Downhaul Question for Engineers

BTW is there a best way to reeve the 6:1 downhaul? Probably isn't critical, and whatever I did seems to run nicely and pull squarely, but if there's a super-awesome way to do it I'm all ears.

I think I did something relatively symmetrical like cleat, up the middle, one side, other side, becket.

_________________
'00 H16 #104691
'78 H16 #32692 ex-rental [gone]
Old Holsclaw trailer
My Hobie 16 pages

MBounds' and MMiller's explanations for the how the downhaul works have been very helpful. However, an ongoing problem for me, is that the mast tends to stay bent the wrong way once the mast rotates on a new tack. For example, on a starboard tack, the mast rotates fully to the left and bends sideways to windward, just as described. But when I tack over to port, the mast often stays bent in the same direction which is now to leeward. As a result, the mast doesn't want to rotate freely because the bend is pushing it back to a central position.

This problem is more of an issue in light air and I assume it is caused by excessive downhaul for the conditions. The dilemma I have is that it requires a lot of downhaul just to remove the wrinkles in the luff. It doesn't seem right that it would be necessary to remove and then reapply the downhaul between tacks in light air but I haven't worked out any other solution.

How do you guys handle this? Thanks a lot!

_________________
Leigh Huff

Bingo!


Wrinkles are not necessarily bad (says the old guy). They may not be as pretty as perfectly smooth sail, but you have to look at the big picture:
Is my sail's draft in the right place?
Do I have enough draft for the conditions? Or too much?

Here's a photo from the latest Australian Nationals. I see a lot of main wrinkles - primarily because the conditions are moderate (single trap) and there's a bit of chop (We need more power, Mr. Scott!). So back off the downhaul in lighter air and chop and your performance (and mast rotation) will improve.

MBounds is correct, racers call those "speed wrinkles". In light or medium air your mainsail is drawing more at the top than at the bottom.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

GREAT ADVICE!
"Get your head out of the boat"....When I first started sailing/racing, I was concerned about all these controls and (as an engineer), I felt that I had to understand them to make them work best...THEN, I had the fortune of getting a "rock star" to sail with me for a season. His favorite phrase to me was "Get your head out of the boat". His point was a good one, enjoy the race and do a good post mortem later in the bar.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

Good observations from two above. The fact that the mail sail halyard hooks at the top in the front and therefore the pull from the downhaul is along the backside of the mast means the mast will bend in that direction. This is part of the reason for that type halyard lock design.

Without the thimble and hook at the top, and the halyard simply being hitched at the bottom and run up, over and then back down the sail luff to the downhaul, only compresses the mast straight down, although enough of that and you'll definitely get mast bend, but not necessarily in the direction you want. It will tend to bend the mast in whatever direction the mast offers the least resistance. There are mast halyard systems that work like this and they can be bent to the rear by situating the mast top sheave at the rear of the mast and from a slight extension which serves as a small lever arm. In such designs the mast can be bent to the rear.

The problem I have found with the latter system is that even the lowest stretch halyard lines do stretch some and it's harder to maintain mast bend without constant retightening. The former system such as the Hobie 16 uses takes half the material out of the equation which means less stretch and more uniform tension/mast bend.

Thanks guys for the great information and insight! I had been focused on trying to achieve a smooth air foil at the expense of the overall sail shape. Can't wait to try out this new technique!

Tom, your comment about the effect on mast bend of where the main halyard is secured is really interesting. I have been wondering about that exact question! I have thought, why can't I just use a regular line and tie it off at the bottom? But as you point out, that applies the load on both the front and back of the mast. That is fascinating.

For a nearly 50 year old boat, its amazing how much there is to learn!

_________________
Leigh Huff

This has proved a great learning post for me, thank you all!

It also explains why on one occasion last summer I felt like I was going waay too slow for conditions. We had light/moderate wind, and I have never used much downhaul. For some random reason on this day, I really tightened it up, and didn't realize it until I was pulling the boat onto the beach to end the day. I had a ton of mast bend compared to usual. I realized that this was why I was having issues with mast rotation that day, also.

I don't have 6:1 downhaul, and have never adjusted it for upwind/downwind. Now I have something new to play with next summer!

Thanks again,

_________________
Steve
2017 Hobie 16 "Cayman" sails 114795
1985 & 1973? Hobie 14 "Sea & Ski"