Seacraft 20 performance help

Walter Sobchak · #1 08-19-2020, 03:45 PM

I have a new to me 1972 20SF with an armstrong bracket and a 2016 F150 hanging on the back. Now, I've been doing a lot of reading and realize these boats were meant for 300 lb motors hanging off the transom and they like perfect balance. But I need to work with what I have. I only have room to raise the motor one more hole. The cav plate is 4.5" above the keel. Speed wise, I am fine with what I'm getting, but ride is where I'm not satisfied. Current prop is a quicksilver thunderbolt 15.3x19P. WOT motor is turning 5400 RPM with a speed of 44 MPH.

Presently, I have a few issues:

1. Hole shot - Bow rise is substantial. Like I lose sight of whats in front of me. It stays that way until the boat finally jumps on plane which seems to me to take too long. I have not timed it.

2. Once on plane, any amount of trim makes the boat porpoise. If I keep the motor tucked, it rides great. Very little or no tab necessary.

Next time I'm able to get the boat out, I plan to check cav plate height while running and time how long it takes to jump up on plane.

I have spoken to Ken at Prop Gods and he has recommended a Powertech SFS4 in 17 pitch. When asked about the mercury rev4 he stated that it was a lot of prop for an F150 and doesn't have as much stern lift.

Any other thoughts or ideas? I was thinking about adding some lead ballast bags to the anchor locker to try and balance the boat further. Thoughts?

Thanks for your help.

PS - I know there is a performance forum but figured I would get more traffic in the general forum.

Walter Sobchak · #2 08-19-2020, 04:36 PM

I forgot to add, the previous owner put a 30" setback bracket on it.

CaptLloyd · #3 08-19-2020, 09:21 PM

Do you have a Dolfin? Trim tabs? Motor height is very important.

Do your best not to add ballast. Shift weight (Batteries, coolers).

The Dude abides

Lloyd

Fr. Frank · #4 08-19-2020, 11:20 PM

https://www.hydro-shield.com/

This will be a great help.

Properly set up it provides stern-lift at all speeds without forcing your bow down. It's a hydrofoil that stays in the water. You can adjust trim without instantly looking like Flipper begging for a snack!

I ran one on my outboard 20' Seafari, both with the XR4 motor and later with the 90 Optimax. I just purchased one for my 18" Superfisherman with a 90 Etec.