Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 30-10-2017, 05:49   #1
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 14,915
Sheeting Angle, CCA design.

I am trying to determine an appropriate sheeting angle for a 90% to 78% jib on a Bristol 32, which has an attached rudder, looks like full keel, but has a cutaway forefoot, and the keel is rounded on the lower edge unfortunately. Designed by Ted Hood in 1969. Displacement 11,000 lbs.

This quetion is trying to determine if it is worthwhile designing a new jib to fit inside the lower forestay and cap shroud to get a sheeting angle of about 10 degrees, which might be 78 to 80%LP that would fit because it needs to hank to a solent stay.

The alternative is a slightly larger jib 85-90% that will fit inside just the cap shroud at about 13 degrees sheeting angle.

I have an old 95% that has been sheeted to the rail all these years at 16 degrees sheeting angle. I have liked the jib size but always wanted to sheet it in more with a batberhaul or another track.

I read an old statement by Dockhead that for his old jib it did not matter where he sheeted it, it really didn't make a noticeable difference.

I don't want to design and order a new jib that is smaller and sheets to 10 degrees or so inside the stays when the design of the boat (40% cutaway keel, heavy, cca design) is such that we would not significantly benefit going upwind.

We have a 135% on the bowsprit rollerfurler and switch that with the 95% during spring and fall. It is a nice overlapping of sails for our area and the sail sizes work well.

Trying to sheet in closer results in a smaller jib, providing a more rational sail change for heavier winds, and the jib then becomes on that is basically deployed during heavier winds on the solent, rather than being dual use on the Roller furler and soft hanked onto the solent. -At least, that what my sense is.

Going from 95% (224 sf) down to 78% (about 188 sf) wouldn't I really notice a big difference (being under powered) if I were to use that on the roller furler spring and fall. On the other hand, I'll be sailing the 135% reefed more often in the spring and fall and hauling up the heavy wind 80%-78% jib when winds go above 20 knots.

I guess having the greater overlap of wind ranges, between the 135% and 95% is useful for seasonal changes, but I'd like to know if heavier wind upwind performance would be improved sheeting to about 10 degrees with a 78%-80% jib with this boat.

If I put the hypothetical 78% on the roller furler, since I handle the sails on the foredeck alone, I am unlikely to deploy the 135% with soft hanks unless it is a long trip, because of the size of the sail. I also think getting it into the bag and strapped to the mast will be a chore (325sf) but it would be in lighter winds.

I am trying to come up with a better sail plan that requires less sail handling. What's new? And I am having trouble with changing from a seasonal sail change plan, with some overlap in jib sizes, to a more gradiated wind based plan that would go up to 30 knots with the storm jib. It would be nice to really understand these changes better before I get the new jib!

I can attach the two sail plans and will do so. Thanks for your thoughts, ideas and experiences.
rgleason is offline   Reply With Quote
Old 30-10-2017, 06:46   #2
Registered User

Join Date: Aug 2011
Location: Hampton Roads, VA
Boat: Bristol 27
Posts: 7,161
Re: Sheeting Angle, CCA design.

Why don't you just get a new say 120% jib and use as much as you want of it.

For heavier wind, you can roll in some of the larger jib.

This would equal less sail handling I'm thinking.

My jib that's on a roller furler is around 120% or so. I also have a smaller jib that's around 90% (and it also has a shorter luff) but have only use that jib when my main jib was in for repairs.

I've been in wind to 30 mph with the 120% rolled in a bit going downwind.....maybe 22 knots or so going upwind
thomm225 is offline   Reply With Quote
Old 30-10-2017, 08:35   #3
Registered User
 
Suijin's Avatar

Join Date: Feb 2013
Location: Bumping around the Caribbean
Boat: Valiant 40
Posts: 4,627
Re: Sheeting Angle, CCA design.

I think the issue you'll run into is that your boat won't be capable of making use of that smaller sheeting angle. The boat is too slow and you won't be moving the apparent wind aft enough to take advantage. If you're anticipating deploying the sail in higher wind that just complicates the issue. You won't be able to hold the boat that high anyway and make reasonable headway.

Not sure of any of this, just know from my racing experience that the faster the boat the smaller sheeting angles it can perform to.
Suijin is offline   Reply With Quote
Old 30-10-2017, 19:51   #4
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 17,560
Re: Sheeting Angle, CCA design.

