Jack plates are not really necessary unless the hull transom design is flush with the planing surface. What a jack plate is designed to do is lengthen the distance between the prop and the planing surface and allow you to adjust the prop alignment to the planing surface. Think of the end of your hull as a pivot point, like a titer toter, as one end and the prop as the other end. The jack plate set back gives the prop leverage to lift the hull out of the water and reduce the length of the wet planing surface. The smaller the planing surface, the less drag the hull creates and your top end speed can increase.
To increase top end speed you need a prop that has better efficiency and higher pitch. This is where a balancing act takes place. To take advantage the hull lift you also need to get the boat up on plane when loaded with heavy gear and the prop must be angled to push the bow done and lift the heavy engine, fuel, batteries, live well and passengers without cavitation air with water and losing efficiency. This is why a hydraulic jack plate can be lowered to help the prop keep from cavitation with the low speed planing and than raise up and engine trimmed the optimize lift and gain rpm's. The most efficient high speed props have only one blade in the water at high speeds, these are 2 blade, high pitch clever degins that are very inefficient at low speeds. The 3 blade, moderate pitch cup design blades are good at both low speed and have 1 1/2 blades in the water at high speeds. The 4 & 5 blade props give you the best low end efficiency or push forward to plane quickly, however have 2 to 2 1/2 blades in the water at high speeds that decrease top speeds.
The bottom line is there is more to this then just a jack plate. You need to combine top end speed performance with low end planing performance. Most of todays hull deigns have built in set backs and do not perform well with jack plates that only further extend the prop leverage and makes the top end boat handling dangerous because of reducing the planing surface to the point of no water contact and therefor limited boat control. You also must be careful to make sure that the engine water pick up ports do not suck in air with the jack plate raised or the engine water cooling will be disrupted and over heat at high rpm's.
Tom
Ps; you may be wondering how could this old fart possibly know anything about high performance boats. My family raced boats and I was raised around high performance boats and cars and became involved with competitive racing for over 20 years. I have owned and driven some very fast boats and cars.
I would just like to know if i'm getting the most out of it. Thanks....Dave
