I’m putting new-to-me laminate sails on my Hobie 18 shortly, which will likely beg for additional downhaul. I have a box of blocks, low friction rings, and line, and have been thinking… and researching a bit.
3:1
The stock H18 downhaul setup is 3:1 (tied to tack grommet, passed through stock cheek block, back through tack grommet, and cleated on mast jam cleat)
This thread shows the boom/gooseneck/cheek part of this minus the sail tack and line routing: https://www.thebeachcats.…ms/viewtopic/topic/14937
5:1
Murrays sells a 5:1 setup, one of which came with my boat…. the single exit block/cleat is nice and can be run from either side.
https://www.murrays.com/product/07-2087/
If you wanted to add a second exit block/cleat, this would become 6:1.
8:1 simple
I’ve also seen 8:1 setups (apparently, this is the maximum class-legal advantage you can run). Most use double blocks on either side of the tack grommet, and 3 cheek blocks at the base of the mast, with double exit blocks /cleats, one on each side that can be adjusted from the trap regardless of mast rotation.
This thread shows a simple 8:1 setup: https://www.hobie.com/for…hp?f=13&t=44323&start=15
8:1 cascade
I’ve not seen but am aware of a system that 2:1 cascades a block on either side of the tack grommet down into a 4:1 base system, for a total of 8:1 advantage.
There’s a sketch in this thread of what that looks like: https://www.thebeachcats.…ms/viewtopic/topic/13011
It would be pretty easy to use a similar 2:1 cascade into the 8:1 base system detailed above, for a total of 16:1 advantage... which would be complete overkill for dacron sails, and a non-trivial stressor to laminate sails.
Harken shows what that looks like: http://www.harken.com/DeckLayout.aspx?id=13768
12:1 double cascade
You can use successive blocks to pull advantage through multiple cascades, but you have to find the space for them to run – higher advantage can multiple the length of line required.
This thread links to an example: https://www.thebeachcats.…ms/viewtopic/topic/12271
I know some of the F boats are running multiple cascades, internal advantage, etc. but if we’re talking about Hobie 18s, that’s back into overkill… and fitting it all in between the mast base and the mainsail grommet becomes difficult, even before you start splitting it up around the fixed gooseneck. Where the H16 uses an attached sail and a sliding gooseneck, the H18 uses loose-footed sail and a fixed gooseneck… so the really simple H16 multi-blocks attached to the bottom of the gooseneck won’t work on the H18. Your downhaul needs to skirt to either side of the gooseneck, and space can get pretty jammed up without careful planning.
Hobie 18 Downhaul
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Posted: Aug 30, 2017 - 06:16 PM
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Posted: Aug 30, 2017 - 07:03 PM
That was a lot of verbiage to get to my questions, but I hadn’t found it in one place.
Go all the way back to the stock 3:1 and the grommet is essentially used as a low-friction ring, added to the 2:1 cheek block, to get 3:1 net advantage. Granted, a block would be less friction still, but since this the highest-loaded portion of the system, below which all mechanical advantage is applied, almost any tension in the sail is going to prevent the line from sticking… at most, you’d have to give a little tug to break the static friction and get things moving and then dial in the desired downhaul. So… why don’t folks use the grommet as the pivot for a basic 2:1 advantage in a top cascade? Seems like that’s be more function and fewer boat bucks spent.
I follow simple mechanical advantage – you’re moving twice as much line at half the effort. Configure 4 sheaves across 5 spans of line, and that’s a 5:1 system. I follow a basic cascade where you add a sheave riding between an anchor and a load, and you’ve halved that load, and that multiplies against whatever advantage you want to hang under the block that drives that sheave. So how is it that the two 2:1 sitting side-by-side and cascading into the 4:1 system linked below don’t somehow add to each other before multiplying the 4:1 simple advantage to wind up as an 8:1 cascade?
(sidebar: I hate that Photobucket changed their policy and broke useful images across the ‘net!)
Google Image Search these words “downhaul estimated diamond wire tension help guidance” and the second image is an paint sketch.
You *may* be able to get there by clicking here: https://www.google.com/se…AUICigB&biw=1536&bih=757
This stuff is more fun to think about than work… and the Google image searches show some incredibly creative ways of multiplying and mounting these systems. The L-36 site has incredible diagrams! http://l-36.com/vang_systems.php
Randii
Edited by randii on Aug 30, 2017 - 05:05 PM. -
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Posted: Aug 31, 2017 - 05:19 PM
Keep in mind that in an 8:1 system, 8:1 is also the ratio of rope on deck compared to movement of the sail up and down. If you want to move your mainsail 12 inches down from where it rests without any downhaul, you will have to deal with 8 feet of line on your tramp after you have pulled it taut.
On cascade systems, you must plan carefully. You may not have the distance on your mast, between the main clew and the mounted cheek blocks, to be able to pull the compound blocks tight enough.
