Halyard Loads? -- Never mind I found the answer.

bottomscraper · Post by **bottomscraper** » Oct 13th, '10, 15:36

On Mahalo CD36 the main halyard runs back to the cockpit. There
is a stand up block near the base of the mast that I would like to
replace. I am trying to select a replacement block but I don't have
a clue what the loading would be. The existing block is a Hood
(no longer made) so I can't use that as a starting point.

Duh, never mind, I found it!

Found a chart on page 372 of "The Complete Rigger's Apprentice"
by Brion Toss (ISBN-13: 978-0070648401) (BTW it's a great book)

It is interesting the chart is based on the LOA of the boat only.

DaveCD28 · Post by **DaveCD28** » Oct 13th, '10, 16:07

Now I'm curious.... what IS the loading?

Also, does it have reference to the loading on a 28 footer?

rorik · Post by **rorik** » Oct 13th, '10, 16:40

There is some info here:
http://mauriprosailing.com/techinfo/Har ... rmulas.htm

Sea Hunt · Post by **Sea Hunt** » Oct 13th, '10, 19:20

Dave:

The chart Rich references in his post is a small line graph chart with even smaller numbers.

It looks like the "Lewmar formula" for a halyard load for an LOA 36 sailboat is approximately 2000 - 2200 lbs.

For a LOA 28 sailboat it appears to be approximately 1000 - 1200 lbs.

I do not really understand how these numbers are arrived at without knowing a lot more information than the LOA. I would think mast height, for example, would be a significant variable.

I guess maybe I should have actually studied for the math test in the GED class I never passed.

rorik · Post by **rorik** » Oct 13th, '10, 19:32

Mast height, sail area, wind strength, halyard routing, type of line and more all play a part...... there are easier to read charts and fairly easy formulas on the link I posted above.

bottomscraper · Post by **bottomscraper** » Oct 13th, '10, 19:36

I guess I should have used the term graph rather than chart
in my description of what's on page 372 of the Riggers Apprentice.
It shows a plot of halyard load vs. LOA. It looks like the load for
a 28 ft boat would be less than 1500lbs, it's a small graph to
interpolate so hopefully I over estimated a little.

FWIW the title at the top of the page for the 4 different loading
graphs is "Lewmar's Formulas", I could not find anything
particularly useful on the Lewmar web pages.

Note that for a turning block like the 90 degree one on our
halyard the load on the block the load will be about 141%
of the halyard load. (see tables from previous post or this link
http://www.harken.com/charts/blockloadvangle.php)

This table shows which Harken Blocks to use vs Maximum "P" Dimension of your main sail:

http://www.harken.com/charts/BBusechart.php

I will probably be using Garhaur blocks rather than Harken since
they are more in my price range and I think they are well made
and the best value.

bottomscraper · Post by **bottomscraper** » Oct 13th, '10, 19:42

rorik wrote:Mast height, sail area, wind strength, halyard routing, type of line and more all play a part...... there are easier to read charts and fairly easy formulas on the link I posted above.

Except it's for sheet loads not halyard

Not that it's bad info!

rorik · Post by **rorik** » Oct 13th, '10, 20:58

bottomscraper wrote:
rorik wrote:Mast height, sail area, wind strength, halyard routing, type of line and more all play a part...... there are easier to read charts and fairly easy formulas on the link I posted above.
Except it's for sheet loads not halyard Not that it's bad info!

Sheets, halyards, tweakers.... the important thing is the formula. Not the name of the line to which you apply the formula. A 1000 pound load on a halyard turning 180 degrees over a sheave is going to have exactly the same effect as a sheet having a 1000 pound load and turning 180 degrees on a turning block - assuming you use the same size line and blocks for each. The formula will tell you what size line and block to use for a given load.

What I did to calculate the size of line and blocks I would need when I replaced all my running rigging was this:
Jib is 216 sqft- multiply sqft x max wind speed (before I reef that jib: 20knots) - square that - multiply by 0.00431 - that means I need a sheet that will have a SWL of at least 373 pounds. Add the physical weight of the sail and the halyard itself - and you need a halyard with a SWL of ~400 pounds. Add 50% to that for some safety - or even 100%. So your halyard and/or sheet need to have a SWL of 600# or 800#. I see no reason for the halyard to be calculated any differently than a sheet. It does the same thing, just from a different angle.

Here's the formula I used:

SL = SA x VÂ² x 0.00431

SL = Sheet Load
SA = Sail Area
V = Velocity (wind speed)

bottomscraper · Post by **bottomscraper** » Oct 13th, '10, 21:41

rorik wrote:
Here's the formula I used:

SL = SA x VÂ² x 0.00431

SL = Sheet Load
SA = Sail Area
V = Velocity (wind speed)

Ahhhh the light goes on!

Thanks!