This is *crazy* !

[dfelsent]

Somewhere along the line I recall that assuming halyard loads are the same as sheet loads is appropriate. For end boom sheeting.

I haven’t tried to calculate the force vectors but I suppose that is the way to do it. Assume the sum of all forces on the sail is zero when not accelerating or decelerating.

[s/v Jedi]

Originally Posted by dfelsent

Somewhere along the line I recall that assuming halyard loads are the same as sheet loads is appropriate. For end boom sheeting.

I haven’t tried to calculate the force vectors but I suppose that is the way to do it. Assume the sum of all forces on the sail is zero when not accelerating or decelerating.

Sounds good and in line with the tables “they” show us. I believe you also have the weight of the sail and the tension from the sheet pulling down on it to cope with. Also, I am more sensitive to the stretch of the line here, because tightening the halyard is much more work than the sheet.

I currently have 6mm Amsteel Blue, which is listed for “racing” in the 45-50’ range which corresponds with our main mast being a ketch. For performance cruising they list 8mm Amsteel Blue so clearly this is about saving weight vs longevity. When the time comes to replace the halyard, I will use 8mm.

I didn’t check for the mizzen yet. I don’t even know yet what size sloop would compare for P=48’ and E=16’.

[Joli]

Daschew designs are not noted for upwind prowess. They motor sail upwind and reach. Sheet loads won't be very high.

[nelly]

I would never take the rope manufacturer's breaking #s and use those for my boat without at least cutting them in half (before adding a safety margin).

The strength they advertise is probably what the rope breaks at (well, investigate for yourself what their number means) and that certainly is in drastically different conditions from what the lines will see on the boat, and I figure boat conditions are unlikely to make the rope break at a higher number!

Even if you splice, you're not getting 100% of the strength. I promise!

Thanks for the numbers and the exercise, it will be a really good reference.

[sailingharry]

Brilliant. A couple comments.

You have a big boat. Strength comes into play more than on smaller boats. On smaller boats, lines are often oversized just to be comfortable. On big boats, high strength lines help make the lines less massive to deal with!

You use a two-part mainsheet. That makes your loads massively larger!

I should use your calculations and run them on our boat, but I suspect that we are good. 43 ft boat with mid-boom sheeting but with a four part sheet. Our sheet is 1/2" Regatta Braid, a wonderful line in the hand, but nowhere near as strong as the lines you are suggesting. I suspect that we are still set.

[fxykty]

Hmmm, interesting and thank you for posting the formulae. I will work the numbers out one day (more urgently when we next replace our running rigging).

For now, I’ve been using the hardware specifications of the blocks and shackles present on the boat to determine their MWLs, then sizing lines to match for the control line running through those blocks. I acknowledge that’s lazy and not optimising for weight, but good enough for now. It also makes some assumptions regarding what was OEM at manufacturer and what has been replaced/upgraded by the POs in the 14 years before we bought the boat. The next owner will have to deal with all of our replacements as components fail or get simplified - another few years and there will be very few original blocks on this boat.

I assume tables based on sail size can be used to determine gennaker and spinnaker sheets?

[fxykty]

Originally Posted by fxykty

Hmmm, interesting and thank you for posting the formulae. I will work the numbers out one day (more urgently when we next replace our running rigging).

For now, I’ve been using the hardware specifications of the blocks and shackles present on the boat to determine their MWLs, then sizing lines to match for the control line running through those blocks. I acknowledge that’s lazy and not optimising for weight, but good enough for now. It also makes some assumptions regarding what was OEM at manufacturer and what has been replaced/upgraded by the POs in the 14 years before we bought the boat. The next owner will have to deal with all of our replacements as components fail or get simplified - another few years and there will be very few original blocks on this boat.

I assume tables based on sail size can be used to determine gennaker and spinnaker sheets?

I just did the numbers for our cat. Wow, intuitively you understand that wind speed is the key factor for loading and the formula sure backs that up. OTOH, if using high modulus line such as UHMWPE the strengths are so high that for larger boats it’s handling rather than strength that determines line sizes.

