Loose footed main with Mid-boom sheeting

[Hayden Watson]

I have a C30 that has 6:1 mid-boom sheeting with 3-attachement points for the main sheet to the boom which is lead to a 16ST winch. The original sail plan had a typical bolt-rope footed main sail. In this configuration, I assume that there there is some upward force applied to the boom by foot of the sail which would not be there if the main is loose footed.
Is there any problem with using this type of boom / sheeting for a loose footed main sail? The boom is pretty robust. The section used is the same extrusion that was used as a mast for the C25 and they were never considered to have a wimpy rig.

 

[Richard19068]

I don't have a Catalina but do have essentially the same mid-boom mainsheet setup as you. I went from a bolt-rope to a loose foot main several (10?) years ago and have not noticed any unusual stress on the boom.

 

[rgranger]

I don't have a Catalina but do have essentially the same mid-boom mainsheet setup as you. I went from a bolt-rope to a loose foot main several (10?) years ago and have not noticed any unusual stress on the boom.

Same with my H26

 

[DrJudyB]

I assume that there there is some upward force applied to the boom by foot of the sail which would not be there if the main is loose footed.

The sail applies only a few pounds of upward force on the middle of the boom, which is not enough to make any practical difference. You can safely substitute a loose footed sail for a footed sail. I have sold many loose footed mains for Catalina 30s over the years, but not a single footed sail.

The strains produced by the sail converge at the three corners. There is a force upward and parallel to the leech concentrated at the clew of the sail, and upward force parallel to the mast at the tack. There's a very small compressive force on the boom, running parallel to the boom.

Judy B
Retired Sailmaker

 

[Parsons]

@DrJudyB gave you theoretical answer. Practically, I changed my C36 from footed to loose-footed four years ago, and there certainly is not 'bending' or stress of the boom, if that's what you're worried about. Join use 'footloose' people at the dance!

 

[Tally Ho]

My O’Day 322 is set up similar to your Catalina. I switched from a bolt rope main to a loose-footed main last year, and no issues.




Greg

 

[dlochner]

Yet another, no problem. We have a loose footed main with mid boom sheeting.

The loose foot has some advantages when purchasing and when using, It is easier to shape the lower part of the main because there is less friction on the outhaul. When sailing in rain, water does not collect in the foot of the sail and dump on deck when tacking.

 

[Hayden Watson]

Thanks @DrJudyB. I assumed that the foot did not apply a great deal of force to the boom so had come to the same conclusion but wanted conformation from someone more knowledgeable on the actual loading. It makes sense that it would not be a problem because I suspect that the vang can exert a greater load on the boom given the angle of the load.

 

[jon hansen]

hayden, your going to love the increase in horsepower from your loose footed main. there really is a bump in power.

enjoy

 

[Stu Jackson]

@Hayden Watson

I agree, no issue. The larger issue is have you cleared your outhaul to actually be useful?

 

[Calif. Ted]

Got a loose foot main last winter, love it, friends with a 320 took these pictures yesterday in very light winds.

 

[Hayden Watson]

I took the bolt-rope foot out of the boom a couple of years ago and fully agree that it is a game changer in light air. I was just curious about if there was any concern about bending the boom. I added a couple of cascades to my 3:1 outhaul to make it 12:1 and it is very easy to adjust.

 

[jssailem]

Hayden, my new sail is loose footed. It is working great. It replaces my footed mainsail. I have boom end Mainsheet sheet.
Your system spreads the forces to control the boom. Where the issue develops is if the boom has a minimal points of mid boom controls. A single mid boom block puts the stress in a single point. This creates the opportunity to break the boom.

 

[sidw]

I know this post is old, but why do folks call this a 6 to 1 sheet? As I see it, it is only a 4 to1 sheet, with the rest of the blocks just bringing the line back to the winch with no mechanical advantage (might possibly be 5 to 1). My question is, if you used a triple block at the traveler with a cam cleat on the car, to make an actual 6 to1 sheet, would that give you enough mechanical advantage to do away with the winch and bring the sheet straight aft from the car to the cockpit? This is an Oday 28 (10-ft boom and cabintop traveler).

 

[Davidasailor26]

I know this post is old, but why do folks call this a 6 to 1 sheet? As I see it, it is only a 4 to1 sheet, with the rest of the blocks just bringing the line back to the winch with no mechanical advantage (might possibly be 5 to 1). My question is, if you used a triple block at the traveler with a cam cleat on the car, to make an actual 6 to1 sheet, would that give you enough mechanical advantage to do away with the winch and bring the sheet straight aft from the car to the cockpit? This is an Oday 28 (10-ft boom and cabintop traveler).

