Discussion Some Rigging Questions

[SHAFT2]

I’m currently building a Graupner Saphir and have a few sail rigging questions I was thinking of adding an adjustable outhaul to the main and a jib lifting line on the jib boom, has anyone experimented with lowering the booms closer to the deck or making the boom height adjustable? My sailing experience is not from the RC world but from sailing dinghies which have more adjustments to shape the sails.


1. I was thinking about making the main boom/ gooseneck assemble adjustable on the mast to raise and lower the boom off the deck this was a good option when sailing dinghies but I don’t see it on RC sailboat builds, is this a worth while modification?

2. Is there a formula or a certain distance that a ridged boomvang should be installed below the main boom gooseneck on the mast?

3. Is jib boom lifting a useful modification?

4. The jib boom pivot point currently attaches to the deck with string, will a ridged pivot point work, does it need to be flexible?

[boater_dave]

Good questions.
1. Since the main is loose footed, you don't need to raise and lower the boom. Fix the boom and install a downhaul. If you must, try something like the first pic.
2. No formula that I am aware of. The bigger the angle the more advantage you have. I've seen booms set up like the giant cats, where the boom goes on an angle from the mast base to the clew. They use a strut on top to control the angle. Your choice.
3. Jib boom lifting? As in topping lift? Yes. Seperates jib leech tension from backstay tension.
4. Jib swivel. I use stainless ball race fishing swivels. Cheap and easy. It's nice that they articulate as well as swivel. Some boats use a rigid pivot, meaning the jib boom rotates around a fixed shaft. You still need an adjustment for the jib leech, usually a set screw. More complex, so it's used on the bigger boats.

[SHAFT2]

Thanks for the reply Dave, I finished the boom vang and built an adjustable boom set up similar to the pic you posted, it should work pretty good the main thing I wanted to do was lower the main sail it seemed extremely high and all these modifications I'm doing will be reversible back to stock if my workbench engineering fails. I assume by your post that if a loose footed main needs to be adjusted up or down you would raise or lower the sail on the boom?

[Dick L.]

I assume by your post that if a loose footed main needs to be adjusted up or down you would raise or lower the sail on the boom?

Ummmm - not necessarily. The common acceptance of the term "Loose Footed Main" generally means the sail is only attached at the tack (next to mast) and clew (end of boom) - as sails often were (and are in some one-design classes) inserted into a groove on top of the boom - much like the luff is inserted into a groove on the mast.

If you want your mainsail to be adjustable from the deck up - then the gooseneck boom fitting and the vang will need to be able to "float" or slide up and down on the mast.

In most r/c classes, the boom gooseneck fitting to the mast is fixed, and the sail is raised using a halyard that usually only goes "up" to the top of the mast. Further adjust is made using a downhaul which pulls the front edge of the mainsail tight, can add mast bend and shifts the maximum camber slightly forward. Add in clew outhaul, and you begin to flatten the sail providing a bit more speed, but sacrificing power to "punch" through waves.

Everything tends to work together to all control over the sail shape. It is hard to adjust one thing which doesn't have an effect on something else.

........ the fun and challenges of sail trim and tune .......

[SHAFT2]

Thanks for the reply Dick, I’ve been doing some reading on rigging and sail trim could you guys check me to see if I have this right.

1. Jib boom counter weight – helps the boom to achieve a balanced swing and counters the aft of the pivot weight of the boom and sail.

2. Topping lift – in light air this takes the tension off of the leech by raising the boom aft of the pivot to help shape the sail which creates sail twist.

3. Jib halyard – shapes the luff of the jib and would need to be adjusted according to weather and if the jib stay tension changes.


Now the questions

1. What exactly does adjusting the jib stay do, it appears to me it would change the angle of the jib boom from horizontal and would be adjusted in opposition to the topping lift, or is this something which is adjusted and left alone or do you adjust this according to wind conditions?

2. Could you use a ridged boom vang to push up on the main sail boom to take the tension off of the leech helping to shape the sail in light air or does the vang only pull down on the boom to flatten the sail?

3. If the answer to # 2 is yes could you use a ridged pivot post to attach the jib boom to the deck and a ridged boom vang to the jib boom to push the jib boom up to shape the jib in place of a topping lift, would you ever want to flatten out a jib like you would the main in heavy air?

[boater_dave]

Can I jump in again? First, let me say that I think you have grasped the concept of all this in a very short time. I think you got all three right.
Now your questions.
1. Adjusting the jib stay, along with the back stay, allows the mast to be raked fore/aft to achieve a sailing balance in the boat.
2. Yes. And there are several available over the counter.
3. If you use a rigid pivot on the jib, all you need is an adjustment to be able to tune the leech. This could be a rigid vang, but on the units I've seen it is a simple set screw. You could instead have an adjustable line on the clew end of the boom, in addition to the outhaul. And yes, you flatten the jib for the same reasons.
When usinig a radial jib swivel, it's the difference in angles between the deck & pivot and pivot & boom that will push the boom up as it swings out over the side. It's like having an adjustable vang without the extra channel.
Dick, did I miss anything?

Dave

[SHAFT2]

Originally Posted by boater_dave

Can I jump in again?

Absolutely Dave ! Thank you, this post is for anyone how cares to comment and help to further my education on the technical do’s and don’ts of sailing. I learned to sail in an El Toro when I was around 9 or 10 , you pulled the rope, pointed the wood handle and you were off across the lake so this technical stuff is all Greek to me.