400: Square top mainsail

[jbinbi]

don't have sq top main and it still catches on lazy jack lines if not careful raising it.

have yet to see a lagoon with a vang.

do wish i had the sq top main for the light air days. I would say to go for it!

[DavefromNZ]

Leisure Furl on Lagoon 450?

http://www.cruisersforum.com/forums/...d.php?t=132743

Can see a vang on a L450. It works well.

[SecondBase]

A couple basic questions-

Would a standard shaped mainsail and a square top mainsail of equal square footage generate approximately the same propulsion or is there some ratio?

Is there any type of upper length limit on the higher battens? E.g. A large crushing sloop with a 22' boom and want to convert to a square top.

[belizesailor]

Originally Posted by SecondBase

A couple basic questions-

Would a standard shaped mainsail and a square top mainsail of equal square footage generate approximately the same propulsion or is there some ratio?

Is there any type of upper length limit on the higher battens? E.g. A large crushing sloop with a 22' boom and want to convert to a square top.

Same square footage I expect would be about the same drive. To actually make them the same square footage would be a bit contrived, since one reason for increased roach/square head is increased sail area. For for a given boat the square top/big roach main with have more sail area.

[UNCIVILIZED]

Originally Posted by SecondBase

A couple basic questions-

Would a standard shaped mainsail and a square top mainsail of equal square footage generate approximately the same propulsion or is there some ratio?
The square topped one will generate more power, as it has a better lift to drag ratio. Meaning it's aerodynamically more efficient (per square foot of sail area).

Is there any type of upper length limit on the higher battens? E.g. A large crushing sloop with a 22' boom and want to convert to a square top.
In theory the upper limit is somewhere in the neighborhood of 2/3rds of the sail's foot measurement. But it depends on the sail cloth, battens, batten hardware, & a few other things. Plus, of course, money.

Back to the topping lift question/debate. Assuming that you have a way to mount the blocks for your lazy jacks in a manner which is structurally strong enough, you can use the lazy jacks in lieu of a topping lift. Though you'll need to adjust them with each tack, so as not to impinge on the sail's shape.

[Stumble]

Originally Posted by SecondBase

A couple basic questions-

Would a standard shaped mainsail and a square top mainsail of equal square footage generate approximately the same propulsion or is there some ratio?

Is there any type of upper length limit on the higher battens? E.g. A large crushing sloop with a 22' boom and want to convert to a square top.

As Uncivilized mentioned a square top of the same sail area produces more power and less lift. The bigger the top the larger the gains. However as the sail gets more rectangular the sheet loads start to climb quickly. Much past 2/3 the foot length and you have to start rethinking the travler attachment, sheet blocks, adding extra purchase... But a 2/3 of the foot length top is a massive roach on the sail. The only boats that I know that are even close to this size are strict race boats with very developed sail plans.

One thing that is a bit different is that the extra sail area need some to be taken into account to rethink the reef points. Typically the reefs will need to be shuffled a bit to keep the sail area reductions by percentage the same. Square tops add a lot of sail area high up so deeper reef points are a good idea.

[tuskie]

Originally Posted by jbinbi

don't have sq top main and it still catches on lazy jack lines if not careful raising it.

have yet to see a lagoon with a vang.

do wish i had the sq top main for the light air days. I would say to go for it!

Yes, mainsail battens catching on lazy jack lines during sail hoisting is something not peculiar to square top sails. A bit of a red herring to this thread.

On the L400 the lazy jack lines lead to the mast below the first spreader, giving a narrowing gap between each set of lazy jacks. This setup is easily modified by reattaching the underside of the spreaders or pulling out the lines to the diamonds using small blocks. I've done the latter and have less batten hookups during mainsail raising.

Vangs may be appropriate for some Lagoon models, especially if retro fitted with inboom furlers, but not appropriate or necessary for a L400 with or without a squaretop main.

[UNCIVILIZED]

Originally Posted by Stumble

As Uncivilized mentioned a square top of the same sail area produces more power and less lift. The bigger the top the larger the gains. However as the sail gets more rectangular the sheet loads start to climb quickly. Much past 2/3 the foot length and you have to start rethinking the travler attachment, sheet blocks, adding extra purchase... But a 2/3 of the foot length top is a massive roach on the sail. The only boats that I know that are even close to this size are strict race boats with very developed sail plans.

One thing that is a bit different is that the extra sail area need some to be taken into account to rethink the reef points. Typically the reefs will need to be shuffled a bit to keep the sail area reductions by percentage the same. Square tops add a lot of sail area high up so deeper reef points are a good idea.

Any thoughts on inner forestay(s) placement, & rig design, to counter what must be some rather extreme, aftwards, headboard loads generated by these sails? With regards to where the reef points in them are I mean. Since on a fair percentage of rigs, the heavier air reef points (#2, #3, etc.) tend to correspond to where inner forestays are connected to the front of the spar, so as to prevent the mainsail headboard loadings from inverting the mast.

