The following is from the Mercury Marine web site in their propeller technology section. Here is the reference: http://sites.mercurymarine.com/port...26_49291:126_49299&_dad=portal&_schema=PORTAL Check out the section on rake and cup. Our water ski boats are essentially "work" or even "tug" boats especially when used for really heavy duty application like show skiing. The props should remain submerged when pulling hard in order to produce maximum static thrust. Once the boat gets moving things get a little easier. Why am I up on my soapbox again??? If you believe the Mercury marine prop technology theories, it begs this question: When was the last time you saw a stock high quality propeller with no cup? Answer: A long time ago. Why? Because there are no stock props that are designed for skiing applications. The market is too narrow. All of the current props are geared to some extent toward speed. Even members of this forum say when looking for a prop recommendation that they do not want to compromise speed. But for the show ski application where twin or even tripple engines are used speed is of less concern except that enough speed for multi-footing is needed. This is not much of a problem even with low pitch ski props. My question is, why spend all of this money on multi engines, expensive multiple jack plate installations and settle for a stock prop that was designed for a bass boat where speed is everything??? Why not spend some of that big bucks on developing a custom modified prop that has maximum static thrust as a primary goal. The technology exists and is contained in the Mercury site not to mention a few custom prop builders scattered around the country. There are some stock props that are worth modifying. jim :yahoo: :smash: :yahoo:
Actually, it does not take big bucks. I have some modified props that suit my applications exactly. I would encourage you to do the same. My next project is to modify a Mercury 15 pitch SS prop to fit my Johnson and then start the blade modification. The prop was given to me so it is a perfect candidate. jim
I have 7 or more props floating around home but none would meet the criteria that Jim has suggested as ideal through various posts on this forum. I'd like to get a hold of one or two to play with and see what Jim's suggestions turn out like. Makes perfect sense to me, but if my wife noticed another prop roll up, well it better be a freebie! With free postage! With outboard ski boats, you are pretty much on your own. It is very hard to get good advice. This is by far the best site I've found. This information applies to any outboard ski boat but unless you own a hydrodyne, why would you think to look here - even though it is probably the best online resource in the world... There is a market for a prop shop or two to sell these perfect props if only outboard ski boat owners understood why they'd want such a prop. A 200 horsepower flightcraft ski boat owner would take some convincing that he'd be better off with a 17" prop. There are plenty of props out there with enough static thrust but the wakes are not perfect. The four blade Merc Bravo One prop is only available in 22" pitch and greater but wow does it have some traction (yes there is a prop by that name it is not just a prop designed to fit the bravo one leg). The BRP Cyclone prop also has a lot of grip but again it is a fishing prop not a ski prop. I'd love to be able to buy a great ski prop and know it is as good as they get. Even better, second hand props are often the best base for this. So a good prop shop can buy a cheaper SS prop, refurb it, do some tricks and sell it for a good price as a top of the line ski prop. If only there was a way to tell all outboard ski boat owners how to make them into nice ski boats that drive better than inboards, there would be such a market for this stuff.
You don't have to pay big $$$ for an experimental prop. 17's do not sell well. click here Since that is a 15 diameter, it would probably handle a big block. You might even be able to trim it down and use it on a small block. It would be a cheap experiment. They show up on e-bay all the time, jim
These are some of my experimental props. The one on the motor started life as 17 pitch new aluminum OMC prop about 1997 vintage. The cup was removed. It has very little rake as I think you can see. This prop works very well. The prop on the right in the other picture is a Torque shift. It starts out at 11 pitch and increases pitch as required to prevent over revving. I have it set to limit at about 5500 rpm which is where the motor develops max power. It has more rake and is double cupped. With a little trim it will stand the boat right up since it has plenty of bow lift and thrust. It pulls very well, but bow rise would be a problem with heavy loads. It is a great play prop when out alone and that is what I use it for. big $$$ and out of production. The white prop is what started all of my experiments. It is very old as you can tell by the color. It may even be an I/O prop. Small pitch I/O aluminum props are cheap and make a good subject for experiments. This prop is a 17 and it never had any cup and not much rake. It has more blade area than the one on the motor and hooks up a little better. The SS prop to the left of the white one is a 17 pitch Mercury prop that I will cut the splines on so it will fit my Johnson motor. It has very little tip cup and a little trailing edge cup with not much rake either. I think it will be pretty good stock. I have not tried it yet. I might re-pitch it to a 16. The SS prop on the left is for a 115 Yamaha. It is double cupped with more rake. I had it on an Ebbtide Campione and it was just OK. It would not be a good Hydrodyne prop. jim
Well, I just came into possession of a 14 3/4 by 17 pitch Viper. I don't think I will even try it. It has a ton of rake and will have a lot of bow lift I think. jim
Jim, You are correct about the massive bow lift on the viper. I can go almost wide open with trim all the way down with the viper on, and at low speeds, the bow sits awful high.
I'm running a 19 pitch Mirage Plus now, but bought two more props over the winter - a new 21 pitch Mirage Plus and a used 25 pitch Mirage Plus. I think the 21 might be a better all around prop for me because I'm really not pulling heavy loads much. The 25? I'm not sure why I bought that. I can't see using that prop for waterskiing but if the water level is high enough and I am going down the chain of lakes I might use it as a cruise prop (read - if it gets damaged, I am not short a waterski prop). I'll report the results with the various props this summer. Markbano
