Trying to optimize setup

[ronward]

I have a 16' starcraft v160 (glass) with an 85 Johnson. A/V plate is 1/2" above bottom most part of transom. No t/t. Tilt rod is in 2nd hole which puts motor as close to 90 degrees to bottom of boat as is possible. A/V plate is right at surface of water when on plane. I have two props, both s/s, one is 13x19, other is 13 1/4x17. No appreciable difference between the two. Boat planes quick and I have no real complaints. Trying to trim out to 3rd hole but starts to porpoise. Was wondering if I am at my optimal setup or could I gain anything from trimming to the third hole and adding a doel fin? Mainly what I'm looking for is a little better fuel economy. Can I get that or am I at my best?

 

[Sea Rider]

Try your current set up at close turns on flat calm no wind waters, does the prop ventilates ? If so, lower engine a bit untill ventilation stops. With well ballanced boat keep trim hole at a position that sits engine at 90 deg while boat rides paralell to water level once on plane.

Happy Boating

 

[steelespike]

It has been my limited experience that very often 2 notches is pretty good but seems 3 may be better but produces porpoising.
You can buy or make wedges to make 1/2 a notch, either adding to 2 notches or subtracting from 3 notches.
If you tell us your wot rpm and gps speed with each prop.
I have never gone to the wedges and have just tried to distribute the weight.I have a 18 ft Crestliner bare utility with a 50 Evinrude tiller.
Battery at the transom,Tank ahead of the middle seat and me 200 plus pounds pressed agaist the transom next to the motor.Motor in the second notch.
Still seems that a little more lift might be better and I have yet to simply raise the motor.

 

[dazk14]

If you have decent Ventilation margin still left, then the next step is to raise the motor up a hole on the transom.

You will then have less parasitic losses, thus better performance of your rig.

At that point you can try to trim up a hole and/or possibly adding a hydrofoil. The value of the foil would be to abate porpoising, particularly in rougher seas , when the bow begins to rise.

good luck!

 

[Texasmark]

Where you are is one of the reasons power trim was developed. For a given speed with a given hull and power source, including the prop particulars, the hull will remain stable for a given thrust angle....your second hole, and vertical is a good place to be with no PTT. When you move out to the 3rd hole you put the bow up but have insufficient speed to control the boat with that much of a step function. With PTT, you can bump the trim, gain a few mph, bump again, gain a few more, etc. allowing you to retain control and get up to a speed that will support the increased trim angle.

Any time you porpose you have 2 choices: Reduce the angle (trim in) or go faster. BTDT and that is why, unlike my '72 125 Johnson that didn't have PTT, all my engines since have had it. I had your problem back then.

On the whale tail, possibly but you won't know till you try it and if it's in the water, where you need it to function, it will add drag and what you have for top end now will be affected.

HTH,
Mark

 

[Mi duckdown]

I would try second hole from the transom. Pics would be nice.