I've tried multiple different Bravo 1 props, Rev 4, Rev 4 xp and currently run Hydromotive p5x 26p. The Cobra is a 31 ft CC on a cat hull, probably closer to a tunnel hull. Motors are a pair of 2012 Etec 300's with nose cones on jackplates and the boat has K Plane tabs.
I was able to get into contact with the guy that built the boat a couple years ago and they sent them from the factory with 4 blade Hoss, 14 3/4 x 29p. He stated I need to be running surfacing props and said I should see 83 - 85 mph. Fastest I have ever gone was 75 running light. In reality, I don't care about the top speed, I want to get the best midrange economy as possible. Normal cruise is 3500 - 4500 rpm. I've never ran a surfacing style prop so I'm concerned about how they behave at cruise. Cruise speed would normally be around 30 - 45 mph but will run at 50 - 55 when it's calm.
The prop calculator says i would need to spin that prop to 6000 rpm and only get about 5% slip to achive the top speed the builder claimed.
Anyone have any thought or recommendations?

I’ve got the same boat, a pair of Yamaha OX66 250hp and I have the pair of the Hoss QDS 29 pitch over-the-hub exhaust props. The Hoss props to give good acceleration, however the mid-range efficiency suffers with the stock setup of the prop shaft’s being 2.75 inches above the bottom of the keel’s. Since the Yamaha’s have fuel flow meters, I’ve been trying to find the sweet spot with jack plate height and rpm/speed. Before I had a hub slip last summer, I was seeing 1.2-1.3 miles per gallon at 3500 rpm and 35 mph. I was disappointed with that and picked up a pair of Maximus-Long Tube 26-inch pitch prop. At the same jack plate position, the efficiency increased to 1.6 miles per gallon at 2900 rpm and 30-31 mph. Interestingly, the efficiency of the Hoss prop gets better with speed/rpm and finally surpasses the Maximus up above 4500 rpm. I’ve not had a chance to build a full dataset at different jack plate heights, but it looks like I may have too much blade area in the water. If I go up above 4.75 inches, my water pressure starts becoming intermittent, plus I test on a waterway that I’m not comfortable writing and driving above 60 mph. I think you’ve made a great prop choice, maybe we both could loose a half-inch in diameter. In my humble opinion, you have a “surfacing prop”. Let me know if you want my spreadsheet/plots/data, we can figure out a way to get them to you.

Thanks for the reply. I see 1.5 mpg at 3600 with the p5x running the nose cone level with the pad but the motors start to run hot over those rpm. The builder says I need to be 1/2" above the pad. With motors 1/2 below pad at 4500 rpm I see 52 mph at 1.4 mpg.
Still trying to figure out how to keep the Etecs running cool. Sounds like those Hoss props may not be the best for me. I was looking at the Hill 4 blades. Mr Cassini said he would see 90 mph running light.

Do y’all know anyone selling a Cobra Predator fishing boat?

I'm thinking about selling mine. If your still looking.

I am, please pm me your contact info, thanks

The site won't let me pm because I have lass then 10 posts. Pm me if you can. If you can't, look me up on Facebook William Tucker in Annapolis MD.

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I am repowering a Cobra Predator 3100 currently and would like to take a look at your spreadsheet/data. Would you be able to share as I'll be making prop purchase in a few weeks?

I am looking to set-up the boat for long distance 45~55mph cruising, seas permitting, to fishing spots way down the Chesapeake. Any additional ideas for props appreciated.

Thanks,
Cobra3100

Good Morning Mr Cobra3100, CouleeCatMan here! Let me know how I can get you my excel spreadsheet with all the data! My Cobra has Bob's Machine shop nose cones and my data was acquired at the Cobra factory prop shaft height! I don't know that number off the top of my head, but I will measure if you need! You can text me at three three 7 six zero zero 3 two 6 two and then we can establish email!