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Old 03-04-2015, 17:52   #1
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Tracks for Blade Jib

I'm trying to have tracks put on my foredeck for cars for my new blade jib.

The ancient Lallow's Boatyard (est. 1867) will do the honors -- I trust them more than myself to maintain the watertight integrity of my deck. Today I got a long and fascinating lecture about the properties of bronze fittings and threads, which they propose to use to back up the tracks belowdecks.

Now I have to order the track. Lallow's want me to use 32mm T track, as it is solid, and will bear solidly without any air space to the deck.

The only problem is the 32mm Lewmar T track only takes up to a Size 2 car.

The blade will be about 60 square meters (about 650 square feet) and will be very high aspect. It will look like this:

Click image for larger version

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The car available is this one:

Click image for larger version

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It has safe working load of 1500kg.

https://www.lewmar.com/products.asp?id=7541&lid=23868

Which compares unfavorably to the existing Size 3 cars for my yankee, which have SWL of 3500kg.


Am I right to assume that the sheet loads for the blade will be about the same as on the yankee, since the leech will be about the same length?

I don't want to contradict the wizards at Lallows, but it looks to me like this might be a mistake. Any advice?
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Old 03-04-2015, 18:41   #2
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Re: Tracks for Blade Jib

You want a size 3 car which has a SWL of 2350kg. It looks like the one in the pic, just bigger. The Harken equivalent is part G326S.
http://www.harken.com/productdetail....4952&taxid=484
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Old 03-04-2015, 19:01   #3
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Re: Tracks for Blade Jib

Hi Dockhead,
I'm thinking that to start with, 32mm track is too small for your boat, if you want it to live a long life. Also, as you're finding out, cars which can take the sheet loads for such a sail, on this size track, aren't quite so common. Particularly as you want hardware which is rated for a good bit more than your load calculations come up with.

In this instance, IIRC, you plan to use this sail in 30kts or so, non? Plugging it into the load calculator Harken gives you a sheet load of 2,527lbs.

Then, you need to look into what the sheet lead angles to the blocks will do to this sheet load. Because past a certain angle, the load on the block is actually higher than the sheet load. Particularly as with a "blade" jib, AKA a #3, or #4, the sheet lead angles are prone to doing this.
For such info, I turn to here Harken And, here's option #2 with an easier way to figure loads http://bethandevans.com/calculators.htm Click on the one which says "Sailing Loads Calculator".

A 75 degree sheet lead angle isn't too uncommon on a sail like this, & looking at the tables, we see that such an angle takes the 2,527lb sheet load & multiplies it by 122%. Yielding a 3,082lb load on the block (jib car). And these figures are static load numbers. AKA they don't factor in anything for such events like, falling off of, or slamming into waves & the shock loads which such sudden stops & starts impart.
Ergo my earlier comment about wanting your hardware to be higher than the figures which you punch up load wise.

So... if you like, compare this 1.5 ton figure to the size (strength) & spacing of the fasteners in 32mm T-track. As at best, a genoa car is 5"-8" long. Plus the footprint of the track on the deck isn't 32mm wide, IIRC it's about 2/3 that width. So your 1.5 ton load is on a piece of deck about 24mm x 150mm. And that's using a bigger car than I've ever seen for this sized track. Typically, at best, they're more like 75mm-100mm on track this size.
Basically, the bigger the footprint the better (on deck & in a backing plate). Plus it gives you a bit more latitude in terms of blocks/cars.

- Also, consider this. The pin which holds the load (prevents the car from rocketing aft down the track) on a car which fits this track is 6mm - 7mm in diameter +/-.
Using 85,000psi yield strength (reasonable for moderate grades of stainless), & a pin size of 6.3mm (1/4"), it fails when the load hits 4,170lbs.
Which means that it's likely going to start to deform at about 2,000lbs. And keep in mind that the track's aluminum, so it's yield strength is a lot lower.

Odds are you're a better engineer than me, & or other folks on here are. But the above's the KISS way to say that the hardware's insufficient. Or you can look at a 20,000lb boat's jib cars in said location, & see that odds are they're more stout than any mid sized gear. You almost have a small Maxi, so the hardware has to match.