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Posted: Aug 31, 2017 - 05:24 PM
regardless of your system - you have a very stiff mast and are not gonna get much bend compared to modern masts
if your rigged w your 5:1 - and used to it . i would keep it - at least for now -
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Posted: Aug 31, 2017 - 08:54 PM
Yup. The physics of straight reduction relates effort reduction to increased length of line. Cascades cause less of that, but you can go too far the other way, and not be able to make fine-tune shifts.
Yes, so you’re constrained vertically in travel between the tack, the mastbase, and the various blocks, and with the H18, you also have to work around the fixed gooseneck… AND all of that has to work vertically in the range of the sail/mast’s 8-inch-or-so downhaul capacity. Complicated!
This was one of the reasons I thought it would work well to get a cascade directly off the tack grommet, as opposed to hooking blocks through that grommet and hanging them down (that burns height). The 5:1 system I have isn’t bad, and the line never dribbles off the tramp, even pulled hard… 5X line is less than 8X line.
Certainly. Especially with the all-aluminum mast I’m using. The comp-tip mast I have needs some work… but would probably respond better to downhaul.
That’s the plan… and light air this weekend won’t need a lot of downhaul regardless.
Change one thing at a time… and Whirlwind squaretop laminates should be a nice change/boost over the dacron rags I’ve been flying. I’m looking forward to feeling how the sail responds to puffs NOT pulling through stretched and aged dacron. Upgrading the sails takes a few variables out of the mix, and leaves me less things to blame… it is tougher to tighten the loose nut connecting the tiller extension and the sheets!
Randii
p.s. I still don’t get how two separate 1:2 side-by-side pulleys cascading into the same 4:1 simple advantage doesn’t somehow result in more than 8:1 advantage. Looks like I may have to buy a rigger a few drinks to get to the bottom of that one! -
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Posted: Sep 01, 2017 - 03:57 PM
I have a dual exit 8:1 on one boat and a single exit 6:1 on the other. Dual exit is a waste because it doesn't bend the mast enough to actively use it in the puffs. Just having a cleated adjustable downhaul is all you need to be able to adjust it to the wind conditions on the fly or upwind downwind. It's not like you need the line coming out both sides of the mast to the traps. Just run a single line and let it just flop around on the tramp. You can always just lean in and make the adjustment as needed, which isn't much really. Keep in mind if you want it maxed you have to sheet in first. If you downhaul first it will be loose after you tighten the main in -
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Posted: Sep 01, 2017 - 04:39 PM
As your mast is stiff, past a certain point you're stressing the sail for no gain IMHO. I'm on a 18 footer with laminate sail and a very bendy/flexible carbon mast, with a 6:1 double exit; and I have enough power to kill the top half of the sail. -
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Posted: Sep 01, 2017 - 05:24 PM
I was going to send you these photos but decided to start a technical album with them. Anyone else that has a setup, especially for "classic" beachcats that didn't originally come with a pulley based downhaul, please share.
Album is at
https://www.thebeachcats.com/pictures?g2_itemId=128883
I've started it off with my setup.
Here is how Kirk at Key Sailing setup my 8:1 double exit on my Hobie 18.
This setup solves the problem of having so little space between the foot of the sail and the rotator as well as below the rotator to the mast base.
The double exit is just a bonus, making it easier for the crew (or me solo) to find the downhaul line. I only wish my line was pink or something (pull the pink line!).
Only downside of this setup is it's permanent, and you have to rivet into the mast.
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Posted: Sep 01, 2017 - 07:35 PM
Damon, thanks for the gallery. Your mast illustrates how many things fit together into little space. Taking the exit blocks that far forward helps move some of it to the side and away from the gooseneck.
Sidenote: is the light blue rope coming up center-of-tramp just aft of the front crossbar your righting line?
If I put together more DH, I’ll probably try to reuse the single stainless steel exit block I have… otherwise I’d have to buy TWO new exit blocks, since one being SS and the other being black plastic just wouldn’t do!
I’m hearing loud and clear from experienced folks that I’m unlikely to be playing the DH on an H18 that much, anyway. My crew or I can probably do it as we cross on a tack…
I’ll put the box of bobs, blocks, and bits aside for now, and just go sail what I have… I’ve got a bit to learn about how the squarehead will open up (or not) based on various existing controls.
Randii -
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Posted: Sep 04, 2017 - 01:12 PM
I really like yelling at crew... so i make them all white
PULL the white line - NO the OTHER WHITE ONE! NOOOO!! the OTHER one! -
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Posted: Sep 04, 2017 - 09:24 PM
I totally disagree with the comments that double exit blocks run out to the traps are unnecessary on a H18. We have used that configuration for years (probably decades) on the race course. I run a 6:1 system as I don't feel that we need the power of an 8:1 (if my crew can't pull it in all the way, all she needs to do is hand the line to me and I can crank it down the last inch or so). We play the downhaul upwind anytime it's double trap conditions. Spot a puff coming down the course and pull it down an inch or two to keep the boat flat and driving. Lull hits, ease off the main sheet and down haul an inch to keep power in the rig. Virtually all of the racers run a double sided system.
sm
