Strut Depth and Angle relative to the Hull Break Section

[BobGutsell]

So the hull break on the 8200 hull I'm building is about 4.5 inches from the transom.

Do I

1. Set the strut depth up on a flat plate with the break section parallel to the flat plate?

2. Set the strut depth such that the Main hull bottom is section is parallel and therefore the break effectively kicks up and creates a turbulent zone maybe even a vaccum effect?

 

[u60]

Set the strut depth at the same depth as the sponsons. Turn the boat upside down, then lay a straight edge on the flat part of the boat. Make sure its long enough to run up to the sponson backs. Lay it along side the airtrap and then Mark the inside of the airtrap at the back of the sponsons. Then measure from that mark to the sponson bottom. That will give you the sponson depth. Then measure from the bottom of the back of the boat to the center line of the strut (at the back of the strut) set it at the same depth as the sponsons. This process will give you the correct strut depth.

You might try putting a 4 to 7 degree angle on the strut. In other words the front of the strut will not be as deep as the rear. Again, try 4 degrees and go from there. Experiment with props.

Hope that helps you.

 

[BobGutsell]

Yup thanks, that is the way I have been doing it. I guess what I really wanted to know is what is the break section supposed to do?

 

[Hydro Junkie]

The bottom break divides the rear bottom that doesn't lift the hull from the sloped front that does. The location of the break, for and aft, and the angle of the forward bottom determine how much lift the bottom of the boat will provide. Too much lift for the boats weight and you have a kite, not enough and you have a dog. I'm not going to add all the rest that affect how a boat performs since you're not asking that

 

[lohring]

The hull should run something like this Jerry Dunlap picture. The Mutt sport 40 hull, a very similar design, has no break and actually runs a little nose down. This much earlier Dave Frank design has a lot of break and needs a forward cg and an air dam to keep from blowing off. Both hulls run at very similar angles.

Lohring Miller