Another Prop Question

[kraw2]

Yes I did a search and found very good information.

I currently have a new Viper SS 13 7/8" x 17 for a 1998 115 Evinrude SPL.  I have not had the boat in the water yet. 1976 170.

I am partial to 4 blade props. Why..? Because on my 31' Ocean Master I could'nt stay on plane at slow speeds. This is a must when you're offshore in bad seas.

On the 1976 170 if I wanted to go with a 4 blade prop which way would I go..?

[akbridge]

I like my four blade.  It's a powertech Rxb4. It helps with ventilation and hole shot. I went down to a 14" pitch. I run the same basic engine as you in a 90 hp version.  You won't regret getting a four blade prop.  The prop you have right now is a great prop.  But it's a higher speed bow lifting prop.  That's not what I want while cruising around and fishing.

[kraw2]

So your prop is a 4 blade 13 7/8" x 14"...Correct.?

[akbridge]

It's a 13.25" diameter by 14" pitch.  Here is a link to the prop: http://www.ptprop.com/index.php?page=sh ... &Itemid=46  I have found that most prop manufacturers drop the diameter to help with hole shot.  You might want to look into a 15" pitch with a 115.  I am running about 5450 rpm on my cross charged omc.  It's at the max with a light load. But that suits me fine.

[alandry100]

kraw - do you know what RPM you are getting at WOT?

[GoneFission]

It's a 13.25" diameter by 14" pitch.  Here is a link to the prop: http://www.ptprop.com/index.php?page=sh ... &Itemid=46  I have found that most prop manufacturers drop the diameter to help with hole shot.  You might want to look into a 15" pitch with a 115.  I am running about 5450 rpm on my cross charged omc.  It's at the max with a light load. But that suits me fine.

Generally more blades means smaller diameter to maintain a similar swept area.  This also means you can trim a 4 blade or 5 blade out a bit more before it begins to ventilate.  Pitch should be about the same regardless of the number of blades.  A 4 blade or 5 blade can run a bit more rake and keep the same hole shot and top end, or run the same rake and get a better hole shot and give up just a bit in top end due to drag.

[kraw2]

Thank you for the indept information.

No I haven't had the boat in the water at all. If it wasn't for the hurricane it would have been done this weekend. I will post the numbers when it gets broke in.

I am just partial to the performance of 4 blade props. I like to stay on plane at slower speeds. If I can accomplish this and still have decent top end that is what I'm looking for.

On my 31' I lost top end by 5 mph but that's fine with me. 90% of the time you can't go full speed offshore anyway. With 310 gallons of gas I like to get the best MPG.

[kraw2]

The 98' 115 Evinrude is now broken in. I have a problem with the Faria 7000 outboard tach. At idle to 3k RPM's the tach is reading correctly. At WOT the tach is reading 7000. But by hearing the engine it is definately not 7000..! GPS and speedo speed are at 37 MPH.

The pole setting is on 12. Any suggestions?

[fitz73222]

Hey kraw,

Make sure the selector switch is fully seated in its respective detent. I had a teleflex tach do the same thing. I know you know this but gently push in and turn the selector switch and give her a little wiggle to make sure it's home. Use an eyeglass screwdriver or something equally as dainty.

[kraw2]

Thank you,

That very well could be the problem.