Re: Just Curious
Andrew;<br /><br />I just wrote this in response to another question and I think it applies to yours as well. <br />Here it is ---<br />"Most people on this site already know that I am not a fan of hydrofoils, for a number of reasons. However you should also know that I have a proprietary interest in Smart Tabs. With that, make your own judgment regarding what I have to say. Unfortunately there are many misconceptions regarding boat performance, and my attempts to answer questions get lengthy. If I offend anyone, I am sorry, if your interested in an opinion read on, if not - - - move on to something else. <br /><br />With the popularity of the "V" hull design (when I was a kid the boats where flat in the back) came performance advantages such as faster boats, better ride through the waves, and better tracking. That is the plus side!<br /><br />The "V" design also made planing more difficult, increased the bow rise on acceleration as well as slow speeds, and increased the sensitivity to port / starboard listing.<br /><br />Most manufacturers provide tilt trim on the motor or out drive which uses the prop to help lift the stern during acceleration, facilitating planing.<br /><br />Given that stern drive (I/O's) and outboards powered boats are heavily weighted to the rear, the bow will rise on acceleration until there is enough water pressure (speed) to raise the stern (planing). Adding more surface area in the rear to help lift the boat and will facilitate planing.<br />The larger the surface the better control and easier it is to plane. <br /><br />The best solution is to use trim tabs which are adjustable, similar to flaps on airplane wings. The tabs should be size in proportion to the boat size to be effective. They also need to be adjustable. You need more deployment upon acceleration and little or none once on plane. <br /><br />Most boaters think that the benefit of trim tabs is simply to help get the boat on plane. This is only a small part of their benefit when used correctly. You can eliminate porpoising, chine walk (on fast boats), correct listing, control attitude in any seas, stay on plane at much lower speeds (good for towing tubes or in rough water), minimize bow rise at slow speeds (no wake zone), improve acceleration and Smart tabs will also improve top speed. In addition, the overall fuel economy will improve, and the stress on the engine will be reduced.<br /><br />The disadvantage with any fixed position devise such as hydrofoils or fixed plates and tabs is that they only provide improvement in one specific area of performance. For example, a fixed plate which is deployed to facilitate planing will impair the top end performance by causing excessive bow pressure which will result in bow steering. Once the boat is on plane the deployment is detrimental to performance.<br /><br />Hydrofoils, because of the limited size, provide marginal lift at low speeds, however once on plane, and at higher speeds (35 MPH+), they continue to lift creating a bow down issue (excessive bow pressure). Like fixed plates this results in bow steering, and lose of both economy and top speed. The economy is not effected (generally) at speeds below 30 MPH, because the speed has not produced the extra lift to push the bow down. <br /><br />It is not advisable to concentrate lift from the center of the boat (especially "V" hull designs) as with hydrofoils. This creates additional stress on the motor mounts and lower unit as well as a "teeter totter effect" with side to side movements and turns. <br /><br />The minimal surface area of the hydrofoil, which has marginal effect at slow speeds, becomes more influential at higher speeds (when lift is no longer required). Look at the bare foot water skier. They can not get up on their feet alone, but once the speed is fast their small foot prints are sufficient to support their weight (lift). Once on plane the boat does not need additional lift.<br /><br />Using the tilt trim on the motor simply uses the prop angle to help lift the boat. This is also marginally effective. The reason that the manufacturers (boat builders) prefer this on small fast boats is that it is safe, and less expensive than manually operated (helm controlled) trim tabs. A side note - Smart tabs are automatic and not driver controlled. <br /><br />Tilting the motor (prop) is not an efficient use of the prop torque (thrust). The most efficient angle for the prop is perpendicular to the water surface. Tilting in or out sacrifices the torque in favor (compromise) of the boat attitude. The prop is for propelling. Let the trim tabs control attitude. <br /><br />Changing prop pitch to achieve better acceleration and planing, will only sacrifice top speed, and run the engine faster than required. It's like driving around in first gear.<br /><br />Most boaters measure the performance of the boat by how quickly it will plane at near full throttle. Full throttle accelerations are costly in terms of fuel, and wear and tear on the engine. It is not necessary! With trim tabs (Smart Tabs) the boat can be accelerated slowly and rise to plane easily. Of course the full throttle accelerations will improve significantly also. <br /><br />In short, having a variable surface (attached to the hull) allows the hull design to change in direct proportion to the changing conditions of weight, speed, waves, etc. The improvement in performance, handling, ride comfort, and fuel efficiency is significant. Smart Tabs go one step further by automatically adjusting and acting like a vehicle suspension system when cruising. Smart Tabs are limited to boats under 22ft long."
