kentuckydiesel
Seaman Apprentice
- Joined
- Jul 11, 2012
- Messages
- 48
This past weekend, I bought a 23' aluminum walk-through type boat which was built using a 1961 Lone Star "Cruise Liner" hull. I had been looking for one of these for about 3 years. Just love the hull design. Warped Vee style...very sharp at the bow, almost flat at the stern. (BTW, I bet you can guess the favorite movie of the guy who built the boat
)


I estimate the boat to weigh around 1500 lbs , including the twin 20" shaft 70hp Johnson outboards. It's a fairly dry running type hull and it gets up on plane very quickly.
Yesterday afternoon, the wife and I took it out on the Ohio river. The first time I went to plane out, I noticed the props were ventilating very badly. Unfortunately, the outboards are down as far as they can go on the transom. The only option I had left was to move the tilt pins 1 hole down (to the bottom hole), just to get the props in the water a little bit more. After that, the ventilation issue got better...plus we put two more people on the boat. It would only start to pull air if I pushed the engines past 4500-5000rpm/got above 20-22mph or so. (but I think I'm looking at around 40-45% prop slip at those rpms)
Two things I'm thinking about doing.
1) The engines are set pretty close to center, and in that area of the transom, it is around 21 1/2" to the bottom of the hull. If I move each engine out to either side of the transom, it should put them in an area where the transom is 20 1/2".
2)The current props are 13"dia x 19" pitch. No cupping...slightly bent in a few places. I'm thinking, since the twin 70s on this boat are pushing the 13x19 props to slip so much, that I should bump up to 21" pitch.
Would you guys think I could do well with cupped 21" pitch props? I'm actually hoping that they would work out, as my 1974 Johnson outboard manual says the 13x19s will give a maximum top speed of 28mph...which just isn't much (and according to a prop slip calculator, it is 32% slip???).
Also, should 20 1/2" of transom be alright for the 20" shaft engines...or am I going to have to modify the transom?
Thanks,
Phillip


I estimate the boat to weigh around 1500 lbs , including the twin 20" shaft 70hp Johnson outboards. It's a fairly dry running type hull and it gets up on plane very quickly.
Yesterday afternoon, the wife and I took it out on the Ohio river. The first time I went to plane out, I noticed the props were ventilating very badly. Unfortunately, the outboards are down as far as they can go on the transom. The only option I had left was to move the tilt pins 1 hole down (to the bottom hole), just to get the props in the water a little bit more. After that, the ventilation issue got better...plus we put two more people on the boat. It would only start to pull air if I pushed the engines past 4500-5000rpm/got above 20-22mph or so. (but I think I'm looking at around 40-45% prop slip at those rpms)
Two things I'm thinking about doing.
1) The engines are set pretty close to center, and in that area of the transom, it is around 21 1/2" to the bottom of the hull. If I move each engine out to either side of the transom, it should put them in an area where the transom is 20 1/2".
2)The current props are 13"dia x 19" pitch. No cupping...slightly bent in a few places. I'm thinking, since the twin 70s on this boat are pushing the 13x19 props to slip so much, that I should bump up to 21" pitch.
Would you guys think I could do well with cupped 21" pitch props? I'm actually hoping that they would work out, as my 1974 Johnson outboard manual says the 13x19s will give a maximum top speed of 28mph...which just isn't much (and according to a prop slip calculator, it is 32% slip???).
Also, should 20 1/2" of transom be alright for the 20" shaft engines...or am I going to have to modify the transom?
Thanks,
Phillip