Cutlass bearing power consumption

We recently pulled the long tail drive from my river boat for inspection/refit. Originally the boom had five antifriction flange bearings along the shaft and one cutlass bearing at the prop. I installed two more cutlass bearings in place of the flange bearings on the wetted section of the boom/shaft. Re-installed and tested, I notice a difference in output power. Just wondering if the cutlass bearings consume energy. Ideas?
Ryland

 

This is the longtail boom

 

Re the difference in output power, were you able to measure this difference, or were you simply noticing that the boat was running more slowly?
How much 'difference' is this?
How many hours have been clocked up since you installed the new cutless bearings?
Are there any signs of wear on them yet, possibly indicating slight mis-alignment?
Do you have any vibration on the shaft while underway?

 

The rubber may be heating up and swelling around the shaft where it does not get constant water cooling.
There are “hard” types of cutless bearings that might be less susceptible.

 

Ryland,
Did you look at the bearing manufacturers spec sheet online?
Or, there may be independent reviews (even better).
What's the brand name and model on the bearings you installed?

 

Cutless bearings are designed to be run wet for cooling and lubrication. As kapnD suggested, you may be destroying the bearings as well as the shaft due to overheating. As far as shafting goes, a cutless bearing should only be used as the last one because it is designed to wear due to the overhanging weight of the prop. Intermediate bearings should not be as long and should spin freely. They are to prevent shaft whirl only.

 

I notice a 50 RPM top speed.
About 15 hours have been run on the new bearings.
I used a tensioned .010" piano wire in mandrels at both ends with dial indicator measurement to align. Most likely not misaligned.
There is vibration above 1800 engine RPM during forward propulsion. No vibration in reverse.
Anti-friction bearings are used in the section of boom that is not submerged.
Fuel consumption shows .3 GPH increase with the new bearings.

Ryland