We had an O’Day 28 with a 4:1 sheet on the bridge deck behind the companionway. It was manageable but in a good breeze I wouldn’t want any less leverage. I don’t remember exactly how far out that mainsheet attached on the boom, but if you figure it was about 8’ that suggests my arrangement gave 32 foot pounds of torque for every pound of pull. If the cabin top mainsheet pulls at the midpoint of the boom your suggested arrangement would be 30 foot pounds per pound of pull. That sounds borderline to me, especially considering the 6:1 will probably have a little more inefficiency than the 4:1.

 

[dlochner]

I know this post is old, but why do folks call this a 6 to 1 sheet? As I see it, it is only a 4 to1 sheet, with the rest of the blocks just bringing the line back to the winch with no mechanical advantage (might possibly be 5 to 1). My question is, if you used a triple block at the traveler with a cam cleat on the car, to make an actual 6 to1 sheet, would that give you enough mechanical advantage to do away with the winch and bring the sheet straight aft from the car to the cockpit? This is an Oday 28 (10-ft boom and cabintop traveler).

Count the vertical line runs, 6 vertical line runs is a 6:1 sheet. See the small diagram in the top left corner.

Harken provides load calculators. Use the Mainsheet load calculator to calculate the loads on the mainsail at different wind speeds and then do the math to see if your plan would work. One caveat about triple blocks is there tendency to induce twist especially if the block is moved a lot as it would be in a mainsheet application.

Calculators | Harken Marine

www.harken.com

 

[thinwater]

Maybe there is another way for Sid to look at it. And no, it is not really 6:1.

• Assume all pulleys are 100% efficient. This is not true, but that takes us down another rabbit hole. All purchases are less efficient than the simple number we assign, but it's an agreed upon simplification that applies to all tackles, and winches too, for different reasons.
• The force from each leg that attaches to the traveller is the same as the number of ropes, because they all feel the same tension. If the pull on the tail is 50 pounds, the tension on the entire length of rope is 50 pounds.
• But, of course, they are not all at a 90 degree angle to the boom, so the vertical component of the load may be only 80-85% for the fore and aft lines. The other component, perhaps 30-50%, is compression through the boom. The components don't have to sum to 100% (study engineering statics). The reason for the spread tackle is to reduce the bending force on the boom.

So yes, the actual purchase may be only 4:1. But not because the posters were wrong, but because of inefficiencies in the tackle pulleys and geometry. Also, a mid-boom tackle has less leverage than and end-boom tackle. I suspect 3:1 at the end of the boom would be as effective. But the traveler would not be.

 

[sidw]

OK, let me rephrase the question... the boom on my Oday 28 is set up like in the diagram above, and the last part of the sheet runs forward and then through 2 additional blocks to a winch on the cabintop. The fiddleblock on the car is only a double block. All ov the existing blocks are old and without bearings, do the friction in there is clearly an issue. Ann having to winch is the sheet is slow and cumbersome.
I was wondering if I used a triple block and cam cleat on the car, so I could run the sheet up-down-up-down-up-down between the car and the boom, and back to the cockpit through the cam cleat, if I would expect to have enough purchase to pull in the sheet comfortably without using the winch and extra turning blocks.
It is midboom sheeting with the traveler on the cabintop, but it is only a 10 ft boom.

 

[dlochner]

All ov the existing blocks are old and without bearings, do the friction in there is clearly an issue. Ann having to winch is the sheet is slow and cumbersome.

Ball bearing blocks will reduce friction and make it much easier to trim the sail.

The majority the time I can coarsely trim the mainsail by hand and I have a 36' boat. Put 2 or 3 wraps on the winch and just pull in the mainsheet until the sail is trimmed or it can't be trimmed by hand. At that point, put the tail in the self tailer and use the winch for the last few inches of trim. Typically I leave a winch handle in the winch, so there is no fumbling for the handle.

When going tacking don't release the mainsheet, set the trim with the traveller and then if necessary adjust the trim with the winch. Going downwind and jibing, sheet in the main and then ease out on the new jibe, won't need a winch for that.

 

[Davidasailor26]

Keep in mind that if you add a block with a cam cleat on the traveler car you won’t have any option to add a Bimini. When the sheet is routed to a fixed point then aft to a winch that’s still a possibility.