The Boating Forum - 2012 Cobalt 210 Prop Change?

We recently bought a 2012 Cobalt 210 and fitted it with the Mercury 5.0L 260hp Alpha One setup. The past weekend the father in-law (advanced skier a decade ago...) and I (novice is giving too much credit) tried to slalom behind my baby and didn't feel like we had enough "pop" to get out of the water cleanly on starts. Now, I'd rather not tell myself I have performance issues and I'd much rather blame the equipment. So, any recommendations for better holeshot performance by switching to a different prop? The current setup is a OEM BlackMax 3-blade aluminum at 17" of pitch and 15" diameter. I care about holeshot and not about losing 3mph top end at WOT, but certainly don't want to hit the rev-limiter after losing 10mph. The boat specs are 20degree deep V hull at about 4,000lbs not including passengers, fuel, and gear - I know she's a beast to ski behind, but a beauty to behold! Oh, and last piece of info is that Cobalt recommended a 3-blade aluminum at 15" of pitch...surprisingly the did not recommend SS or 4-blade contrary to what pretty much EVERYONE else on the face of the earth says - thoughts as to why? I am well versed on the math of top-end WOT, slippage, etc (thanks to this forum!) but am wondering if anyone has actually changed on this boat and their results??? Thanks in advance!

I will tell you from first hand experience with that particular boat that the power/outdrive combo you have is just not enough to slalom ski with and still carry a load in the boat.

That said, if you have a shop that can loan you props to try out then that would be best and most affordable. I'd try every combo of pitch and number of blades as you can to see what suits you best. Personally, I've seen 15s work well but you will sacrifice top end and rpms pretty heavily. Good luck!

What is your rpm and wide open speed with your normal load?

I think a Mirage Plus 15 pitch would be a big improvement over the 17 pitch aluminum.

When you were pulling the skier up was the rpm revving up a good bit, but it took a while for the boat to get up an running?
Or was the motor lugging and slowly getting up on plane?

This is a good place to start:

http://www.mercurymarine.com/propellers/prop-selector/#

Believe me. You have PLENTY of HP to pull a slalom skier. We would ski forever behind a 140hp Mark Twain and brag about how much power it had over an 85 hp outboard.

Your boat is propped from the factory to sell boats. That means getting the most speed per hp for some BS magazine review. Pulling skiers and water toys all day has NOTHING to do with top speed. A GOOD prop can completely transform your boat. Talk to ken2 above. Pick his brain and try a few. A good shop or your dealer should loan you a prop at a time to try until you get one you like. Ken should help narrow those choices to a managable couple of reccomendations, but ultimately it is still a bit of trial and error.

The right number of blades, the right material, the right shape, the right lift, the right cup, the right pitch, the right diameter, on and on. There is a science to props, and the people that know them can unlock potential you never thought was possible.

What is your rpm and wide open speed with your normal load?

I think a Mirage Plus 15 pitch would be a big improvement over the 17 pitch aluminum.

When you were pulling the skier up was the rpm revving up a good bit, but it took a while for the boat to get up an running?
Or was the motor lugging and slowly getting up on plane?

I have not really tested WOT numbers due to the minimal 15hrs we have on the boat and less than ideal conditions for me to let her loose. I have hit upper 40's without getting crazy with trimming up and squeezing out MPHs - that being said I did not note what the RPMs were at the time. Mercruiser puts this setup at 4600-5000...and they were less than helpful in helping me decide with props....

When attempting to pull the skier up (albeit without perfect form!) the boat revved good but seemed to not get forward momentum built quickly...no lugging evident.

My local prop shop, recommended by a multitude of people and dealers, recommended going stainless, Cobalt recommended aluminum and drop in pitch, and you recommend all of the above - may I ask why? Can you add insight to; efficiency, lower plane holding speeds, top end changes? Unfortunately I cannot readily swap props to find the perfect fit in an afternoon as I trailer her to local lakes, none with a prop dealer on sight. Thank you in advance!!!!!

