SloopJohnB 329 Posted April 25, 2020 Share Posted April 25, 2020 2 hours ago, Bradz said: Need some light hearted Saturday night reading. Try this! https://issuu.com/nbaddour/docs/alexbergeron_undergradthesis Quote Link to post Share on other sites
Bradz 20 Posted April 25, 2020 Share Posted April 25, 2020 23 minutes ago, SloopJohnB said: Try this! https://issuu.com/nbaddour/docs/alexbergeron_undergradthesis Crikey, 94 pages, that will require more attention with a few less quite rums than currently consumed. Thanks for the link. Quote Link to post Share on other sites
armchairadmiral 411 Posted April 25, 2020 Share Posted April 25, 2020 Thanks for putting that up IT. I've waded through that lot last night and this morning, Pity the diagrams are lost. However knowledgable the written points may be I still can't understand how mast compression is reduced although it seems those with the experience say it is. Thanks again Quote Link to post Share on other sites
jim s 34 Posted April 26, 2020 Share Posted April 26, 2020 So i've done a couple of sketches and they show in a 1:1 setup with 50 kg (technically should be called 500 newtons) of force holding the sail in position there is 50 kg of "pull" in the halyard going from the sail going up to the sheave and of course the same 50kg pulling down inside the mast - so the sheave is compressing the mast by 100 kg. With a 2:1 set up there is only 25kg of load on the halyard so 25 kg where it terminates above the sheave plus the 25kg going from the sail up to the sheave as well as the 25kg coming down inside the mast giving a total of 75kg now... I'm pretty sure i've got this right , if needed i can get some help and post my sketches. It looks to me that armchairs drinking buddies are onto it 2 Quote Link to post Share on other sites
Island Time 1,313 Posted April 26, 2020 Share Posted April 26, 2020 Yep, that's about it... Quote Link to post Share on other sites
armchairadmiral 411 Posted April 26, 2020 Share Posted April 26, 2020 Thx Jim....I think I've just about got it now. It's the down ward force on the main luff that is the confusing point. But the anchor point for the halyard is at the mast crane. Then to a block on the main headboard so the load is 100 kg at masthead. So logically ( to my mind) the load at the mast step has to be 100 kg ? even if the load on the halyard is as you say? Thanks again for explanation Quote Link to post Share on other sites
Island Time 1,313 Posted April 26, 2020 Share Posted April 26, 2020 No, the compressive load on the rig is taken by the mast structure, between the mast top sheave, the tack fitting and the mast crane termination. If your halyard is fastened on the mast somewhere, then NO compressive load from the halyard is transmitted to the step. Think about this, if the rig is out of the boat, and you fasten the halyard to a cleat on the mast, can you still tension the sail?? Of course you can, but there is no step! Quote Link to post Share on other sites
armchairadmiral 411 Posted April 26, 2020 Share Posted April 26, 2020 Thanks....I'm thinking..... Quote Link to post Share on other sites
Adrianp 137 Posted April 26, 2020 Share Posted April 26, 2020 On freedom we had a low friction rig with a wide stainless steel shackle over it. It meant the pin of the shackle was very close to the top of the main and halyard. Simple and cheap! Quote Link to post Share on other sites
ScottiE 174 Posted April 26, 2020 Share Posted April 26, 2020 On 25/04/2020 at 11:51 AM, Clipper said: Dont think thats right? Bit worried to have a go at this, but in the 1:1 case, the sail applies a 50kg load down, the halyard the same vaule to hold it up there, therefore masthead has 100kg of compression. In the 2:1 case, the load required in the halyard becomes 25kg each side of the main, and another 25kg tension, so maybe 75kg compression? Im ssure ScottiE or Ed will correct me if Im wrong. Missed this sorry Clipper - yes you are correct - back yourself mate. As well as lowering mast compression, it also halves the load needed for the halyad size - weight aloft. Not so critical for halyard itself but good for those guuchi masthead halyard locks - ie. the load to release it is half! Quote Link to post Share on other sites
MartinRF 76 Posted April 26, 2020 Share Posted April 26, 2020 2 hours ago, Adrianp said: On freedom we had a low friction rig with a wide stainless steel shackle over it. It meant the pin of the shackle was very close to the top of the main and halyard. Simple and cheap! A home made version of this? https://marine.wichard.com/rubrique-Captive_pin-0201110100000000-ME.html Any photo? /Martin Quote Link to post Share on other sites
armchairadmiral 411 Posted April 26, 2020 Share Posted April 26, 2020 So I'm still thinking........ so many scenarios...Main halyard comes down to block on mast collar then back to clutch aft. Say 50 kg. So upwards lift on mast collar 50 kg ? Surely that transfers back up mast thence to mast step ? Or am I overthinking / over complicating. BTW I wasn't good at Physics ! Quote Link to post Share on other sites
armchairadmiral 411 Posted April 26, 2020 Share Posted April 26, 2020 Brilliant.....thanks KM. I'll sleep tonight unless I overdose on Appletons in celebration of your stunning scientific solution. Bill Gates has got nothing on you ! Quote Link to post Share on other sites
armchairadmiral 411 Posted April 26, 2020 Share Posted April 26, 2020 And thanks to you other contributors too. This has bugged me for years. This shutdown hasn't been entirely wasted. Quote Link to post Share on other sites
ballystick 79 Posted April 26, 2020 Share Posted April 26, 2020 Where is the 2 to 1? Quote Link to post Share on other sites
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