Re: jon boat plaining
Benelli;<br /><br />Do you make motorcycles, I used to own a Benelli made in Italy. Actually still very popular in Europe.<br />You asked the question, now you will get the long answer, because I believe there are gross misunderstandings regarding the use of trim tabs, props, and hydrofoils on smaller boat ( under 22').<br /><br />Anyway, Trim tabs are very similar to flaps on the wings of airplanes. At take off they are deployed down to gain extra lift and as the speed increases they are moved up. In turns one is moved down and the other up to keep the plane more level and the turn more accurate. These variable surfaces change the hull shape to compensate for the speed, load, balance, and outside forces ( wind) conditions. For the most part airplanes won't fly without flaps, trim tabs and rutters.<br /><br />Boat perform very similarly since they are going through a liquid ( remember both air and water are liquids). Nearly all larger boats have trim tabs which are mounted to the bottom of the transom, and used in the same manner as flaps on airplane wings. These are operated with up - down switches on the helm. There are two reasons you do not see trim tabs on smaller boats; one, is the cost of these electric or hydraulic systems in relationship to the cost of the boat. Typically $400.00 ( lowest pricing) plus 4 hour installation. The second reason is not talked about very often, and that is safety. The deployment of one tab ( say port side) without deploying the other (starboard) by accident, at high speeds, can be dangerous. Most trim tabs companies purposely make the operation slow, however this too can be a problem with an impatient operator who is deploying the tab and doesn't see the correction soon enough, and deploys the tabs even more. Over correction can also be a problem.<br /><br />The same is not true on larger boats ( 26' and up) since these boats are typically heavy, and slow ( cruise at 18 to 24 mph). Improper adjustment will cause a heavy list (leaning) but not critical. <br /><br />In short manually operated trim tabs in the hands of less experienced captains can be an issue.<br /><br />This is why electric tilt and trim is offered on I/O's and Outboards. The boat manufacturer recognizes the need for helping the boat compensate for speed, load, and sea conditions. By trimming the motor down ( also notice that the transom is tilted backward at the top) to angle the propeller so that it pushes up on the stern during take off. Once on plane the motor can be trimmed out ( perpendicular to the surface of the water) to improve the propeller bite (efficiency) and boat speed. <br /><br />The problem with this is that the propeller is very good at propelling and poor at controlling boat attitude. Does the prop angle make a difference in planing? Most certainly, but not as much as trim tabs. The good side is that it is safe. Using the propeller to fix boat handling is not efficient. For example; to improve the hole shot (acceleration to plane) you switch to a lower pitch prop, but the motor now runs more RPMs at any speed, reducing the top speed, and consumes more fuel. To increase top speed, the low speed performance is reduced. It is always a compromise when the prop is required to do double duty.<br /><br />Hydrofoils provide extra planing surface by increasing the size of the cavitation plate. They will provide some additional stern lift on take off at slow speeds. However, at cruising speeds (especially above 35 mph) they may create too much lift pushing the bow down. The motor can be trimmed up to compensate but this effect is limited, and reduces prop efficiency since it is now doing double duty, again. Lifting the boat by the motor is not advisable, for two reasons, one the stress of this extra weight on the motor components, and two, changing the concentration of lift to the center of the boat (especially on a V hull) which creates a teeter totter (side to side) effect in turns.<br /><br />Your local boat dealer and manufacturer will likely tell you that "Our boats don't need trim tabs". The key word is "need". Ask them to define their performance criteria. Will it plane without them? Sure, but the bow may point to the stars before getting on plane, and the minimum plane speed may be too much for the sea conditions, or towing the tuber,or you may need to ask Bubba Smith to move forward. Why does it porpoise? Why does it wander at no wake speeds? Why does it lean hard and slide through corners? And the list goes on! <br /><br />Please understand that I have a vested interest in one brand of Trim Tabs (automatic and self adjusting, specifically designed for boats 22 feet and under) therefore you will be best advised to research all options. There are some good conversations on this site under "Trim Tabs", Doelfin", Etc.
o you know if there is a dol-fin available for a single prop volvo penta 4.3.I have a 19 ft.cuddy (Wilker) and I do get a lot of annoying banging in any chop with the motor trimmed all the way in (which should bring down the bow for rough seas.Any ideas would be much appreciated.Thanks