Prop Blows out on 97 1710 cobra

I have a 1997 17'10" cobra w/ a 115 Johnson and I need to replace the prop. (Lost the old prop) . I am trying to find a replacement but need some help. First off I do not have a jack plate the motor is as low as possible directly bolted to the transom. Not into speed and all that anymore ( My Bullet days are gone.) Just want to get good efficiency out of the boat with decent performance. I'm currently running an 18 pitch PowerTech RXB4R18POM140. It will run almost 48 MPH on GPS @ 5600RPM, Good hole shot, good bow lift. Problem is that it blows out at the drop of a hat. Coming up on plane it blows out so I pull back on the throttle to let it hook up and it goes on. Slightest over trim and it blows out, minor steering corrections and it blows out.

HELP PLEASE!!!

Does it have any exhaust holes? Similar to mercs pvs

No it isn't vented and fits tight/close to the gear case. This is the first experience with propping a Cobra hull. I've had great success with several other Bassboats hulls. I have a local Prop repair/dealer trying to help me out (No good dead but goes unpunished.) and he is scratching his head.

An 18 sounds too small for a 115 and it maybe over revving and not blowin out . A 21 inch 3 blade with some sort of adjustable vent holes is what you need . My dad runs the same boat with a 115 merc opti and it runs great on a 21 . Only issue he has is hole shot is terrible because the 115 merc opti is a 3 cylinder and it has no torque for hole shot. That and he is 300 and so am I .

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Originally Posted by BullShoalsbasser

An 18 sounds too small for a 115 and it maybe over revving and not blowin out . A 21 inch 3 blade with some sort of adjustable vent holes is what you need . My dad runs the same boat with a 115 merc opti and it runs great on a 21 . Only issue he has is hole shot is terrible because the 115 merc opti is a 3 cylinder and it has no torque for hole shot. That and he is 300 and so am I .

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I agree totally My grandpa's boat ran great with a 21 ballistic good hole shot good top end

I wish I was at your guys' elevation! I'm running a 23 on my 200 with medium vent holes and its almost too much prop

My boat blows out the same pitch three balde prop no matter what depth I have the motor set at, the four blade prop digs harder and no blow out, but doesn't load as well. These hulls just tend to work better with four blade props, particularly if you are running a Mercury which doesn't trim out as high as a Johnson/Evinrude/Yamaha.

Sorry guys. The real question here is which brand/design of OMC prop will work best with the hull. Not all props are created equally, we all know that. Blade design has a huge impact on performance and the Cobra hull has been a challenge to prop since its first production run. Why do you seldom, if ever, see a Cobra hull without a jackplate; its because the design of the hull required the setback to preform. They knew this from the get go and never fixed it. I DO like the boat don't get me wrong. I just want to get it to perform without buying 20 different props of which 19 will not work correctly. Some will say I'm being picky but I know what I want out of this rig and I know it can be done.

Why do you seldom, if ever, see ANY bass boat without a jackplate?
Why don't ALL bass boat manufacturers "fix" their hull designs to perform without a jackplate?
Why do Rangers, with all their built-in setback design, still most always have an external jackplate added also?
Setback increasing performance on a planning pad type hull like a bass boat is more a matter of physics than specific hull design features.

I think the reason you are not getting more specific prop recommendations is not because your hull has a design problem, but that people on here lack experience with your specific boat/motor combo and just don't know. Not a lot of us have 1710s, many of those probably have 150s on them, and most are Mercs.....

As Tx201 says, testing seems to show (at least on the bigger models) that the Cobra bass boats tend to perform better with 4 blade props.
98cobra201 gave a specific recommendation of a 21"Ballistic being run well on what sounds like your exact rig.
BullShoalsBasser suggests an 18" is too small & recommends a 3 blade vented 21" prop.

On my Coral rig, 4 blade props slip like bald tires on wet pavement. But a long eared 3 blade 25" Tempest hooks up so hard without slipping on the dig that the whole boat slightly shudders & vibrates till it breaks over. You might try a 21" Tempest with a OMC hub adapter.

When my dad had one of the older merc 115 that had 4 cylinders on it he ran a 24 trophy on it with no backplate . And it ran awesome . Great hole shot and top end . The prop was vented with the small square holes . But this new 115 opti 3 banger stinks for holeshot. Just no bottom end torque . If your 115 is strong on the bottom than you may be able to push a 24 .

A quick lesson on these boats, and probably most brands. There were four molds for the 188/190 (same hull, just changed numbers for different year model) one of those molds had more hook in the pad than the other three. Friend of mine had one with the big hook in the hull and he could never get the front end, and I mean the KEEL up and out of the water. The smaller hulls have some hook built into them so the front end will break over on takeoff instead of just standing up on their tails for too long. The 201 models have little to no hook since they have enough length and weight upfront to drop the nose over during holeshot. You may get the exact advise you want that fits another 1710 to a "T", but it may not work on your boat at all if it came out of a different mold, even though the same model. You have been given some sound advice as a starting point, but if you are going to get the most out of this hull, you will probably end up with a couple jack plates and a couple props. Just take good care of the ones that don't work so you can sell them and recoup some of your money. Sorry, but full performance is kinda like searching for the Holy Grail, some may find it, others can only hope to come close. Good luck and try to look at this as an adventure finding the just right setup for your boat. Let us know when you find it and what your final setup is.

I got a Jackplate with a 5 1/2 inch set back I will try that and see what I get. Thanks for everyone's input!!!

I don't know if anyone is still interested in this blog or not anymore, but I have found the setup I was looking for. I found and rebuilt a 2001 150 Merc and hung that along with the jack plate I had. Stuck a 24 pitch Turbo prop on it and voila no blowing out no porpoising good bow lift but RPM is a touch high. I'm looking for a 4 blade 24 pitch TRO PowerTec prop or a Trophy. I think that will be IT.

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Originally Posted by bokinfish

I don't know if anyone is still interested in this blog or not anymore, but I have found the setup I was looking for. I found and rebuilt a 2001 150 Merc and hung that along with the jack plate I had. Stuck a 24 pitch Turbo prop on it and voila no blowing out no porpoising good bow lift but RPM is a touch high. I'm looking for a 4 blade 24 pitch TRO PowerTec prop or a Trophy. I think that will be IT.

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Curious what you ended up at on you prop centerline to pad measurment, and did you ever pick a 4 blade and try it?