Quote:
The boat is too slow and you won't be moving the apparent wind aft enough to take advantage.
Could you explain this statement a bit more, please? I'm not understanding the action here!

Overall though I do agree that very narrow sheeting angles on a boat that makes a lot of leeway and has a lot of drag probably does not lead to best VMG to windward. My gut feeling is that one should foot off with powered up sails in such vessels, but I've limited experience in them.

Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet once again.
Jim Cate is online now   Reply With Quote
Old 31-10-2017, 03:49   #5
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 14,915
Re: Sheeting Angle, CCA design.

Suijin and Jim Cate. I agree with this. The boat is short loa 32' and lwl 22 and slower than modern light boats thus the apparent wind does not move as far forward. Thus the sheeting angle does not need to be as tight.

That helps, but I need to figure out how many degrees is best. Just sailing the boat with different angles would be one way to do it, but the smaller angles require a smaller jib than I have at the moment.
rgleason is offline   Reply With Quote
Old 31-10-2017, 04:02   #6
Registered User

Join Date: Aug 2011
Location: Hampton Roads, VA
Boat: Bristol 27
Posts: 7,161
Re: Sheeting Angle, CCA design.

Quote:
Originally Posted by rgleason View Post
Suijin and Jim Cate. I agree with this. The boat is short loa 32' and lwl 22 and slower than modern light boats thus the apparent wind does not move as far forward. Thus the sheeting angle does not need to be as tight.

That helps, but I need to figure out how many degrees is best. Just sailing the boat with different angles would be one way to do it, but the smaller angles require a smaller jib than I have at the moment.
Worrying over the exact degree or angle of the jib on an old slow boats like ours, is probably a waste of time.

The speed is what I go for to get a bit more pointing, but it's still nothing to write home about.

On a high tech catamaran, you can easily see what speed does to pointing (due to the apparent wind)

About all you can do to get there faster is to tack on a header and use the land effect when possible plus fall off some for speed before coming back up.
thomm225 is offline   Reply With Quote
Old 31-10-2017, 04:21   #7
Registered User
 
Suijin's Avatar

Join Date: Feb 2013
Location: Bumping around the Caribbean
Boat: Valiant 40
Posts: 4,627
Re: Sheeting Angle, CCA design.

Quote:
Originally Posted by Jim Cate View Post
Could you explain this statement a bit more, please? I'm not understanding the action here!

Overall though I do agree that very narrow sheeting angles on a boat that makes a lot of leeway and has a lot of drag probably does not lead to best VMG to windward. My gut feeling is that one should foot off with powered up sails in such vessels, but I've limited experience in them.

Jim
Brain fart. I meant moving the apparent wind forward. And I think your comment about leeway is part of the equation.

The faster the boat, the higher it can point with less power. The Bristol is simply cannot generate enough power relative to it's displacement and hull form to point effectively to tighter sheeting angles. She'll just stall out.
Suijin is offline   Reply With Quote
Old 31-10-2017, 06:25   #8
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 14,915
Re: Sheeting Angle, CCA design.

I've been trying to follow this excellent thread
Installing an Inner Forestay - Page 2 - Cruisers & Sailing Forums

I said I would post some drawings of the boat and various sail plans.
1. New Hood 135% LP with shorter luff which can fit on roller furler or solent (soft hanks). Our old North genoa was 140% and delaminated after many years.
2. Older North 95% LP with shorter luff which can fit on roller furler or solent, will be delaminating.
3. The question is what sheeting angle should I work with for the new jib as it affects the size of the jib.
4. I really like the old 95% Jib for spring and fall sailing on the Roller Furler, but this sail has too much overlap with with the 135% for a rational sail reduction strategy. (see spreadsheet sheet load calcs attached.)
5. I am very interested in reducing headsail handling in difficult conditions as it is just me on the foredeck.
6. I'd like the new sails to be effective in the conditions intended.
7. I am having difficulty deciding between the 135% summer & 95% fall-spring mindset to a rational strategy for reducing sail area (spreadsheet).
8. One other thing, to consider, this Bristol32 has a factory installed custom bowsprit, unlike other B32. It's LP=13.875' and the standard Bristol 32 LP is 12.68'. This boat has a balanced helm and sails nicely in heavier winds. In less than 5 knots proper headsail trim is really important or she'll get leeward helm.

