The old single-hose cylinders were for tilt only (no trim) and were pressurized to lift the drive, gravity was used to lower the drive. There was a latching pawl and trim pin to lock the drive in the down position. My '67 V174 was originally like that and I hated it, couldn't adjust the trim on the fly and it often came unlocked when driving in reverse, the drive would swing up to the water surface. The cylinders with two hoses each were used from 1967 for trim but was an option, the boat had to be ordered with it. By 1973 two-hose trim cylinders were standard equipment but required a reverse lock-out valve on the hydraulic hoses which was controlled by the shift mechanism to prevent the drive from swinging up. The trim system was greatly improved when the Alpha gear came out in 1983, no reverse lock was required, the trim stayed where it was set and was much more reliable.
