Outdrive fin

[Jr1]

Hello, I’m new to boats! My wife wanted a bow rider ski boat because her family had such awesome memories of the cobalt they purchased in 1979, we could never afford a boat. Now maybe, to surprise her I found the same year and model, during my search I learned this is the Cadillac of boats. It has the merc 260, first trip out someone mentioned a horizontal fin on the outdrive would help it get on plane. Is this true? Is it worth looking into?

[Big Block Power]

Yes it does. But I rather drop pitches in the prop before doing that or add smart tabs.

[Jr1]

Unfortunately I have no idea what either of those mean, could you explain the pros and cons of all three, pitches, tabs and fin?

[Jr1]

Should I post this in general also, not just older boats?

[AsLan7]

Should I post this in general also, not just older boats?

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Hey jr1
Welcome to the Cobaltchat forum. So glad you found us!

This is fine where you are posting. The fins you see on boat outdrives are mostly for under powered engines to help the boat get up on top of the water while starting out (on plane we call that) vs ploughing thru the water like a barge. What bbp is suggesting is purchasing or swapping your prop with one that has less of a twist (pitch) to it. That way it can spin faster underwater and help get the boat on plane easier. The prop normally has a number stamped on it like 23P saying it’s a 23” pitch prop. You could drop down an inch to a 22” prop as an example.

Any pics?

Again welcome aboard mate!

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[jhnmdahl]

Trim tabs stick out past the back of the boat's running surface (the bottom), and can be adjusted to change the direction the bow points (up and down) independent from adjusting the outdrive trim itself. A lot of Cobalts use Lenco trim tabs, which can be found here:

https://www.lencomarine.com/en/Products/Trim-Tab-Kits

As far as dropping pitch in the prop, the idea is that your boat may be trying to push too much water with each turn of the propeller, so if you go with a propeller that doesn't move as much water per rotation the boat can get on plane faster and run more efficiently. Basically, if your propellers are too aggressive they can "slip" and waste some of your engine's power. Some info regarding your boat's top speed and RPM at top speed can help the members here ballpark whether your propellers might benefit from such a change.

John

[Jr1]

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Thanks guys. I’ve only used it once and don’t have any other boating experience so I don’t even know if it’s a problem or not! Just researching to make sure I have everything optimal for the boats performance and longevity! A related question would be, when I gun it to get up on plane where should I have the trim? I know these sound like beginners questions, because I AM A BEGINNER! I love classic stuff and I’ve fallen in love with this cobalt!

[Bfun220]

Trim should be down. Then once your boat is up on plane you can start to trim up. If the bow starts to bounce up and down you've trim up too far and need to trim back down until the bow stops bouncing.

[Jr1]

Awesome

[BigGib]

Trim up just a little at a time after the boat is on plane. You will feel the bottom of the boat have less resistance with the water. Like BFun said, if the bow starts to bounce up and down trim down a bit. Also, if you hear and see the RPMs increase all of a sudden, you may be too high as well and the prop may be slipping. If you are towing the boat, always remember to raise the drive all the way up before pulling the boat/trailer up the ramp (after it is hooked on the trailer and the motor is off).

I'd run ethanol free fuel if you can find it, otherwise run Stabil or some kind of ethanol treatment with each tank of gas

I'd also change the oil, oil filter, fuel/water separator, and impeller ever season.

Always make sure to leave your blower off while fueling and run for 4 to 5 minutes after fueling before starting the motor.

Most important tip, drive it like you stole it!

[Jr1]

Thanks

[Big Block Power]

Then just for fun

[Cruiser64]

If you're running a single prop you can also look at using a 4 or 5 blade prop. When I had a 18' Crownline with a 4.3 V6 I found that a 5 blade prop helped a ton for getting up on plane faster and it made skiing and tubing much easer.

[Big Block Power]

If you're running a single prop you can also look at using a 4 or 5 blade prop. When I had a 18' Crownline with a 4.3 V6 I found that a 5 blade prop helped a ton for getting up on plane faster and it made skiing and tubing much easer.

Good point. Also go down pitches and switch to a stainless steel prop. They don't flex like a aluminum one does.

[Jr1]

Great vids and info. I am enjoying learning this! On an admin note how do I set up my account to email me with each new response to a post?