Which Prop? - Crap Shoot - 1974 Mercury 650 on a 15' tri hull

[Berryn]

Hi again Jimmbo,

I've been looking through all my stuff to find the pictures of the old boat (I took the pictures because it was sold through eBay). I do remember it was a blue stripe and didn't look to have been altered. I know they're on a hard drive around here somewhere. I remember I had a mid 80's kicker on one of the whalers that I put a different cowl on to match the 1962 Mercury 1000. It (the kicker) originally had a 3 toned brown stripe. I'll post what I find.

P.S. I found this pic of a 50horse like the one I had. Apparently I was mistaken about the clamshell.

 

[Berryn]

Thanks Sea Rider will do.

 

[jimmbo]

That's the 4 cylinder 50hp

 

[Berryn]

Hmmm... I was certain it was a 3 cylinder. 13 years ago. 65 years old. Must be losing it.

I just looked on eBay to see if pics were in my history. At that time I was under a different "handle". No luck. Now I'm not sure if it was a 3 or 4 cyl. Just remember it was a blue stripe. Still thinking it was a 3. 1986 + ? Anyway, the motor was on it when I got it. Just thought it would have been closer to the boat year (1973).

 

[Berryn]

Looking through old pics, I found some pictures of one of the Whalers. These were taken in 2007 which means the other ArrowGlass was somewhere around 2005. My memory should be better. Seems like so much longer ago.

 

[jimmbo]

The Merc 1000 is 1962 or 63. 90 cubic inches. Love the recoil grip and the choke knob! The kicker looks like a custom decal 1978

 

[Berryn]

UPDATE:

Cheers All,
I ordered and received the new prop and finally had a chance to get to Lake Anna yesterday. First let me say this - I ordered a 13p prop and received a 14p prop. Well, why not try it. I switched to a RELIABLE Teleflex tach. When I powered up the boat the difference was immediately noticeable. It would JUMP on plane (although I normally prefer to take it slower to avoid spinning the prop). The water was somewhat rough - no whitecaps, but not as smooth as I would have liked, so we fished a while until the wind backed down so we could test the prop. When we were able to get on smooth water the boat quickly got to about 31mph although just for a second because the tach was reading 6000 plus. Still looking for the right prop only now I have a good starting point. All said it was a good day at the lake right up until the downpour while putting the boat back on the trailer. All in good fun.

 

[WesNewell]

If I'm not mistaken, rpm range for that engine is 5000-5500. If that's the case you should go to a 17P prop Something similar to this.Solas 1311-110-17. Should get you ~40 mph and bring your max rpm down to ~5500.

 

[Berryn]

Thanks Wes,
I found a used 48-73144A Mercury Black Max ( 10 x 17p ) on eBay for $50 so I ordered it. I'll let you know what happens. Thanks again.

 

[Berryn]

Hmmmm,,,,, Strange surprise. I received the prop. 10 X 17p. The 1" diameter difference between the 11x14p and this one makes this one look small. Anyway, I put it on and found a good excuse to head for the river. When I throttled up I DID NOT have the immediate jump onto plane, but a slightly struggled one - although it did plane out within about 15 seconds. All that was expected. What wasn't expected was the tach read around 5000 at WOT but the gps speed would not get past 28 mph. I thought it might be current or tide, but this happened in either direction (+ or -). Slippage? So far, the best was the 11 x 14p. Maybe a 11 x 15p or 16p next? Curious. Now I'm puzzled again.

 

[jimmbo]

Just out of curiosity, what is your tachometer set at?

 

[WesNewell]

Somethings wrong for sure. Theo speed for a 17p prop with 1.64gr @ 5000rpm is 49 mph. 28 mph is 43% slippage. None of this makes any sense. Some of your numbers have to be wrong or your hub is spinning.

 

[Berryn]

Hi All, I found this in an old post....

So I set the tach to 5. Actually, that's the ONLY setting that was anywhere near looking right. Teleflex said to set a 12 pole to 3 - nowhere near it - and a few people that I've read say that the 650 three cylinders HAVE to be set at 5 to work.

I too have done the calculations for prop slip. You're right... That CAN"T be right. Both props were used props, but usually a spun prop will lose "traction" when throttled up suddenly. That didn't happen. I've ordered yet ANOTHER prop. This time a new one - Solas 1311-110-16 Prop Mercury Mercruiser Amita 3 11'' x 16'' Pitch 3 Blade and looking for yet ANOTHER tach. I will keep you all posted.

Thanks for all the helpful comments.

 

[jimmbo]

I did some calculations based on your reported speed with the 17" prop, allowing for 10% slip I came up with 3120 rpm, 15% slip 3356 rpm.

 

[Berryn]

Hmmm... So many things don't make sense. If the 11x14 sent the tach to 6000 and the 10x17 sent it to 5000 WOT (which is understandable), then why would my speed be so slow? The boat is very light. If the tach were reading half figures, then why is it reading only 6000/5000 (respectfully).. Can my slip really be that bad? Like it's pulling a parachute? Thanks again guys for all your input. I may end up with a room FULL of props, but this has become an obsession and it WILL get right. lol... Dave

 

[jimmbo]

I think your tach is reading too high. Beg/steal/borrow, or even purchase an inductive tach, one that clips around a spark plug wire, make sure it is set for 2 stroke and see how it compares to the dash tach.

 

[Berryn]

Will that work with a 3 cylinder? With only 1 coil, don't all plugs fire at the same time? I mean, The ones I've seen have a wire wrapped around the #1 plug wire (or any plug wire for that matter) and count how many times that one cylinder fires. That would be multiplied by 3 if all plugs fire at the same time.

 

[jimmbo]

No, all plugs do not fire at the same time, they will fire 120 degrees apart. That's why there is a distributor

With an inductive tach, you are choosing one sparkplug wire as a trigger.

 

[WesNewell]

No, they fire in order. That's why the distributor is called what it is. It distributes the current to each cylinder.

 

[Faztbullet]

When you refurbished boat you changed center of gravity as now the weight is on the nose...