Loose-Footed Main

[savoir]

Originally Posted by Ex-Calif

Im currently with cwyckham on this. But don't get me wrong. I would sell him out for a twinkie ;-)

Hypothetically lets have a loose foot main and sheeting 3/4 out the boom.

The boat is sailing at 7 knots. That requires X sail pressure. The main load is perpendicular to the lift, hopefully forward of the beam so the boat is going forward not backwards.

The mainsheet counteracts this load. It should be obvious that 75% of the load is forward of the sheet and 25% is aft.

Aft of the sheet the boom is trying to break off downwind. Forward of the sheet it is too. But it is restrained at the tack. The load should be centered between sheet and tack trying to fail the boom in the middle.

After reefing the boat is still observed to be going 7 knots. X must still equal X. Higher windspeed is the reason. Therefore the load on tack and clew must still be X.

After reefing lets say the clew is now adjacent to the mainsheet for our test case.

100% of X is now carried between sheet and clew. Boom load forward is actually higher! Boom load aft is less except outhaul load which is probably constant.

Comparing race boats with carbon fiber spars and huge rig loads and need for lightness is probably not useful for us.

Could you sleep on this post and try again tomorrow or something ? The rationale is seriously dodgy.

[s/v Jedi]

About the "every reefed sail is loose footed" statement; this is true of course but also over simplified. First, one should tie a line around the boom to the leech reef point when reefed and I suppose we all do that right? Now, we have brought the force from the clew forward on the boom, shortening the arm or span of the boom. Here we also have the reason why it is always advised to tie that line there: it drastically reduces failure rates.

With modern, roached sails the reef point barely comes forward, that's true. On my main we're talking about 1 foot for 3 reef points (!). But these designs are generally loose footed by design and thus the conversion to loose footed is irrelevant (boom is already dimensioned for it).

Related is the "same heel when reefed so same forces involved" idea. That is also a fable for the same reason: the arm has shortened and thus much higher forces are needed for the same heel angle.

We're getting close to drawing vector diagrams now

ciao!
Nick.

[GorillaToast]

Originally Posted by psk125

No one seems to have mentioned one additional plus for a loose foot. Besides all the other ones, a loose foot should cost a good bit less than a "standard" foot. We switched about 8 years ago.

When getting quotes for my Catalina 22, such was not the case. "Loose footed" was an "option" that cost more. Maybe if I was dealing with custom measured and made sails from a smaller loft that might be true.

[delmarrey]

Originally Posted by s/v Jedi

I find the piece of track on the end of the boom the best way to go when changing to loose footed.

When I'm running before the wind I run the boom out about 45º then bring the car forward just enough to keep the sail off of the shrouds, allowing the mainsail to balloon out, and that's when I tighten up the foot cunningham and create the belly. Depending on the wind I'll attach a preventer forward to keep the boom steady and use the car/outhaul for adjustments.

The naysayers can say what they want but I do have a 16.5' boom and I've seen the bend in that thing, even with end sheeting. Mostly due to the vang I'm sure, but I can imagine it with centered sheeting. One thing I've learned right off was to release the vang pull when going before the wind and move the traveller to the lee to pull the end down rather then the vang in the forward 1/3. I've pulled the rivets from the vang attachment once already rounding a bluff when I got hit with a strong gust. The forces on these big sails are nothing to play with.
The last picture is a cut-off section of the boom.


.

[s/v Jedi]

Originally Posted by delmarrey

When I'm running before the wind I run the boom out about 45º then bring the car forward just enough to keep the sail off of the shrouds, allowing the mainsail to balloon out, and that's when I tighten up the foot cunningham and create the belly. Depending on the wind I'll attach a preventer forward to keep the boom steady and use the car/outhaul for adjustments.

The naysayers can say what they want but I do have a 16.5' boom and I've seen the bend in that thing, even with end sheeting.
[...]
I've pulled the rivets from the vang attachment once already rounding a bluff when I got hit with a strong gust. The forces on these big sails are nothing to play with.

The forces on boom are always underestimated because most people "feel" how much tension is on the sheet and think that's it... while it is just one of three parts and the smallest one most of the time.

What is really underestimated is the forces on the gooseneck attachment. There are many failures there and I see so many on boats that are about to break without the owner even aware of the problem. Some I would question on a small open sailboat.



ciao!
Nick.

[skipmac]

Originally Posted by s/v Jedi

The forces on boom are always underestimated because most people "feel" how much tension is on the sheet and think that's it... while it is just one of three parts and the smallest one most of the time.

What is really underestimated is the forces on the gooseneck attachment.

Well, it may be a coincidence, but I have had two rigging failures in my sailing career, one was a gooseneck, the other a slide on the genoa track which produced some serious SS shrapnel.

