Sunday, March 11, 2018

Fixing a Lame Bowsprit

It's not that I work slowly, but often I make changes in small increments, careful to make certain each change and the entire project is optimized. This one took nearly 6 months to completion.

I didn't photograph the original mess of cracked welds and failed screw repairs. I just ground it all away.  The original fitting did not cradle the butt end of the bowsprit and did not extend completely to the end.

The Failure. The original hinge mechanism included an undersized butt cradle that ended up cracked on most F-24s. It was simply under-designed.Often the sprit was also dented. There was no line to hold it up, and sheets often snagged down low, around the jib furler.

The new aluminum cradle is both wider and built from heavier material. The plastic insert is curved to match the pole. These dimensions are approximate--you will need to measure your own.
This should be as strong as the pole. However, I always tension the up-haul snugly to carry the opposing load, should the bobstay be inadvertently over-tensioned.

Larger bolts (#10) were tapped into the side pieces. Additionally, the cradle is wider and reaches to the end of the pole.

Then there was the matter of articulation. The original design incorporated a fix bobstay and could only be folded or extended at dock, or by hooking your legs around the pulpit and reaching for a pelican hook at the waterline. Not fun under way in any weather. Some owners fitted a tackle using blocks, but they're certain to collect junk and accumulate lime. Ball bearing blocks large enough to handle the sustained high load would be awfully bulky. I also wanted more purchase, to reduce the load on the line clutch. Enter low friction rings (LFR). Although higher in friction than ballbearing blocks, this tackle is not adjusted under load.

Fortunately Amsteel is super easy to splice. The yellow is a Dyneema Climbing sling. The safe working load of this tackle is about 3000 pounds, stronger than original.

I used rings from Antal, Ronstan, Harken, Nautos, Wichard, and Scheafer, all part of a Practical Sailor research project. Though I reported my favorites, they all work just fine. An up-haul was also added, not apart of the original design. This relieves the load from the butt cradle and keeps the reacher sheets from going under the pulpit where they can hang-up. It also secures the sprit against the pulpit when not in use (I wrapped a sort section of the pulpit with 3/16-inch line so that it would not bang when stowed). A lucky coincidence of geometry, the travel of the 4:1 down haul and the 2:1 up-haul are the same, making a continuous line a neat solution. Because Amsteel is slick, I covered (bury splices) the center section of the line with polyester cover so the clutches would hold properly.

A surplus Easy-Lock clutch is mounted to an aluminum plate (tapped), which is in turn mounted by bolts through the hull flange, neatly out from under foot. Another LWR keeps the line tail neat.



The final result is easy to use, and lighter and stronger than factory. The side stays are looking a little rusty, so they will be replaced with Amsteel soon as well.

How fast? Over windspeed on a reach. Mid-teens are common, though a little scary if it's gusty.

5 comments:

  1. Drew - I have the same issue with the butt cradles and wonder if you have dimensional drawings for the revised aluminum cradle? I would love to get it made by someone local here. Also - what size are the screws? Also - if it is easier, my email is devinvanzandt at gmail.com

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  2. Your bobstay system is exactly what I've been seeking! What thickness aluminum plate did you use as backing for the clutches? Looks like 1/8 or 3/16?

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  3. I used 3/16-inch aluminum for the top plate. I forget, but there was some problem with the bolt pattern, so I tapped and bolted to that. I them bolted that to a matching plate under the hull flange. Because it is a 4:1 tackle, the load is high but not extreme, and the angle is low. And don't forget to cover the line where it goes through the clutches; Amsteel won't hold.

    It's been about 18 months now, and still going strong. The only change is that I had to re-do one splice as the line stretched in over time; I didn't allow enough length for the splices to compress under load.

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  4. The geometry of the line passing over the roller through the cradle is such that it wants to sneak down the edge of the roller. Did you place a fairlead, turning block, or perhaps one of the low friction rings attached to a stanchion to guide it over the roller on the deck side?

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  5. In my case, the roller is taller than the cradle and very tightly fitted; this has not been a problem. But the roller is not factory.

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