Mast Deflection

[Potcake boy]

Multimedia_smith - IMHO you would be better off not adding lowers to your rig for a couple of reasons.
1. Extra maintenance - and adjustment - if it was necessary ComPac would have done it
2. If you have the lowers too tight the uppers will stretch more from the static position and bring the mast out of column increasing the risk of breaking the mast at the lowers.  If the single shroud breaks, damage may well be limited to the tabernacle instead of a broken mast.  In fact if you replace the bolt at the mast base with some sort of breakaway pin you may only have a slightly bent tabernacle to repair.
3. You will encounter the same sheeting issues as 19 owners have.  Although this isn't a big deal - you sheet the jib in between the shrouds and a genoa outside.
Remember the KISS principle - that's an important part of the ComPac success story.

Wishing you wind in your hair - or is that hair in the wind.

Ron

[Steve Ullrich]

Hi Nate,

I've noticed the posts you have been making.  Good to see you are getting out on the water a lot this summer, more than I have for sure. 

I think we are on the right track with shroud tension.  For sure they don't need to be anywhere near as tight as they needed to be on my Hunter 23.  I backed off the tension a little bit more when I was out on Monday afternoon.  Light air so not a real test but the slight bow we both noticed when out on Mille Lacs was almost impossible to see. Heavy air is going to be the test. Breezy today, might get out yet this afternoon on Prior Lake.  I'm recovering a bit from too much brew at the Buffalo Wild Wings last night so I might lay around and watch a movie instead.

Steve,

    I'm still messing with my shroud tension too. The mast deflection is definitely due to tension on the side stays. Whether it is bad, good, or indifferent, I don't know? A few weeks ago when I was on Pepin, I had my shrouds fairly tight, and even reefed in 25-30 mph I was getting some deflection (and quite a bit before I reefed). Before my lee shroud would be visibly slack and there was no noticeable deflection in the mast. I'm going to keep messing with it, there has to be a happy medium between slack and deflection. Probably going to depend on whether it is a I or a II also.

Nate

[multimedia_smith]

I think you must be talking about Mast "bend" or "curve"... that would be deflection fore and aft.  In the RC sailboats and some racing sailboats there is an angled piece at the masthead that the backstay attaches to called a Crane.  When tension is increased on the backstay, it pulls Down as well as back allowing you to increase the amount of (fore and aft) curve in the mast.  Several sets of my expensive carbon fiber sails for the RC boats were actually cut with a curved luff.  This would only shape correctly when the exact matching curve was introduced into the mast.

Since we don't have a backstay on the 16s, we can only cause or remedy the fore and aft deflection by the amount of tension in the leech of the sail (how flat we make it or how tightly we sheet it) or through the amount of tension in the headstay.  The headstay tension can be affected by it's own turnbuckle OR by how much tension is applied to the shrouds.

The deflection I was correcting for  with my "lowers) was sideways deflection caused by more force being applied to the center of the mast when running reefed in a strong wind.  Real lowers are set on chainplates that are further aft than the uppers and pull back on the middle of the mast correcting for the amount of curve (straightening it out).  The uppers are set on chainplates that are paralell with the mast.  Since we only have one set they are already set aft of the mast foot... we really wouldn't want anything further aft as the boom already hits them on a full downwind run.  The three form a triangle and thus we don't bother with a backstay... the sail leech essentially becomes our backstay.

As far as the tension on the shrouds, they should be tight enough not to slack on the leward side when sailing... if they are allowed to be slack... they will snap tight with a bang when you tack and that's not a good thing.  The rule of thumb when tensioning shrouds or headstay is that they should be sort of like a bass guitar string... not a high note, but still a note.

Just my 2c

Dale

[Steve Ullrich]

Hi Dale,

Thanks for the post.  Actually, I am also talking about a slight bend port and starboard. Caused, most likely, by heavy winds, a baggy main and too much shroud tension. I understood your post and am still considering adding lower shrouds.  As reducing shroud tension seems to have corrected the bend almost completely since my original post I may not have lowers made.  I have a new main on order from National Sails that should help too as there is absolutely no way to flatten my current main. The original main is just blown out and needs to go.  I'm expecting the new sail any day now, I can hardly wait...  It is worse than Christmas!

Thanks,

Steve

I think you must be talking about Mast "bend" or "curve"... that would be deflection fore and aft.  In the RC sailboats and some racing sailboats there is an angled piece at the masthead that the backstay attaches to called a Crane.  When tension is increased on the backstay, it pulls Down as well as back allowing you to increase the amount of (fore and aft) curve in the mast.  Several sets of my expensive carbon fiber sails for the RC boats were actually cut with a curved luff.  This would only shape correctly when the exact matching curve was introduced into the mast.