If your motor revved up easy but didn't seem to have any forward momentum, you need more traction.
You have plenty of power, but your not getting it to the water.

You may not need to go to a lower pitch if thats the case.
Once you figure out your wide open rpm and speed, we can figure out if you actually need to go down in pitch or not.

To get more traction, you can either go to a larger diameter Stainless 3 blade like the Mercury Mirage Plus which has a decent amount of cup which will be a big improvement.
Or you may like a 4 blade prop like the Revolution 4 if you plan to water ski and wakeboard often.

The Revolution 4 will be slower on top end (compared to the Mirage), and less efficient at fast cruise speeds, but it will be better at slow and midrange speeds, and the transition to plane will be smoother. (helpful if you plan on wakeboarding and skiing most of the time)

The Mirage Plus will still pull much better then your current aluminum. And likely faster on top end, with better economy at cruise.

But before you do anything, find out what your wide open rpm and speed is.


Here is a good thread with a similar size and style boat and the guy has run both the props I'm talking about.
http://www.propgods.com/forum/default.aspx?g=posts&t=841

FWIW Cobalt Specs put this setup at 48mph/5150 rpms

Believe me. You have PLENTY of HP to pull a slalom skier. We would ski forever behind a 140hp Mark Twain and brag about how much power it had over an 85 hp outboard.

Your boat is propped from the factory to sell boats. That means getting the most speed per hp for some BS magazine review. Pulling skiers and water toys all day has NOTHING to do with top speed. A GOOD prop can completely transform your boat. Talk to ken2 above. Pick his brain and try a few. A good shop or your dealer should loan you a prop at a time to try until you get one you like. Ken should help narrow those choices to a managable couple of reccomendations, but ultimately it is still a bit of trial and error.

The right number of blades, the right material, the right shape, the right lift, the right cup, the right pitch, the right diameter, on and on. There is a science to props, and the people that know them can unlock potential you never thought was possible.

First, HP is not the issue and your little 140 HP Mark Twain was not pushing a 21 foot Cobalt, which is probably the heaviest 21 footer made.

Second, the problem is the alpha drive. At about 21 feet, it starts to make sense to go to a dual prop system like Volvo Duo Prop or Mercury Bravo instead of alpha. An alpha, at 17, would struggle with this boat. A bravo at maybe 26 would not. Maybe 24.

I think the 15 may be the way to go. A Bravo3 outdrive would be far preferable IMO to this boat's hull-block package.

Just typed up a lengthy and eloquent rebutal to the above complete with specs and pictures only to delete it. I came to the conclusion that those who know...will know you don't.

The wife and I ;):

http://i1193.photobucket.com/albums/aa352/rcskywalker/photo-21.jpg

Only persons information I do not second guess here on THT, is Ken at www.propgods.com. He has responded to you.

Listen to him, and you will be fine.

:tht_rulez:

Just typed up a lengthy and eloquent rebutal to the above complete with specs and pictures only to delete it. I came to the conclusion that those who know...will know you don't.

;?
Shall I post all my pics of all my previously owned bowriders, including Cobalts, to get "in the know" in your opinion? Should I list all the re proppings I've done to my previous boats?

Hey, you brought a 140 outboard into a discussion about Cobalt IO's and claimed it as realistic anecdotal evidence. That destroyed your cred more than one transom shot will reinforce it.

I am surprised nobody has reommended the High Five, they are amazing hole shot props when skiing. I have replaced many aluminum and even Mirages/Vengeance props with High Fives for people that do a lot of skiing, it is a great pulling prop, five blades so it bites well, small diamter so it spools up quickly. Only issue here is I would want to try it first as the smallest they make is a 17 pitch, but the design is definitely hole shot oriented.

Only persons information I do not second guess here on THT, is Ken at www.propgods.com. He has responded to you.

Listen to him, and you will be fine.

:tht_rulez:

My sentiments exactly.


THE 140 is not an outboard. Its a 4cyl Mercruiser I/O. You knew that...right?

