Changing pitch

[tom28571]

Originally Posted by TollyWally

Tom,
Could you expand on the trim tab and bottom loading thing. If this is not the appropriate thread I would gladly start another one. Does the surface area of the trim tabs help to lower the bottom loadong by supplying more surface area? Ever since reading about your Bluejackets, I've had the notion of large trim tabs increasing the surface area and lightening the bottom loading. I do like the attributes of those boats of yours. If I didn't already have one mistress and had more time I'd love to build a 28'.

Wally,

Trim tabs are actually high drag things. That they can often get a boat on plane that would not otherwise do so only says that the boat was poorly set up for planing to begin with. Usually it is because the boat is very heavy. A heavy boat creates a larger bow wave that is harder to get over. With enough power, such boats do get over the bow wave and plane. Adding lift aft can reduce this bow wave height by increasing the waterline length. Whether the boat planes or not depends on whether the total drag is lesser or greater than before, including the reduced resistance of the longer and lower bow wave. I suggested that CDK try the wedges because that is an easy and cheap test to see if that was the reason for his boat not planing.

The trim angle of a planing boat will always adjust itself to produce the amount of dynamic lift needed to support the boat at that speed.

There are volumes written by experts on the aspects of planing boats.

Edited to add: I know that I have not answered your question completely. Every element of the boat is interrelated to every other and making simple statements is often very misleading.