Prop Size - top speed / quick

[11craigt]

Have an opportunity to buy a new stainless steel prop for $100...someone offered me. Wasn't really looking, but seems like a deal. Anyone know the proper size for an 83' Evinrude 115? My looks fine now...a few knicks and a slight dent on one fo the propeller wings - not stainless though...worth the while? Don't really need too much speed, right now I think I am about 40mph WOT @ 4500rpm on an 83' Cobia 18' center console? Does that seem right? Thanks in advance.

 

[walleyehed]

Re: Prop Size - top speed / quick

4500RPM at WOT is 1000RPM short of where you should be.<br />Need to know the pitch of the prop you have now...by what your tach says, we need to drop 5" in pitch to get the RPM where it should be, technically, but that's not how we'll do it.<br />Need to know how the engine is mounted and what prop you have now.

 

[11craigt]

Re: Prop Size - top speed / quick

I may have been off a little, as my buddy who is part owner of this yacht says we were at 5,000 rpm WOT. <br /><br />I measured the length of the outer-part of the prop blades and I come up with 9" from base of blade to its furthest point at which it starts going back to the base.<br /><br />I don't know how to tell the pitch? I took some pictures to show how the engine is mounted...keep an eye open for them on a future post here soon.<br /><br />Thanks again walleyehed.

 

[JB]

Re: Prop Size - top speed / quick

Prop topic.

 

[11craigt]

Re: Prop Size - top speed / quick

Well, here are the pics to go along with my questions:<br /><br />As for the pitch of the prop I can only tell this measurement of the length of the blades..9"<br /><br />

<br /><br />AND as for the way the motor is mounted...looks like it is set low? What are the advantages / disadvantages of up or down and when do you change it?<br /><br />

<br /><br />AND LAST...do I need a new hydrofoil?<br /><br />

<br /><br />Please notice my question in this last picture...what is this adjustment for? Boats goes straight now.<br /><br />Thanks in advance.

 

[QC]

Re: Prop Size - top speed / quick

My advice . . . lose the foil. They are usually added to correct a weak hole shot or porpoising, but there are definitely better ways to affect those issues. My .02<br /><br />It is very hard to tell what the pitch is of that prop as you probably don't know it's actual history. The 9 inch dimension isn't helpful. Pitch is the distance that the propeller would travel in one revolution "through" a solid. i.e. no slip. There may be some numbers stamped in the back of the hub look for 15, 17 ,19, 21. Those would be pitch references. Anyway, the pitch can be changed in a shop, so even with that number you really don't know . . .<br /><br />You need to have a spare prop anyway, so I would find out who the local prop gurus are and have them check that existing prop for pitch. Then select a prop based on your current 5000 RPM (still too low) and go from there. The old one then gets to go for boat rides . . . Good luck!!

 

[11craigt]

Re: Prop Size - top speed / quick

I'll have to take the prop off...cotter pin and bolt. How do I keep eveything from spinning - put into gear?<br /><br />What is proper maintenance to this area - prop, behind the prop (hub)?<br /><br />Thanks...oh by the way, I think this is probably the orginal prop...83' trailer, 83' hull, 83' motor? Do you happen to know what would have went on it originally?

 

[QC]

Re: Prop Size - top speed / quick

I have no clue as to the original prop. The biggest maitenance issue back there is to grease the propshaft when you go back on. You may find out why when you got to remove the existing one . . . <br /><br />The best way to get leverage on the prop nut is to wedge a block of wood between the propeller blades and the lower unit.

 

[QC]

Re: Prop Size - top speed / quick

anchorguy,<br /><br />I just noticed your possibly wet foam thread elsewhere. You should consider the extra weight you might be carrying before spending a lot of money on props. If you plan to check into the foam soon ,then I would maybe wait on the experimenting.

 

[11craigt]

Re: Prop Size - top speed / quick

Good point, thanks very much.