Prop help, have the data now! 19.5ft bowrider with 4.3

[gixxerjim]

This is a new to me boat, runs great, very happy after one trip to the lake. Would like to get another 3 or 4 mph out of it. It is very smooth over waves and responsive compared to our old 1988 Sea Ray Seville 19' Bowrider wsith 3.0l. Just like riding on pillows compared to the harsh slap of the hull on waves with the SR

1). performance issue to correct

None really, runs great, but would like to achieve a little more top speed
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
Michigan Wheel Aluminum, Good condition, 3 blade
3) Current prop diameter and pitch (required).

14.5x17P note it does have a whale tail on it from the previous owner.
4) Wide open throttle RPM and speed with an average load (very helpful)
4800rpm @ 39mph with average load
5) Engine/drive make, model, year, and HP
Mercruiser 1992, 4.3 2bl, Alpha1 1.84:1 (don't know hp for sure when new, was rebuilt in 2007, receipt lists flat top pistons for higher compression, moly rings, roller rockers, no details on cam)
6) Boat make model, year, length and weight
Century Mustang II Bowrider, 1992, 19.5ft, 1850lb with no motor, with motor and full load of fuel and passengers I estimate 2950lb

Thanks for any advice on brand/model/pitch. Prefer to go with a Mercruiser prop since they are readily available secondhand in this area but willing to consider all alternatives. Don't want stainless, would consider plastic if recommended with experience.

Thanks so much for your help, really love this boat's behavior and what a relieve to buy a used boat and have no surprises first time out!

 

[steelespike]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

I think typically a 4.3 in a 19 footer would run a 21" to a 23" prop about upper 40s to 50+ mph.
The 17" seems small.
Probably need to do some simple stuff check that the throttle opens all the way.
Check that timing is set right and advancing as it should.Be sure it firing on all cylinders.
Do a compression check.
Don't assume anything just because of a recent rebuild.

 

[starsnstripers]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

I just posted a similar problem, im running a 21 x 14 1/4 and only getting 28mph @ 4000 rpms with my 19.5 4.3 mercruiser alpha 1. I lost 2mph going from a 19-21 couldn't believe it.

 

[gixxerjim]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

I am okay with the current performance given a short prop. I am running out to the max rpm rating for the motor. I suspect with a 20p I would get 43 mph out of it. Not bad for this size boat IMO. Anybody have specific prop or pitch recommendations for my setup? Is good all around performance and 43 mph or so attainable?

 

[jestor68]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

Before you do anything, you should test with that "whale tail" removed. I suspect it is costing you some speed. Depending on the brand and design, some of those things can slow you down several mph; but they do help the boat plane faster.

 

[trebor7970]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

something is definitely wrong. Your size boat with a 4.3 should be hitting top speeds closer to 50mph. The prop seems small as well. Im surprised a 17 doesnt bring you into the 5000 plus rpm range. Are you using your trim ?? Is the throttle going all the way? Maybe have someone check the cables to make sure.

 

[gixxerjim]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

I do use the trim and get it planed well, but the trim NEVER is in the level position. I suspect the whale tail is dragging the boat on top end. FWIW it is a "SE Sport 300". With my wife at 130lbs, me at 165, and our 3 boys all 50-75 each, we don't really have a lot to pull around. Looking around online some folks say they lost 1-3mph.

Any advice or experience with these hydrofoils? I am going to remove it before our next trip out and try the boat without.

Another question did they ever put a 4 barrel on these 4.3l? Seems like the motor was hopped up at rebuild but only a 2 barrel? Seriously? Maybe I am way off...

 

[steelespike]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

Removing the whale tale should help. Again the 17" should be over revving.
after your run without the tale check the engine don't assume that a recent rebuild was done right.
Be sure the throttle opens all the way,be sure timing is set right and advancing as it should.
Higher compression may require a timing change.Also might require higher octane.
maybe cooler plugs.
If any of the hop up stuff was automotive related it won't work right.
The marine engine is set up to peak at about 4600-4800 automotive setup is something like 5500.
If the there was a cam change timing and carburation probably would need to be altered.
Not only the timing setting but the timing curve.I don't know whats needed to get these things right
only that these changes may be needed.
Don't get all worried about these things until you check that the motor is sound with the normal stuff.
A compression check is a good start. check the throttle.

 

[Bondo]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

these hydrofoils? I am going to remove it before our next trip out and try the boat without.

Another question did they ever put a 4 barrel on these 4.3l? Seems like the motor was hopped up at rebuild but only a 2 barrel? Seriously? Maybe I am way off...

Ayuh,.... Good idea....

The 4.3l, with a 4bbl carb is rated 'bout 20/ 25hp Higher....

I'm got 1, 'n I wouldn't have it any other way....

 

[gixxerjim]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

I ran without the foil. Sorry to complicate things but I also had 200lbs more stuff in the boat and the weather was different. Here's the two tests:

1992 Century Mustang II 19.5ft, 4.3L 2-barrel, 1.84:1, 17P Michigan Wheel 3blade Aluminum, 4400-4800rpm
70^F, dewpoint 63^, 500lb gas and gear, w/ hydrofoil, 39mph @ 4800rpm,
87^F, dewpoint 60^, 700lb gas and gear, w/o hydrofoil, 38mph @ 4700rpm
Runs great, although I noticed a slight fuel odor in the boat while sitting hot not running, and on restart I had to floor it like it was flooded, then started immediately and ran great.

Anybody have any ideas here? There have been references to checking timing and so on, but do these speeds/loads/rpm seem so far out of line as to warrant investigating the health of the motor?

 

[Maclin]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

Is that all the engine will do? Or is there some throttle left and you were holding it back to keep from over-revving?

What altitude are you boating at?

If that is all the engine will do, and the altitude is 2000ft or below then the engine is not generating the power I would expect.

 

[gixxerjim]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

That was full throttle, elevation is 770 ft as I recall. Could a marginally worn prop have much effect? It's not beat up or badly chipped but it's not perfect either.

 

[jimmbo]

Re: Prop help, have the data now! 19.5ft bowrider with 4.3

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