I just purchased a 1969 Javelin 357A bass boat with a 1996 50 hp Johnson on it. When i put it in the water i could not get it to plain. Took it back to dealer and they are telling me i need dolphin fins on motor? the recommended prop is a 11 3/4" 17pt. it has a 12 3/4" 15pt on it now, some one has changed it before i bought boat. the dealer got it on plain by having someone riding the bow and said they tack up to 6000 rpm’s. factory recommends 4500 to 5500rpm. I am heavy and the boat has two trolling batteries and a cranking bat., 16 gal. tank and 3gal oil tank. Mech. is telling me that a prop change won't help and that i need the rpm to plain?? I though a higher pitch, say 19pt and maybe a 4 blade would do the trick. Am i thinking right, or is the mech right. i can not picture a bass boat with the original motor not being able to plain if the right prop is on it with out having to use dolphin fins.
Increasing pitch will slow the hole shot even more.First thing I think of on an older boat is
water absorbed by the hull, or foam under the floor.If the boat was stored out side carelessly
over long periods this is possible.Do you know the manufacturers dry weight of the boat?
What size and material?
One way to check is to weigh the boat and subtract the motor and gear etc.
If the batteries are in the stern move them forward even temporarily to see if it helps.
Even just to the midsection would help.
The foils are kind of a bandaid over a poor setup and should be considered last resort.
The motor is probably a little undersized. Is the antivent plate(just above the prop) about even with the bottom of the boat.A 15" prop should be about normal for your setup .
Be sure you trim down for hole shot.
A 4 blade prop in the same pitch should help the hole shot cost more than a foil but do a better job.And should lower the rpm slightly.
Move weight forward first. That will make a substantial difference. The foils are a bandaid but you have an old inexpensive boat and they are a very effective inexpensive fix. There are several types and can cost about $50. Other than that, listen to steelespike.