[Bash]

Originally Posted by cwyckham

First reef Cringle is about 6" closer to the mast on my main. Hardly going to make a difference.

That's called a "flattener reef." While it doesn't reduce the sail area much, it will significantly alter the shape of the sail, helping not only to flatten it but also to make it point higher.

Play with that reef, and you'll find it can make a huge difference.

[s/v Jedi]

Here's my main with reefs 2 and 3 visible, first reef is just under bottom of picture. As you can see, the leech is almost vertical and reef points are all within 1 foot forward of the clew.

p.s. wow, those were pretty blue skies... Gulf of Mexico 2002.

ciao!
Nick.

[Ex-Calif]

Originally Posted by s/v Jedi

We're talking loose foot right? Then the clew is aft on the boom and the tack is on the gooseneck fitting, making the clew the only point where force is put onto the boom. This force is countered by three other attachments: gooseneck fitting, vang fitting and sheet attachment. The brunt is taken by the gooseneck fitting because most of the load is compression forces (the sail tries to collaps the boom). The sail also tries to lift the boom in it's 2nd dimension want of collapsing. This is countered by the vang and that is the point of failure I've most often seen with broken booms. If the boom isn't ridiculously thick-walled, you need a reinforcement sleeve inside the boom around the vang attachment... like 4' long, to spread the load, with tapered ends etc. now the last attachment, the sheet. this counteracts the force that wants to swing the boom outwards. The failure most often seen here is that the fitting is pulled off the boom. That is why a rope around the boom attachment is better. If there is a single attachment point and it is at 1/3th from the end of he boom, the last 1/3rd is unsupported. This is more a problem with the clew attachment than with the sheet, but an often used solution to deal with it is two-fold:

- put a section of track on top the aft end of the boom and attach the clew to a car that trvels on that track. The outhaul also attaches to the car. This reinforces the boom and it distributes the force from the clew over a section instead of a point, just like the sleeve insert does for the vang.

- spread sheet attachment over wider area. There are two methods: using multiple blocks like the diagram posted earlier, or a single block attached with multiple webbings around the boom, or even a net or piece of sailcloth around the boom. I have multiple webbings with an aluminium spreader-plate which is somewhat dated

So, it's much more complicated than just force forward and aft of sheet. It is also more about spreading the load, while preventing ripped-off attachment point by wrapping around the boom. Don't forget the leech reefing lines that can also wrap around he boom with loose foot.

I find the piece of track on the end of the boom the best way to go when changing to loose footed.

cheers,
Nick.

All fair ponts Nick. I should have drawn it out on paper for clarity.

I guess I still dont see the argument that bolt rope vs loose foot is going to change it all that much. At least no one has espressed changing the boom or sheeting if switching.

All, things are good to consider though.

[savoir]

Originally Posted by s/v Jedi

Here's my main with reefs 2 and 3 visible, first reef is just under bottom of picture. As you can see, the leech is almost vertical and reef points are all within 1 foot forward of the clew.

p.s. wow, those were pretty blue skies... Gulf of Mexico 2002.

ciao!
Nick.

In the overall scheme of things the shape of that main is quite unusual. Not too many reading this would have one like it.

[estarzinger]

Originally Posted by savoir

In the overall scheme of things the shape of that main is quite unusual. Not too many reading this would have one like it.

Just for comparison . . . here is a pic of our sail with one reef in.

[colemj]

Originally Posted by savoir

In the overall scheme of things the shape of that main is quite unusual. Not too many reading this would have one like it.

Every catamaran owner here will have one just like it or with even more roach.

Mark

[Ex-Calif]

Originally Posted by savoir

Could you sleep on this post and try again tomorrow or something ? The rationale is seriously dodgy.

Sleep didn't help - LOL

[delmarrey]

Originally Posted by Ex-Calif

Sleep didn't help - LOL

Maybe you need to go back a few years. http://www.cruisersforum.com/forums/...tml#post106157

I think we're all getting to be like Romney.

[Ex-Calif]

Originally Posted by delmarrey

Maybe you need to go back a few years. http://www.cruisersforum.com/forums/...tml#post106157

I think we're all getting to be like Romney.

Changing the sheeting point is way more complex than changing the sail attchment type - IMO

I have lighlty perused sailmaker sites and no one is talking about big risks in changing to loose footed sails, and apparently a lot of folks are doing it.

Aesthetically some don't like Jedi's full roach sail. Some hate square head sails (they only look "right" on beach cats imo) I am considering full roach, square head, loose foot for my next main. I may stop short of square head as its kinda fugly...

But I live at the equator and <10 knots happens >70% of the time. I'd love to get more main sail, higher up to go with my 150 genny. Full roach, full batten and square head is about the only practical way to do that...