Deck-block options/suggestions?

GeoffS

GeoffS

Member
I'm planning the upgrade of my Laser's controls, so I've been reading the various articles on drLaser. One detail that I'm still not clear on is the kind of blocks that will work as the deck-blocks. I was hoping to get some additional information from those out there who have already upgraded.

Specifically, it sounds like the shackle-to-sheave distance is a critical dimension in order to have a good lead into the cleats. I would like to keep the option open to use 5mm (3/16") line for the part that ends up in my hand. This would seem to require at least a 20mm diameter sheave on the turning block. My original thought was to use a Harken 29mm carbo Tie-Lite block for low weight, low cost, and really low friction (due to the over-sized sheave). I noticed that this block isn't marked as suitable for the deck-block in the drLaser article "Blocks, Cleats and Accessories for 'Laser 2000' control systems". However, I checked the published dimensions and configurations of the 29mm carbo and some of the blocks marked for deck use, and it looks like it might work OK. Has anybody else tried it? (or any of the other 29mm carbo blocks)

In case the 29mm carbo just won't work, what alternatives do people suggest? I'm kind of predisposed to Harken (I like their engineering and attitude; they're also just down the highway from me...). In the drLaser article, only two Harken blocks are marked "D": the 16mm airblock (404) and the 22mm microblock with swivel (292). The latter seems like it would be longer between the shackle and the sheave than the 29mm carbo tie-lite (?). There is a new "Micro Forkhead Block" (http://harkenstore.com/uniface.urd/scpdinw1.ShowProd?409Z56LC51Q8U) that would seem to be nearly ideal for this application. Has anyone used it?

Cheers,

Geoff Sobering
 
Dear Geoff,

You are too fast for me :)

That drLaser article was just revised circa 16:00 GMT to include the new "forkhead" blocks, and probably some other NEW RIGGING articles on drLaser will need modifications tonight or tomorrow, too.

Waiting for more details from Harken's New Products Manager.

I currently use tiny 19 mm sheave Frederiksen SBA19's as my deck turning blocks. Harken's new 376 forkhead block may be better than the SBA 19 for some people: it is shorter AND stronger.

But SBA 19 has a slightly larger diameter sheave than Harken's new 376, and hence may be better for the application, especially if you will use 5mm covered line. (I don't.)

Harken's 29 mm Harken H351 CarboAir Ti-Lite single will NOT do as the deck turning block. The 44 mm length reported is WITHOUT the tie, which will invariably add ad least anither 5 mm. It will sit too high. Especially if you bend your wire guides down at the Deck Cleat Base.

With only a 90 degree turn and low loads at the Deck Block Fitting, you do not need large diameter sheaves like 29 mm for your deck turning blocks, anyway.

I have to leave now. But after I get back, I will read your message more carefully to see if I missed anything.

Shevy "drLaser"
 
I currently use tiny 19 mm sheave Frederiksen SBA19's as my deck turning blocks. Harken's new 376 forkhead block may be better than the SBA 19 for some people: it is shorter AND stronger.

But SBA 19 has a slightly larger diameter sheave than Harken's new 376, and hence may be better for the application, especially if you will use 5mm covered line. (I don't.)
Click to expand...
I'm confused (nothing new there...); I've been meaning to ask about this before, but this seems like a good juncture. The Harken Micro's have a nominal sheave diameter of 22mm, which _sounds_ like it's larger than the Frederiksen SBA19's 19mm. I haven't seen an SBA19 for real, but in some photos I've seen of people's rigging they look larger than the Harken micros. Is the Harken sheave deeper (or something) making the effective diameter (i.e. the diameter where the line runs) actually smaller than the SBA19?

I have to leave now. But after I get back, I will read your message more carefully to see if I missed anything.
Click to expand...
I don't think so, but perhaps you'll see something else I'm missing, or about to do wrong...

Cheers,

Geoff S.
 
Harken Forkhead blocks............

I got 'em. They're closer to deck level than the Holt blocks which are similar in design.
16mm sheave though so you'll probably want to use a line no thicker than 4mm. But nobody uses anything thicker these days anyways, right?
 
Hoipoihoi: Name, please! Just three days to the 25th :)

Dear Geoff,

Don't be fooled by any photographic evidence, especially if the photo is a collage of different fittings. Probably the different products are not shown to exact scale.

Frederiksen's SBA19 Ultra or SB19 Multi blocks are MUCH smaller than the Harken's H377 Micro forkhead. Just check that drLaser article on "parts". For instance:

SBA19 and SB19 weigh 10g; H377 weighs 16g. SBA19 and SB19 are 39mm long; H377 is 42 mm long. SBA19 and SB19 have narrower sheaves (for 4 mm - 5/32" - rope for SBA19, and for 5 mm - 7/32" - rope for SB19); while the H377's sheave will accommodate a 6 mm - 1/4" - rope. SBA19 and SB19 have a tiny, swiveling shackle head; H377 has a hefty forkhead.

In you hand, SBA19 will feel much smaller than the H377. But the two blocks have the same SWL! (SBA19 in the Ultra line is hard to find, though. )

So, you are also right: the Harken sheave is 40+% wider and hence much deeper than the Frederikson SBA19 sheave.


IMHO... the new 2003 Harken H377 offers a solution for Lasers with its low-profile Forkhead which requires no shackles (thus allowing the sheave to lie close to the deck)... but ONLY IF you MUST use 6 mm control lines. Also, IMHO, the H377 has no advantages if you will use lower diameter lines. I will try to confirm this with HARKEN.

In particular, for 5 mm control lines, SB19 - 60% lighter, slighly shorter and of sufficient diameter- will be better than H377 (apert from any subjective "brand" or "qauality" or "service" differences). Since the line turn is only 90 degrees at the mast base, the 19 mm sheave of the SB19 will just do fine.

For 4 mm control lines, Harken's own 16 mm H376 will do the job much better than their H377, and Frederiksen's SBA19 or SB19 will probably do even better (due to 19 mm rather than 16 mm sheave diameters, especially if you use lines that have "memory" and keep their kinks).

The "strange" contradiction here is that Harken's larger and longer H377 has a lower SWL than their smaller and shorter H376. You would think that a larger control line diameter would be needed for better handling of control systems with lower power ratios. But lower power ratios imply greater loads at the deck level. But this H377 block which can handle large diameter ropes has lower SWL than the H376. Figure!

Does this mean the H377 is no good for high loads at the mast base? No. Remember that the cunningham loads will be at most (about 250 kg) and the outhaul loads will be at most 80 kg. (See the drLaser website, "Designing Custom Control Systems".) