Prop / Set-Up Questions

[fishinggman]

I have a 00 Cobra 201 with a 200hp Opti, The boat came with a 25 Tempest. I was able to get 59-61 mph gps at 5500 rpms. I heard about how well the cobras ran with a 4 blade prop so I tried a friends 24' Trophy Plus, with the Trophy I was able to run 63-64 mph gps at 5800 - 6000 rpms. I thought that was a little high for rpms. I just got a 25' Turbo TXP ot4. With the TXP I get 64-65 mph, but I only get 5000 to 5100 rpms. I really like the lift and hole shot with the TXP but I think that my rpms need to be a little higher. Just so everyone knows I am running a 10 in manual jack plate, and all tests are with a tournament load. I was wondering if I raised the motor if i would get better RPM? Maybe I just need to drop down a couple of pitches on the TXP and run a 23' Turbo. I know the TXP has longer blades but I have a hard time beliving there is that big of difference between the Turbo and the Merc props. Any help would be awsome.

[Backlash Ar]

Garrett...What is your current measurement from the pad to the center of the prop shaft; and what is your water pressure at WOT? If you're not sure how to get the measurement, this might help:

Take a long straight edge, (long carpenter's level or long steel ruler, etc.), and place it on the bottom of the pad in the center. Tilt your motor until the bullet of the gearcase is parallel with the straight edge.
Measure from the top of the straight edge to the center front of the "bullet" on your lower unit. This will be the center of the propshaft. This measurement will be in inches. Another alternative to get this measurement is to level your boat, level the cavitation plate on your engine and then take two measurements: 1. Distance from the pad to the ground and 2. distance from the center of the prop shaft to the ground. Subtract the smaller from the larger and that will leave you with a measurement in inches below the pad.

Your definitely on the right track adjusting the engine height and testing different props to find the best combination and sweet spot. Always be aware of your PSI and to be on the safe side don't let it go below 12-15 psi at WOT.Your doing pretty good on the speed end of things considering your rig is a little underpowered with only a 200HP engine on that boat, which isn't the lightest thing around. Keep us informed of your progress.

[fishinggman]

Just to make sure I got this right, measure from the bottom of the pad to the ground, then I would assume you trim the motor up to were it would be at wot and measure from the middle of the nose cone to the ground. The difference is were the prop shaft is below the pad. I am thinking that mine prop shaft may be a little low becouse I get almost 30psi for water pressure at wot. Any ideas how many rpms I can gain by raising the motor, also is it hard for my motor to run lower rpms?
Thanks

[Dwayne]

No that's not right. While the boat is trailored lower the engine to where it is squared to the boat. Take the flat edge from the bottom of the boat, directly in front of the engine, and run it to touch the lower unit. From where it touches to the center of the cone is the measurement Backlash is talking about.

[Backlash Ar]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fishinggman &raquo;</TD></TR><TR><TD CLASS="quote">Just to make sure I got this right, measure from the bottom of the pad to the ground, then I would assume you trim the motor up to were it would be at wot and measure from the middle of the nose cone to the ground.....</TD></TR></TABLE>

No, not quite....Measure from the bottom of pad to ground with the boat level on trailer (not just that your trailer is level. It could be that your boat WILL sit level on the trailer when your trailer is leveled) but it's the pad that must be level to the floor. Then trim engine to where the propshaft is parallel to the floor, not where it would be at WOT....then take your two measurements and subtract to get the distance below the pad (measured in inches).

[fishinggman]

Ok I figured it out, you'll have to bear with me this is the first time I've planned on keeping a boat long enough to worry about it. If I did everything right the shaft was 5" below the pad so I raised it up 1 1/2". I will give it another test tommarow night and post the results.
Thanks Again

[Backlash Ar]

Nothing to be embarassed about! The folks here have a lot of patience and will bear with you as long as you need us to. Good move raising the engine up. Cobra's seem to run best between 3.25" & 3.5" below the pad. Keep your eye on the psi gauge. Keep us informed. Also, be sure you know what the rev limiter of your engine is supposed to be. You'll want to get as close to that as you can at WOT. Also, keep in mind that the warmer the water the less speed you'll get. Your speed will increase as the water cools in the Fall and if you want to record your best speed make sure the water as just a hint of ripple on it.

[fishinggman]

I don't think the water psi will be to big of issue becouse before at wot I was getting almost 30psi. I will post the results tomorrow night. Is there a equation for raising the motor like there is for pitch to rpms ? Like each pitch equals 200 rpms, each inch equals 100rpms???

[MNCobra1]

Garrett

I don't think you'll gain much in the way of RPM's from raising with the Turbo prop. I have the same prop 25P, with a hydraulic jack 12" setback, runs the same as you describe, but RPMS are low as well. Doesn't matter where the motor is up and down for the most part, and I can run up to 1 inch below the pad. I have a worked 26P Trophy Plus, which I can pull more RPMS out of.

On second thought you might gain a little, since you are 10" behind the boat, the last 2 inches seems to make a big difference on this hull as far as getting into cleaner water.

Hope this helps.

[Psychologist]

Mark Croxton and I have talked a lot about the TXP. He says that he can loosen the prop up a lot to gain RPM and the speed will come up as well. I run a stock 27 TXP o/t 4 at 5500 RPM. It turns more like a 28 pitch prop. It will run higher than any of my other props and still maintain lift and acceleration. I would just lift your engine an inch and run it. See if you loose speed and watch your water pressure. You can measure if you want, but I don't see the need. I always drop my engine down low, run it and then raise my engine until I loose too much water pressure or speed. Remember to load the boat like you are going to run it 90% of the time.