Since we don't have a backstay on the 16s, we can only cause or remedy the fore and aft deflection by the amount of tension in the leech of the sail (how flat we make it or how tightly we sheet it) or through the amount of tension in the headstay.  The headstay tension can be affected by it's own turnbuckle OR by how much tension is applied to the shrouds.

The deflection I was correcting for  with my "lowers) was sideways deflection caused by more force being applied to the center of the mast when running reefed in a strong wind.  Real lowers are set on chainplates that are further aft than the uppers and pull back on the middle of the mast correcting for the amount of curve (straightening it out).  The uppers are set on chainplates that are paralell with the mast.  Since we only have one set they are already set aft of the mast foot... we really wouldn't want anything further aft as the boom already hits them on a full downwind run.  The three form a triangle and thus we don't bother with a backstay... the sail leech essentially becomes our backstay.

As far as the tension on the shrouds, they should be tight enough not to slack on the leward side when sailing... if they are allowed to be slack... they will snap tight with a bang when you tack and that's not a good thing.  The rule of thumb when tensioning shrouds or headstay is that they should be sort of like a bass guitar string... not a high note, but still a note.

Just my 2c

Dale

[multimedia_smith]

Hi Steve,
They make some really nice sails at National... for those who don't know, they are actually Rolley Tasker Sails out of New Zealand and are fabricated in Thailand I think.  The ones I've gotten show terriffic workmanship.

Since 2004 I started with a full batten light air main and a 155 genoa (cut to fly high off the deck on a 10" pendant.
Next, I got a storm jib.  They worked with me to come up with a custom design for the CP 16... it comes out to be about a 60%.  It still gets me up to hull speed in a blow (with mannerly control of the boat).  In order to save my new light air main.  I was using my original Johnson main in heavy air with a boom roller reefing.  Combined with the new storm jib, I experimented with different luff lengths in different wind conditions and made measurements.  What we came up, National now calls their CP 16 heavy air main.  It is loose footed (when you reef, you lose the foot rope anyway) and I changed the dimensions a bit to keep the forces low on the boat.  I shortened the luff by 3" and lengthened the foot by 8" and removed the roach.  It has two reef points...  The first reef point takes out 3 1/2' of luff and the second reef takes another 3 1/2'.  I have used this combination in some pretty strong conditions and the boat handles great... Hull speed plus without the fear of a knockdown.

Back to the "lowers"... although they are not really lowers because they have the same attachment point at the hull.  They DO have a different place along the mast though, and here's where it helps.  When we reef, we are placing most of the lateral strain on the middle of the mast.  The shrouds are 7/8 to the top (almost the top).  Thus, I saw an improvement in performance and less tension in the nerves of the skipper from not seeing the mast bend 6" off center each way on a beat.

I just added some pics of the new main... here's the link...

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/826731363/view?picmode=&mode=tn&order=ordinal&start=21&count=20&dir=asc

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/826731363/view?picmode=&mode=tn&order=ordinal&start=21&count=20&dir=asc

Also a couple of pics comparing the Storm Jib to the Genoa.

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/236597013/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/2138080087/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

Happy sailing

Dale

[Steve Ullrich]

Hi Dale,

I wish I could see those pictures but all I get is an error message...  I bought sails from National for two other boats and they were beautiful sails.  Their main loft is in Thailand I think but the sails are made from dacron from the US, good material.  I believe I delt with Dirk.  I bought the heavy main but I asked for a rope on the foot.  I probably don't need the heavy sail but the material sure lasts longer in normal winds.  I'd love to have the measurements for the 60% storm jib you had made.  Can you post those?

The tack pennant on the 155 is a great idea.  I have enough room between the head of the sail and the mast to put a tack on mine as well so I'm going to do that before I go out the next time.  That might shift the center of effort a bit forward as it raises it to a point where the main isn't as wide but it would sure make it easier to see the bone heads on the personal water craft and the clueless fathers pulling tubes across my bow.

I had the same experience you did in heavy air with a reefed main.  I could see that mast bowing and my butt puckered up a bit. Easing the shroud tension reduced the bow greatly though now I can detect a slight mast deflection to leeward.  Maybe I just shouldn't be out sailing when the gusts are hitting 30 but I just can't help myself.  It is a hoot out there when the other boats are chickening out.

Steve

Hi Steve,
They make some really nice sails at National... for those who don't know, they are actually Rolley Tasker Sails out of New Zealand and are fabricated in Thailand I think.  The ones I've gotten show terriffic workmanship.

