frustrated

[kerrylunn]

i have a 2009 rinker 192 captiva with a 4.3l with an alpha drive. the boat came with a 14.75x21 p aluminum prop. we do a lot of wake boarding and skiing and getting up on plane was terrible especially when the bigger people wanted to play.i tried a 14.75 x 19 p aluminum prop with helped but still not what i would like to see.i have read where a 4 blade would help so i purchased a 4 x 20 p prop and with out even pulling anyone i can tell the prop is not what i want as it's a dog out of the whole with my wife and i and our 3 kids. all props are manufactured by quicksilver. what am i to look at trying now to improve getting on plane with these boarders on behind the boat???? any suggestions appreciated. thanks in advance.

 

[steelespike]

Re: frustrated

We need to know your wot rpm and speed with the 21" prop.and typical load.
wot rpm and speed with the 19" and finally the same with the 20" 4 bld.
If the 19 was performing within the rpm range of the motor you should
have gone with an 18" 4 bld.Do you trim down and move some weight forward for water sports?

 

[kerrylunn]

Re: frustrated

4600 rpm and about 42mph with the 21 p prop
48-5000 rpm and 38 mph with the 19 p prop. was told not to run over 4600 rpm.
not able to comment on the 4 blade yet as we were only out once and did not run it up to max but it is a dog just getting to plane not pulling anything.
typical load is about 550-600lbs of family. when water sporting i try to run with couple people on the bow is only way to get some of the heavier guys up quick.

 

[craze1cars]

Re: frustrated

#1 question: Not to insult your intelligence, but proper use of trim can make a 10 second holeshot into a 3 second holeshot...Steelspike asked this also, but you didn't answer: Are you fully trimmed down for take-off? This is mandatory for watersports...only trim up after getting on plane. If you're a "set the trim and forget it" type of person (many are), the person on the end of the rope will pay a BIG price on takeoff....

Other comments: Who told you not to exceed 4,600? Mercruiser themselves spec a 4,400 to 4,800 operating range on that motor. So even Mercruiser says 4,800 is entirely safe, and IMO short blasts up to 5,000 are equally safe...and IMO this is where you want to be for watersports. This is why the 19 helps. So I say prop it for 5,000 since watersports with a load of people seems to be your most important aspect, and just go easy with the full speed runs and don't actually hit that 5,000 mark for too many extended periods of time.

When switching to 4 blades you need to go DOWN in pitch, not up. So since the 19 3 blade is getting you in a good rpm range, a 4 blade would need to probably be an 18 pitch to get you in a similar range. However instead you bought a 20. This is probably going to under-rev and come out of the hole much like your 21 pitch 3 blade...poorly. Seems to be what you are reporting.

Which 4.3L do you have in this boat? If it's the base carburated 190 hp version, I believe that's the smallest engine they offered in that model, and therefore it will always be a bit underpowered for a 19 ft runabout boat...so you will only be able to do so much and it'll never be a rocket out of the hole....but it can be improved.

What is your drive ratio? It would be nice to do some calculations to see if maybe you have other problems...like an inaccurate tach for example...which may completely screw up your prop selection. If you share your drive ratio we may be able to identify or exclude a possible non-prop related problem.

Without much more information, I believe an 18 pitch 4 blade will suit your boat much better than anything you have now.

And a stainless would be even better. Aluminum props can slip a lot, and are a bit inefficient. I hesitate to offer a stainless suggestion that might be off-base however because they are 3x the cost or more....but if you find the correct stainless, it will put the spanking on ANY of those aluminum props you are running, and will be worth the investment. Will your marina or a local shop allow you to try one out for a day? If yes, try a nice 17 or 18 pitch stainless 4 blade...should be pretty close to what you need.

And a product called Smart Tabs will help MANY underpowered runabouts get up on plane in a bigger hurry for less than $200. Might want to look into them as well.

 

[kerrylunn]

Re: frustrated

yes i always trim down on take off and play with it once on plane for speed and lower rpm. very seldom when boarding and skiing. the 4.3l i have is the carbed version. the dealer i got the boat from is who is telling me not go over 4600 rpm so much that i put a note on the dash for all others driving the boat to see . drive ratio is 1:81

 

[craze1cars]

Re: frustrated

Knowing your drive ratio tells me you have a fair amount of slip. As much as 22% with the 19 pitch. This isn't awful, but it's not great. Frankly it's typical for a basic aluminum prop on an I/O.

