posted 11-01-2002 12:42 PM ET (US)            

I'm not sure why it happens when you have two on board and doesn't when you have four, may have something to do with where they are located and what the weight distribution is. I would play with the trim a little and try trimming the motor down (bring the lower unit closer to the transom) and see if that doesn't eliminate the slippage. I have found both on my Outrage 22 and my Parker 2520 that the motors (both 225's) will run without slipping (ventilating) at higher trim once the boat is up and well planed than they will when we are coming up on plane.

If that doesn't fix the problem, your motor may be set too high on the transom, and you would need to drop it one notch at a time until the condition goes away. Your hydrofoil in and of itself is not causing the problem; all it might be doing is intensifying the condition brought about by the motor needing to be trimmed in some.

posted 11-01-2002 02:58 PM ET (US)            

What Bigshot said-

(He read your question more carefully than I did; I didn't pick up on the whalerdrive aspect.)

posted 11-01-2002 04:30 PM ET (US)         

Here is some definitive info on the subject from Mercury's prop catalog:

"CAVITATION: Even slightly chipped or bent blade edges can cause surrounding water to BOIL ("cavitate"). Gas bubbles then condense elsewhere on the blade, releasing energy that causes metal erosion or "cavitation burn".

"VENTILATION: Air from the water surface or exhaust gases from exhaust outlet being drawn into the prop blades causes ventilation. This reduces normal water load, causing the prop to over-rev and lose a lot of thrust.
Ventilation is most common with high transom mounting, extreme trim-out and sharp turns. Mercury props are designed to minimize ventilation."

So, summarizing, cavitation is from damaged blades, and ventilation is mostly from high mounting, without a prop that can handle it.
To get rid of ventilation, you generally have to either drop the engine down, or use a surface piercing performance prop, as described below. I use these on both of my Whalers.

Mercury's performance line of props, mostly for boats that will do over 40MPH, have a "Performance Vent System", which uses ventilation under controlled circumstances, as opposed to the description above. They describe it as following: (quoting)

"PVS allows you to adjust for changes in load and environment simply by changing the propeller's vent plugs for optimum acceleration. On acceleration, exhaust is drawn out of the vent hole. When the propeller blade strikes this aerated water, it pushes through it much easier than it would solid water. By controlling the amount of aerated water (by size of hole in vent plug) you can control how quickly your engine RPM rises. Once you're on plane, the water then flows over the vent holes, and seals the exhaust, allowing the propeller to again operate in solid, nonareated water."

I would think that anybody operating a 4-stroke engine could make good use of a large vented prop, to help overcome sluggish acceleration.

posted 11-07-2002 09:09 AM ET (US)            

Under the category of "nit-picking", I guess, I have to take issue with your blanket statement denigrating OMC props. I have a cupped and raked stainless OMC prop on my looper Evinrude 225 that has pushed my Outrage 22 to 53 mph and it grabs and holds the water even with the motor mounted two holes up so well that it is really difficult to get it to ventilate no matter what I do.

posted 11-07-2002 03:25 PM ET (US)         

Gary, in your post above, items 2, 3 & 5 are all the same thing. There are basically three Mercury props you should be looking at, the "Laser II" (which is almost identical to the OMC "Raker" prop that Kingfish is using - I use Laser's on both of my Whalers), the 3 bladed "Mirage", and the 4 bladed "Offshore Performance". For your application I recommend the latter, and by going to "Offshoreperformance.com" and e-mailing them for a quote, you can get one for about $400.
For less money, more like $300, you can also get a Stilletto or Michigan Wheel Rapture that will do the trick.

Regarding pitch, here is the data on your engine from Mercury's prop catalog: (engine red line is 5800, gear ratio of 1.87:1, Revenge WD dry weight 2655#)

17" pitch prop, for load range of 2900-5000#, speed range 38-48MPH. I believe this is what you want, assuming your engine is running good compression and putting out correct HP.

posted 11-13-2002 09:32 PM ET (US)            

I've got a 13' Super-Sport with a 1984 40HP Johnson on it. It is currently running a 12 X 15 aluminum prop for about 35 MPH at 5000 RPM (3/4 throttle). If I open up the trottle all the way, it over-revs. I've been thinking of trying an 11-3/4 X 17 prop (Michigan Propellers) on it. Think this will cure the over-rev problem???

posted 01-21-2003 06:18 PM ET (US)         

Your engine is too high for the prop, and the prop is shot, probably a slipping (spun) hub.
Beg, borrow or steal another prop, any Mercury 17" pitch prop, and see what get. A single engine mounted on a Whaler Drive should be down all the way in order to use a non-performance elephant ear aluminum prop. Whaler Drive wasn't even designed for single engines, as evidenced by the structural support dead center.