You can always send it to Mark and have it work it and gain you some RPMs and speed. He is located on the Prop Board.

[Backlash Ar]

Ben and Chris....don't disagree one iota about running your prop higher than 3.25"-3.5" at WOT but both of you have hydraulic plates. I ran my Cobra with a 250 Yammy 1.5" below the pad at WOT depending on the conditions, but I don't think Garrett is running a hydraulic jackplate or low water pick-up (could be mistaken about that though), so he is going to have to find the "best overall" height to run his engine and I don't believe it's going to be less than 3" below the pad, so that's why I suggested starting at 3.5" below the pad for him and then he can adjust upward in 1/4" intervals until he finds the "sweet spot." Granted, if speed is his top priority he will need a hydraulic plate...and a few other things too...but when it's all said and done there is no substitute for HP...the more the better, and he's going to find out that achieving speed can get to be very expensive and can take a big bite out of a person's wallet.

[Psychologist]

I don't run a hydraulic plate. Mine is just a plane ol' 12" slidemaster. The TXP will run very high. Much like that T1 you were running Larry. I have a VMX which is a 15.25" diameter prop and the TXP will run higher than it. I am running around 1.5-2" below the pad. Now, granted I believe that the extra 2" I have on my jackplate allows me to do that.

Here's how I setup a prop. 1.) Load the boat the way you are going to run it 90% of the time. 2.) Make a WOT pass and get GPS max speed, RPM, and water PSI. 3.) Put boat on trailer and lift jackplate 1/2". 4.) Make another WOT pass and get GPS max speed, RPM, and water PSI. 5.) Put boat back on trailer and move plate up or down according to your data.

Rule of thumb is that if you are not losing speed or water pressure keep moving the plate up. Speed should increase due to less drag in the water. If speed is not increasing but your RPM's are then you have an inefficient propeller for the engine height you are running. Try a higher pitch. Also, watch for porpoising at low speed. That can be a side effect of a high engine height. My holeshot actually got better the higher I raised my engine. This is not always the case, but I am confident you are not going to blow out a TXP 4 blade on the holeshot with a Mercury.

[Backlash Ar]

Sorry Ben, thought you were running a hydraulic plate on the 12" slidemaster. Looks like that TXP o/t 4 is the ticket for some Cobra bow lift.

[MNCobra1]

Larry Mark -

Agree to both.

I was just stating my final height is around 1" to 1.5" below pad.

Physco is right on the TXP, can be run very high, without losing water pressure.


Never thought about loosening it up to gain RPMs and speed. BTW top end on my rig with a 25 TXP OT4 is 68. I can't comlain a bit about holeshot, or mid, because it's better than any other prop, but the top end, and final RPMs are something to be desired, maybe a little prop work and it would be the cat's butt.

Physco - I thought you were running a Bravo prop my Mark now, course it must be hard keepin track of which one is on the boat with so many props???

Later...

[Psychologist]

Yeah, I like the Bravo a lot. It is my fishing prop when I am heavy loaded. It has a killer holeshot and mid-range. The TXP 4 blade is my favorite stock prop period! DAH stated they have picked them up as much as 5 mph thinning the blades and working there magic. I run around 74 loaded with the TXP and 73 loaded with the Bravo. The Bravo is just much stronger out of the hole. It revs to like 4200 RPM and then takes off like a sling shot.

I finally found a 3 blade that will run really well on the Cobra. Powertech VMX with PVS holes. It spools hard and has the more bow lift of any prop I have run so far. The holeshot and mid-range are actually stronger than my TXP. With a little tip work and sharpening I think it will out run the stock TXP.

[fishinggman]

First of all I would like to thank all of you guys for your help and info. After raising the motor 1 1/2" it brought me up to 5600 rpms and I run at 65.3mph gps. Plus I still have 20psi of water pressure at WOT. I have never been a big fan of 4 blade props but in this case I am definitely sold. I just cannot believe how much more bow lift I get with the TXP ot4. It feels as if I am riding on air or the only thing in the water is the prop. I really don't think I can get any more out of the boat with a tournament load unless I put on a bigger motor. I would definitely recommend the Turbo TXP to anyone that asks.
Thanks again, these boards and this web site is awsome for talking to other Cobra owners.

[Backlash Ar]

[MNCobra1]

I.M.O. that's pretty good for a 201 with a 200 Opti on it. I ain't running alot faster than that on top, but I carry alot of tackle too.

[moldman]

Garrett I have a 1995 Viper 201D with 1995 200 2.5 EFI (motor in great condition) that is running 65.5 gps at 5600 rpm. The first time I ran it with a 6' Rite-Hite plate and 2 1/2 below pad it would only run 59 and loosing water pressure when I tried to trim it too high. Dropping to 3" helped water pressure but didn't help speed. I had two props I was playing with, 24" 3 blade raker and 25" 4 blade power tech. The 4 was better out of the hole but both were the same on speed and rpm. I got a 12" plate and started at 3" below pad and my speed went to 63 gps. I was able to trim higher and still keep water pressure. I started coming up in 1/4" increments and the best was 65.5 gps at 2 1/2 below pad with good water pressure. I would sure like to try one of those TXP OT4 so I could get some more bow lift, as mine runs very flat. I may never see 70 from this combo but I believe I can improve it some without breaking the bank. Good luck with yours Garrett. Jim

Hey Cobra owners. Is "physco" the guru of props for Cobras or what?

[fishinggman]

Pretty much, "Physco" has a ton of info and has helped me a couple times with questions.