Prop for a 62 Merc 700 on a 58 Commando Sport?

[jobrown]

Hey guys, helping out a buddy with a really interesting boat. He rebuilt the boat a few years ago, but the prop on the Merc 700 is a 15 pitch Aluminum 3 blade, its pretty knicked up and only gets up to 35 mph... Doing a little research and we figured that 15 was way too low of a pitch! So what do you guys think about a higher pitch? And wheres a good place to buy it?!

Heres the boat!


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[steelespike]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

A cool boat.
Without your speed and rpm you can't really tell even which way to go with the prop or if the new selection is right.Get yourself a tach.Portable,or induction type, or permanent A prop shop should be able to repair the prop.Is the speed by gps? Is the antivent plate(just above the prop) even with the botton of the boat? Check out Johns Old Mercury Web Site.

 

[jobrown]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

I'll look to see. Yeah I need to get a tach on it, but I know that it has a lot of bottom end. Actually if you punch it it will kind of hop and cavitate. We worked to adjust the trim which helped a bit. The speed we got riding next to our buddies moomba wakeboarding boat. So it's actually probably less.

Found a chart on the web, says that a merc 700 running less than a 1000 gross pounds of weight should be running a 19 to 23 pitch prop. Does that sound right?

 

[jobrown]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

It appears the antivent plate is lower than the bottom of the hull... Bad? Good?

 

[steelespike]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

Usually plate should be even with to up to an inch above.
The idea is to drag as little as possible through the water and still pump water and not have excessive ventilation.There are props that resist venting better and allow maximum height.
I guess that prop range seems reasonable.The selection would depend heavily on the type of hull
a displacement type hull would require less pitch while a light planing hull more pitch.
Is the present prop aluminum,brass or stainless?Al is light,brass and stainless heavy.ss is magnetic al and br not. any numbers on it?

 

[jobrown]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

Its stamped 15P and its aluminum.

Is there anyway to know this prop will fit a 700 Merc??

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=250592986549&viewitem=&sspagename=STRK%3AMEWAX%3AIT

 

[steelespike]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

You need a spline count at least.
There may be part numbers where the prop nut goes.
Prop is a 21 pitch speed prop intended for a light fast boat.Won't work on your boat.
And may not fit anyway.
According to the prop listing here at I boats the biggest prop is a 17.
Said to fit 70 hp up to 83. My info indicates the 70 has a 1.7:1 gear ratio.Makes a 15" pitch seem reasonable.It is rated at 70hp @5,500 rpm.If you get her on the water and with the wot(wide open throttle) rpm and speed you can tell a lot better if prop is right and motor performing as it should.

 

[jobrown]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

Right, I figured a 21 would be for a light boat, it's a 70 hp motor on a 14 foot 250 pound hull, that seems a little light, and it should be a little faster than 35! ( I don't even think it's going that fast, we will know more when we gps it.)

We found a chart, that I will post as soon as I'm off work. It says the 15 pitch on a merc 700 was for a boat up to 2000 pounds, and 21 was for a boat up to 1000. Very neat chart, part numbers and everything.

Oh and the output shaft on his lower unit is 15 spline, and the one on eBay was a 15 as well. Also the chart says you can go up to a 14 inch prop on the 700, and this one is 13.5. I'm just wondering if output shaft diameters are different sizes. I'm sure they are. We will prolly order it, just see what happens.

 

[steelespike]

Re: Prop for a 62 Merc 700 on a 58 Commando Sport?

Have you weighed the boat? 250 seems light for fully upoholstered seats,windshield,
a full front deck and those great fins. I have a 65 Merc 500 I believe with the same ratio as your 70. It has been on my 330lb 57 Crestliner Bucaneer since new It runs an 11" pitch prop.
I don't think it would be a stretch for a 15 or 17 to work for your setup.
I could be full of hot air. It will be interesting to see your rersults.