Also, remove the hydrofoil. Those things are performance killers.

posted 01-21-2003 10:23 PM ET (US)            

Based on my experience I think I would go with a 19" Stiletto. However, lhg and Sal are recommending 17" and they both have much more experience than I do. As river mentioned, Surplus Unlimited https://www.surplusunlimited.com carries both Stiletto and Rapture.

posted 01-22-2003 05:00 PM ET (US)            

Decreasing pitch from 19" to 17" should increase RPMs by 200-400. However, going to s/s and adding more cup should offset some of that. Based on my experience a 19" s/s would be fairly close and since you could always raise the engine which should increase RPMs I think I would go with a 19.

posted 01-22-2003 06:07 PM ET (US)         

But I'm sure Stiletto, Cabela's (made by Mich Wheel/Rapture) or Mich wheel would be fine also. But make no mistake, Mercury's props are superior, and have the patented adjustable vent system & interchangeable hub, so they can be used on any brand engine. You do get what you pay for. No manufacturer has more experience with performance prop applications & design, outboard and sterndrive, then Mercury. Just look at the huge selection they offer, for every conceivable boating application. See props on their website, and order their free catalog.

You often cannot tell a spun prop just by looking at it. But your description certainly indiates a slipping rubber hub, which won't carry the torque under load. Mercury's new props do not have the rubber hub any longer, but instead use an interchangeable, and easy to replace yourself, plastic drop in spline. Mich Wheel has recently been licensed by Mercury on this design, called a Flo Torque II.

You can also go to Mercurymarine.com's prop selector and see what it gives you. Be sure to choose the 200 EFI model, which is the current equivalent to your engine.

I'm still recommending the 17" pitch 4 bladed Offshore prop for your rig, because of the weight of the Revenge model and Whaler Drive. Other viable alternative would be a Mirage model.

Mercury's prop chart shows the following for your engine regarding the 19" prop recomendation:

posted 01-22-2003 11:17 PM ET (US)            

However, when I use Mercury's Prop Selector www.mercurymarine.com/prop_selector I also get 19". If I use: Length(feet)=22, Engine Type=Outboard, Year=2000, Engine Class=2-Stroke, Engine=200 EFI, Performance Goal=Overall, and Gear Ratio=1.87 it shows an Estimated Boat Weight of 3954, Estimated Speed of 46.9, and Theoretical Pitch of 18.7. If I use Weight instead of Length and set that equal to 4000 the Theoretical Pitch is 19.4. I'm assuming that Weight is total boat weight which would include the boat(2,600), engine(500?), fuel(77galx6lb/gal=462), batt(100?), persons(350?), etc.

posted 01-23-2003 07:22 PM ET (US)         

Barry, I think the Whaler Drive could throw a monkey wrench into the prop calculator's figures. It does offer additional drag.

I've not been able to figure out what Mecury means by "theoretical pitch". Sounds like a hedge to me, with unknown factors such as tee top drag, bottom paint drag, etc. Even the radar arch took 2 or 3 mph off my top speed.

posted 01-24-2003 08:36 PM ET (US)            

Got M, your buddy should drop his old prop off at a prop shop and get it cupped (like the new one is). Then keep it around for a spare...

If you're running aluminum props, it's easy to wear your cupping off on a sand bar. With stainless, it takes a little more, but not as much as you'd think to sand it off. My local prop shop puts the cup back in with a hammer for around $40, which is good considering the cost of a new SS prop. Unless the rigger was a fool, it's hard to believe any dealer would rig a boat which cavitated as much as Monna and Get M are saying. However, it's easy to expect the cupping to get worn off over time.