When you tell a guy asking for PROP advice that the rig he has is crap and that he should have gotten a Bravo III or DP, your cred is...?

260hp from a 5.0 in a 21ft boat is PLENTY. For decades 260hp was the standard for carbed 5.7's.

Also for DECADES Alpha drives have been propelling boats and towing skiers without complaint. Formula (among others) often mated an Alpha to a 242 (heavy) to a 454 at approx 300hp and so long as you kept the prop in the water, the drive gave excellent service.

In conclusion: Tweak your prop. Love your boat. You'll either learn how to ski or your body will tell you to give up trying.

My sentiments exactly.


When you tell a guy asking for PROP advice that the rig he has is crap and that he should have gotten a Bravo III or DP, your cred is...?



I was a Cobalt Dealer for a number of years and dealt with this problem until I stopped ordering boats this way. However, PropGod is right and that will certainly help. Also, I have had good results with the High Five props.

I was a Cobalt Dealer for a number of years and dealt with this problem until I stopped ordering boats this way. However, PropGod is right and that will certainly help. Also, I have had good results with the High Five props.

Zeiss21: Just for clarification, are you saying the problem you dealt with was public perception or unsatisfactory performance from an Alpha drive?

THE 140 is not an outboard. Its a 4cyl Mercruiser I/O. You knew that...right?

When you tell a guy asking for PROP advice that the rig he has is crap and that he should have gotten a Bravo III or DP, your cred is...?

260hp from a 5.0 in a 21ft boat is PLENTY. For decades 260hp was the standard for carbed 5.7's.

Also for DECADES Alpha drives have been propelling boats and towing skiers without complaint. Formula (among others) often mated an Alpha to a 242 (heavy) to a 454 at approx 300hp and so long as you kept the prop in the water, the drive gave excellent service.

In conclusion: Tweak your prop. Love your boat. You'll either learn how to ski or your body will tell you to give up trying.

It doesn't matter what the 140 is, the notion that because it was plenty for one boat that it will be plenty for another boat is ludicrous. So it could power a 1000 pound Sunbird 17 or whatever. That is irrelevant to a 3500 pound Cobalt (guessing what the 21 would weigh, maybe more). And in the carbed 5.7's 260 is enough because we are talking about hole shot and torque, not top speed here.

I still say that at 21 feet, the IOs should move to dual prop drives - especially the heavier brands like a Chap or Cobalt 21. With a stepped Regal or a light Stingray, I would say stay with the alpha drive on a 21. That advice, apparently agreed with by A COBALT DEALER now - is my advice regardless of what that little 140 was.

Short of that, I would tend to think that a prop expert would recommend down propping or perhaps going four blade.

Zeiss21: Just for clarification, are you saying the problem you dealt with was public perception or unsatisfactory performance from an Alpha drive?

In reality, probably more of perception. The biggest problem was that most customers had ridden in a DP or Bravo III boat and could not get over the difference. There's no published data from Cobalt with a lower pitch prop so you'll just have to give it a try. Me personally, I would tend to think a 4 blade would be your best bet.

Enjoy your wonderful boat!

In reality, probably more of perception. The biggest problem was that most customers had ridden in a DP or Bravo III boat and could not get over the difference. !

Well perception IS reality in this case. People don't buy most boats, especially a great brand like a Cobalt, to get "adequate." The alpha is adequate no doubt. But the boat rocks with a B3 or Duo VP. Far more time is spent in a boat a 0-30 than it is above 30. The oomph on the low and middle ends of the dual prop set up, not to mention dock area handling, is a huge improvement over the single prop usage.

We chose not to go for the BIII drive. Reasoning? We trailer our boat to a multitude of area lakes and are highly likely to bump into something on the bottom sooner rather than later - couldn't justify the additional prop repair costs of two stainless when it happens.

