Max weight of shat/prop on cutlass bearing - SailNet Community

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Old 05-30-2008
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Max weight of shat/prop on cutlass bearing

Am refitting and old steel ketch. Deleted the old grease filled prop shaft system in favor of a cutlass bearing and a prop shaft seal in the seven foot tube. Will pump water into the tube for lubrication of the PSS and Cutlass bearing.

It has about a 12 foot by 2 1/2 inch prop shaft. Weight of the shaft is about 140 pounds and the prop is about 60 pounds. The support of the overall shaft and prop weight comes from the transmission flange connection, a bearing 2 feet aft of that connection and the cutlass bearing at the stern. In short. the majority of the weight of the shaft and prop are likely carried by the cutlass bearing.

The question is-- how much shaft/prop weight can a cutlass bearing support without excessive wear or deforming? The cutlass bearing is about 3 1/8 by 2 1/2 by 10 inches. This info may be on a website somewhere but I have not found it.

Thanks,

Keith
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Old 05-30-2008
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That should not be simple. The weight you mention has influence on statical support only, what means almost nothing to the propeler system. Major stress are posed by dinamic forces. So, imagine the forces acting on your cutlass when spinning, while boat pitching, a stern waves, missalignement of the flange, non homogenous shaft and prop creating centrifugal forces, bad balancing, etc ... These are in fact the real stress and wear over your cutlass bearing. Now, how much yours can stand, will depend on material type, age, thickness, etc... Not a simple answer, and probably manufacturer could give you the rule of thumb plus safety factor ....
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