Prop for 115 2S on SF 20
 

Yesterday I picked up a 72' SF and towed it 500 miles with a 4-cyl standard Toyota Tacoma. I don't recommend anyone else trying this, considering that I could smell my truck burning on the steep hills. I guess it was the clutch. It will be fine when I get it home where everything is flat as a pancake.

Anyway, the boat has an old 115 Mariner that supposedly only has 20 hours which might be true considering it still has paint on prop and lower unit and has not been started in 17 years. One blade on the prop is bent (aluminum prop). Before I go buy a new prop or get this one fixed I wanted to find out if it is the right size. It is a 17 pitch prop (dunno the dia. If you can decipher the serial, it appears to be 48 77344A-4 17P (not certain about that first number though). I would have guessed a 15 pitch prop on a 115 on a 20 SF, but I really dunno. Motor S/N is 5940375. Anybody have any information on this motor? Since it says Fond du Lac, Wis I guess this motor was produced after Merc bought Mariner but I don't know much else about it beside the obvious stuff.

Thanks
-Muddy

Re: Prop for 115 2S on SF 20
 

I had Yammie 130 hp 2S with a 13" by 19" SS on a '75 20' SF and it was just right.

Re: Prop for 115 2S on SF 20
 

I think my 115 swung a 17 should be right.

Re: Prop for 115 2S on SF 20
 

Some of the old Mariners were supposedly built by Yamaha.

Re: Prop for 115 2S on SF 20
 

Thanks everybody for the replies. Keep em coming.

Michigan Wheel has a prop selector program which I entered the information into and it said 13 1/4 x 15 pitch. Of course, a Seacraft 20 is right on the line, so I guess it could go either way (15 or 17). I was thinking about occasionally wakeboarding so the lower pitch prop might be better for me? I was looking at the Rapture props. If you go from Al to Stainless, don't you need to drop pitch if the stainless prop is cupped? I think the Rapture is high rake, which might not be so good for stern lift, but then again, this is an ancient light 115 so I probably don't need to worry about that.

Anybody know any good places to look for cheap props besides Ebay? I saw a couple Rapture props on ebay in the right size and diameter but haven't figured out whether they all work on all manufacturers motors or not (or whether they all have a replaceable hub or not). I could not find any Mirage's or Laser's below 19P (short of buying a $$$ new one).

Oh btw Reelscape, how old were the Mariners that were built by Yammie?

Anyway, thanks again everybody :)

Re: Prop for 115 2S on SF 20
 

Hey Muddy-

Congrats that you finally got our boat!! :cool:

strick

Re: Prop for 115 2S on SF 20
 

Laser only goes down to 19 Pitch and Mirage plus only fits the large hub Mercs. Try PowerTech . . .

http://www.ptprop.com/catalog/

Re: Prop for 115 2S on SF 20
 

Thanks for the welcome Strick. It's been a long time coming. It's gonna be a while before I can hit the water in this thing. You know how that goes.

Thanks for the heads up on the Mirage and Laser BigShrimpin. I will prob go with a Powertech when I get a new motor. For now, I am just trying to come up with something relatively cheap to stick on this old motor. It looks like I might be able to get a Rapture (SS) for the same price as a new Al prop on Ebay. Will post numbers when I get this thing running.

The motor is actually in inline 6. Since it was a 115, I was thinking 4-cyl before I popped the top. It will definitely need some rewiring, an impeller, and probably a carb kit, new gas lines, filter, steering, yeah.. pretty much everything... Should be fun ;)

Re: Prop for 115 2S on SF 20
 

muddy - I found the rapture prop to make the bow way too light compared to other props. Your boat may behave somewhat differently since the rapture prop for the inline 6 is a smaller diameter prop with less blade surface, but I didn't like the rapture prop I tried for the 20. I got much much better performance out of a dinged up aluminum blackmax prop (both were 17 pitch and the rapture was in perfect condition)

Re: Prop for 115 2S on SF 20
 

Thanks BigShrimpin! I will skip the Rapture then and see what else I can find.

-Muddy

Re: Prop for 115 2S on SF 20
 

FWIW - I've been running an old Johnson V4 - 115 on my Seafari 20' - the prop is a 13-3/4 by 15, and it spins it readily. I think my voltage regulator is blown, my fishfinder reads input voltage and shows 16+V, and consequently I believe my tach is way off, WOT it's showing close to 8000 rpm, can't be right, the motor would blow...

make a long story short, I'm picking up a 13-1/4 x 17 to give a try.... and gonna fix the voltage regulator. One thing I hear over and over is to Not lug a 2S motor, you need to let them spin up where they want to be, so proppage and tach reading is important.

Bill

Re: Prop for 115 2S on SF 20
 

Oldbluesplayer... 8000 rpm... I certainly hope your tach is off
I am eyeballing a 16 pitch Mercury Vengeance right now and wondering if the diameter is too small (13 1/8 I think). Let me know what happens if you happen to get that 13 1/4x17.

I am getting a little ahead of myself here. I just pulled a wiring harness out that crumbled in my fingers, so I have some work to do before I can do any testing.

-Muddy

Re: Prop for 115 2S on SF 20
 

I change my answer, I thought it was an 18', your right should be a 15 on a 20 I would guess, sorry.