Let me be one of many to offer Ken a huge thank you for excellent and seemingly unbiased information - that's why I reach out to forums to find gentlemen like you to assist me in progressing from my novice stature in prop knowledge. Great link to the other thread...hate to find out that the boat is going to handle even poorer in reverse. Maybe this is why Cobalt suggested a simple drop in pitch with the same aluminum 3-blade. I don't know if I should be as concerned as I am about this...

As an add-on; the boat is dry-weighted at about 3900lbs and with a 40gal. tank we will pretty much always be running an additional 700+lbs of people/gear/fuel/etc. Handling gains are not a concern as she is glued to the water at all speeds in her current setup. I could care less about top speed as I will almost always have the wife hanging on to my daughter giving me the evil eye when she hears the throttle open up!!! Skiing/kneeboarding/tubing are all secondary and occasional past times, but it is important to me to never be lacking when participating in said activities. Most of our time is spent as you see rcskywalker above - floating with our beauties :)

Looks to be a busy weekend on the water (mid-90's and sunny) here in central MN so I doubt a top-speed and RPM run will be possible, but perhaps an evening jaunt early next week will give us the data we need to make the best decision.

We chose not to go for the BIII drive. Reasoning? We trailer our boat to a multitude of area lakes and are highly likely to bump into something on the bottom sooner rather than later - couldn't justify the additional prop repair costs of two stainless when it happens.....Great link to the other thread...hate to find out that the boat is going to handle even poorer in reverse. Maybe this is why Cobalt suggested a simple drop in pitch with the same aluminum 3-blade. I don't know if I should be as concerned as I am about this...

As an add-on; the boat is dry-weighted at about 3900lbs and with a 40gal. tank we will pretty much always be running an additional 700+lbs of people/gear/fuel/etc. Handling gains are not a concern as she is glued to the water at all speeds in her current setup. I could care less about top speed as I will almost always have the wife hanging on to my daughter giving me the evil eye when she hears the throttle open up!!! Skiing/kneeboarding/tubing are all secondary and occasional past times, but it is important to me to never be lacking when participating in said activities. Most of our time is spent as you see rcskywalker above - floating with our beauties :)
.

The cost of repair thought process is valid, and points out a reality about all boats: they are always compromises in some regard: cost, weight, room, performance, handling, cost, speed, and did I mention cost?

And as you are in the process of finding out, there are performance compromises you made by going alpha over bravo. That does not make it the wrong choice, because you did gain some piece of mind with the repair potential piece and on the initial price point. It is what it is.

It's not the choice I would have made, but as you pointed out, a boat is a lot of fun when they are not moving - and certainly one as nice as a Cobalt.

We chose not to go for the BIII drive. Reasoning? We trailer our boat to a multitude of area lakes and are highly likely to bump into something on the bottom sooner rather than later - couldn't justify the additional prop repair costs of two stainless when it happens.

Let me be one of many to offer Ken a huge thank you for excellent and seemingly unbiased information - that's why I reach out to forums to find gentlemen like you to assist me in progressing from my novice stature in prop knowledge. Great link to the other thread...hate to find out that the boat is going to handle even poorer in reverse. Maybe this is why Cobalt suggested a simple drop in pitch with the same aluminum 3-blade. I don't know if I should be as concerned as I am about this...

As an add-on; the boat is dry-weighted at about 3900lbs and with a 40gal. tank we will pretty much always be running an additional 700+lbs of people/gear/fuel/etc. Handling gains are not a concern as she is glued to the water at all speeds in her current setup. I could care less about top speed as I will almost always have the wife hanging on to my daughter giving me the evil eye when she hears the throttle open up!!! Skiing/kneeboarding/tubing are all secondary and occasional past times, but it is important to me to never be lacking when participating in said activities. Most of our time is spent as you see rcskywalker above - floating with our beauties :)

Looks to be a busy weekend on the water (mid-90's and sunny) here in central MN so I doubt a top-speed and RPM run will be possible, but perhaps an evening jaunt early next week will give us the data we need to make the best decision.

AWESOME PHOTO! Should be your Christmas card.