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Bobthebuilder heading back to the Islands, looking for a new adventure

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Old 05-16-2010, 02:24 PM
  #131
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Sailflow is showing projected winds for Friday ranging from 12 to 18 knots out of the NE. We should be able to make T & C but winds pick up after that and not sure if we can go further or not. Will be watching this and other sites as the week progresses. I should be doing this in the summer time but it's kind of between boating season in FL and CAN for me and my insurer does not want me in the Islands during hurricane season. Not sure why it matters when I have waived my coverage for any named windstorms. LOL
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Old 05-16-2010, 06:10 PM
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The center prop which is deeper in the water has never failed. All 3 prop failures have been either port or starboard side which are closer to the surface. I think there is a connection there.
Bob, the propeller failures you are experiencing are the direct result of what's known as high-cycle fatigue. This happens because on surfacing piercing props, the blades flex in one direction as they enter the water and become loaded, and then flex back to the unloaded position as they break the water's surface and become unloaded. This load /unload and associated flexing happens once per revolution of the propshaft. With all the hours you put on your boat compared to most others, you are going to experience more failures. Also, as you've experienced, the center prop lasts longer because it's deeper in the water so the blades don't come out of the water as much at the top of the rotation and thus don't unload as much resulting in less "unflexing" and thus less fatigue.

I don't know if you can trim your drives down a little more or if that would upset your boat's attitude too much, but it's something to consider.

Also, it's always wise to inspect your props for cracks anytime the boat is out of the water. Pay particular attention to the trailing edge of the blades near the base, as this is where the cracks are likely to start. Use a good magnifying glass and you may be able to spot the start of a crack before it has propagated far enough to sling a blade.

Good luck with the rest of your trip. I'm looking forward to you and your crew's updates!
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Old 05-16-2010, 07:13 PM
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Bob, the propeller failures you are experiencing are the direct result of what's known as high-cycle fatigue. This happens because on surfacing piercing props, the blades flex in one direction as they enter the water and become loaded, and then flex back to the unloaded position as they break the water's surface and become unloaded. This load /unload and associated flexing happens once per revolution of the propshaft. With all the hours you put on your boat compared to most others, you are going to experience more failures. Also, as you've experienced, the center prop lasts longer because it's deeper in the water so the blades don't come out of the water as much at the top of the rotation and thus don't unload as much resulting in less "unflexing" and thus less fatigue.

I don't know if you can trim your drives down a little more or if that would upset your boat's attitude too much, but it's something to consider.

Also, it's always wise to inspect your props for cracks anytime the boat is out of the water. Pay particular attention to the trailing edge of the blades near the base, as this is where the cracks are likely to start. Use a good magnifying glass and you may be able to spot the start of a crack before it has propagated far enough to sling a blade.

Good luck with the rest of your trip. I'm looking forward to you and your crew's updates!
Thanks msm. That makes perfect sense. I can tuck the drives in some. We will use a bit more fuel with more boat in the water. I will try and find a happy spot. In hindsight I would have been wise to install both my spares that had zero hours on them for a trip like this. The next time I am out of the water I will change out the starboard side prop. Port side was changed in Nassau. That would be a good time to have a close look with a magnifying glass as you have suggested.
Again, thank you,
Bob
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Old 05-17-2010, 05:34 PM
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Bob presenting 1bagger with my retired original SPOT tracker. Paul guessed closest to our arrival time in Nassau on May 8th. He was only off by 20 minutes and probably would have been spot on had we not done a detour to check out Atlantis from oceanside. Congratulations and enjoy, Paul. He will use it on his Harley as well as his Top Gun.
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Old 05-17-2010, 10:53 PM
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Love these threads, Bob. Thanks!
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Old 05-17-2010, 11:33 PM
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Love these threads, Bob. Thanks!
Thanks. Looking forward to my return to Bahamas on Thursday and getting back on the water Friday morning. All being well should make T & C late afternoon Friday, spend a couple of days there and head for DR likely on Monday.
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Old 05-18-2010, 10:08 AM
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Thanks msm. That makes perfect sense. I can tuck the drives in some. We will use a bit more fuel with more boat in the water. I will try and find a happy spot. In hindsight I would have been wise to install both my spares that had zero hours on them for a trip like this. The next time I am out of the water I will change out the starboard side prop. Port side was changed in Nassau. That would be a good time to have a close look with a magnifying glass as you have suggested.
Again, thank you,
Bob
Here is an easy to use crack detection kit. Similar to those used on cylinder heads, blocks etc.

http://www.drillspot.com/products/28..._penetrant_kit

step 1 clean any grease etc.

step 2 apply dye pentrant and let set.

step 3 remove excess dye

step 4 apply developer and any cracks will show up in the developer as the dye is drawn out of the crack.
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Old 05-18-2010, 10:33 AM
  #138
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Here is an easy to use crack detection kit. Similar to those used on cylinder heads, blocks etc.

http://www.drillspot.com/products/28..._penetrant_kit

step 1 clean any grease etc.

step 2 apply dye pentrant and let set.

step 3 remove excess dye

step 4 apply developer and any cracks will show up in the developer as the dye is drawn out of the crack.
Thanks, Wobble. When I get back I will have all of my props checked. I really appreciate all of the help I have received on OSO over the years. Many knowledgeable people that are willing to share. That's what makes for a great forum.
Bob
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Old 05-19-2010, 07:01 AM
  #139
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Have a safe trip Bob, looking forward
seeing more pictures.
Rick
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Old 05-21-2010, 08:48 AM
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Hey bob, any more progress??
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