1999 225 EFI on 203 Champion. Cavitates while coming on plane

Hi folks. Here is the story... I have a 1999 Champion 203 (20' 3") with a Mercury 225 EFI of the same year. The engine is mounted to a Hydro Jackplate, the prop is a Stainless Steel Trophy 4 blade 25 pitch prop I believe it is a 13-3/4” Diameter. My problem is right as the boat gets on plan the engine revs, and seems as if the prop just spins in the water, I think that is what you refer to as cavitation. I have lowered and raised the engine via the jackplate. It seemed to get a little better as when I lowered it but it still cavitates. I really have to lay off the gas to keep it from happening. The prop is in great shape by the way. Not kicks, dents or anything like that. One person mentioned to me it could be the exhaust causing the cavitation. Another theory is the prop either small in diameter or I need a higher pitch... maybe both.... Your thoughts?

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

It's called ventilation.....sucking air in from above the prop. First of all look at your prop and see if any holes are in it just below the leading edge of the blade. If so it's probably the holes doing their job. The process is called "porting the prop".

Second, if you are trimmed out too far it can cause the problem.....sometimes I do it deliberately as it gets my rpms up faster and I get a dazzling hole shot.

3rd your jack plate is too high for the other conditions at the time.

Too much slippage is obviously unwanted. But some is desirable and some props are ported (first thing I mentioned) deliberately to cause the engine to over rev (revving over what would be normal). HP is rpms x torque and a constant of proportionality. If you want to get the hp up which twists the prop and makes you go, getting the rpms up is the fastest way to do it in the stressful hole shot....stressful meaning you have the biggest load on the engine fighting your getting your developed hp.

Balls in your court.

Mark

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

Your Trophy Plus prop came with the Medium(9mm) PVS plugs installed(unless someone changed them or removed them).

These plugs control the amount of rpm rise while accelerating onto a plane.

Four sizes are available; small(7mm), medium(9mm), large(12mm), and solid.

If you're getting too much induced ventilation, you can change the PVS plugs to the next smaller size, or install the solid plugs to block it off completely.

They are available from your friendly Mercury dealer.

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

You may be on to something. The plugs are completely removed. I am going to call local baot shop to see if they have any and give it a water test tonight.

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

JohnnySCV said:

You may be on to something. The plugs are completely removed. I am going to call local baot shop to see if they have any and give it a water test tonight.

Click to expand...

You cannot run with no plugs in there; the hole is WAY to large without a plug in there. That's like a 16/17mm hole; too much exhaust is entering the propeller stream.

Google "Mercury PVS system" and find a PDF you can open that describes the system and shows the different plugs with part numbers.

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

No luck so far. Tried a bunch of boat shops in the Los Angeles area. I have a trophy not a trophy plus. Holes are about 1/2 inch not the larger 17 mm size on the trophy plus. Any ideas on where I could find PVS for just a regular Trophy, or is there something else I could shove in there????

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

JohnnySCV said:

No luck so far. Tried a bunch of boat shops in the Los Angeles area. I have a trophy not a trophy plus. Holes are about 1/2 inch not the larger 17 mm size on the trophy plus. Any ideas on where I could find PVS for just a regular Trophy, or is there something else I could shove in there????

Click to expand...

Tell you what. Get some JB Weld (auto parts store) and plug the holes. Make a test run and get some numbers. Then get your drill out and drill out the JB starting at 1/4 then 5/16 then 3/8. You should have found your sweet spot by then. Half inch is a BIG hole! Then there are several things you could do. One would be to take your prop to a welding shop and have the holes plugged then go to a machine shop and have them drill out the plugs to the diameter you found that best suited you. I drilled holes in my Ballistic with my drill press and titanium tipped drill bit and I guarantee you the SS props are made from is one tough nut. Machine shop should be better equipped with milling bits.

Lot of trouble and all, but if you are serious about solving your problem it might take that. For what it's worth, I haven't found any place to buy plugs either.

Mark

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

Ok so the plot thickens. While asking the local marine shop about the plugs, they convinced me to let them take a look at the boat and give it the once over. The found that the gasoline lines were corroded from within and needed to be replaced. They showed me the lines, the fuel filter and the water separator and there were parts of the hose everywhere. So much so that I could cut 2 or 3 inch lengths of the hose and I and could see through it. Once replaced they ran a compression check and found the highest PSI to be 110 and the lowest was 108. Once they leveled the boat and took some measurements they determined that the motor was about 4 1/4 inches too low. They raised the engine and off I went. Tomorrow afternoon I will water test it, hopefully it will be ok, but at least I can lower the engine 3 inches right on the water with the manual jack plate.... If that doesn't work I guess it JB weld on the holes for me....
edit....not sure if any of this could have caused the cavitation, but it sounds as though it needed to be done.

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

The big guns on here always preached that you get your "setup" right, then go after your prop. Being on a jack plate, your engine is sitting quite a ways back from the end of the bottom of the hull. On pad, at WOT, properly trimmed for max MPH, the bow of the boat is up 10ish degrees putting the engine down in the water that much deeper. For the engine to push the boat at 65 mph or so, it needs to be sitting well up from a straight line you would draw from the pad straight back. The antivent plate may be 4-5 inches above that line.

In my opinion, I would expect ventilation problems in being too high, not too low. I haven't seen your rig and I'm no expert but that just seems like the wrong direction.

You didn't mention how you trim your rig. Do you get the boat up to speed before you start jacking the trim out to get her on up to pad speed, or do you start out with it trimmed out appreciably? If you do, it could explain ventilating.

Course if you went to a dealer who does this for a living and is experienced in the process, having the boat right there and taking measurements, who am I to argue with that......I'll answer the question: Nobody! Ha

Keep us posted.
Mark

Re: 1999 225 EFI on 203 Champion. Cavitates while coming on plane

Ok so I got the boat out late afternoon yesterday. 1st run the boat hopped up on plane and ran like a champ.... No issues at all with any cavitation. Left the engine right where it was and continued the focus on some LMB. Thanks for all your input. I guess fuel is important to those big outboards after all....