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| Hobie 16 Mainsheet & Jib working weights http://www.hobie.com/au/en/forums/viewtopic.php?f=14&t=65555 |
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| Author: | Moroni 10:4 [ Wed Sep 18, 2019 5:29 pm ] |
| Post subject: | Hobie 16 Mainsheet & Jib working weights |
I am trying to discover the working weight of the mainsheet of a Hobie 16. How many pounds of force is on the shackle that attaches the mainsheet to the boom at speed? "At speed" is defined as: hull out, block block, shorts brown. Also the jib. Thank you. |
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| Author: | mmiller [ Thu Sep 19, 2019 9:08 am ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
Not something I have ever heard. |
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| Author: | jclarkdawe [ Thu Sep 19, 2019 10:33 am ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
Take a look at https://www.riggingdoctor.com/life-aboa ... ting-loads. Harken provides a more exacting formula, although more complicated. Using that formula, we're looking at about 151.8 pounds of pressure at 20 mph wind speed on the main sail. At 30 mph wind speed, that pressure increases to 341 pounds. Those numbers would translate to about 57 pounds of pressure on the main sheet in your hand, a number that seems consistent with the pressure I'm pulling in those conditions by feel. (Think about picking up a 5 gallon pail of liquid. Weight is approximately 45 pounds.) At 10 mph wind speed, the pressure is down to less than 40 pounds. Actual numbers would need a strain gauge just before the boom. I doubt it would be worth the cost and difficulty to actually measure this. If you're just curious, this should be enough to get you going. If you're breaking something, you need to say what part. Jim Clark-Dawe |
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| Author: | Moroni 10:4 [ Thu Sep 19, 2019 3:28 pm ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
Thank you Jim. This is excellent! Thank you for the web site, the information, and the quick response. I am looking at purchasing spare mainsheet shackles and possibly some snap shackles. With this information it appears that the smallest of the snap shackles at the web site below (990 pounds) will be sufficient. https://www.westmarine.com/buy/lewmar-- ... de=3734415 Forgive me being vague in my purpose. I phrased the question as I did, because, while searching this forum for an answer, I saw a very similar question asked, but with great detail. Although there were many answers, the specific question was not answered. Thanks again. |
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| Author: | AntonLargiader [ Thu Sep 19, 2019 4:08 pm ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
57 pounds sounds amazingly correct to me, with a 6:1. Higher with a 5:1. |
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| Author: | jclarkdawe [ Fri Sep 20, 2019 6:29 pm ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
Moroni 10:4 --Personally I've never worried about the formulas for smaller sailboats. I'd contact my local Hobie dealer, or alternatively an online site that specializes in the type of boat I'm interested in, and ask them what to use. Beyond my local Hobie dealer, I've found Murray's Catamarans very helpful for figuring out what I need. I do use West, but have found they tend to be better for cruising boats and fiberglass work. Hobie's part list makes sure you keep your Hobie within class rules. Hobie knows from years of experience what works best with its boats. Jim Clark-Dawe |
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| Author: | srm [ Sat Sep 21, 2019 4:59 am ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
This is just a simple application of Newton’s Third Law, Action - Reaction. The load on the shackle is equal to the load exerted on the mainsheet blocks. So the only question is how hard do you pull on the mainsheet when fully sheeted, cranking upwind in a blow? My guess would be an average sized person, trapped out on the side rail, using their upper body and legs to pull in the mainsheet would put somewhere around 100lbs max. Multiply that by the 6:1 mainsheet purchase and you’re looking at 600 lbs on the shackle (not accounting for frictional losses in the blocks). That may be something of an oversimplification, and it’s possible that the rig will see higher peak loads during gusts or when the boat smacks into waves, but I think this is enough to get you in the ballpark. A shackle with a 1,000 lb working load should be sufficient. A shackle with a 2,000 lb working load would have no issues. sm |
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| Author: | hrtsailor [ Sat Sep 21, 2019 5:57 pm ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
I think there is some confusion here about the forces on the sail and how they are transferred to the boat. Because the sail is triangular, the center of effort would be about one third back from the mast. That is the point where calculations can be made concerning the force. Wind velocity pressure, according to previous posts, might equal 350 lbs. Assuming the blocks attach to the boom at least two thirds back from the mast, rough calculation would indicate a force of 175 lbs. to resist the wind force. With a 6 to 1 block, the force would be about 30 lbs. on your hand. The other 175 lbs. is put on the mast and base plate. I can remember sailing in strong winds where I exerted considerable force on the main sheet but never 100 lbs. I used to sail an 18' Cape Cod Catboat in addition to sailing my Hobie. The single sail was much larger than the Hobie and it had about a 5 to 1 block set up. The pull on the main sheet was strong at times but not unmanageable. |
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| Author: | AntonLargiader [ Sun Sep 22, 2019 10:30 am ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
The fact that the sheet system pulls down changes that a lot. It at least doubles the tension. 60 pounds, maybe 70 on the sheet sounds about right, so rounding up a bit maybe 400 or 450 total on the shackle won't be too far off. |
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| Author: | Moroni 10:4 [ Wed Sep 25, 2019 5:10 pm ] |
| Post subject: | Re: Hobie 16 Mainsheet & Jib working weights |
Thank you for all you help. I've enjoyed and appreciated reading all the comments. |
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