Thread: GIS Yawl

Thanks Robert.

I wasn't clear enough with my question. Let me try again.

When rigged as a yawl, the mainmast is moved forward and the mizzen is added. I understand (I think) the moving of the mainmast is to keep the CE in approximately the same place as it is with just the lug'sl (or is this not right?).

What happens to the CE in the yawl rig when the main is reefed? Is the mizzen reefed, too?

(If that doesn't make sense, I'll try again. )

Howdy Bob,

Generally the mizzen is assumed to be only producing about 50% or a bit more of its area in the calculation for the centre of effort.

This is for two reasons.

The mizzen is working in the deflected and sometimes turbulent air from the mainsail reducing its efficiency.

As a failsafe - in a sense the calculation assumes the mizzen is sheeted easy and is luffing a little. This means that if the balance calc is a bit out (it always is because it is a rough approximation) then the mizzen can be sheeted out a little or sheeted in a little to get the right real balance.

So when the main is reefed then the mizzen can either be reefed or just the sheet eased.

It is a little bit more complicated than that though, because on a run (wind behind) the mizzen will cannot be depowered. One of the factors with the RAID41 that went in the Texas200, that year a very blowy event with strong winds from behind averaging 20 to 25+, that the unreefable mizzen and reefed main may mean there is too much sail at the back of the boat.

This will tend to make it round up.

In that case I would reef it, or roll it around its leach to get rid of it completely and proceed under main only. Or if looked like days of tricky downwind sailing, just move the mast back to the original hole so the boat will have its original mainsail only balance restored.

MIK

Here we are with a reefed main and full mizzen. Our mizzen can be reefed, but as of yet we have not sailed with it reefed. You can just see the mizzen reef points above the main boom. This was a very comfortable sailing arrangement for us.

I have sailed GIR with reefed main and full mizzen when I wish I would of rolled the mizzen around it's mast and moved the main mast back to it's aft location. It was a deep reach with the gusts hitting 20 knots and big very cold waves. During those conditions the mizzen was sheeted just enough to keep itself from flogging too much. In the biggest gusts I could feel the boat try to change direction slightly, but never a out-of-control roundup.

We never rounded up, but the mizzen sure was noisy from the flogging. That was ok for an hour, but on a long sail it would of been very distracting/fatiguing and hurt the sail in time.

I plan on trying a mizzen reefing system that allows me to roll the sail around itself. Something like: release the sheet, pull the snotter off, then rotate the mizzen mast until I have rolled up some of the sail. I think I can pull the sprit off or have some type of way to rehook the snotter. Last thing I want to do is hang off the transom trying to retie the clew onto the sprit.

Originally Posted by Boatmik

In that case I would reef it, or roll it around its leach to get rid of it completely and proceed under main only.

Just right - in strong winds and running, the mizzen should be reefed or completely dropped - just like we run with the wind under the jib only on sloop rigged boat.

Originally Posted by john goodman

Here we are with a reefed main and full mizzen. Our mizzen can be reefed, but as of yet we have not sailed with it reefed. You can just see the mizzen reef points above the main boom. This was a very comfortable sailing arrangement for us.

Just like me - usually sailed under reefed mainsail and under full mizzen:



and I saw that Boatmik doing it also:

Thanks for the explanations. I learned quite a bit reading this entire thread and your additional explanations help.

My understanding so far:

1. The yawl rig requires the main mast to be moved forward to adjust the CE to account for the mizzen (sail area and placement);
2. The mizzen's sail area is discounted somewhat (50%?) for a number of reasons in calculating the CE for the rig;
3. The mizzen doesn't really add driving power - except downwind and then you don't want it because it can cause the boat to head up;
4. When the main is reefed the mizzen can be eased, trimmed, reefed or struck depending on circumstances (although, if the mizzen is struck the main mast should be moved aft).

What I don't fully appreciate is why - if the mizzen (even the discounted sail area) is enough to require moving the main forward - doesn't reefing the main (reducing sail area by considerably more than the total sail area of the mizzen) substantially affect the CE requiring moving the main aft? (I realize that question is poorly written but hopefully it makes some sense? Or am I just not getting 'it?')

Thanks for the help.

Bob,
Please note: modern yachts have rejected the concept of yawl rig - they are mostly rigged as a sloop.

Originally Posted by BobWes

What I don't fully appreciate is why - if the mizzen (even the discounted sail area) is enough to require moving the main forward - doesn't reefing the main (reducing sail area by considerably more than the total sail area of the mizzen) substantially affect the CE requiring moving the main aft?

I'm just guessing here, but it might be due to careful design by MIK in the first place, or possibly an inherent feature of the Balance Lug?

With the single mast, original design you reef the lug without shifting the CE fore or aft enough to affect the helm's balance. That same characteristic holds true in the Yawl set-up. I agree it's not intuitive. But it makes sense in light of the fact that the main doesn't normally need shifting when reefed.

