Alpha One Prop selection

[MarkB05-200]

Hello everyone! I new to Cobalts, boating, and this site so please bear with me.

We recently bought a 2005 Cobalt 200BR with a 5.0l MPI mated to a Alpha One drive. It has the High Five 21 pitch prop on it now. I have read the dry weight is around 3,800lbs, with me, guests, gear and fuel we add about an extra 800lbs. The lake we frequent is about 4,400ft above sea level. WOT RPM label on the engine says 4,600 to 5,000 RPM's. We finally got to take her out and she was extremely sluggish out of the hole and WOT RPM's were only hitting around 3,600. From the different prop selector websites (Mercury and Prop Wizard) i used, both are recommending a 4 blade 15 pitch. I have read that for every inch of pitch change you can average 200rpm gain/loss. If this is accurate, changing from 21 to 15 would calculate to about 1,200 RPM increase. Which would put me right in the WOT sweet spot for my engine.

Sorry for the long post, but does anyone have any input or experience with this issue? Also, I would really like the boat to pop out of the hole, would changing the prop and adding Smart tabs help that a lot?

[Big Block Power]

High five is a good prop and yes you are way over propped. Every 2 pitches you will gain about 200 rpms.
You want to get to 5000 rpms though. I spun mine to 5200 but I'm sure the tach was off some. But each prop is a diff diam so changing pitches isn't that easy. Look for a mercury rev 4 15 pitch if they Make one that low. It is a stump puller. That is the best prop you will find for what you want to do. I also used a vensura prop it was nice. Look for a mercury enertia prop also. Very good prop. Or stick with a high five.
I had a 2004 Cobalt 200 but it had a b3 drive with a 350 mag and it came from Colorado to here. So I was opposite of you. I didn't have to change anything it still hit wot rpm range. But it was slow out of the hole. Hence the reason I now have a 220 with a bb.
I wish I had a alpha just so I could change the props less expensively.

[MarkB05-200]

Thank you for the input and knowledge! Im hoping to remove the High Five and sell it to help pay for the new prop. What are your thoughts on Bennett auto tabs or Nauticus Smart tabs? I want to give the 5.0l as much help as possible out of the hole. I just don't want to waste money and possibly have one part counteract another part.
Oh yeah, it does have a "hydrofoil" (not sure of the brand) on it as well. Are these worth it? If tabs are recommended, should I remove the hydrofoil or keep it on.

Told you I was new to this ha ha!

[Big Block Power]

Ok first sign of any boat having time on plane issues is a hydrofoil. They work for what they are. They can grab though on really tight turns. Yes I bought and sold many props to pay for other ones.
Tabs will be next to impossible as the transom is not flat back there. It's all curved. So I never added them on mine. That. 5.0 is a good engine but that is a heavy boat. My 350 had issues. But if I kept it I would have gone down 1 pitch and it would have been fine. You with a alpha have alot more choices then I had. Find a rev 4 17p might be still too much but they sell really fast as they are a wanted prop. If you can find a 15p that might be your golden ticket and then take off that hydro.
Check eBay

[MarkB05-200]

Thanks BBP! So if I'm understanding you correctly, (Ok first sign of any boat having time on plane issues is a hydrofoil) the hydrofoil is definitely not helping my situation, if not making it worse correct?! The good part is that I didn't pay for the foil and it is an easy removal process if I want to try it while at the lake.

[Big Block Power]

Thanks BBP! So if I'm understanding you correctly, (Ok first sign of any boat having time on plane issues is a hydrofoil) the hydrofoil is definitely not helping my situation, if not making it worse correct?! The good part is that I didn't pay for the foil and it is an easy removal process if I want to try it while at the lake.

No the hydrofoil helps you get on plane. When you see that you know they were having a issue getting on plane so they added that to help out. It does put extra stress on the drive. Also you will want to get a drive shower. Best addition you can add to help keep your drive cool and clean.

[MarkB05-200]

Oh ok. I definitely misunderstood you. I am hoping the different prop really helps a ton. The way she performed last time at the lake, there is no way she would get an adult skier up. I'm hoping that's not the reason the last owner sold it. I'm wondering if the seller had a better prop they wanted to keep and just threw on the high five they had laying around. I also don't see that being the right prop for that boat at any elevation really, but I could definitely be wrong.

[akorcovelos]

High 5 is a great prop, but in this instance I would wager it’s another attempt to address the issue of getting on plane. You shouldn’t have any problem selling the High 5 for $400-500 for an Alpha drive. I think you have an underlying issue someone else tried fixing the symptom and not the problem. Have you done a compression check on the engine yet?

[Big Block Power]

A 21 high prob worked at sea Level. It's a very small diameter prop. I have no idea what gear ratio your drive has. Could be a 1.47? Look on the side of it on the Merc sticker I think it will be there for you. It could be like a 1.69 too somewhere in that range. Altitude is a killer.
Yes a compression check would show a weak cyl. Akro a used high five I wouldn't pay more than $350.00 for one. Yes they are a very good prop. I've used them on a bunch of boats.

[Bleil05]

Try a 4 blade aluminum prop
15 or 17
4 blades usually work better on a heavy boat it will give you more lift than a 3 blade
I only used a high 5 once and had too much motor for the pitch we had so I can’t speak to your current prop other than it’s to big

[Big Block Power]

Try a 4 blade aluminum prop
15 or 17
4 blades usually work better on a heavy boat it will give you more lift than a 3 blade
I only used a high 5 once and had too much motor for the pitch we had so I can’t speak to your current prop other than it’s to big

I would not go with anything aluminum. You just lose too much efficiency with them.

[Bleil05]

Do you dock or trailer the boat?
If it’s docked stainless props have a tendency to cause electrolysis on the outdrive and if you’re not sure on the pitch a lot cheaper
I prefer Stainless as well but have run Mercrusier 4 blade 22 on my old chaparral

[MarkB05-200]

High 5 is a great prop, but in this instance I would wager it’s another attempt to address the issue of getting on plane. You shouldn’t have any problem selling the High 5 for $400-500 for an Alpha drive. I think you have an underlying issue someone else tried fixing the symptom and not the problem. Have you done a compression check on the engine yet?

I picked this boat up in Phoenix and the dealer said they went through it, but you never know with dealers. Besides the snap in carpet backing coming off, the boat is in great shape. But that obviously doesn't mean something isn't wrong with the engine. I will do a compression check on it soon and see what I can find.

[Big Block Power]

The backing coming off the carpet is very common. Some of us have used rubber roofing compound to help stop that.

[MarkB05-200]

A 21 high prob worked at sea Level. It's a very small diameter prop. I have no idea what gear ratio your drive has. Could be a 1.47? Look on the side of it on the Merc sticker I think it will be there for you. It could be like a 1.69 too somewhere in that range. Altitude is a killer.
Yes a compression check would show a weak cyl. Akro a used high five I wouldn't pay more than $350.00 for one. Yes they are a very good prop. I've used them on a bunch of boats.

My gear ratio is the 1.47. The lakes around here in New Mexico are right around 4,400ft. Im really hoping that the current prop and altitude are the culprits.