Orkot Cutless Bearings

We've had them come already installed on some custom cast struts and I can't say I've seen much difference in wear or longevity compared to standard rubber cutlass bearings. I have noticed they seem to be machined at a slightly larger diameter than the shafts, and at least in the 2-1/2" and 3" sizes there is about thirty thousandths of slop around the shafts. To their credit, a conventional rubber lined beearing also has some play but it is usually more the rubber crushing on new ones from the weight of the shaft.
Orkot and Vesconite are the standard on larger yachts and ships so there must be something to them but they are not my preference on smaller craft.

I too was concerned the much harder bearing would not do as well with abrasives like sand in the mix when in operation. That's not to say it isn't possible the softer rubber wouldn't trap the same particles against the shaft and wear grooves either.
My main dislike for the harder bearings is the slop left in the shaft which could induce some vibration, especially if the wheel and shaft was slightly askew already. We have been using the composite version of the "standard" brass bearings for years with no problems so far and they are also slightly cheaper! When we do shaft tubes though, I've been sticking with the metal sleeves.

Composite bearings

Things have moved on quite a long way from the bearings already discussed and there are significant differences in composite or plastic materials and how they perform.

Vesconite and Orkot are both materials that melt and hence soften with heat (either friction or warm water)

In global terms I don't see orkot/vesconite as standard or that common on yachts or ships ,maybe in the States, but one of the latest subs in the states is now using Maritex for shaft and rudder/dive planes.

Clearances for bearings are a combination of moisture and thermal swell, if you look at the data on the bearings already discussed the thermal swell is the biggest factor that has to be allowed for.

If you are looking for better performance and smaller clearances then you may want to look for Maritex. on a 2.5" shaft mrd (min radial displacement) is 0.26mm or 10thou from new. Trials in small commercial vessels (2" shafts) have shown wear rates at 1/3 of that of nitrile rubber (Pilot boat that operates in deep as well as shallow silted estuary)

Maritex is a hard phenolic (most others are polyester) resin based composite, moulded not fibre wound, it hardens with heat rather than softening, it also has a surface chemistry that is designed to resist marine growth and has had succesful trials on some 50-60m high performance naval vessels. It's Lloyds approved and used by a number of high performance military gun boats in the 50 - 150' range.

It also has the benefit of being designed for a clearance fit, no press or squeeze or freeze fits which can help if you need to check bearing carrier alignment. You can do a dry run with shaft chocked sliding bearings into carriers as they should be free to rotate.