Coral Performance/Setup Question

[OverRHeads]

Boat: 1998 20' Coral
Motor: Merc 225 EFI
Prop: 25" Trophy Plus
Jackplate: 7" Slidemaster
Propshaft to Pad: 3.5" below pad

This past weekend I was at LOZ and reaffirmed what I had already thought. This thing doesn't run like it used to. Granted, I had 3 guys weighing about 190 each, 1/2 tank of gas, emply livewells, full tourney tackle. However, the only thing in front of the windshields are rods (about 10 in each rod locker). With air temps in the mid 60's and water at 70, the best I could get was 60 (gps) at 5200 rpm's with light chop on the water. When I put this into a slip calculator, it said I had 14.708% slip. Isn't that really high? Shouldn't I be around 7 or 8?

About a year after we bought it, this thing ran 74 mph (gps) on a 40 degree day in March with only me in the boat. I know that I will NEVER see performance numbers ANY BETTER than that! Since then, we took the Motorguide off and put a Minn Kota Genesis on. Love the motor, but this thing has to weigh double the Motorguide. About the same time, we hit something and had the lower unit replaced and the prop repaired by Mazco in St. Louis. I talked to my dealer today and he said that often when props are repaired, they do not have the exact same cup and never perform the same. However, Mazco is a reputable name in the stainless/performance prop game. The dealer gave me a 24" Trophy to try in order to see if more (correct amt) cup and lower pitch will get my RPM's and bow up a little. I tried a 25" Tempest last year and the rpm's were even lower due to how hard it was biting. The bow did not come up either. Should I try a 23" Tempest?

I know I do not have a race boat here but 60 mph at 5200 rpm's seems low to me. Any other thoughts? I thougt about sending it to Mark but I don't want to spend that kind of money on a prop that may not be right for my boat now due to the extra weight on the bow!

[Backlash Ar]

No, you'll never see 7% or 8%. More than likely 12%-14% is where you'll be. Lighter boats like Allisons, Bullets, Strokers etc will be able to get 10% slip but not Cobras or Corals....too heavy. Over time, and through use, prop blades become dull and they actually do become a little distorted and lose some of their cup. When you say that Mazco repaired your prop, what exactly did they do to it? After the prop repair did your boat perform like it did before? I would definitely have Mark rework your prop and maybe even raise your engine up another 1/4 inch. Keep this in mind about props...companies don't know what kind of rig their props are going on, anything from a high performance bass boat to a pontoon, so they turn them out sort of "generic like" when it comes to rake, cup, leading edge, trail edge, etc. and even then they aren't all that much the same. The only way you'll get all the performance out of a prop is to have it blueprinted for what you what it to do for your boat. You won't see as good a top end with a Trophy Plus but you will see a little better hole shot. I do think the 25" prop is what you need. Have you tried plugging and unplugging some of the vent holes? An extra 380 lbs will surely make a difference in performance but it shouldn't be 14mph. Keep us informed please. Also, you might consider having the compression checked and look into getting some 2" spacers to give you 9" of stetback.

[AlanW]

Just some thoughts here...what kind of average WOT rpms were you getting before? More like around 5500-5600? Thinking that if the rpms were down significantly to the 5200 you said, it would NOT indicate prop slipage because the rpms would stay high with slipage.

Unless you have changed something with the boat setup, and I am assuming you did not, I think the problem would be one of 3 things:

>the engine has lost some compression or has some other problem and is weaker now. You might get a compression check and new plugs if you haven't already .

>the prop might not be as good or as cupped as before the damage.

>you have too much weight and too many people in the boat to go any faster than you are.

I would try this first though, take off the detactable trolling motor and remove the TM batteries. Remove all gear possible from the boat. Take it out by yourself on a good cool dry day with about 1/3 tank of gas and a GPS unit. See what it will do max-out now. If it still runs low 70s light, the problem is the weight.

Also, a bigger, 10" jackplate would help top end performance. Good luck and let us know what heppens.

[OverRHeads]

The strange thing is, when it ran the best, it had a 6" Rite Hite on it. I later had problems with it so Greg Wood warrantied it out at the factory for a 7" Slidemaster. Wouldn't that extra inch help a little or at least not hurt? I have thought about taking the trolling motor off but that will be a bit of work due to the transducer being wired to it and all excess wires being cable tied down under the front panel in the bow.

Backlash....when you asked if I had played with the plugs. Do you mean the vent plugs in the prop? If so, aren't those only for holeshot? I am getting great holeshot with the current setup. I have tried raising the plate and it did no good. It merely starting dropping psi while gaining nothing on top.

I also forgot to mention in my original post the I am getting 17 psi of water pressure at WOT.

