Boat porpoise problem

[CajunChristian]

Originally Posted by Gerald

In the interest of learning......

How do you "Hook" the bottom of an aluminum boat like shown in the picture holding the tap measure? I am thinking maybe using a big hammer [sledge hammer???] but think that would probably not look good after a few good hits.

Do you have to put the boat in some kind of big "press" to make the bend in the bottom?


I once tried putting a 15 hp outboard on my 12' Alumacraft boat that is rated for 8 hp max. Just me and the engine, no other weight. I don't know how fast I was going, but once that boat planed out, it felt like it was "dancing" on the smooth water. I don't remember if I tried running WOT, but for me that was too much hp for that 12' boat and did not feel safe.

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I use a 12" piece of 2X4 and a loaded rubber hammer. It takes much less blow than you think. I measure with a straight edge constantly to insure a smooth curvature. I usually just slide the boat back about 2' on the tail end of the trailer, lay on my back and tap away. About 10 minutes to completely hook both sides.
You want your boat to sit up on the tail and run, but, you don't want to use all available horsepower to lift the bow.
Stop this video at 2 seconds and notice the trim angle of the engine and how much boat is out of the water.

good3.mp4 Video by 1995US1 | Photobucket

good3.mp4 Video by 1995US1 | Photobucket

Less boat in the water=less drag. Less trim angle=less wasted horsepower. You have, let's say 50hp, how much will you use to lift the bow and how much to push forward? That is what makes our tunnel race boats so fast, air flys the boat and the motor only pushes forward.
Notice the trim angle on this race boat, and notice how much boat is out of the water:

Photobucket (Videos)

Photobucket (Videos)

The ways to control the bow on a loaded aluminum boat is:
weigh the bow down, not practical
trim the engine all the way down, a tremendous waste of horsepower
trim tabs, takes speed away, angle too sharp
hook the rear bottom of the hull, no speed loss