Hobie Cat Forums

It is currently Wed Jul 30, 2014 4:21 am

All times are UTC - 8 hours [ DST ]




Post new topic Reply to topic  [ 7 posts ] 
Author Message
PostPosted: Wed Jan 10, 2007 6:54 am 
Offline
Site Rank - Deck Hand

Joined: Tue Oct 17, 2006 5:47 pm
Posts: 10
I have a beautiful H20.

Normally me and my first mate depower the boat by three lines: main sheet, traveler, and we ease up on the jib sheet if the leeward pontoon is going under.

I've been scanning thru this forum, and I have seen a few times that by loosening the downhaul, that also depowers the boat. I'm not sure how or why this works, could someone please explain? I also dont see it as that practical since we are hiked out in the harness, I would have to come in and release it. And then if i release it too much, the boom would rise and come out of the track? The more I think about this, the more I dont get it.

Thanks
Noah

Is it April yet?


Top
 Profile  
 
 Post subject:
PostPosted: Wed Jan 10, 2007 7:41 am 
Offline
Site Rank - Old Salt

Joined: Tue Jul 05, 2005 8:45 am
Posts: 759
Location: Clinton Lake Lawrence, KS
Noah,

Applying downhaul tension depowers by stretching the luff rope to flatten the sail, reducing the amount of draft and thus the power generated. Releasing the downhaul has the opposite effect by letting the sail become fuller.

Double trapped and still popping up the hull?

Crank on more downhaul (still raising?)
Main Traveller out (still raising?)
derotate the mast, point rotator arm towards back of boat.

Somewhere in there comes crack off the jib a bit.

Quote:
Is it April yet?

Man, I wish! :roll:

_________________
hobiejohn at earthlink dot net
Fleet 297


Top
 Profile  
 
 Post subject:
PostPosted: Wed Jan 10, 2007 8:20 am 
Offline
Site Rank - Deck Hand

Joined: Tue Oct 17, 2006 5:47 pm
Posts: 10
What is the luft rope?


Top
 Profile  
 
 Post subject:
PostPosted: Wed Jan 10, 2007 9:50 am 
Offline
Site Rank - Old Salt

Joined: Mon May 09, 2005 10:25 am
Posts: 2524
Location: Jersey Shore
Proper use of the downhaul is critical to performance of the Hobie 20. You should have the downhaul rigged with enough line so that it can be operated by the crew while on the trapeze from either side of the boat.

The downhaul is tensioned to decrease power/increase speed and loosened to increase power. When sailing upwind, double trapped, the crew should be adjusting the downhaul through gusts and lulls (in conjunction with the skipper's steering) in order to keep the windward hull just above the water. The mainsheet should only be adjusted if a major change in windspeed occurs (i.e. a powerful gust that requires a fast decrease in power). The jib sheet and main traveler should generally be set for the conditions and and not adjusted unless a major, sustained change in windspeed occurs.

Tensioning the downhaul (in conjunction with the mainsheet) acts to flatten the mainsail. In it's normal, un-rigged state, the mast is essentially a straight pole. The luff (leading edge) of the mainsail is cut with a curve. When you raise the mainsail up the mast, it gets all wrinkly because you're trying to attach something curved to something that wants to be straight (this is how sailmakers get shape into sails). Applying moderate tension to the downhaul forces the mast to bend because the mast is trying to match the luff curve of the sail. It also smooths the surface of the sail and introduces shape into the sail. Further tensioning of the downhaul causes the mast to bend such that it nearly matches the luff curve of the sail. This causes the sail to become quite flat, particularly at the top (a good thing).

You can mess around with the settings on the beach to see how tensioning different strings causes changes to the sail shape. As a general rule of thumb- flat sails = less power, more speed, full sails = more power, less speed.

sm


Top
 Profile  
 
 Post subject:
PostPosted: Wed Jan 10, 2007 10:09 am 
Offline
Site Rank - Admiral

Joined: Wed Nov 01, 2006 4:44 pm
Posts: 165
Location: Raleigh, NC
The better approach to the downhaul would be:
Have it run to the base of the crew's trap bungee so that it can be accessed while trapped. Use it to get the boat into a zone such that puffs and lulls can be addressed by sheeting the main in or out, but only within a 10-14" range. Oversheeting is a common problem with many sailors.

The downhaul pulls the luff (area along the boltrope) of the sail down, which causes the upper portion of the sail to spill off air. Go to your boat, hook up the downhaul, and pull it very hard while watching the sail up around the 3rd batten from the top. The sail will flatten out in that area, which reduces its power. Since much of the heeling moment is due to sail are up high, depowering the top of the sail can significantly depower the boat. Use the downhaul to control power in the boat such that you can control the flying hull with just adjusting the mainsheet in or out several inches. When you sheet in fairly tight, if the the hull pops way too high or fast, crank a little more downhaul on, and then continue to run the boat with the mainsheet. If you find you are lacking power, try loosening the downhaul a little bit and then sheeting in some.

Also, you may find that applying a little extra downhaul in very light conditions will help you to go faster. I use the same amount of downhaul in 0-4 as I do in 12-15. By slightly flattening the sail, I can sheet in a little more without being oversheeted up top. This works for me very well in the light stuff.
I hope this helps some...?

_________________
Trey Brown
www.velocitysailing.com
2006 N20 1017
1998 H16 102698
www.sunjammers.com ftw!


Top
 Profile  
 
 Post subject:
PostPosted: Thu Jan 11, 2007 7:05 pm 
Offline
Site Rank - Deck Hand

Joined: Tue Oct 17, 2006 5:47 pm
Posts: 10
Thanks for the great comments. I would never had known had I not asked!

Noah


Top
 Profile  
 
 Post subject:
PostPosted: Fri Jan 12, 2007 10:10 am 
Offline
Site Rank - Captain

Joined: Mon Jun 26, 2006 6:49 am
Posts: 82
Captain Noah,

you may want to also check your mast rotator. I've heard this can be really important for depowering.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 8 hours [ DST ]


Who is online

Users browsing this forum: Bing [Bot] and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group