Propeller Numbers translated...

[Franki]

Hi guys, <br /><br />Anyone that read the story of my fishing weekend knows I trashed my propeller..<br /><br />Looking at it, Its a "13 3/4" x "15"<br /><br />This prop came with the motor, and I'm wondering if its the right size for my boat. (don't know for sure cos I never got to try it at WOT and see what the RPM 's were)<br /><br />My boat is a narrow beam, flat bottom 17 foot clinker style Fiberglass Halfcabin... its also a good bit heavier then one would expect such a boat to be...<br /><br />Am I in the right range here with this prop?<br />(with a 100 HP Johnson 100ESL72)<br /><br />Which one of these measurments is the pitch and what does the other number specify? diameter?<br /><br />regards<br /><br />Franki

 

[rickdb1boat]

Re: Propeller Numbers translated...

Franki <br /><br />13 1/4 is the diameter and 15 is the pitch. Can't be specific without the WOT RPM's, but a 17"-19" pitch sounds close, depending on the weight of the boat. A flat bottom boat will require more pitch to perform properly, because of hull design. A 15" pitch would be better suited to a 20'-24' Boat. If you don't have one, Install yourself a tach. so you know for sure what you are turning. If you do have one, find out what the reading is, so that we can give better propping advice.

 

[walleyehed]

Re: Propeller Numbers translated...

It takes a 15" at 4000ft above sea level on my 97' 115 to get 6k....my boat is 18ft.<br />I don't think 15" pitch is far off on your heavier boat. That OMC 391198 13-3/4X15 has huge blade area, and it's got good cup.....matter-fact, it pulls the same RPM as a Michigan wheel 17" pitch, with no speed advantage.

 

[Franki]

Re: Propeller Numbers translated...

Cool, <br /><br />I guess I'll carry on chasing the same size I had before it got rock challenged...<br /><br />thanks for the info.<br /><br />rgds<br /><br />Franki

 

[walleyehed]

Re: Propeller Numbers translated...

Franki, as Rick said, it IS best to have a proper tach reading to give the best advice....can you tell us what your WOT RPM was???<br />EDIT: I just realized you said you didn't get the chance to go WFO, but a tach is a must, and getting your hands on a test prop would be the best way to determine where you are, and we can go from there on recommendations......

 

[Franki]

Re: Propeller Numbers translated...

Oh, I do have a tach.. <br /><br />I have a dash full of very nice guages.. including left and right bank temp guages, tacho, speedo etc.. and I am trying to figure out how to add water pressure..<br /><br />The reason I never got to WOT was because of the torgue steering problem I had. (fixed now I think) and the water was not smooth enough to go that fast.. The torque problem was bad, because over a certain speed, the boat would just suddendly turn to starboard.. and there was nothing I could do to stop it.. (except back off the throttle).. was quiet scary when it happened at 35knots.. also at that speed, it was VERY hard to turn to port.. it just didn't want to go.. <br /><br />(I only got to about 35knots and that was at about 3500rpm...)<br /><br />Next time I go out.. I'll try to do so on a calm day with no chop.. I I can get a good idea of WOT rpm's. (I'm also curious as to the top speed at present, I'm gonna borrow a GPS to see how fast Im moving.)<br /><br />rgds<br /><br />Franki

 

[rickdb1boat]

Re: Propeller Numbers translated...

Have you adjusted the trim tab to see if that helps? Turn the rear of the tab to the right in small increments until it straightens out.

 

[Franki]

Re: Propeller Numbers translated...

Yes, I've adjusted the tab...<br /><br />I have to find a new prop before I go back out and test.. cos the last one is mostly on a rock in the river... <br /><br />rgds<br /><br />Franki