Replace 13.25/17 with 13.75/15?

[seedlings]

New to boats and boating, and this site is a great resource. Thanks in advance for your help!

This prop -->FOR SALE ON CRAIGSLIST<-- is 13.75/15. I need to know if it is OK to replace the pictured 13.25/17 I have now. Boat has been used few times, then in storage since the mid 80s. I believe my mom is responsible for the current prop.

I just want to be able to pull the kids in a tube or skis. Not interested in speedboat performance.

Boat:
1978 70Hp Evinrude Manual says 4500~5500 rpm, 5000 is the target.
1979 Crestliner Muskie 550 14' (don't know weight)

Current Prop:

Worst Blade:

Thanks again,
CHAD

 

[junior1113]

Re: Replace 13.25/17 with 13.75/15?

my target would be 5500 that will give you the most out of your motor. 70 hp is at 5500 rpms. your motor will last longest if your in the upper limits of rec. range. 2 strokes live on rpms. not giving them enough is what kills them early

what was your wot rpms with the one you were running beat up and all???

 

[MikDee]

Re: Replace 13.25/17 with 13.75/15?

It would help if we knew your wide open throttle (WOT) rpm, but if the 17" prop was the original one set up by the dealer when new, then it is a matched combo, and the 15" would probably be fine to use for tubing & skiing, because it's bigger in diameter (beefier), but without a load on it, it might over rev your motor at WOT so be careful, till you get a tach on your boat. Yes, I would go for it!

 

[seedlings]

Re: Replace 13.25/17 with 13.75/15?

Thanks for the fast responses.

To answer questions, I haven't started the motor yet, so I'm not sure the RPMs with this prop. I read that replacing the water pump was a must

I figured for $18, if the prop is acceptable, the price is. Local places want $80 to repair this aluminum prop... I can buy one new here on iboats for a few dollars more.

Can you all say if this current prop is "ok" to use? it has nicks here and there as you can see.

CHAD

 

[MikDee]

Re: Replace 13.25/17 with 13.75/15?

File, & sand the edges smooth, to take the nicks off it, and try it, to get an idea of how it works. Again, Is this the orig. prop on the boat from new? That would give us a baseline.

 

[seedlings]

Re: Replace 13.25/17 with 13.75/15?

I'm told this is not the original prop, but a replacement. I can't say what the original spec was.

I'll gently hammer and file the dings, get it started and see. This may give me an excuse to get it on the water ahead of schedule.

CHAD

 

[seedlings]

Re: Replace 13.25/17 with 13.75/15?

There are what amounts to about 1/2 a dime's worth of material removed from 2 of the 3 blades. I tapped and filed down, and will probably just use this prop.

This is the bottom blade from the above photo:

I did find the original flyer for prop selection, which says a 13.25" x 17" should get me to 30-35mph with this 70hp Evinrude. It goes up to a 12" x 23" and says it should hit 50-60mph... somehow I'm skeptical.

So, I'm just hoping for good rpm range and just enough to throw a tube around.

Thanks for the help - I'm trying to absorb as much of your insight as I can.

Also just called for insurance on the boat... $37usd for $30,000 liability, $250 deductable. That's crazy cheap. (probably because I said the boat and motor was worth maybe $1000).

Thanks again,
CHAD

 

[MikDee]

Re: Replace 13.25/17 with 13.75/15?

Not a bad job on the prop I've seen worse in use, this will give us all a starting point if you can get us the WOT (wide open throttle) rpm.
good luck, Mike

 

[junior1113]

Re: Replace 13.25/17 with 13.75/15?

you might get 60mph with that motor on a 14 jonboat. its all about being in recom. rpms, with that motor on a big pontoon it would need like a 13p and on a jon boat it would need like a 23p has to do with the load being pushed if you put a 23 on yours it probobly would take a while to get on plane and when it did get up it would prob. only hit 3800rpm and still go close to as fast as a 17p and will kill the motor quickly

i would pay the 18 an give it a shot if revs over 5600 have it repitched up to16 or 17 always nice to have a couple props at hand

 

[MikDee]

Re: Replace 13.25/17 with 13.75/15?

you might get 60mph with that motor on a 14 jonboat. its all about being in recom. rpms, with that motor on a big pontoon it would need like a 13p and on a jon boat it would need like a 23p has to do with the load being pushed if you put a 23 on yours it probobly would take a while to get on plane and when it did get up it would prob. only hit 3800rpm and still go close to as fast as a 17p and will kill the motor quickly

i would pay the 18 an give it a shot if revs over 5600 have it repitched up to16 or 17 always nice to have a couple props at hand

Ditto!

 

[seedlings]

Re: Replace 13.25/17 with 13.75/15?

Well, we're playing phone tag - keep missing each other.

CHAD

 

[jam1ej20]

Re: Replace 13.25/17 with 13.75/15?

Whoa...looks like everyone is jumping the gun a little here. This motor hasn't been started since the 80's! The prop is LAST of your worries. You don't even know if this thing will turn over, let alone reach WOT. Get the motor running and the prop turning before you worry about what the prop looks like.

 

[junior1113]

Re: Replace 13.25/17 with 13.75/15?

Whoa...looks like everyone is jumping the gun a little here. This motor hasn't been started since the 80's! The prop is LAST of your worries. You don't even know if this thing will turn over, let alone reach WOT. Get the motor running and the prop turning before you worry about what the prop looks like.

i agree 20 yrs is a long time to sit