PIT BULL

I know I will need seat time but it felt like somone threw an anchor off the back of my boat. had my 22 for 9 years and dialed it in perfectly. 76.5 on gps with a 22" chopper. This thing makes me think IM driving a truck, got 66.5 on gps. I would like to know what the best set up is for the rough as well as top end. If these two meet. Engine height,drive,prop. It has a 502 with an estimated 400-450 hp for know. After its dialed in I will add power.

convincor

It's only a 4' difference but 4' is a lot of boat.
I went from a 22' to a 25'. Sure it maybe a little slower, but in rough water I'll take the 25' any day.

convincor

the 22'

convincor

the 25'

Padraig

Is this a 260 (24 ft) or 280 (26 ft)?

What prop and rpm are you running? 66 mph is slow. I would expect you to be in the low 70s with a 502 in a 260 and 69-70 wit a 280.

Steet

I agree with Padraig. I had a 280 w/stock 454/300 and the boat ran 63.5 GPS with a 24 hydromotive at 4400 rpm. With 502/415 the boat should run about 70 running a 26 hydromotive @ 4800 rpm.

blue thunder

This is the way street's number shake out of my slip calculator. 13.5% is probably generous. This calculator has proven quite accurate for me.

----------------------------
MPH
Input:
rpm 4800
pitch 26
constant 1056
gear ratio 1.5
slip % 13.5



Output:
mph 68.15

------------------------------

MPH
Input:
rpm 4400
pitch 24
constant 1056
gear ratio 1.5
slip % 13.5



Output:
mph 57.67

-------------------------

I personally think 66.5mph is quite respectable, especially when you get into larger boats. The fun of a larger boat is in the rough, not the flat. This is probably a pardigm shift from the 22' boat. In fact, I don't even like to go out when it is flat. Running a 30' scarab w/ twin 468cid turning 4900rpm with 25p mirages, 68.1 gph so far... still optimizing. My slip is high for some reason.


BT

blue thunder

I take that last statement back... haven't plugged my numbers in for a while. This is what the calculator says about my slip now. It was previously 16.5% before some improvments.

SLIP
Input:
rpm 4900
pitch 25
constant 1056
gear ratio 1.5
mph 68.1



Output:
Slip 11.94%

I'm not going to get any more speed until I find some more rpm (ie hp) to support a higher pitch.

BT

Steet

Blue thunder, won't the slippage get worse as the prop size goes up? I know that on the hydromotive when you get to the 29 and above the efficiency gets worse and I assume on Bravo's to

blue thunder

I am certainly no prop expert Street, but I have heard that effieciency (slip) goes up with blade surface area (diameter). Pitch should not affect it. Again, I am no prop expert and if my answer is wrong, let me hear it. My calculator does not take into account blade area, only accounts for it as slip.

BT