Does anyone know how much it costs to have an outboard put on a dyno? Maybe I am not getting enough horsepower. We did have a new powerhead installed about 1 1/2 years after we bought it new. Could this powerhead be really weak? Combine that with a worn out prop and that could result in a bunch of speed loss....Right?

[Backlash Ar]

17 psi is good! To be on the safe side don't let it get below 14-15 psi. OK, sounds like you found the sweet spot at 3.5" below the pad...good deal. If you're happy with your holeshot then leave the vent plugs alone. So, you said... "About a year after we bought it (<U>around 1999</U>?), this thing ran 74 mph (gps) on a 40 degree day in March with only me in the boat. I know that I will NEVER see performance numbers ANY BETTER than that!" So after originally getting a GPS top speed of 74 mph you got a new powerhead about 1 1/2 yrs later (<U>2000-2001</U>?) and never checked your GPS speed or RPM's again until last weekend??? (<U>5 years</U>?) What's up with that? Seems like that's the first thing you would have done after the break in period of the new powerhead to make sure everything was running properly. I hope you didn't buy your "new" power head from Blackbird's Remanufactured Outboards. Sorry to say you best take that engine to a certified Mercury mechanic and let him go over it with a fine tooth comb.

[TerryPettle]

Backlash, I am running a '97 188S, '02 200 Opti, 8" Rite-Hite, straight out of the
box 24" Ballistic, 4.5" below the pad and am getting 62mph gps @ 5300 rpm.
Am I using the wrong prop slip Calculator or what?
When I bought this boat, it had a 10" jp on it with a '94200 efi, and the transom
was showing damage,so when I got the heavier motor I changed to 8".
The holeshot may have slowed by a half second, but the top end is still the same.
The '94 ran 60 gps @ 5600 @ 3.5".
Terry

[OverRHeads]

I did check the speed just after break in and it was about the same (higher water and air temps so slightly slower). However, immediately after that is when the Genesis was installed and we hit something with the lower unit/prop. Since then it has not been the same.

I am just wondering what kind of performance others are getting with this setup to know if I am in the ballpark.

By the way. What kind of compression should this motor have?

I do know one thing that I am sure ALL Cobra owners know........I NEED BOW LIFT!!!!!!!

[Backlash Ar]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by OverRHeads &raquo;</TD></TR><TR><TD CLASS="quote">........I NEED BOW LIFT!!!!!!! </TD></TR></TABLE>
Yes sir, know what you mean. Such is the nature of the beast, Cobra's run very flat. Get your prop re-worked by Mark and be sure he knows you're looking for more bow lift. Also, make sure your rostertail doesn't go higher than the top of your cowling. Keep us informed.

[OverRHeads]

Thanks for all of the input! I will keep you posted after I try the 24" Trophy.

[Backlash Ar]

Hey Terry, welcome to the Cobra Forum. What kind of transom damage are you talking about? If it's just spider cracking, no need to worry. Your 8" jackplate is OK. Most of the Viper 188's originally came with a 6" Rite Hite manual jackplate. (Nothing wrong with a 10" plate either). It looks like your prop shaft is a little low in the water. Raise your engine up on the jackplate until the middle of the prop shaft is 3.5" below the pad and then adjust in 1/4" intervals from there if necessary until you find the sweet spot. I'm not overly familiar with the Ballistic prop but I would get yourself a 25" Tempest and eventually have Mark (from the BBC) re-work it for you. Put one medium plug in the prop vent holes and re-test to see what you've got. (Many dealers will let you "try out" a prop if you give them a credit card number...you know, return it in the same condition and all is well, nick it up and you bought it...so be careful). Seems like you should be turning more than 5300 rpm's. As a general rule, for every inch you raise your engine it should increase your rpm's by 200. With the right set-up you should be around 68-70 mph. Make sure your psi doesn't get below 14-15lbs., and keep your roostertail no higher than the top of your cowling. Also, experiement with the number of vent plugs as well as different size vent plugs in your prop so you can get the best hole shot possible. Don't get discouraged...finding the max speed (sweet spot) can take a while. Let us know what your new numbers are.

[Backlash Ar]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by OverRHeads &raquo;</TD></TR><TR><TD CLASS="quote">..... By the way. What kind of compression should this motor have?</TD></TR></TABLE>

Sorry OverRHeads, forgot to post about your other question. Compression numbers should be somewhere between 90-110psi for each cylinder but the important thing is that there isn't more than a 10% difference between any of the cylinders. 5 psi difference between cylinders is good, 10 PSI diff needs to be looked into a little more but it's OK, 15 PSI difference and you have a problem that needs repair.

[OverRHeads]

Thanks! I guess that should be the next step. I may take it in this fall for winterization and have it thoroughly inspected.