Hi! New vintage Cobalt owner. '74 Tri-Hull

[MoneyPit]

Hello all! I recently bought a "Barn Find" 1974 Cobalt. Ok, so it was in my dad's barn so not so much a find. LOL
All the interior is original and in remarkable shape, which is why I call it a barn find. In the car world I think they would consider it a survivor.
I'm in the process of making a new cover to protect the interior, the original cover is long gone. If anyone has information on these early '70s Cobalt Tri-hulls please share. The biggest thing I'm trying to find out now is what size and pitch prop the boat came with. It's a Mercruiser 140.
Thanks!

[AsLan7]

.
So glad you found us MP.

Great intro and pics.

There may be a few owner's on the site that can help you with tri hull questions.

She looks to be in great shape for a '74.

My guess is a 15" or 17" prop with a 140. Possibly a 19" depending on length. How long is she?

And welcome aboard mate.

.

[Dudley67]

Nice! I just picked up a 74 too.

Here is what I searched:

“The 3.0 is one of the easiest outfits to prop.Your 17 footer would typically use a 17",19", or 21"prop.With a 21" prop should run around 40 mph with reasonable hole shot. May struggle a little with water sports and a heavy load. A 19 would have better hole shot and higher wot rpm might over rev with a light load.
A 17" prop is usually suggested for heavy loads with water sports and will over rev with a light load.
There are 3.0 boats that manage a 23" prop but with more limitations than the 21.
The 21" prop is like overdrive in a car, 19 more like high gear and 17 so on.

[Big Block Power]

I liked the mercury high five prop for those engines. Maybe a 19p you are going to have to experiment a bit to get the right one.

[MoneyPit]

Thanks for the help guys, Great info! AsLan7-she's a 16ft. Probably the shortest boat Cobalt ever made LOL.
I have a 17 and a 19 pitch so looks like I'm on the right track. Sounds like a trip to the lake to see which one I like best. Years ago my dad tried a 23 and it was too much, bogged down on takeoff and really worked the engine.

[AsLan7]

Thanks for the help guys, Great info! AsLan7-she's a 16ft. Probably the shortest boat Cobalt ever made LOL.
I have a 17 and a 19 pitch so looks like I'm on the right track. Sounds like a trip to the lake to see which one I like best. Years ago my dad tried a 23 and it was too much, bogged down on takeoff and really worked the engine.

.
Sounds like a 19 would work well. The way to tell is the rpm range at wide open throttle (WOT). It should be within a certain range for your 140 HP engine. Do you have an owner's manual for the engine? Maybe an engine pic would help us out a bit.

.

[sailor55330]

That's cool. I love that they proudly call out the HP on a badge on the side at 140hp....yet today we cry at 300.....

GIves me an idea for another thread.

[Krob1114]

Welcome!
Hull looks pretty clean. I wonder how well she'll take a shine.

[Big Block Power]

That's cool. I love that they proudly call out the HP on a badge on the side at 140hp....yet today we cry at 300.....

GIves me an idea for another thread.

Or 240

[neckturtle47]

Awesome

[jhnmdahl]

That's cool. I love that they proudly call out the HP on a badge on the side at 140hp....yet today we cry at 300.....

GIves me an idea for another thread.

Reminds me of a relative with a 25th anniversary Corvette. Looks sharp, but has a 185hp engine and doesn't keep up with a Civic or Corolla today. Of course he didn't buy it to race, and he loves it.