Okay, it isn't intuitive. Having read quite a bit about the yawl rig for small boats, I think I understand the benefits of the rig.

Let me ask a different but related question: what size yawl configuration (main sail area and mizzen sail area) would work using the original (lug only) mast position? Hey, I realize that (reduced sail area) probably means less "performance" that the full size rig but that may be okay for me. OTOH if the original mast position dictates a ridiculously small main, too much performance would/could be lost.

I'll do some research to see if I can answer my own question (seems to me I have seen explanations of the math involved - hopefully, I can find those again) but I'd appreciate additional input.

Thanks.

Originally Posted by john goodman

I plan on trying a mizzen reefing system that allows me to roll the sail around itself. Something like: release the sheet, pull the snotter off, then rotate the mizzen mast until I have rolled up some of the sail. I think I can pull the sprit off or have some type of way to rehook the snotter. Last thing I want to do is hang off the transom trying to retie the clew onto the sprit.

The best way of getting rid of a sprit sail can be to roll it up around its own leach.

Unhitch the snotter and let the sail stream downwind and roll it up around the leach with the boom inside. Or the boom can be placed parallel with the mast creating a fold in the mizzen and then wrapped up with the fold at the centre.

The sail can then be held to the mast with a single tie - or maybe two in stronger winds.

It can then be unrolled with no need to reattach the sprit boom to the clew (no reaching back over the transom)

MIK

Originally Posted by robhosailor

Bob,
Please note: modern yachts have rejected the concept of yawl rig - they are mostly rigged as a sloop.

Pure racing rule and fashion related.

In the best of all possible worlds the handicap calculation rules would give any rig equal chance - but the problem is that mizzen masts are a really nice place to add more sail area when reaching - assuming a big enough gap between mizzen and main mast - so it is difficult to make sloops and ketches compatible in ocean races. Ie treat both fairly in all conditions.

MIK

Originally Posted by davlafont

I'm just guessing here, but it might be due to careful design by MIK in the first place, or possibly an inherent feature of the Balance Lug?

With the single mast, original design you reef the lug without shifting the CE fore or aft enough to affect the helm's balance. That same characteristic holds true in the Yawl set-up. I agree it's not intuitive. But it makes sense in light of the fact that the main doesn't normally need shifting when reefed.

Maybe I am not explaining well now!

When racing a mizzened boat you trim the mizzen the right amount to get the helm balance you want.

The good guys on a sloop rigged keelboat will do the same - the guy trimming the mainsheet in gusty weather will watch how much helm the skipper needs and trim in or out to keep it about the same.

Same with the mizzen. Upwind to keep about 2 to 4 degrees tiller angle to counter weather helm. Reaching - ease in the gusts so that the rudder doesn't have to go to silly angles to keep the boat running straight.

It is a dynamic balance. When the main is reefed it doesn't change anything - just means when the same helm balance is aimed at that the mizzen will be a bit (or a lot) more eased.

The problem point comes with reaching and running when it may not be possible to ease the mizzen out far enough to keep the helm in balance without it going too far (boom out farther than 90 degrees) and starting to create a windward roll situation.

That is where reefing or dousing the mizzen will become useful. It could be allowed to flog - but not a good strategy for long term.

MIK

MIK

Originally Posted by BobWes

Okay, it isn't intuitive. Having read quite a bit about the yawl rig for small boats, I think I understand the benefits of the rig.

Let me ask a different but related question: what size yawl configuration (main sail area and mizzen sail area) would work using the original (lug only) mast position? Hey, I realize that (reduced sail area) probably means less "performance" that the full size rig but that may be okay for me. OTOH if the original mast position dictates a ridiculously small main, too much performance would/could be lost.

I'll do some research to see if I can answer my own question (seems to me I have seen explanations of the math involved - hopefully, I can find those again) but I'd appreciate additional input.

Thanks.

That was an experiment I was kinda interested in the result of.

The Goat's sailing balance is so close to neutral that I think even the standard rig could handle a mizzen. Add the possibility of moving the mainsail a little forward relative to the mast and it might just work out nicely. There are real limits to how much the main can be moved forward because of not being able to move the halyard block position on the yard further back than halfway.

Particularly if the mizzen is not too big. But that is all experimenting - which maybe John can try out some time. The best approach for a first attempt was to have two alternative mast positions - that way it was less likely to turn out to be a cow. And if it did the mast could be moved to make it balance again under the original rig.

MIK

Would it make sense to keep the original mast step, but make the centreboard case wider at the top so you can pivot the centreboard a bit and move it's centre of effort back a bit when the mizzen is in place? Perhaps an easier mod to make to enable adjusting the balance to take account of the mizzen than adding an extra mast step forward of Bulkhead 1.

Ian

That's certainly another mod that is possible.

MIK