Mainsail Reef Line Load Calculation

[deluxe68]

We have a 390sf main with two reef points, the approximate sail area after the first reef is 292sf. I am looking to clean up the winch/cleat farm around the mast. Currently we have 3 pairs of winches, 2 clutches, and 4 cleats. My question is, where do I find calculators for determining the worst case load of say 40 knots wind speed with 292 sf of main sail? I am trying to size the blocks and clutches to use. The link below shows the type of setup we have.

Barton Marine - Tech Info - Sail Handling - Slab Reefing Kit Fitting 8.5m

[Suijin]

It's notoriously difficult to calculate that load given all the variables. I would simply size the clutches and the cleats to the line. If you're choosing between say the Lewmar DC1 series and the DC2 series for a given line size, just go with the heavier clutch.

In truth what you should be most concerned with is how your lines and hardware perform in the event of an accidental gybe in a squall. I've seen the covers on halyards and reef lines parted by that. I don't think there is away of calculating that load fwiw.

[deluxe68]

Originally Posted by Suijin

It's notoriously difficult to calculate that load given all the variables. I would simply size the clutches and the cleats to the line. If you're choosing between say the Lewmar DC1 series and the DC2 series for a given line size, just go with the heavier clutch.

In truth what you should be most concerned with is how your lines and hardware perform in the event of an accidental gybe in a squall. I've seen the covers on halyards and reef lines parted by that. I don't think there is away of calculating that load fwiw.

How do I know that the lines on the boat are correctly sized?

[Dsanduril]

Check out the various links here as a starting point.

[Suijin]

Originally Posted by deluxe68

How do I know that the lines on the boat are correctly sized?

I’d go with 12mm/.5 in, probably a hybrid like VPC. Affordable but strong and relatively low stretch. Save the high tech stuff for halyards.

[estarzinger]

probably the best you will find is Harkins mainsheet calculator Harken Sailboat Hardware and Accessories

the loading on the clew reef line will be at least roughly similar to a mainsheet load (using the reefed sail size, wind speed, and reefed clew location).

all these calculators have to be taken with a large grain of salt.

[deluxe68]

Originally Posted by estarzinger

probably the best you will find is Harkins mainsheet calculator Harken Sailboat Hardware and Accessories

the loading on the clew reef line will be at least roughly similar to a mainsheet load (using the reefed sail size, wind speed, and reefed clew location).

all these calculators have to be taken with a large grain of salt.

The problem I am having with those calculators is the current (factory) layout. The outhaul is fed to a #12 winch with an approximate safe working load of 1,000 lbs. I think Nautor over-built everything on the boat and the boat has been sailed like this for 30 years. If you use the mainsheet calculators then you would need to plan for about 4,000 lbs at that winch.

Harken has a chart for mast base blocks just using sail size, they do not show loads but just recommend which blocks to use. I sent them an E-mail, will be interesting to see what they say.

Thanks

[Cheechako]

Don't forget an important factor: size the line for ease of handling/hands. Even if you could use 1/8" Dyneema you wouldn't want to! In theory I suppose your reefing lines take as much or more static load as your mainsheet. Albeit not the shock loads. Start there.
No need to overthink it. Use what has worked in the past if it's big enough for handling ease...

[deluxe68]

Originally Posted by Cheechako

Don't forget an important factor: size the line for ease of handling/hands. Even if you could use 1/8" Dyneema you wouldn't want to!

I currently have Sta-Set 12mm.

[hellosailor]

Harken are generally very helpful about calculating which bits of their gear will do a job properly. After all, it helps sales when the customer knows which product might work.(G)

I think they are matching gear to sail size, because that makes the choices simpler for the buyer. Less of those pointy Arabic numbers to get hurt by.

https://sciencing.com/calculate-wind...s-6104140.html
Happens to discuss the case of 40 knots. Which could mean 4 pounds per square foot, roughly 1200 pounds for your case, and if you wanted to add a generous 50% safety factor that should still mean "trivial" lines and gear to take it.

Garhauer are also very good at customer service, you could ask them about gear sizing, and see if they come up with the same numbers as Harken. If not, go with the more conservative of the two. And consider the instance where someone might make an "oops" and the load of the full sail might be taken on just that reefing line, a worst-case scenario. (We know, that never happens on a boat.(G)

[cyan]

Originally Posted by hellosailor

Harken are generally very helpful about calculating which bits of their gear will do a job properly. After all, it helps sales when the customer knows which product might work.(G)

I think they are matching gear to sail size, because that makes the choices simpler for the buyer. Less of those pointy Arabic numbers to get hurt by.

https://sciencing.com/calculate-wind...s-6104140.html
Happens to discuss the case of 40 knots. Which could mean 4 pounds per square foot, roughly 1200 pounds for your case, and if you wanted to add a generous 50% safety factor that should still mean "trivial" lines and gear to take it.

Garhauer are also very good at customer service, you could ask them about gear sizing, and see if they come up with the same numbers as Harken. If not, go with the more conservative of the two. And consider the instance where someone might make an "oops" and the load of the full sail might be taken on just that reefing line, a worst-case scenario. (We know, that never happens on a boat.(G)

Samson has a clew force estimation formula which would put your reef line at about 2500 pounds with 40 Knots- probably a bit high IMO, but there's nothing wrong with getting in the right ballpark. (knowing that manufacturers have reasons for shooting high.)

(windspeed in mph)^2 x 0.004 x (sail area in square feet) = Sheet Load at Clew in pounds

You COULD go to West Marine and shell out about $1500 for a Spinlock digital load cell and look at your real world numbers in 40 Knots. Please share if you do. However, we're not sending a man to the moon here. These various formulas should get you in the ballpark close enough for the proper running rigging.

Side question: Do you ever find it difficult to snag that reef hook at the mast in around 40 Knots without a tack-side reefing line?

[StuM]

All the above info is good, but remember that your slab reefing system has a double line from the boom to the clew and back to the boom, so the line load is very roughly halved.

[cyan]

Originally Posted by StuM

All the above info is good, but remember that your slab reefing system has a double line from the boom to the clew and back to the boom, so the line load is very roughly halved.

It's rare that gotchas are such good news!

[deluxe68]

Originally Posted by cyan

Samson has a clew force estimation formula which would put your reef line at about 2500 pounds with 40 Knots- probably a bit high IMO, but there's nothing wrong with getting in the right ballpark. (knowing that manufacturers have reasons for shooting high.)

(windspeed in mph)^2 x 0.004 x (sail area in square feet) = Sheet Load at Clew in pounds

You COULD go to West Marine and shell out about $1500 for a Spinlock digital load cell and look at your real world numbers in 40 Knots. Please share if you do. However, we're not sending a man to the moon here. These various formulas should get you in the ballpark close enough for the proper running rigging.

Side question: Do you ever find it difficult to snag that reef hook at the mast in around 40 Knots without a tack-side reefing line?

We are fairly new with this boat, have not had it out in 40 knots yet.

[cyan]

Originally Posted by deluxe68

We are fairly new with this boat, have not had it out in 40 knots yet.

Thanks, was looking at different reefing solutions and I have to admit I err on the easy side.