Our jibs, all using the same 2:1 sheet system, have maximum clew load of 2200#. Blocks and traveller cars are sized for that, yet our current sheet is oversized. Next one will have a stripped cover and UHMWPE core and sized for handling.

For the mainsail, if we carry the third reef to 50kts then our maximum clew load goes up to 3771# (otherwise only 2857#). Reefing lines are uncovered UHMWPE and already at minimum handling size (8mm). The main sheet due to 4:1 is like the jib way oversized. The next main sheet can be sized for minimum handling. Blocks and traveller cars are sized correctly, but pretty close to MWL. Good enough for now, but will need to monitor when using high modulus lines that transmit all the force of a wave pump or gust.

[Pete7]

Originally Posted by s/v Jedi

About these sail areas: we are at almost 70% of the area formed by the mast - boom rectangle. Compare to in-mast furling where it is normal to be at 45% of that same rectangle.

This is the mistake people make: they state that their boat performs good enough with in-mast furling but they don’t realize that their mast is much longer because of that.

Jedi, sorry don't agree with this, though it may apply to some yachts. We have a masthead rig so the real power comes from the Genoa. Our in mast main has no roach but comparing it to our sister yachts with slab reefing there isn't that much difference in sail area. The boom and mast are identical in length between the yachts.

Originally Posted by s/v Jedi

So you like the 8mm halyards to work with? I think 10mm is the smallest I want to handle. When I sailed a 30’ boat I also had 10mm halyards

Agree with that. We used to have a very long length of 8mm rope on the dive boat for the shot weight, 26lbs. Pulling that up from 50m was tough on hands and could cut into the rib tubes unless careful. 10mm is more comfortable to handle, unless your racing and really need to shave the last ounce of the boat.

Harken do a series of calculators for loads. This is the main sheet one. How do your calculations compare with theirs?

https://www.harken.co.uk/en/support/...ng-calculator/

[s/v Jedi]

Originally Posted by Joli

Daschew designs are not noted for upwind prowess. They motor sail upwind and reach. Sheet loads won't be very high.

This is true for all ketches, but because of our powerful sails and the 64’ waterline, the upwind performance is still much better than most cruisers.

In comparing, the first one that is able to beat us 50% of the time is a Beneteau First 47 (47.7?). Much smaller, but a modern performance sloop.

Of course when falling off a bit to a beam reach we take off so in a race circuit with all points of sail and a little wind we would still easily beat it.

But our sheet load is surprisingly high. I can not change genoa car position with the sheet loaded and I have a Lewmar 48 winch at that control line. With just a 105%, my calculations show a 2,600lbs load at the sheet at 30 knots apparent, which is the upper range for this high aspect jib.

The issue with a genoa is that there normally isn’t a sheeting ratio, although I just read someone posting to have a 2:1 ratio on their jib…. I suspect a self tacking jib.

[s/v Jedi]

Originally Posted by odonnellryan

I would never take the rope manufacturer's breaking #s and use those for my boat without at least cutting them in half (before adding a safety margin).

The strength they advertise is probably what the rope breaks at (well, investigate for yourself what their number means) and that certainly is in drastically different conditions from what the lines will see on the boat, and I figure boat conditions are unlikely to make the rope break at a higher number!

Even if you splice, you're not getting 100% of the strength. I promise!

Thanks for the numbers and the exercise, it will be a really good reference.

When you use a reputable rope manufacturer like Samson, New England Ropes, Yale Cordage, Marlow etc. then I am convinced their tables are correct because it has been tested and demonstrated many times incl. on countless YouTube videos and by members of this forum.

Did you see that my calculations limit the load on these lines to a maximum of 20% and much less for most of the time? This is what is recommended for maximum longevity.

We have broken lines. A genoa furling line, a genoa sheet and almost a main sheet which was down to half the fibers. But in every one of those cases it was a problem with chafe (wrong block installed by previous owner) or the lines should have been replaced earlier.

