tfrancois]

Originally Posted by Dink

I had a small diameter 19p. Could t get over 4900. Got a large diameter 17p and my boat now handles like a sports car!!! The difference is amazing!! Boat is way up out of the water now.....

How high did you rpm's get with the 17 pitch?

[Montauk17]

He has a 90.....not the same prop as a v6 150-300 prop. 19 pitch is high for that setup,those cape horns are pretty heavy. Doing the numbers your going to need a 15 pitch to get your rpm's right. I would get a use a powertech http://www.ptprop.com/index.php?page...mart&Itemid=46 call the prop shop in lafayette. If you buy from them they will adjust the pitch if it still is not 100% right for no extra cost. Should run you about 350 bucks or so....

[msu-tfrancois]

larger diameter prop will lower your rpm's not raise it..the smaller the diameter the higher you rpm's will get.....

[Montauk17]

Originally Posted by msu-tfrancois

larger diameter prop will lower your rpm's not raise it..the smaller the diameter the higher you rpm's will get.....

Pitch changes your rpm's more than anything. A shop can change the pitch by 2 degrees up or down. Every pitch you go up/down you will see a 200rpm change. On a heavier style boat like the one mentioned it is better to use a larger diameter prop to carry the weight,ect. Diameter,pitch,rake,blade shape all comes into play.

[msu-tfrancois]

Originally Posted by Montauk17

Pitch changes your rpm's more than anything. A shop can change the pitch by 2 degrees up or down. Every pitch your go up/down you will see a 200rpm change. On a heavier style boat like the one mentioned it is better to use a larger diameter prop to carry the weight,ect. Diameter,pitch,rake,blade shape all comes into play.

I agree with you...the lower pitch will jump up you rpm's and the larger diameter will help with efficiency and getting more speed out of a lower rpm... you can also get it doubled pitched....keepin ya top end at a 19p and get the lower end pitched to 17p...gives you better take off without losing ya top end

[Montauk17]

Originally Posted by msu-tfrancois

I agree with you...the lower pitch will jump up you rpm's and the larger diameter will help with efficiency and getting more speed out of a lower rpm... you can also get it doubled pitched....keepin ya top end at a 19p and get the lower end pitched to 17p...gives you better take off without losing ya top end

Rolling the leading edge only changes your holeshot,not your WOT rpm. I worked at a propeller shop for years,there is alot more to it than most people think.

[msu-tfrancois]

Originally Posted by Montauk17

Rolling the leading edge only changes your holeshot,not your WOT rpm. I worked at a propeller shop for years,there is alot more to it than most people think.

I hear that man....well I'm sure you alot more than me I just know from a lil bit of me messin around wit mine...i'll stay out of it haha!.....goodluck with the project ain't nothin more aggravatin then ya boat not performing up to par

[msu-tfrancois]

if the prop thing don't work out i'd check ya carbs...with gas today it doesn't take much to get them things gummed up

[Montauk17]

Sho nuff

[Gasper Master]

thanks guys, just cleaned my carbs, motor is running great

[msu-tfrancois]

Originally Posted by Gasper Master

thanks guys, just cleaned my carbs, motor is running great

good deal

[Gasper Master]

finally got to pull the prop and went to the prop shop. They will pitch it down to a 17 for me. Hopefully that solves it. Will let ya'll know after i get it back. They said the 19 was way too much.

[BigChaf]

You should still get 5500 rpm's wide open with the right prop, you loose top end speed, but you will gain power out of the hole, I don't know if the same rule applies to a 4 stroke.