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Old 10-18-2020, 02:01 PM   #21
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I am not sure if an inch shorter matters or not, but why not put in the correct ones to start with? You donít have as much bearing surface so I would expect that it will wear out sooner.
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Old 10-18-2020, 02:23 PM   #22
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I am not sure if an inch shorter matters or not, but why not put in the correct ones to start with? You donít have as much bearing surface so I would expect that it will wear out sooner.
Thanks but the yard has already installed them. They are an inch or so shorter than the struts that house them. Before I go to war with the yard, Iím trying to find out if this is actually a problem.
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Old 10-18-2020, 02:25 PM   #23
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I am not an expert like I said but I would still want to know why not the correct bearing. Maybe ask Steve D.
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Old 10-18-2020, 02:45 PM   #24
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Bearing length:shaft diameter is usually around 4:1 by the prop and shorter further away.

The advantage of a shorter bearing would be less friction. Fairly negligible factor for a recreational boat.

The disadvantage would be less load capability. Again, probably negligible. But may lead to shorter life.

Think about it. The same boat can have a range of horsepower and different prop pitch and diameters. No one thinks about the cutlass bearing load.

Really the modulus of elasticity of the shaft and distance between bearing centres would be in there too. Other variables would be the elastomeric material, groove size and diametrical clearance relative to the old ones.

I would imagine there is a fair amount of thumb rule and over sizing for our applications, and not much actual engineering.

I would venture the design is mostly empirical and based on experience.

I know this isn't much of an answer, but I really don't have a lot of practical experience. None of the rotating engineers are here at work this shift.

If your boatyard mechanic doesn't have issue, and seems like a reliable source of opinion, then there probably isn't much risk.

I would venture it would be like fitting tires to your car. Some are better, some are worse, but they will all more or less function. And the measure of success or failure is also subjective, depending on what one wants.
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Old 10-18-2020, 02:51 PM   #25
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As I now see that they have already been changed, ask for the old ones back.

If things go wrong, it would be easier to point out the difference with them in hand. It would also be easier to source new ones before you pull the boat in a few years.
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Old 10-18-2020, 02:57 PM   #26
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As I now see that they have already been changed, ask for the old ones back.

If things go wrong, it would be easier to point out the difference with them in hand. It would also be easier to source new ones before you pull the boat in a few years.
Good thoughts, all, Spy. Thank you. Pretty sure the old ones were tossed, but Iíll ask.
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Old 10-18-2020, 07:35 PM   #27
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So who manufacturers cutlass bearings. Can they give you some insight? But agree comparing to old ones is an excellent suggestion.

Also sounds like periodic inspection is right on.
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Old 10-18-2020, 07:56 PM   #28
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Can anyone offer a knowledgeable opinion on whether there is a problem having cutless bearings that are an inch or so shorter than the struts that house them? Please see post 12.
I recently redid a cutlass bearing. My strut is about a foot long. (Behind keel)

The cutlass bearing was 5 inches. Works fine.
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Old 10-18-2020, 08:29 PM   #29
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I recently redid a cutlass bearing. My strut is about a foot long. (Behind keel)

The cutlass bearing was 5 inches. Works fine.
Thanks, Alisske. Others Iíve heard from are pretty much saying the same thing. Iím going to stop obsessing now.
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Old 10-18-2020, 08:33 PM   #30
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I recently redid a cutlass bearing. My strut is about a foot long. (Behind keel)

The cutlass bearing was 5 inches. Works fine.
It looks like your prop nuts are reversed. The full height nut goes on second and the half height nut goes on first. As you tighten the second nut it unloads the first nut somewhat. Unless I am not seeing the photo correctly, it is hard to see exactly.
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Old 10-18-2020, 09:16 PM   #31
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It looks like your prop nuts are reversed. The full height nut goes on second and the half height nut goes on first. As you tighten the second nut it unloads the first nut somewhat. Unless I am not seeing the photo correctly, it is hard to see exactly.
Thank you. Ill check it out. I just got a new prop shaft and thats the way it came from the prop shop. But thanks for looking out.
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Old 10-18-2020, 09:33 PM   #32
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For prop install, I've seen the recommended method as using the big nut first to make sure the prop is fully seated. Then remove, install and tighten small nut, then big nut and cotter pin.
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Old 10-18-2020, 09:44 PM   #33
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For prop install, I've seen the recommended method as using the big nut first to make sure the prop is fully seated. Then remove, install and tighten small nut, then big nut and cotter pin.
That is the way that I do it. But since his prop is already seated I omitted that step.
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Old 10-19-2020, 01:07 AM   #34
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Can anyone offer a knowledgeable opinion on whether there is a problem having cutless bearings that are an inch or so shorter than the struts that house them? Please see post 12.
I believe I read in an earlier post that your shaft's are 1-3/4" in diameter. What was the length of the new bearing? I just checked the Johnson Duramax Cutless Bearing catalog and the bearings for 1-3/4" shafts are only available in a length of 7". If that's what was installed, I'd think you will be OK since it appears to be the "standard" length for that size bearing.

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Old 10-19-2020, 05:16 AM   #35
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I believe I read in an earlier post that your shaft's are 1-3/4" in diameter. What was the length of the new bearing? I just checked the Johnson Duramax Cutless Bearing catalog and the bearings for 1-3/4" shafts are only available in a length of 7". If that's what was installed, I'd think you will be OK since it appears to be the "standard" length for that size bearing.
Thanks much, Larry. Iíve read that a second cutlass bearing can be cut to fit the remaining space inside a strut if a single bearing is too short. Not sure how many yards actually do that or if itís necessary. Iím going to try to find out what they removed if thatís possible but itís sounding like using a single, standard-sized bearing per strut is acceptable.
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Old 10-19-2020, 05:34 AM   #36
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I would point out that long shafts internally have pillow blocks only a couple inches wide for support and whip....

Sure shafts outside the hull have hydrodynamic forces....but I got to think a cutlass bearing of standard dimensions would be adequate....cutting one down would bother me more or if I knew my strut spacing was at max recommended. But having one an inch shorter than my strut cavity feels OK.

I would document, present to the yard and keep investigating even if the boat went into the water. If I found out somehow this is a bigger issue than thought....the yard would get to do it all over again.
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Old 10-19-2020, 06:29 AM   #37
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Folks that operate in shallow sandy water may find the shaft is worn , as well as the bearing.

There are cutlass bearings made to cure this , a collar is pushed into the bearing housing and a collar with the new bearing material slid on to the shaft.

The bearing could be considered inside out.
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Old 10-19-2020, 09:07 AM   #38
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I heard back from two folks that I respect greatlyóSteve DíAntonioówho is well known hereóand Bill Gladding, one of the best marine surveyors in the business.

Steveís reply:

Common shaft bearings, there are others but Johnson Duramaxís Cutless model is the most well-known, are availed in a wide range of sizes; you can view the list here. https://www.duramaxmarine.com/pdf/CutlessBearingMS.pdf

Iím not sure of your DeFeverís shaft diameter, however, for 1.5Ē for instance, naval brass shell bearings are available in 6Ē length alone (they are available in two different outside diameters). If the strut bore is longer, itís not unusual, and not harmful, to have a cavity on the leading edge. It can be helpful in funneling water into the bearing, however, it can also trap debris, so it should be checked when the bottom is cleaned by a diver and at haul outs.

You can read more about shaft bearings here
. https://stevedmarineconsulting.com/c...g-etiquette-2/

Bill largely concurs with this and verified the standard/normal length of Johnson shaft bearings.

I appreciate all the replies and hope this discussion helps others with similar questions.
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