We never had a line less than 10 years old break and we have had very tough sailing, incl. through named storms.

[s/v Jedi]

Originally Posted by sailingharry

Brilliant. A couple comments.

You have a big boat. Strength comes into play more than on smaller boats. On smaller boats, lines are often oversized just to be comfortable. On big boats, high strength lines help make the lines less massive to deal with!

You use a two-part mainsheet. That makes your loads massively larger!

I should use your calculations and run them on our boat, but I suspect that we are good. 43 ft boat with mid-boom sheeting but with a four part sheet. Our sheet is 1/2" Regatta Braid, a wonderful line in the hand, but nowhere near as strong as the lines you are suggesting. I suspect that we are still set.

On our mizzen sheet, MLX3 in 8mm would work but decided to use 10mm for ease of handling.

You have a 4:1 main sheet (are you sure?) but by having it mid-boom, you give up half that so you can only divide the calculated clew load by 2 because the calculations are for sheet attachment at the end of the boom.

1/2” (12mm really) Regatta Braid has a tensile strength of 8,000lbs. But it can not be spliced so you loose 50% at the knot, leaving only 4,000lbs breaking load. At the 20% max load, it should not be loaded more than 1,600lbs so this leaves you a very small range to failure: from 1,600 SWL to 4.000 breaking.
I suggest you run the numbers

I made the mistake of using 16mm Regatta Braid for the genoa sheets. This is a really big rope. The problem is that NER doesn’t give any numbers for stretch but it is significant, I think more than 3% and this means that in gusts the shape of the jib gets fuller, exactly opposite of what you want
Also, by loosing half the strength at the bowline knot to the genoa clew, it isn’t even strong enough.
I am adding MLX3 10mm genoa sheets to the inventory which will be good up to 25kts before partially furling, which is exactly what we do anyway. This line can also be stripped to make it much lighter for better performance in light weather.

[s/v Jedi]

Originally Posted by fxykty

I just did the numbers for our cat. Wow, intuitively you understand that wind speed is the key factor for loading and the formula sure backs that up. OTOH, if using high modulus line such as UHMWPE the strengths are so high that for larger boats it’s handling rather than strength that determines line sizes.

Our jibs, all using the same 2:1 sheet system, have maximum clew load of 2200#. Blocks and traveller cars are sized for that, yet our current sheet is oversized. Next one will have a stripped cover and UHMWPE core and sized for handling.

For the mainsail, if we carry the third reef to 50kts then our maximum clew load goes up to 3771# (otherwise only 2857#). Reefing lines are uncovered UHMWPE and already at minimum handling size (8mm). The main sheet due to 4:1 is like the jib way oversized. The next main sheet can be sized for minimum handling. Blocks and traveller cars are sized correctly, but pretty close to MWL. Good enough for now, but will need to monitor when using high modulus lines that transmit all the force of a wave pump or gust.

You mean 3771# sheet load, right? Your main must be larger than mine and very large roach as well.

We only have 2:1 main sheet and at 40% from the aft end if the boom so only a 0.83 factor against clew load for the sheet, but we have a big Lewmar 58 winch for it which makes it work and we only have a small tail to deal with. I could add a 2nd block to the boom and 3rd block to the traveler car to create a 3:1 but that results in a 0.56 factor which doesn’t make me ecstatic enough

I think your boat is a very good example for all of us to study the systems (modern, performance oriented). What halyards and handling for those do you have?

[s/v Jedi]

Originally Posted by Pete7

Jedi, sorry don't agree with this, though it may apply to some yachts. We have a masthead rig so the real power comes from the Genoa. Our in mast main has no roach but comparing it to our sister yachts with slab reefing there isn't that much difference in sail area. The boom and mast are identical in length between the yachts.

Agree with that. We used to have a very long length of 8mm rope on the dive boat for the shot weight, 26lbs. Pulling that up from 50m was tough on hands and could cut into the rib tubes unless careful. 10mm is more comfortable to handle, unless your racing and really need to shave the last ounce of the boat.