PS: What do you have for winches, hydraulics? Or a beastly set of primaries & dual coffee grinders ;-)
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Old 03-04-2015, 19:04   #4
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Re: Tracks for Blade Jib

I found this, which will fit the 32mm t-track Lallow's want to use:

32 101 Barton Marine 32101 - Heavy Duty Genoa Car Fits 32mm (1-"

SWL of about 3,000kg, and costs only $230 each (versus $1,000 each for the Lewmar Size 3). They're not ball bearing, but probably doesn't matter for non-towable cars.
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Old 03-04-2015, 19:21   #5
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Re: Tracks for Blade Jib

Quote:
Originally Posted by UNCIVILIZED View Post
Hi Dockhead,
I'm thinking that to start with, 32mm track is too small for your boat, if you want it to live a long life. Also, as you're finding out, cars which can take the sheet loads for such a sail, on this size track, aren't quite so common. Particularly as you want hardware which is rated for a good bit more than your load calculations come up with.

In this instance, IIRC, you plan to use this sail in 30kts or so, non? Plugging it into the load calculator Harken gives you a sheet load of 2,527lbs.

Then, you need to look into what the sheet lead angles to the blocks will do to this sheet load. Because past a certain angle, the load on the block is actually higher than the sheet load. Particularly as with a "blade" jib, AKA a #3, or #4, the sheet lead angles are prone to doing this.
For such info, I turn to here Harken And, here's option #2 with an easier way to figure loads Calculators Click on the one which says "Sailing Loads Calculator".

A 75 degree sheet lead angle isn't too uncommon on a sail like this, & looking at the tables, we see that such an angle takes the 2,527lb sheet load & multiplies it by 122%. Yielding a 3,082lb load on the block (jib car). And these figures are static load numbers. AKA they don't factor in anything for such events like, falling off of, or slamming into waves & the shock loads which such sudden stops & starts impart.
Ergo my earlier comment about wanting your hardware to be higher than the figures which you punch up load wise.

So... if you like, compare this 1.5 ton figure to the size (strength) & spacing of the fasteners in 32mm T-track. As at best, a genoa car is 5"-8" long. Plus the footprint of the track on the deck isn't 32mm wide, IIRC it's about 2/3 that width. So your 1.5 ton load is on a piece of deck about 24mm x 150mm. And that's using a bigger car than I've ever seen for this sized track. Typically, at best, they're more like 75mm-100mm on track this size.

Basically, the bigger the footprint the better. Plus it gives you a bit more latitude in terms of blocks/cars.

- Also, consider this. The pin which holds the load (prevents the car from rocketing aft down the track) on a car which fits this track is 6mm - 7mm in diameter +/-.
Using 85,000psi yield strength (reasonable for moderate grades of stainless), & a pin size of 6.3mm (1/4"), it fails when the load hits 4,170lbs.
Which means that it's likely going to start to deform at about 2,000lbs. And keep in mind that the track's aluminum, so it's yield strength is a lot lower.
Thanks very much; that's exactly the kind of info I was looking for. I will play with the Harken thing -- extremely useful!




Quote:
Originally Posted by UNCIVILIZED View Post
. . .Odds are you're a better engineer than me, & or other folks on here are. . . .
Unfortunately I am no kind of engineer whatsoever, so this info is extremely useful, thanks!
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Old 03-04-2015, 19:58   #6
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Re: Tracks for Blade Jib

This is a good aid for anyone semi-competent with a calculator The Elements of Boat Strength: For Builders, Designers, and Owners: Dave Gerr: 9780070231597: Amazon.com: Books
It'd walk you through the math which I just posted, & has a Lof of NEAT & Useful info in it too.

- It seems that in my earlier post I forgot to mention that the link named "Calculators" will take you to Beth & Evans web page. And in particular, a spread sheet which will do all of the math which I did & more, for you, automatically. Just plug in the numbers. With the exception, perhaps of calculating the sheer strength of steel pins, & such things.


PS: Here's a Plan B on blocks, albeit a not inexpensive one. Though you can find such blocks used, in varying types of condition. http://www.mauriprosailing.com/us/1-...SCH3233UC.html
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Old 03-04-2015, 20:12   #7
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Re: Tracks for Blade Jib

Quote:
This is a good aid for anyone semi-competent with a calculator The Elements of Boat Strength: For Builders, Designers, and Owners: Dave Gerr: 9780070231597: Amazon.com: Books
It'd walk you through the math which I just posted, & has a Lof of NEAT & Useful info in it too.
I second the recommendation of Gerr's book.
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Old 04-04-2015, 10:42   #8
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Re: Tracks for Blade Jib

Dockhead,

I would HIGHLY recommend on a very high aspect sail like this to go with adjustable (string) cars not fixed ones like shown. The higher aspect the sail the more critical the lead angle is since the tolerance for incorrect leach load is so small. Particularly since you don't have any existing hardware the additional cost will be small, but the utility is huge.
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Old 04-04-2015, 13:03   #9
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Re: Tracks for Blade Jib

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Originally Posted by Stumble View Post
Dockhead,

I would HIGHLY recommend on a very high aspect sail like this to go with adjustable (string) cars not fixed ones like shown. The higher aspect the sail the more critical the lead angle is since the tolerance for incorrect leach load is so small. Particularly since you don't have any existing hardware the additional cost will be small, but the utility is huge.
Thanks, and your point is well taken.