Since 2004 I started with a full batten light air main and a 155 genoa (cut to fly high off the deck on a 10" pendant.
Next, I got a storm jib.  They worked with me to come up with a custom design for the CP 16... it comes out to be about a 60%.  It still gets me up to hull speed in a blow (with mannerly control of the boat).  In order to save my new light air main.  I was using my original Johnson main in heavy air with a boom roller reefing.  Combined with the new storm jib, I experimented with different luff lengths in different wind conditions and made measurements.  What we came up, National now calls their CP 16 heavy air main.  It is loose footed (when you reef, you lose the foot rope anyway) and I changed the dimensions a bit to keep the forces low on the boat.  I shortened the luff by 3" and lengthened the foot by 8" and removed the roach.  It has two reef points...  The first reef point takes out 3 1/2' of luff and the second reef takes another 3 1/2'.  I have used this combination in some pretty strong conditions and the boat handles great... Hull speed plus without the fear of a knockdown.

Back to the "lowers"... although they are not really lowers because they have the same attachment point at the hull.  They DO have a different place along the mast though, and here's where it helps.  When we reef, we are placing most of the lateral strain on the middle of the mast.  The shrouds are 7/8 to the top (almost the top).  Thus, I saw an improvement in performance and less tension in the nerves of the skipper from not seeing the mast bend 6" off center each way on a beat.

I just added some pics of the new main... here's the link...

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/826731363/view?picmode=&mode=tn&order=ordinal&start=21&count=20&dir=asc

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/826731363/view?picmode=&mode=tn&order=ordinal&start=21&count=20&dir=asc

Also a couple of pics comparing the Storm Jib to the Genoa.

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/236597013/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

http://groups.yahoo.com/group/com-pac/photos/album/712582202/pic/2138080087/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

Happy sailing

Dale

[multimedia_smith]

The photos are posted on the "other" ComPac site here:
http://groups.yahoo.com/group/com-pac/
go to "photos" here:
http://groups.yahoo.com/group/com-pac/photos/album/0/list
and then, my album is called  "1988 Sweet Little 16 Projects"... you'll find the pics there.  We used to have a gallery here, but it seems to be gone.  I clicked on the links in the reply post and they work for me... it might be due to the fact that I'm registered there, but you can go to the site without doing that.
I looked up the photo that had the dimensions.  Dirk Sharland at National has it on file as one of their items now... it's listed as:  Inventory #3296 Compac 16 Heavy Jib.  The dimensions (in meters) are: Luff 3.36m, Leech 2.44m, Foot 1.83m, Weight 6oz
(in the pic, their "1" looks like a "7", but the Europeans put a line through the 7 to avoid mistakes.  You can clearly see the label in the picture of the overlay.
Since I now use that sail for anything over about 16kt winds, the boat can handle GRACEFULLY pretty high winds while other folks are hanging on... overpowered... Yes, it is fun to go out while others are heading in... What's wrong with us?  Wheeee!
Happy sailing to you...  Our season is about to begin in late september as yours is winding down.... can't wait 'till fall.

Dale

[Steve Ullrich]

Well... I get an error message that states that I need to be a member to see the pictures.  I needed another email address and account like I need another hole in my head but I signed up for one and requested membership in the group...  I'll get in eventually.

Your sailing season is just about to begin? Where are you?

The photos are posted on the "other" ComPac site here:
http://groups.yahoo.com/group/com-pac/
go to "photos" here:
http://groups.yahoo.com/group/com-pac/photos/album/0/list
and then, my album is called  "1988 Sweet Little 16 Projects"... you'll find the pics there.  We used to have a gallery here, but it seems to be gone.  I clicked on the links in the reply post and they work for me... it might be due to the fact that I'm registered there, but you can go to the site without doing that.
I looked up the photo that had the dimensions.  Dirk Sharland at National has it on file as one of their items now... it's listed as:  Inventory #3296 Compac 16 Heavy Jib.  The dimensions (in meters) are: Luff 3.36m, Leech 2.44m, Foot 1.83m, Weight 6oz
(in the pic, their "1" looks like a "7", but the Europeans put a line through the 7 to avoid mistakes.  You can clearly see the label in the picture of the overlay.
Since I now use that sail for anything over about 16kt winds, the boat can handle GRACEFULLY pretty high winds while other folks are hanging on... overpowered... Yes, it is fun to go out while others are heading in... What's wrong with us?  Wheeee!
Happy sailing to you...  Our season is about to begin in late september as yours is winding down.... can't wait 'till fall.