Harken do a series of calculators for loads. This is the main sheet one. How do your calculations compare with theirs?

https://www.harken.co.uk/en/support/...ng-calculator/

I think there is a big difference between a Moody slab reefing main and the modern full batten mainsails with big roach. I agree that at the time your boat was designed it made sense. It’s probably also based on racing rules. When you take a modern catamaran with big roach full batten sail and replace that with an in-mast furling main, their masts would need to be much higher.

Yes, large genoa. I remember that. A very different sail plan.

The Harken calculator. Yes I started there but didn’t believe them (of course they want to sell bigger blocks and travelers haha) so let’s do that again and compare back! I attached the results for my mainsail.

Result is 16,728lbs at the sheet attachment point. The sheet load in my calculation sheet is divided by two because I have a 2:1 sheeting arrangement so my comparable load is 7,668 x 2 = 15,336lbs. This is reasonably close, but we have that large roach and I think for other mainsails their calculator is much too high.

Interesting they also state that traveler car adjuster load is 1/5 of the car load. This means our adjuster load is 15,336 / 5 = 3,067lbs. We have a 4:1 ratio control line so the line load is 767lbs.

Edit: this means I could downsize my traveler control lines, which are in a 4:1 arrangement from 10mm to 8mm XLS3. Hard to handle but smoother running through the little blocks and I need a winch anyway:-)

[fxykty]

Originally Posted by s/v Jedi

You mean 3771# sheet load, right? Your main must be larger than mine and very large roach as well.



We only have 2:1 main sheet and at 40% from the aft end if the boom so only a 0.83 factor against clew load for the sheet, but we have a big Lewmar 58 winch for it which makes it work and we only have a small tail to deal with. I could add a 2nd block to the boom and 3rd block to the traveler car to create a 3:1 but that results in a 0.56 factor which doesn’t make me ecstatic enough



I think your boat is a very good example for all of us to study the systems (modern, performance oriented). What halyards and handling for those do you have?

Our 86.6 sqm mainsail has a large roach and is approximately 76% of the rectangle. It is a round top, not square. The gaff batten is horizontal and 2.6m long. Luff is 17.08m and foot is 6.54m.

The numbers are the clew loads (FOC) in your formula. Our main has a 4:1 double ended sheet that attaches via 2 strops within 10cm of the clew. Mainsail traveler lines are 2:1. Jib sheet is 2:1 and self-tacking.

We have 4x 2-speed Harken 54s for all of our cockpit lines (everything other than halyards and reef lines). On our mast we have a 54 and a 48. Thankfully the original owner chose larger winches than standard (48s and 42s).

All halyards except for spinnaker are UHMWPE core. Reef lines are 8mm single braid UHMWPE, with inserts and covers where they are jammed when reefed (plus a cover for the clew when reefed).

[s/v Jedi]

Originally Posted by fxykty

Our 86.6 sqm mainsail has a large roach and is approximately 76% of the rectangle. It is a round top, not square. The gaff batten is horizontal and 2.6m long. Luff is 17.08m and foot is 6.54m.

The numbers are the clew loads (FOC) in your formula. Our main has a 4:1 double ended sheet that attaches via 2 strops within 10cm of the clew. Mainsail traveler lines are 2:1. Jib sheet is 2:1 and self-tacking.

We have 4x 2-speed Harken 54s for all of our cockpit lines (everything other than halyards and reef lines). On our mast we have a 54 and a 48. Thankfully the original owner chose larger winches than standard (48s and 42s).

All halyards except for spinnaker are UHMWPE core. Reef lines are 8mm single braid UHMWPE, with inserts and covers where they are jammed when reefed (plus a cover for the clew when reefed).

How can you only have 3,771lbs clew tension with the third reef at 50kts wind? I am over 4,000lbs at 45kts already, while my main is only 65 sqm vs 86 sqm for yours plus you have more roach? I have 35 sqm left with the third reef… is your 3rd reef that much more aggressive?