A high quality stainless will reduce the slip. Less slip = better accelleration and better top speed. It'll be better, but it won't knock your socks off or anything. My recommendation for trial pitch remains the same as I wrote above...probably 18 for aluminum, maybe 17 or 18 for stainless. 4 blades is better than 3 for your purposes.

If you provide a full-speed WOT trimmed-out RPM and speed data from that 20 pitch 4 blade aluminum you currently have, it will help me be more accurate on a recommendation.

I disagree with your dealer on the 4,600 thing...have no idea why he beat that into your head, and I believe it has contributed to your frustration. To make yourself feel better read the sticker that Mercruiser installed on the top of your engine...I figure Mercruiser knows more than a guy at a dealership does. I'm willing to bet you most likely the Mercruiser sticker says "4,400 to 4,800" for a recommended operating range...heck it might even say 4,600 to 5,000? But I doubt it...I think it was the MPI's that sometimes recommended up to 5,000 and not the carb'd motors. Notice I don't believe Mercruiser even uses the term "max" on that sticker....it'll survive running faster than 4,600 no problem as long as you don't go hog wild.

Granted 4,600 is right in the middle of the range, which is fine for "average" boating. But it's not ideal for holeshot, which is your priority. You'll hurt absolutely nothing if you keep it under 5K the majority of the time...and even if you sustain it for a little while when you feel the need for speed...

If you insist on keeping it propped for full speed at only 4,600, you will not be able to maximize your holeshot without throwing a LOT of stuff overboard and reducing weight...that's why I say you gotta prop it for 5,000.

I realize I'm just a monkey giving free advice on the internet, but if it makes you feel any better, I have my boat specifically propped for 5,000 rpms (mine is a 20 ft 5.0L, but it also has a 4,400 to 4,800 sticker on it), and frankly I run it at those top speeds and RPMS rather frequently. It's a 1999 model with 800 hours on it. It runs as good as new, burns zero oil, compression specs still same as new...and it rips outta the hole like you wouldn't believe...on plane in about 2 seconds. Wanna pull up 2 fat guys on slaloms out of a deepwater start at the same time? Probably closer to 4 or 5 seconds but still NOOO problem...

 

[kerrylunn]

Re: frustrated

ok got in touch with my dealer and got a 4 blade 18 p aluminum prop to try.had 560 lbs pounds of people and full tank fuel. with 250 pounds on bow was 5 secs to plane. with everyone in the back was 7 secs to plane.usually would be another 200 lbs or so that was at work today. wot was 4700 rpm with top end around 37-38 mph(gps).is the time to plane average for this and am i going to find a setup that will give me the hole shot i want???? or am i just lacking hp????

 

[craze1cars]

Re: frustrated

I think 5 seconds is fairly typical for a carb'd 4.3 runabout in a boat that size/design. I found a bit of a discussion on the topic over on the Rinker forum:
http://www.rinkerboatowners.com/forum/index.php?topic=3511.0

You might nose around there a bit more and see if you can find some more info specific to your model.

Is that 18 pitch 4 blade better than the other props you have been using, or did it seem about the same? Overall even your top speeds sound a little bit low to me for a rig like this. Many 3.0's will run at your speed. I would expect a 4.3L 19 ft boat to run mid-40's rather easily....45 or maybe more? Almost like you're a bit down on horsepower maybe? I know the boat is not that old, but maybe it would be worth checking ignition timing to ensure it's not a bit retarded, and make sure the throttle butterflies are opening fully, etc....

If a problem is actually found and corrected, prop search starts over....

Smart tabs are almost always a helpful add-on for improving planing speeds, not horribly expensive. I would seriously consider a set if I were you. Again, I suggest propping for closer to 5,000 rpm WOT and your holeshot will improve a bit more...which would mean dropping in pitch yet again, maybe a 17 pitch would be in order...will not improve your top speed any, but probably no worse either.

If the motor is confirmed to be running at its peak, and a 17 pitch prop/Smart tab combo doesn't satisfy yer needs, then I'm out of ideas. My next suggestions will be far more expensive and you probably won't like 'em....repower the boat to a 4.3 MPI or 5.0L motor...or trade up to a stronger boat....

I owned an 18 foot Rinker at one time...older 1992 18 footer. It struggled a bit to get on plane (was only a 3.0L) with most any prop. Smart Tabs REALLY cured it...I'm not a huge fan of them for boats that don't need the boost, but yours seems to need it...and they do bump holeshot notably.