Re: Prop for 115 2S on SF 20
 

The inline-six motors are all Mercury, no Yammie stuff there. They were nicknamed "Tower of Power", and Mercury made them in everything from 70 to 165 hp. They are very good motors. The 115 Mariner should be more than adequate to push a 20'. I agree with going to a smaller pitch prop to keep the rpm's up. PowerTech will custom pitch any of their props for a very small fee.

Here is a very good prop for what you describe as your needs. PowerTech prop

One caveat: the inline 6 motors are naturally balanced (no balancer) and they ALL will self-destruct if run for more than a few minutes at 6600 to 6800 rpm. For some reason, this rpm sets up a harmonic vibration that causes connecting rod failure. Fortunately, if you are not racing, you have no reason to need more than 6200.

In my much younger days I got to oversee the destruction of 2 XS1500 motors from harmonics while racing.
It would be an understatement to say I love the "Tower of Power". I still have 2 inline six motors. The '73 XS1500-EL produced a genuine 165 hp and weighed only 274 lbs. (Mine were on the back of a 14' boat. Yeehaa :eek:)

Re: Prop for 115 2S on SF 20
 

Fr. Frank :) I was hoping you would respond. Thanks for the info and the warning.

When I was a kid, I had a 1960something Merc on a 12 foot boat that I sank 3 times. You would think I would have learned after the first time not to make hard turns when only the prop is in the water. That motor was still running when I gave it away a few years back. You have got me beat though. I have seen some of the other crazy cajuns around here with 115's and 150's on 14 foot aluminum flats. It is fun to watch. The guy with the 150 had to stack a bunch of people in front to keep the boat on the water. There is even a Seacraft 20 for sale with a 250 on it over in Baton Rouge. :D

Re: Prop for 115 2S on SF 20
 

My dad got me started racing in spade-hulled "kneeboats", similar to class G when I was 8. My 1st boat was 6 1/2 feet long with an 18hp Merc racing engine.

My fastest "Tower of Power" was an XS1500 on a 14' Cacci Craft, which threw a rod one day at about 82-83 mph at, you guessed it, 6750 rpm. The connecting rod just missed me.

The fastest I got on the water personally was when I was managing a marina and Alan Green, the founder of Quicksilver Surf products, brought me a new 21' Allison with a 225 SuperSix Suzuki, complaining that it would only go 74 mph. The dealer told him he couldn't make it go any faster. I told him for $6K plus expenses I would get him 20% more speed, 90 mph. After blueprinting the hull and changing him over to a Merc 225 EFI, adding a jackplate, nosecone, etc., etc., we got the boat to radar a true 112 mph at 6700 rpm. Only cost him $19K including the motor.

The fastest boat I ever rigged was in Ocean City, MD, when I rigged a homemade 25' plywood and glass Chincoteague Scow with twin 300hp 3.4L big block Mercury motors for . Chincoteague Scow racing is a phenomenon at the Eastern Shore. This boat ran a reported 118 mph, although I never ran it over about 85 when testing it.

BTW, I quit going real fast on the water after I stuffed a 30' Velocity at 65-70 mph off of Ft. Lauderdale during a regatta in 1985. That one hurt. I had bruises in the shape of the throttles for a couple weeks. :(

Re: Prop for 115 2S on SF 20
 

Great stories Frank!! My first boat was a pirogue when I was 5 or 6. You would have smoked me ;)

I might be needing my prop sooner than I thought. I replaced the crumbley wiring and the stator (since the wiring was completely gone on it). I rigged up a new ignition and refilled and bled the trim/tilt which was bone dry. We took the boat to the ramp today. It was it's first time in the water in 17 years. The motor had not been started in 17 years and it is a 27 year old motor. Keep in mind that I did not rebuild the fuel pump or carbs or anything else except wiring and splicing some new stuff onto the idle stabilizer. I did take the advice of some people on THT and sprayed Marvel Mystery oil in the cylinders and stuck some new plugs in it. It started in under half a minute. Another guy who was bringing in his boat came over to look and we noticed that it had a couple dry-rotted internal gas lines broken in half squirting gas all over the place but the motor was running even with the broken lines!!!! It probably would have been easier to start but every time I would pump the bulb on the gas line, the gas would just squirt out one of the broken hoses (which is a really bad thing if you are on the water and trying not to kill fish). Sooo, I will need new gas lines before I do anything else to it. I would not have gotten very far anyway though. The starboard deck drain through-hull has a severe leak and would have sunk the old girl after an hour or so especially since there was no bilge pump. When I got the boat, there was enough mulch in the bilge to plant a garden. You could not even see the bilge pump.

-Muddy

Re: Prop for 115 2S on SF 20
 

I ran a 115 on a Seafari for years with a 133/4x15 SST prop, motor raised 1 hole (cav plate +1" above keel). Was best all around prop for this boat. Would run 5400-5700 rpm, 32-35 mph depending on load.

Re: Prop for 115 2S on SF 20
 

Thanks for the input Bushwacker. Anybody have any comments on a higher diameter/lower pitch prop vs smaller diameter/higher pitch and it's effects on Seacraft speed and handling? What diameter is too small?

For example Mercury Vengeance 13-1/8 x 16" vs 13-3/4 x 15" SS Powertech