The cost difference is actually very large, since towable cars will need to be ball bearing cars -- $1000 EACH, versus about $230, so more than quadruple.

But that was not actually what was stopping me -- the new tracks will be inboard and ahead of the coachroof (the sheeting angle is actually making me aroused), and I have no idea how I would lead the control lines back. In fact, for that matter, I'm not really sure how I'm going to get the SHEET back to the winch. I need to work on all of that.
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Old 04-04-2015, 13:12   #10
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Re: Tracks for Blade Jib

In reading this thread I am noting that two units of measure are being used, kilograms and pounds. A kilogram is equal to 2.2 pounds.

Be sure to cross reference as to calculations and as to specifications of componentry so as to not mix up the actual forces and strengths.
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Old 05-04-2015, 17:42   #11
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Re: Tracks for Blade Jib

This is an Olympic Jib 95% approx

Why calling it BLADE !?

I thought the thread was about a storm jib......

The width of track means little, important is the allowable weight force, and pace and size of bolts (8mm, not 6!! Every 12cm or 5") and counterplate

Do not ever dream of moving that car manually, even in mild conditions

?looks like the boat had none at all, before!?
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Old 05-04-2015, 17:53   #12
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Re: Tracks for Blade Jib

Quote:
Originally Posted by TheThunderbird View Post
This is an Olympic Jib 95% approx

Why calling it BLADE !?

I thought the thread was about a storm jib......

Do not ever dream of moving that car manually, even in mild conditions

?looks like boat had none at all?
Hereabouts we call very high aspect, non-overlapping headsails "blades". We use them for hard upwind work in strong wind. Since they can be sheeted inside the shrouds, and due to the smaller area, and higher aspect, they are perfect for this -- beating in 20 to 30 knots of true wind, which is so common here. You would have to reef the yankee above 22 knots or so, then its shape goes to hell, and the sheeting angle is all wrong. Hence the urge to have a sail like this.

I'm not sure what you mean by "?looks like boat had none at all?" None of what? The standard headsail is a 120% high clew yankee jib. This is sheeted, obviously, outside of the shrouds, on burly remote-controlled Lewmar Size 3 cars. With 3:1 purchase on the car control lines. The sheet lead is my main control for the headsail, by the way -- what I adjust most when trying to get sail trim right.

But obviously I can't sheet the blade with those cars.
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Old 05-04-2015, 17:55   #13
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Re: Tracks for Blade Jib

Quote:
Originally Posted by Montanan View Post
In reading this thread I am noting that two units of measure are being used, kilograms and pounds. A kilogram is equal to 2.2 pounds.

Be sure to cross reference as to calculations and as to specifications of componentry so as to not mix up the actual forces and strengths.
I think everyone contributing to this thread is very familiar with the conversion between English and Metric units of weight and force, but thanks for the reminder.
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Old 05-04-2015, 17:59   #14
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Re: Tracks for Blade Jib

Quote:
Originally Posted by UNCIVILIZED View Post
This is a good aid for anyone semi-competent with a calculator The Elements of Boat Strength: For Builders, Designers, and Owners: Dave Gerr: 9780070231597: Amazon.com: Books
It'd walk you through the math which I just posted, & has a Lof of NEAT & Useful info in it too.

- It seems that in my earlier post I forgot to mention that the link named "Calculators" will take you to Beth & Evans web page. And in particular, a spread sheet which will do all of the math which I did & more, for you, automatically. Just plug in the numbers. With the exception, perhaps of calculating the sheer strength of steel pins, & such things.


PS: Here's a Plan B on blocks, albeit a not inexpensive one. Though you can find such blocks used, in varying types of condition. Schaefer Half-Moon Genoa Lead 3 1/4 in (83mm) OD | Mauri Pro Sailing
Thanks; all great advice.

The Schaefer cars are half the cost of the Lewmar ones, but are a bit less robust, with SWL of 2.3 metric tons vs 3.5. Based on your calculations, I'm inclined to think that I need the full 3.5. But I'll have a closer look.
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Old 05-04-2015, 18:46   #15
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Re: Tracks for Blade Jib

The Schaefer blocks will do the job. A set of those have been holding my #3 for years. They are roughly the same strength as the Harken ones.
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