Inner boom blocks

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Cleanhull
Posts: 7
Joined: Tue May 11, 2021 8:17 am

Inner boom blocks

Post by Cleanhull »

I am a new owner of a F35 and am preparing to rplace all running rigging.

The PO's friend has advised me and wrote to me "remember the pully blocks inside the booms dont lose it on the inside when pulling through the lines"

What is he refering to, any explanation very welcome.
Thank you

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RadioZephyr
Posts: 259
Joined: Mon Jun 27, 2016 10:04 am
Location: Boston, MA

Re: Inner boom blocks

Post by RadioZephyr »

If you have Isomat booms, he's probably referring to the single line reefing setup. This picture is from the F45 manual, but it's the same system.
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Josh
Sunset Spy
F38, Hull #152
Boston, MA

Cleanhull
Posts: 7
Joined: Tue May 11, 2021 8:17 am

Re: Inner boom blocks

Post by Cleanhull »

Many thanks I feel sure that is the information I require.
Best wishes
Michael

iansan5653
Posts: 101
Joined: Sun May 09, 2021 4:39 pm

Re: Inner boom blocks

Post by iansan5653 »

He may also be referring to the outhaul - I'm not sure if it's different on the larger boats but on my Freedom 21 the outhaul has two blocks inside the boom (not to scale):
Freedom 21 Outhaul.jpg
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Ian Sanders
1983 Freedom 21 - Shoal Draft
St Petersburg (Tampa Bay), FL

Cleanhull
Posts: 7
Joined: Tue May 11, 2021 8:17 am

Re: Inner boom blocks

Post by Cleanhull »

Thank you Ian, very helpfull.

Mark K.
Posts: 60
Joined: Sun Jul 31, 2016 4:32 pm

Re: Inner boom blocks

Post by Mark K. »

There is a thread titled Reefing Blocks in the Boom. There is a lot of good information there.
The lines and blocks inside the boom are easily accessed through the large hole in the aft end of the boom and the lines can be untangled, inspected replaced etc.
Here is what I wrote. I found that there was too much friction with so many lines moving around inside the boom for the reefing system to work as intended. After several years this solution is still working for me:

1994 F35 Reefing lines. On this boat each of the single line reefing consists of two lines - one for the out haul and one for the clew. Inside the boom they reverse direction with the use of a butterfly block. So I went ahead and replaced the 7/16" stay-set but only the outhaul line with 1/4" Dyneema (aka Amsteel) for my reefing lines. The Dyneema is a smaller diameter and slippery so it glides though the butterfly block and up through the outhaul grommet in the sail rather easily. For the clew half of the reefing line I removed and washed the existing 7/16" stay-set line and treated it with fabric softener and reinstalled it. All the lines run according to the manufacturers diagrams and specifications with this exception. I can now raise/reef the main sail as it was intended without having to tug on the reef outhaul lines to get them moving through the system. I am pleased with the result. I was worried that if I changed everything over to Dyneema (which is essentially zero stretch) it might rip out or damage hardware when the boom moved around so I kept the stay-set for the clew half of the reefing rather than converting it all to Dyneema. This way there is still some stretch in the lines to accommodate the movement of the boom. I have sailed with this system several times now and the system now works as it was intended. Take the time to make sure none of the lines are twisted so everything runs smoothly.

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