Mainsail Reefing Concept

sailingdog · Jul 7, 2009

I generally tie a bowline around the standing part of the line that goes up to the reefing cringle. This allows the reefed sail to come down as tight to the boom as possible.

Bob S said:
Can I ask a general question about reefing systems? What kind of knot do you use to tie the line to the boom?

Bob S · Jul 7, 2009

Thanks Dan, that's what i did. Another dumb question. My sail has three reefing points. As Stu said, Catalina's have a single line slab or jiffy reefing system. You have to pick one of the sets of reefing points. If you needed a deeper reef you would have to untie the whole system and set it up again. Not an easy task if it's blowing.

Paul J. Rusyniak · Jul 7, 2009

This single line set-up works well on our boat.
Paul

ChuckThomas · Jul 7, 2009

Phil, just my 2 cents. After you have reefed, put in a small safety line through the clew and around the boom. A friend had a similar setup and when the block failed the line went slack at the clew and the nettles ripped the sail like a paper shredder.
I think the reason most people go from the end of the boom, through the clew and back to the boom is for sail shape. It balances the shape of the leach and the foot. Similar to what the outhaul does.

sailingdog · Jul 7, 2009

A single line slab/jiffy reefing system doesn't necessarily mean there is only ONE reefing line. It usually means that there is a single line to handle both the clew reefing cringle and the tack reefing cringle. You could easily have a three reef main with three separate lines, one for each reef.

Bob S said:
Thanks Dan, that's what i did. Another dumb question. My sail has three reefing points. As Stu said, Catalina's have a single line slab or jiffy reefing system. You have to pick one of the sets of reefing points. If you needed a deeper reef you would have to untie the whole system and set it up again. Not an easy task if it's blowing.

sailingdog · Jul 7, 2009

Disagree all you want, but simple physics says that the downward force on the cringle will be less if you only have a line going aft, to the end of the boom, than if you have the line coming up from the boom to the cringle and then to the end of the boom—and it gets worse with the deeper reefs, since they are effectively pulling at a shallower angle, since they are further forward on the sail

I'd also point out that if you crank down on the line enough, you're far more likely to tear the sail than if the line goes to the boom—since all of the force is on the sail.

philwsailz said:
'Dog-

Show me measured tensile proof of your argument....

I respectfully disagree. I can apply as much force this way as if I went through the clew cringle; probably more based on my observations. The force to overcome the resistance of the line going through the clew cringle is substantial. Eliminate that source of resistance and I am able to apply all the force directly to the reef. The force on the line is greater yes, but well below breaking/tensile strength. The force holding the sail down and back is way more than sufficient, if not equal to going through the clew cringle considering losses.

The cringle ends up in the same place either way. There is absolutely zero negative effect to the shape of the sail in this instance. Remember this is a 22-foot boat. I would not advocate the same for a larger boat / larger sail without testing. It works for this sailor on this boat...

HEINZIR · Jul 7, 2009

sailingdog said:
Disagree all you want, but simple physics says that the downward force on the cringle will be less if you only have a line going aft, to the end of the boom, than if you have the line coming up from the boom to the cringle and then to the end of the boom—and it gets worse with the deeper reefs, since they are effectively pulling at a shallower angle, since they are further forward on the sail

I'd also point out that if you crank down on the line enough, you're far more likely to tear the sail than if the line goes to the boom—since all of the force is on the sail.

What am I missing here? SD's argument makes perfect sense if we are talking about a reefing line that just goes to the end of the boom. But in the picture it appears that the reefing line does not go to the end of the boom; it appears to go to a cheek block a bit forward from the end. If the block is strategically located so that the line from the sail comes at the correct angle (45 degrees?) the pull will be both down and aft. Cheek blocks for the second and third reef could be mounted farther forward to keep the pull both down and aft.

I had thought that the reason many boats are rigged with reefing lines that come straight up from the boom, through the cringle, and back to the end of the boom is to take advantage of built-in sheaves at the aft boom fitting which lead the lines forward internally. External cheek blocks are used on booms that do not have sheaves at the end. The cheek blocks can be located far enough forward on the boom so that the reefing line pulls both back and down. Harken "reefing kits" used to come with a short track so that the cheek block could be positioned properly.

sailingdog · Jul 8, 2009

Heinzir—

When the sail is in the position of being reefed, the line will be nearly parallel to the boom... and most of the force on the line will be aft, with very little in terms of a downward component, as seen here, unless his drawing does not accurately represent the location of the block in question.

