1991 FourWinns OMC 4.3 reccomendation?

[duke3478]

Hi, hwsiii and other posters. I'm looking for the best prop recommendation for my boat:

1. 1991 Four Winns 195 Freedom (closed bow)
2. 19.5'length, 6' beam, 2580lbs.
2a.4.3 V6, about 160 HP.
3. 4 adults, 2 small kids, 15gal. normal load
4. Used for kneeboarding, tubing, and cruising
5. Deep V, unknown deadrise.
6. 1991 OMC 4.3 V6
7. 165or so HP; 1.68:1ratio
8. Manf. WOT: 4200-4600
9.N/A
10. N/A
11. Nauticus Smart Tabs installed*
12. Quicksilver 15x17 3 blade prop installed, aluminum
13. WOT RPM: 5000
Speed: 38mph (2 adults, 2 kids, 10 gal fuel, 200lbs gear, etc.)
14. Used at Lake Mead, NV, about 2000 feet asl, I think.
15. Fresh plugs, wires, coil. 89 octane fuel
16. Prop is stock, needs replaced due to being chipped on driveway while
backing
17. N/A
18. Would like a 40mph top speed or thereabouts, and a 30mph cruise.

*just installed, after speed/RPM data calculated

I just installed a second quicksilver, a 3-blade 15x19, but it's shorter than the stock one and doesn't insert into the lower end like the old one did. I'm afraid I'm going to get BAD exhaust ventilation in this new one. There's a 1.5" gap behind the prop.

 

[hwsiii]

Re: 1991 FourWinns OMC 4.3 reccomendation?

Duke, I would not use that prop on the boat the way it is, something is wrong, it shouldn't be that way if it is the correct prop put on correctly.
I show you should be using a 19" prop, but you are showing a 21% prop slip right now at WOT with the 17" prop and that is too high. So I am going to recommend a 17" pitch 4 blade in the Solas Amita and in my opinion it will bring your prop slip down enough to make your top speed reach 40 MPH and also dramatically increase your hole shot and acceleration at all RPM to WOT and should turn about 4,700 RPM. Here are my postulations for your old and new Numbers and prop slip.

Prop Slip

 

[duke3478]

Re: 1991 FourWinns OMC 4.3 reccomendation?

hwsiii, thank you so much for the info. I ran the 15x19 today and had no issues other than a slightly more sluggish than normal hole shot. I dove on the prop with my mask and snorkel while my wife ran the engine (in neutral) thru 4000 rpms, and hardly any exhaust exited behind it. Does it vent thru the prop all the time or only while in gear? I thought ventilation was going to be an issue, but it isn't. The gap between prop and flange is only 1/2", I measured wrong, but it's definitely installed correctly. My guess is that the PO bought the wrong prop.

We were about 200lbs heavier than normal today. With the 15x19 my top speed was about 36, but my WOT increased to 6000. I'm going to chalk that up to the smart tabs, and manufacturer difference between the new and old prop.

I'll be ordering the SA 4-blade 15x17, thank you again!

 

[hwsiii]

Re: 1991 FourWinns OMC 4.3 reccomendation?

Duke, do me a favor before you order the prop, put the old prop on and rerun it again to make sure the RPM didn't increase another 1,000 RPM. There is no way that the 19" should have gone to 6,000 RPM and the 17" only 5,000. The Smart Tabs shouldn't have increased the RPM anywhere near that much, as I have installed them on my boat a long time ago myself.
Please send me a picture of the 19" prop installed on the boat.


H

 

[duke3478]

Re: 1991 FourWinns OMC 4.3 reccomendation?

H,

I would re-run the old prop but I chipped off too large a part of one of the blades when I backed it out (on the trailer) with the drive down. I really wanted to make the first run with the SmartTabs with the original prop setup, too, but that's how it goes. The old prop was in rough shape, anyway, terribly rough leading edge and a lot of alkali scale from being slipped for a long time. It was time.

I suspect my tach a little, since it just doesn't seem right to me, either. The problem is certainly not exhaust ventilation.

I am a little concerned though, about going 19" pitch or 17". If your original calcs said 19, I almost lean that way. But I've been using a 3-blade, so I think 17" might be just right in a 4. Besides that, the Amita line is very reasonably priced so I don't mind if the 17" doesn't hit the nail exactly on the head. I could get a 19" down the line.

My wife left our camera in CA last time she went. (Sure hope the new 'owner' is enjoying it.) I'll get some pics with my phone and post them when I can.

Update:

 

[duke3478]

Re: 1991 FourWinns OMC 4.3 reccomendation?

Sorry I never posted results! My top speed at WOT with this config was 43 mph at 5000 rpm, too much throttle! The solas amita 4-blades are everything they say they are. Hole shot was ridiculous and with the smarttabs, I'm on plane at about 11mph. It just bobs up, and out, and I'm on top.

Unfortunately I installed without a safety washer after removing it to clear away some fishing line. First reverse dropped the prop in 110 feet of water... Anyone with nitrox need a 14.5x17 prop?

I just ordered a 19" pitch. Hoping to hit 45mph at 4800.

A note on nuts-stainless top-lock nuts don't have any nylon to degenerate, and allow for use of a cotter or safety wire. I switched and I love them.