23 w/ twin 225 OPTIs....

[james34]

I have rebuilt 23 with twin 225 OPTIs. I was wondering if anyone else is running this setup and if so what props are you running?? Im running 25 Mirages cruise 40MPH at 3800 burning 18GPH, but they cavitate in a sea.

[peterb]

I have a 23' with twin 200 OX 66's on a full flotation bracket. It is very important to have the engines at the right height, and essential to have working trim tabs (otherwise my boat porpoises).

Currently, I have 21 x 14 3/4 Yamaha props on her. Also, i have a set of 19 x 15 1/4. I just got my engines lowered one notch and will try out both sets of prop's.

Here were my previous numbers with the 21 inch prop's.

I would cruise between 3k and 4k & my mph would equal the rpms. For example, at 3,500 rpm's I am probably going around 35 miles per hour. On decent sea conditions I would get around 1.7+ miles per gallon.

WOT was around 57 MPH (and 5,400 RPM's).

With twin 225's you should be able to go around 60 MPH, if not higher (or so I would think).

[peterb]

When you say that you are cavitating, do you mean that your prop's are coming out of the water as you go from wave to wave?

[Trey1096]

I expect that is the case Peter. My 23 SF has twin Merc 200’s on the transom and it’s bad to suck air into the props when the seas kick up.

What’s the best way to prevent it?

Trey

[Fr. Frank]

When you say that you are cavitating, do you mean that your prop's are coming out of the water as you go from wave to wave?

That would be "ventilating" not cavitating. If you're ventilating unintentionally, you need to get the propeller deeper in the water during the conditions wherein the ventilation occurs. Cavitation is the production of air bubbles on the backside of the blade caused by the pressure differential between the front and back surfaces of the blades in their relationship with the surrounding fluid pressure. Ventilation is the Introduction of air onto either front or rear surface of the blade, but usually the front side.

Here's an easy way to understand the difference: a submarine that's 500 ft underwater can cavitate when too much shaft speed is applied too quickly. But it must be at the surface to ventilate.
A powerboat whose propellers are piercing the surface of the water is ventilating.

Another note, Most new stainless props are designed to both cavitate AND ventilate. Their designed to cavitate at the sudden application of power at slow speeds to allow the propeller shaft rpms to rise rapidly, getting the engine quickly into it's power band. They are also designed to ventilate slightly at high speed, running right at the surface, to eliminate as much fluid drag (or friction) as possible. That's why the trailing edge of each blade is cupped. The cupping allows the blade to run at the surface, and the cupping holds water against the rear face of the blade, minimizing ventilation.

End of lesson.

[manuelfadra]

I also have a 23 Seacraft with twin 200 where did you get your bracket and price.