Dale

[multimedia_smith]

I'm on the North side of Lake Ponchartrain... Went out this weekend for the first time since the spring... GREAT! 
Post and Pics under "My Best Day Yet" topic here under the 16s posted a couple of pics there too.  (7.3 on the GPS.. Whoooo!)
later
Dale

[Al]

Hi All,

Have there been any updates on this topic ?

One of the things I love about the CP16 is it's heavy weather capabilities. However, after sailing several times in high winds, I also noticed the mast  bending 2 inches inboard when on a close reach. After further examination, it appears that when the sidestays are under tension they push the spreaders into the mast thus bending it like a bow and arrow. My solution is to take the spreaders off and tighten the shrouds. This should reduce the sideload on the mast, keep the mast in compression, and keep the standing rigging tight. I'll let you know how it works when I get out on the water. Has anyone else done this ?

Al

1990 CP16II

[skip1930]

Well when we use race are Star Boat we would induce a curve to our spruce spar by sliding the port and starboard rigging fore and aft for the perfect sail bend.
But on Com-Pac's forget it. Up and down is fine. You'll never induce anymore speed. And curving an aluminum mast with an extruded backbone internally is like peeing into the ocean to make it overflow. Hardly gonna happen with any beneficial results. But you guys go ahead and bend them up.

skip.

[Al]

Hi Skip,

I agree with you. The mast is designed to take load in compression not bending. That's why I took the spreaders off.

Al

[Bob23]

Al:
   You'll have to ask yourself: If the spreaders were a bad idea, why did Compac add them to the 16? If I'm correct, 16/1 did not have spreaders but your's does. I believe your problem is an incorrectly tuned rig. Be careful of over tightening the shrouds...you could cause some damage as you put too much downward pressure (compression) on the mast and thus the deck it sits on. Except for the additional set of lowers, my 23's rig is just like yours, only a bit bigger. When tuned correctly, my leeward shrouds are a tad loose while sailing. I'd call Hutchins about this...
Bob23

[mattman]

Hi all, I have read this thread 3 times trying to figure out what you all are seeing. Here is what I think you are describing on the compac 16 only.

1 on a nonspreader rig in heavy air, the top of the mast can fall off due to pressure above and no support, the windward shroud will stretch some and the bottom load on the  sail may fall off in the lower part of the mast (athwartship bend). (We see this in a headstay, the luff of the sail will originally have a bit of an "s" cut into it to give the optimal shape with the optimal tension and wind strength). Shroud tension might effect how much fall off you would see. Mainsheet tension can put some fore and aft bend into the mast due to the fractional rig. By doing so you are taking some belly out of the mainsail and depowering the main some. Note also that the mast column falling off to leeward is also taking draft out of the main but also moving the leading edge of the luff leeward. 

2 on a spreader rig, no lowers, shroud tension increases would put a prebend into the mast (fore and aft) taking draft out of the main,  the top of the mast can fall off as described above. With the mast at rest I believe that the spreader is in compression from the force of the bend resistance on the mast, but when sailing in really heavy air could be in tension, helping to hold the mast in column depending on the amount of prebend put in and the amount of stretch in the shroud. (I have never sailed a rig like this just visualizing the forces there to the extreme).

3 on a spreader rig with lowers added, everything applies however, the lowers take the tension for mast column and the spreader are in compression helping to reduce the top of the mast from falling off. Sail shape is built in accordingly.

In summary regarding our cp16's,
1 I would think hand tight on the turnbuckles is about right, I can't imagine the need for pliers and crewdriver for leverage.

2 If you think there is too much force on the mast reduce sail.

3 Lowers seem unnecessary however I don't see them as not helping-and although I would not add them to my 16 if they were there I wouldn't get rid of them.
Although the nonspreader boats do not allow for prebend in the mast, prebend is a way of getting closer to a hyperbola shaped foil which is the shape that is most efficient for drag giving a more efficient sailplan. ( I read that somewhere years ago, a discussion on foil shape and compromises therein would require more coffee this morning and not be relevant to this thread )

4 To really get and idea of shroud and spreader interplay, spend an hour looking at some of the mid 80's Hunter B@R rigs. You could spend all day chasing loads on one of those, but they do hold a relatively light spar in place with the proper shape, and makes a standard 8 stay rig child's play.

Thanks so much for this forum, I really enjoy you guys.
Happy Sailing.



 

[Al]

Hi All,

Unfortunately I didn't make it to the lake this weekend to see if the mast bent less without the spreaders. For those of you without spreaders, does your mast bend side to side when sailing in high wind ?

Al

Clarification: My mast does not bend like a fishing pole, it bends like a bow and arrow with the spreader being the arrow. Mast fixed on top and bottom, bent at spreader.

Note: The spreader appears to be in compression at all times except when dangling on the leeward side.