[tuskie]

Originally Posted by UNCIVILIZED

Any thoughts on inner forestay(s) placement, & rig design, to counter what must be some rather extreme, aftwards, headboard loads generated by these sails? With regards to where the reef points in them are I mean. Since on a fair percentage of rigs, the heavier air reef points (#2, #3, etc.) tend to correspond to where inner forestays are connected to the front of the spar, so as to prevent the mainsail headboard loadings from inverting the mast.

Why on earth would you wish to modify a rig that is already designed for a square top main?

The mast of a L400 is quite substantial and in addition is reinforced with 10mm double diamonds and 2 × 10mm "martingales" or "front diamonds". These martingales would probably interfere with an inner forestay if one was silly enough to try to meddle with a rig that is properly designed and fairly bullet proof.

[Stumble]

Originally Posted by UNCIVILIZED

Any thoughts on inner forestay(s) placement, & rig design, to counter what must be some rather extreme, aftwards, headboard loads generated by these sails? With regards to where the reef points in them are I mean. Since on a fair percentage of rigs, the heavier air reef points (#2, #3, etc.) tend to correspond to where inner forestays are connected to the front of the spar, so as to prevent the mainsail headboard loadings from inverting the mast.

On the L400 the rig was designed for a square head, so no real change. If anything rig placement could be an issue now...

Generally you see the first reef on a big square head being relatively shallow, almost more of a nighttime reef than a true deep reef. It's been a while, but iirc the first reef on Comanche, for instance, is about 6' or less than 5% the luff. Then you get into deeper reefs to depower.

Personally I think forums overthink the issues with reefs lining up with rigging. I can't think of any articles or discussions where it was even raised amongst professionals (saying this i am sure someone will point one out). It is just in a few very exceptional cases where it can be linked to a rig failure, and even then I have my doubts about how they relate.

I am not saying it is impossible to see inversion from headboard loads, but I can't think of a boat I have been on where it was an issue. To the extent it could exist square headed mains should limit it since the higher leech tension tends to add mast bend not reduce it. I might be a little hesitant about a reef point right at an unsupported bend apex, but that's it.

[UNCIVILIZED]

I wasn't posing the question with Lagoon's in mind at all really. But rather, generically. And some of it was based on some wicked cases of mast inversion that I've seen due to mainsail loadings in mast panels which weren't anywhere near strong enough to support them.
The fact that the masts in question didn't outright fail was due to the quick actions of the crew, & to that alone. Though despite this, several of these spars had to be rebuilt after said incidents.

[Stumble]

Originally Posted by UNCIVILIZED

I wasn't posing the question with Lagoon's in mind at all really. But rather, generically. And some of it was based on some wicked cases of mast inversion that I've seen due to mainsail loadings in mast panels which weren't anywhere near strong enough to support them.
The fact that the masts in question didn't outright fail was due to the quick actions of the crew, & to that alone. Though despite this, several of these spars had to be rebuilt after said incidents.

I am not saying it can't be an issue, just I think it I should generally overblown. The biggest fear would be a reef that puts the head of the sail just at the apex of the rig, without a babysta to keep the mast from pulling back. But it would take a massive amount of preassure to invert a well tuned rig, that is appropriately tuned for heavy weather.

My guess is that the instances where inversion happened occurred with a rig tuned for much lighter winds, then when a deep reef was put in for heavy weather the shrouds weren't putting enough preassure on the rig. In other words, tune for 15, get caught in 45, and all sorts of weird stuff is going to happen. Where exactly the headboard is may play a part, but if the rig was properly tuned for 45 in the first place I still doubt it would be an issue.

So for rig design... If the rig is being treated properly no I don't think it is a major issue. If the rig is not going to be treated properly then additional redundancy may be needed.

[meirriba]

Originally Posted by UNCIVILIZED

Any thoughts on inner forestay(s) placement, & rig design, to counter what must be some rather extreme, aftwards, headboard loads generated by these sails? With regards to where the reef points in them are I mean. Since on a fair percentage of rigs, the heavier air reef points (#2, #3, etc.) tend to correspond to where inner forestays are connected to the front of the spar, so as to prevent the mainsail headboard loadings from inverting the mast.

While it may be of interest for some boats the L400 has no inner stays.

[arsenelupiga]

Originally Posted by UNCIVILIZED

I wasn't posing the question with Lagoon's in mind at all really. But rather, generically. And some of it was based on some wicked cases of mast inversion that I've seen due to mainsail loadings in mast panels which weren't anywhere near strong enough to support them.
The fact that the masts in question didn't outright fail was due to the quick actions of the crew, & to that alone. Though despite this, several of these spars had to be rebuilt after said incidents.

my guess is mast is bent more than other boats on L 400 so that inner shrouds can counter inversion forces better.

[Factor]

just do it