The CYAN line represents the forces on the reefing clew cringle, and there is very little to oppose the upward component on that without the line going down and around the boom. This is basic physics... the loads on the reefing cringle will be multiplied by the fact that there is no downward line, and the sail will likely tear at or near the cringle without it in heavier winds.

If the block is further forward, it may in fact be located in such a position that the reefing line can be terminated at the reefing clew cringle without an issue, but from what I see on the drawings, as opposed to what was just posted by Phil, the reefing line would need to come down to the boom to work properly.

I'd also point out that bringing the line down and around the boom would allow the sail to be pulled down more centrally to the boom and not induce a torquing moment on the boom as would occur with the side-mounted cheek block alone.

HEINZIR said:
What am I missing here? SD's argument makes perfect sense if we are talking about a reefing line that just goes to the end of the boom. But in the picture it appears that the reefing line does not go to the end of the boom; it appears to go to a cheek block a bit forward from the end. If the block is strategically located so that the line from the sail comes at the correct angle (45 degrees?) the pull will be both down and aft. Cheek blocks for the second and third reef could be mounted farther forward to keep the pull both down and aft.

I had thought that the reason many boats are rigged with reefing lines that come straight up from the boom, through the cringle, and back to the end of the boom is to take advantage of built-in sheaves at the aft boom fitting which lead the lines forward internally. External cheek blocks are used on booms that do not have sheaves at the end. The cheek blocks can be located far enough forward on the boom so that the reefing line pulls both back and down. Harken "reefing kits" used to come with a short track so that the cheek block could be positioned properly.

HEINZIR · Jul 8, 2009

Thanks SD,

I see that Phil has corrected the drawing to show that the cheek block is directly in line with the CYAN line in your rendition. This is the way I have both reefs rigged on my boat. If I am reading the posts correctly, The difference in Phil's rig, compared to most, is that the reefing line does not pass thru the cringle (or block) and go back down to the boom; it terminates at the cringle. He did this to reduce friction and it seems to work for him.

There would be no torque on the boom if the line went through the cringle and terminated on the other side of the boom. There must be some torque on his one-sided set up but I believe that it is negligible. Remember, we're talking about small boats with no winches involved in the reefing system. His boat is basically the same size as mine and the boom diameter (I'm guessing) is only about two inches. I have had my reef lines pass thru the clew cringles for years but recently added light blocks (attached with shackles and rings as per your suggestions in previous posts) to both tack and clew reefing cringles. Both parts of the line from the aft block come down to the boom on the same side, one end to an eyestrap, the other thru the cheek block. Torque on the boom is definitely not a problem.

sailingdog · Jul 8, 2009

LOL... that's what you get for using MS Paint...Chaos and confusion.

Just didn't want you out there with a reefing setup that might result in a torn mainsail, which is what would probably happen if the block were where it was located in your previous drawing.

Given what you've said and the revised drawings... I don't see any issue with not leading the line through and down... since you should have sufficient downward force on the cringle.

philwsailz said:
Ahh...

Okay, dog, we are really on the same page, I think. As I look to what you have done with the drawing, indeed the cheek block is in a position on the boom that draws the clew cringle exactly to it. I apologize for the discrepancy in the location of the cheek block in my sketch.

My intent for this thread was to look at the options for the line and the path of the line, not the details of block position, else I would have spoken to it. My asssumption was that we all have a basic understanding of reefing and that the standing blocks would be positioned in a location appropriate for the task.

I appreciate your insight, and am glad that we are now to the root of the misunderstanding; rest assured the purchase angle at the clew cringle is appropriate.

So I guess your only real gripe with the enntire thread is that I used my MS paint to illustrate on top of a stock Catalina drawing, rather than firing up my SolidWorks to create a 3D solid assembly complete with accurate materials strength data and FEA stress and loading analysis? Sorry, had I done that I probably would have figured out that I drew the block in the wrong place... my bad..

Here is a modified pic, (still in MS Paint) showing the approximate location of the block.

Mainsail Reefing Concept

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