okay main sheet to boom relocation - SailNet Community

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  #1  
Old 02-21-2009
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okay main sheet to boom relocation

okay i want to add a dodger to my boat this year, and the main sheet is in the way. right now it bridges the companion way, but is not a travler, and it attaches with 3 bails to the boom. each bail is about 6 inches apart, and what i want to do is to move the rear 2 forward of the front one so it would now be the rear. this will leave me with 2 3/8 inch holes on each side of the boom but i dont think that will weaken the boom too much. the boom is not reinforced where the bails attach. basicly this will move the attachment about 1 foot forward on a 10 foot boom.

second part, the sheet runs thru blocks on the hull, behind a curved ridge meant to shed water off to the sides. i want to relocate the blocks up front of the ridge and attach the dodger bottom to the ridge. this also gets the main sheet forward of the companion way so the dodger would fit. this is only about a 10 inch movement forward, on the port side there is a block between the liner and hull for a grab rail so mounting that side is fine, and i would need to cut an access on the starboard side for a backing plate, not a big deal.

basicly any thoughts on relocating the attachments on the boom forward, i have never had a problem pulling in the main, so i dont think it will be a problem if i move it. in fact it will line up better ie less forward angle when on a reach to the blocks on the deck if i move em forward.

i could not find any decent pics showing the area but i plan on taking pics

if you want to search its a 83 27' hunter
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Old 02-21-2009
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okay here is the best pic i have you can see where the blocks attach to the deck. and you can also sort of see the boom attachment.

sorry i left the pic big for detail

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Old 02-21-2009
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If I understand correctly the finished job would be very much the way we had our O'Day 322. See if you can find a good picture of that model to work with. I liked the arrangement on that boat even though the mainsheet position was way forward.

ALSO...The boom on the 322 was too low. It swept across the cockpit at about temple height, so I raised it to accommodate the bimini.
It was simpler than it sounds. I raised the boom, and then sent the mainsail off to have the headboard cut off and repositioned a foot lower.

We ended up with stand up room under the bimini. Neat!
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Old 02-21-2009
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my boat has about 6 foot under the boom now, and bimini is also 6 under it. the boom ends right at the bimini, the dodger would be closer to 5'8" which is fine because it wont come very far over the cockpit mostly just over the companion way
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Old 02-22-2009
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Just be aware that by shifting the main sheet forward, you're putting greater stress on the boom, and it is will be more likely to snap or bend under the forces because of that.

Moving the blocks 1' is 10% of the boom's length. Going from 7' to 6' is going to increase forces by about 17%, while going from 6' to 5' is going to increase the forces on the boom by about 20%, and going from 5' to 4' is going to increase the forces by 25%.

BTW, it will also increase the force you need to control the boom accordingly.
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Old 02-22-2009
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i under stand what your saying SD, i do. here is just a simple question, the mast and boom are made by kenyon, and some boats have end of boom sheeting so they thought they could move it some about 4 feet but thats why it has 3 blocks on the boom. does having a roop foot on the sail (ie not loose foot) help spread the load on the boom out? now could just moving the blocks on the deck forward which would change the pull angle from roughly 90 when the boom is centered to say about 80 make a huge difference?

TIA
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Old 02-22-2009
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Moving the mainsheet further aft along the boom reduces the loads on the mainsheet, by giving the mainsheet a longer lever arm to use. Moving it forward increases the loads on the main sheet, by effectively reducing the lever arm the mainsheet has and also creates a bending point for the forces applied against the boom. Given two identical sailplans, the boat with the mid-boom sheeting generally requires a heavier boom than one with end-boom sheeting.

As for moving the block on the deck forward, yes, that will make a difference, since you'll have a forward component to the mainsheet when sailing close hauled that wasn't present previously.
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Old 02-22-2009
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Quote:
Originally Posted by scottyt View Post
i under stand what your saying SD, i do. here is just a simple question, the mast and boom are made by kenyon, and some boats have end of boom sheeting so they thought they could move it some about 4 feet but thats why it has 3 blocks on the boom. does having a roop foot on the sail (ie not loose foot) help spread the load on the boom out? now could just moving the blocks on the deck forward which would change the pull angle from roughly 90 when the boom is centered to say about 80 make a huge difference?

TIA
Would loose-foot or not make any difference? Very little. If the sailcloth were very tight, I can see your thought and your understanding, but the sail cloth at mid-boom is relaxed enough to allow draft, and thus not carrying much load.

There will also be some effect on the goose neck, but I do not know your boat.

Back to the drawing board. It is hard to know how much safety factor is in the design, but booms have been bent... and it will bend when it is blowing hard and you need it. A tough puzzle. I would be considering my options for a stronger boom.
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Old 02-23-2009
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I would say that your boom was never designed to have the sheeting moved 10% forward on the boom. The fact that the manufacturer used three bails instead of one suggests that they were close to the maximum safe loading for the boom and needed to spread out the load.

Jeff
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Old 02-25-2009
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I once owned a 1976 Hunter 27, and moved from end of boom sheeting to center. From your picture it appears that all three bails are close together, while the sial load is spread across the entire boom. I believe only the lower blocks attached to the deck are in the way of your dogger. So I'd actually look at moving one boom bail forward, and one back further over the dodger. This would spread the load over a longer section of the boom, and even though you moved the base forward, it should result in lower loads on the boom. If you took some better pictures it would be easier to say for sure.

Gary H. Lucas
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