Attached:
90%LP - early drawing, should sheet to 13 degrees.
85%LP - sheets to 13 degrees inside cap shroud for sure.
78%Lp - sheets to 10 degrees on cabin top
Nell-Hood-Genoa-Wind-7.xls Spreadsheet - See tab "135-RF-Wind-Press"
Lines 27 to 51 using sheet load pressures from Evans Starzinger calcs (thank you Evans) and Harken's sheet loads calcs to estimate max wind for each sail size. I've set the max wind for the 135%LP genoa at 15 knots (317 lbs) which may be a little conservative, but the boat sails better when it is at 15-20 degrees heel. It could be set at 340 lbs with more heel and greater wind range for a given sail.
Attached Files
File Type: pdf Hood78-LP-Jib-10-27-17.pdf (262.9 KB, 54 views)
File Type: pdf Hood85-LP-Jib-10-27-17.pdf (265.6 KB, 32 views)
File Type: pdf Hood90-LP-Jib-RF+Solent.pdf (140.6 KB, 32 views)
File Type: xls Nell-Hood-Genoa-Wind-7.xls (138.5 KB, 36 views)
rgleason is offline   Reply With Quote
Old 31-10-2017, 06:43   #9
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 14,915
Re: Sheeting Angle, CCA design.

I am pondering Jim Cate's post here
"So, I would never rely upon a reefing jib or staysail for heavy weather sailing."
I have shown jiffy reef points in these jibs.
rgleason is offline   Reply With Quote
Old 31-10-2017, 08:03   #10
Marine Service Provider
 
Kestrahl's Avatar

Join Date: Jun 2012
Location: Malaysia
Boat: Laurie Davidson 35
Posts: 375
Re: Sheeting Angle, CCA design.

10 degree's - forget about it for this boat, you will sit there pointing high but going nowhere. Even on my Davidson cruiser/racer with fairly good foils for its age the No3 is at 13 degree's.
Attached Thumbnails
Click image for larger version

Name:	10606123_1004038576277541_5532332176831796472_n.png
Views:	65
Size:	305.1 KB
ID:	158621  
Kestrahl is offline   Reply With Quote
Old 31-10-2017, 08:52   #11
Registered User
 
Suijin's Avatar

Join Date: Feb 2013
Location: Bumping around the Caribbean
Boat: Valiant 40
Posts: 4,627
Re: Sheeting Angle, CCA design.

I'm looking back at your posts and trying to figure what your primary question is. In the original post, it was whether a 10 degree sheeting angle was appropriate/feasible. Sounds like that question as morphed into what size jib would be most useful...or is it what is the appropriate sheeting angle for X sail?

I personally think that sheeting inside the shrouds on your boat is going to severely limit your options off the wind, unless you rerun the sheets.

Is this sail going to go on the forestay? You've mentioned solent and I'm wondering if that is an option.

FWIW, I have a 110 yankee and a 135 genoa for my boat, which I single-hand 99% of the time. A cutter rig, she also has a staysail with an appreciable slot.

The 135 is too much for the boat, given that the mast is almost midships. There is a dramatic difference between the two sails and the boat just sails better with the 110 which is also significantly easier to handle, and the genoa I no longer even keep on the boat. The 110 is on a furler and the staysail is hanked on a detachable inner forestay (which I rarely detach...I just furl and unfurl to tack, except going up a smaller body of water). Staysail goes up when working to windward, almost always.

I believe Jim is talking about storm jibs, which is a whole other matter.

I personally think the 90% will be the most versatile sail. You could furl it to 80-70% and not loose as much shape and performance as with your 135, and it will only really be an issue if you're close hauled.
Suijin is offline   Reply With Quote
Old 31-10-2017, 09:13   #12
Moderator
 
Don C L's Avatar

Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 10,007
Images: 53
Re: Sheeting Angle, CCA design.

I think you have it right Suijin. In my ol CCA boat there is more con than pro to trying to increase the sheeting angle. And btw the beam is already pretty narrow. Nah I’d just be sliding sideways more than foreways, we just don’t have the speed andor acceleration to make it make sense. I love my old boat, but it’s not going to point much higher than I got.
I have a jib with reef points, and like it for the option it provides, but I don’t consider it a replacement for a real storm jib. It has a more limited wind range but is still useful for where I am. My boat points higher with what we called in the old days the working jib, 90% or so. I hank on though so factor that in. My headsails are somewhat more efficient than a lot of furlers.
I’ve only once sailed a boat with staysails long ago and it seemed to me there was more drag than drive with those to windward, but maybe I wasn’t trmming them right.
Don C L is offline   Reply With Quote
Old 31-10-2017, 11:34   #13
Registered User

Join Date: Jun 2016
Posts: 35
Re: Sheeting Angle, CCA design.

