Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

[felclin]

I'm having some unexpected performance with my current prop/engine combo and am hoping to get some feedback regarding prop selection before purchasing a new prop and moving my current to backup status. After some forum research, the speeds/performance with my prop/engine combo is consistent with what I would expect out of a 19 or 17 pitch prop, not my current 23. I don't have enough experience to figure this out on my own.

-boat is a 2005 bayliner 185, approximately 3000 lbs with gear and 2 to 3 passengers

-the powerplant is a 4.3l carb'd v6, Alpha one outdrive with a 1:81 gear ratio (approximately 190 hp)

-current prop is an aluminum, 3 blade, 23 pitch, 14 in diameter (serial # Mercury 832834A45P23). I purchased this boat second hand and do not know if this is the original prop or replacement. Very minor dings on prop - likely not the culprit

-currently the prop gets on plane relatively quickly (3 to 6 seconds?) and pulls a skier out of the hole in about 3 to 5 seconds.

-top speed is limited by RPM's - at 4800 I'm only getting 30mph (gps confirmed) and I have to watch not to push to WOT or the rpm's will shoot to near 5500 very quickly, maybe pushing only 35 mph.

-Engine/drivetrain have run sound since we bought the boat three months ago, and the engine was checked out by a marina prior to purchase and by another marina for service when we had a fish finder/gps installed a month ago - no issues.

Any help or information that can be offered will be greatly appreciated.

Clint

 

[SparkieBoat]

Re: Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

it sounds like you may be cavitating or some bad prop slippage. . what is the HP of your motor?? also make sure you are not over trimming the gear case. but you need to figure out why the high RPMs. at 4800 RPMs and 30 MPH and a 1.81 gear you are having %48 prop slip. that is way too high. maybe you have a bad tach, or a spun hub on your prop. you need to figure out whats up.

 

[felclin]

Re: Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

HP is 190. I'm a new boater, so inexperienced at driving. As of now, I've been putting trim full down off of the trailer and running it that way until putting it back on. Could this be contributing to the low top end speed?

 

[John_S]

Re: Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

HP is 190. I'm a new boater, so inexperienced at driving. As of now, I've been putting trim full down off of the trailer and running it that way until putting it back on. Could this be contributing to the low top end speed?

Once on plane, start triming out until it "slips" cavitates. Trim back down a little, to prevent the "slip".

Also, put a mark on the prop hub, such that you could tell if spinning on the hub. I think that prop has a flow Torq hub. If so, make sure prop nut is tight. (55lbs) Note: there are locking tabs that have to be pulled away before loosening or tightening.

 

[steelespike]

Re: Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

Yes you must trim up for the fastest speed.It will bring the bow up and get more boat out of the water.Speed should be around 50.trim for the best rpm and speed
I suspect the unnatural attitude of the poorly trimmed boat is the cause of the venting, it likely is handling strangely as well.
Start with down trim and as the boat planes gradually raise the trim to the best setting.
usually as you decrease speed you gradually lower trim so it will stay on plane longer.
In rough conditions less throttle and trim may be necessary to better control the ride and handling.

 

[HopinImFloatin]

Re: Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

im not a pro by any means but i would sure think being trimmed all the way down while underway will kill your top end. Its a little funny to me that you can overspeed your engine while plowing with the trim all the way down as it should actually be bogging the engine a bit, kind of like running a standard trans car in too high a gear at too low a speed. Trim the boat by sound and feel; once up on plane, begin to trim up until it begins to porpoise (kind of diving up then back down at the bow repeatedly), then trim down a bit to stop that and that should be your max trim at speed. Sounds like you will REALLY need to keep an eye on the tach because if it was overspeeding before, it will be MUCH worse with the boat trimmed up. with a 23 pitch, i would think that boat will fly. I have a similar size boat and same size motor(but 175hp) and mine will do 38 gps with normal load with a 19 pitch. maybe your tach is inaccurate?

 

[felclin]

Re: Prop selection for Bayliner 185 (2005) w/ 4.3 L carbed

thanks for the help everybody. It looks like it was a tach issue and a driving/trim issue.

I checked the tach and it was set for a 4 cylinder, not the v6 I've got. I changed the setting on the back to match the engine.

Took it out today and worked through trim adjustment. Noticed an immediate difference - saw 46 top speed today, handled much better, tach was much more in line with what I have been told regarding the mercruiser 4.3 w/ alpha one and a 23 pitch prop (you'll see 4800 rpm at WOT and about 50 mph).

It was very loud at about 4400 rpm so I didn't push it higher, but no knocking or overheating (mainly just freaked the wife out) and the speed (46) and throttle (90%) was consistent with what I was expecting so I'm confident that the tach is now reading correctly.

thanks for the input everyone