Re: NewGuy PROP???
Boilermaker;<br />Since you are new to the site let me help you qualify everything I say by letting you know that I am from Nauticus, Inc. the manufacturer of Smart Tabs (Trim Tabs). Our experience and development work with trim tabs is concentrated on boats in you size range. <br /><br />Let's look at your boat as the individual it is and separate the performance issues, and address them one at a time.<br /><br />Let's assume all things are equal, and there are no mounting problems, or particular load balance issues, or defects in hull design then the prop situation becomes easier. Changing the pitch of the prop is like changing gears in a car. Lower pitch helps acceleration (or load pulling) like first gear in a car, but the top end suffers. The lower pitch will also make the engine turn more RPMs per MPH which will increase fuel use and reduce the life of the engine. As far as life is concerned, it is unlikely that you will ever use the boat enough to ware out the engine. Rebuilding is more common because of lack of use. Mercury Marine studies show that the average boater uses his boar less than 60 hours per year. In car terms at an average speed of 25 MPH that's 1500 miles. So don't worry about engine life.<br /><br />More pitch gives you more top speed (within reason) but you loose the low end pulling power or planning ability.<br /><br />Included in this prop choice may be the stainless or aluminum cupped props which are designed to provide other characteristics such as lift and holding power in high speed turns.<br /><br />Your issues are more general, you simply want a larger window of effective use. Better acceleration and towing capability and a bit more top end. <br /><br />The hydrofoil adds more surface area which provides more lift. This additional lift may be noticeable or not depending on the size of the hydrofoil and the weight / balance of your boat. In many cases the foil effect is noticeable, in other (like you indicated) it may be less effective.<br /><br />What you need to understand is that for low end performance (separate from gear changes / props) you need additional / adjustable surface area that is proportionate to your boat size. And, as the boat increases in speed, gets on plane, the lift is less necessary since the hull is now supporting the load. The problem with any fixed planning device is that at speeds ( the faster the more influence) they produce increasingly more lift. This drives the nose of the boat down which creates a plowing issue, and nose heavy turns. If you have electric tilt trim on the motor, then you tilt the motor out to push down on the transom (which at this point has too much lift) and raise the bow. Now the prop is going through the water at a downward angle which reduces it's best bite. The prop should run perpendicular to the surface of the water for it's best performance. When the prop is trying to overcome the extra lift of the hydrofoil you end up with a compromise between prop efficiency and boat attitude.<br /><br />You can also create a port to starboard balance issue when the concentration of lift (hydrofoil) is in the center of the boat i.e.; a teeter totter or a balancing act. The boat is also likely to lay over hard in turns and blow out the prop. <br /><br />The other common problem with stern heavy boats is porpoising at cruising speeds. Since the center of balance is in the last 30% of the boat it is easy for the front to get pushed up by the least wave, and what goes up must come down. What is required to control this is more bow pressure or stern lift. Sometimes this can be controlled by the electric motor trim (trim the motor down to lift the stern up and bow down. This however is once again using the motor and prop to do something other that propel - not efficient. Hydrofoils can help eliminate the problem but usually provide excess bow pressure.<br /><br />Trim tabs ( helm controlled - electric or hydraulic) can be deployed to give the boat extra lift at slow speeds (reduced bow rise, faster acceleration, and slower minimum planning speeds), then adjusted up at high speeds, without using the prop energy. Since they can be adjusted up at cruising speeds, the top end performance is generally not effected. The porpoising can be eliminated with a slight deployment of the tabs at cruising speeds.<br /><br />Smart Tabs will do all of the above even more effectively (for small boats) as the system is active / automatic, with no need for helm switches. The system uses a nitrogen gas actuator to pre load the plates and then allows the water to regulate their position. This pre load is adjustable during or after installation to suite the specific boat.<br /><br />The separation of the duties which allows the prop to propel and the trim tabs to adjust the (hull design) boat attitude and handling makes for a far more efficient and useful boat. Just like flaps on an airplane.
<br /> #1, make sure your tilt pin is in the hole nearest the transom.<br /> #2, the 14X19 with the "longer" blade design was fitted to the "loopers" of newer vintage. I've been through this with extensive prop testing on an 18' deep-vee starcraft, with a 97' 115 Johnson.<br /> #3, your engine is rated at the crank, and anything newer than 85', is rated at the prop shaft-your engine should like a 13.25X17, and maybe even a 15" pitch, depending on engine hiegth above the transom.<br /> #4, The goody....IF your stingray is causing a nose-down situation, you are trimmed too far down, (in). The stingray will actualy let you trim farther out, than without it.<br /> #5, I'm very fond of the stingray, but I would recommend, and welcome comments from 2 guys that have taught me a bunch about this.<br /> I CAN tell you, there is NO perfect magical setting but some time and alittle work, taking notes here, of course, will put you on track better than most dealers can do...... 