Here's something you can try and not have to add any new sail to your inventory. I did this on my 40 steel cutter sloop.

If it is at all possible try and rake the mast further back by lengthening the forestay and shortening the backstay. This goes a long way in helping the boat point further to windward without having to sheet inside the the shrouds. In my case, when I got the boat, it was decidedly set up as an off wind sort of thing and I could barely make a close reach, let lone a close haul. I ended up cutting 4.75" off the backstay (yes that's nerve wracking) and reconnecting it using a norseman fitting. The boat now sails all the way to the "feathers" on the windvane on the same headsail and doesn't lose any speed. While the downwind speeds dropped a bit, it's nothing compared to the gain going to weather.

If you have enough play in your turnbuckles, you might be able to do this without cutting anything. Also, if you can tension your innerstay to put a little bow in the mast, that helps even more as it tends to flatten the main a little and make it more useful at the tighter angles.

I can't say for sure if this will work for you but it turned my boat into a whole different animal and squashed the rumour that steel boats are slow and can't point.
SeaBreeze-1 is offline   Reply With Quote
Old 31-10-2017, 13:53   #14
Registered User
 
rgleason's Avatar

Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 14,915
Re: Sheeting Angle, CCA design.

It is good to try to understand the whole picture when it comes to sails, because they are inevitably a compromise.

The main question is regarding what sheeting angle is appropriate for this boat, for the "working jib". The new genoa is 135% (old one was a North 140%) and we use that exclusively all summer on the Roller Furler. This new genoa has a shorter luff and grommets behind the #6 wire for soft hanks around the solent stay. Right now I'm now not sure the 135% will be used on the solent stay that much, as it is quite big for me to deploy. The 135% on the RF a good fit for our area during the summer.

The new "working jib" is intended to be used on both the RF and solent as well. One of the determinants of the size of the working jib is the "optimum" sheeting angle. As different sheeting angles result in different maximum size jibs due to rig interference considerations. Another consideration is the logical steps in headsail sizing, (including reefs) to have control in heavier winds, this conflicts with the size of working jib I would like to have for spring and fall (we found the 95% was very good, but would be comfortable with 90%.)

For the design of our 2003 140% genoa, North Sails' notes show an optimum sheeting angle at 11 degrees. I don't know if this would apply to a working jib on this boat, but I do know that sheeting angle, translates to apparent wind entry angle, which governs the amount of draft and power a sail can have.

The points about pointing in heavy winds and seas are good, but it would be nice to know for sure that I should be sheeting inboard of the cap shroud, but not inboard of the lower forestay, as that would set the max size of the working jib.
rgleason is offline   Reply With Quote
Old 31-10-2017, 14:45   #15
Registered User
 
Suijin's Avatar

Join Date: Feb 2013
Location: Bumping around the Caribbean
Boat: Valiant 40
Posts: 4,627
Re: Sheeting Angle, CCA design.

You might benefit from asking these questions over at Brion Toss's forum at SparTalk - Powered by vBulletin. That or ask your sail maker.

I'll just add that I assume your solent stay is aft of your forestay, which is obviously going to impact where you need to put tracks for any sail you put on it, depending on the distance aft. If you could realistically sheet the 140 to 11 degrees outside the shrouds, then yes, I'd say that with a flatter blade you'd be running inside the shrouds and maybe hitting 10 degrees after all, although that strikes me as aggressive for your boat. But you know her, how you sail her, and how she sails.
Suijin is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
CCA type yawls... 6227 General Sailing Forum 12 01-11-2016 10:21
CCA test accuracy? ontherocks83 Electrical: Batteries, Generators & Solar 16 14-11-2014 08:16
Catana Mainsail Sheeting System ? cvondo Multihull Sailboats 14 12-10-2012 11:28
Batteries - Amp/Hours or CCA ? fishingaz Monohull Sailboats 2 05-10-2010 05:58
SSB Info' from CCA GordMay Marine Electronics 3 23-09-2005 19:17

Advertise Here


All times are GMT -7. The time now is 20:39.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.