JM, since you have multiple problems I will try to explain this in steps so it's clear, and offer some solutions:
1. Vibration: this has two sources wiplash of the long shaft and the U-joint not beeing CV.
2. Axial load: having the torque bearing after (or before if you count from the motor) articulation. U-joints can carry some axial load, but they are not happy doing it.
1. The elegant one is to replace the U-joint with a CV-joint designed to transmit all axial loads. Such things exist but are speciality items.
2. Move the torque bearing before the articulation and use a true CV-joint that does not carry axial loads. This will require articulation of the thrust block.
3. Remove whiplash by adequatly supporting the propshaft. This you already figured out but there is room for improvement.
I will deal with wiplash first. In order to support the shaft adequatly put a bearing every foot. If you want waterlubed bearings (cutless) you have to insure they get enough water
, meaning a pressure system is needed injecting water
at every bearing. A superior system is to use sealed roller bearings, in wich case you need to fit a waterseal at the prop end. Every single outboard
uses one so it's not as if it can't be done. Since most of the propshaft is not submerged you can also use a cutless at the prop end and sealed roller bearings for the rest. To assure a rigid shaft I propose: take two 1-2" fiberglass
tubes and glue them togheter like the barrels of a shotgun. One will serve as water pickup, the other as exhaust
. On this double tube you can now glue roller bearing carriers to support the driveshaft. Then the whole thing gets a fiberglass
fairing glued onto it that aditionally stiffens the assembly and cuts the drag. Think of it as building a wingmast, rudder
Now for the rest. The brutal option is to use the biggest U-joint you can find (something from a big truck maybe) to transmit the axial loads to the thrust block. It will still vibrate and be unpleasant but will last another circumnavigation
. Not something I endorse but possible. You don't need another U-joint on the motor
side, you already have a flexible coupling there.
You have to decide by yourself if you have the money
for the elegant option.
Articulating the thrust block is not so complicated as it seems and can be acomplished cheaply. If the shaft is to only rotate up and down you simply mount the thrust block on a round bar that pivots on the frame in plain bearings. If you want it to also pivot sideways you need those plain bearings mounted on pivoting arms, basicly creating a gimball. The propshaft - motor
connection is via a true CV joint, if necessary with additional length compensation. You can have the whole thing custom made in stainless steel
or you can go cheap
and use automotive components. Front wheel
drive cars have all components you need on the front wheel
. Power comes from the motor via a driveshaft with CV-joints at each end. The wheelhub is a bidirectional thrust block. The hubcarrier is made to rotate in two directions. A double whisbone suspension with kingpins would be the best for adapting to your boat
since all you need to do is mount it on it's side.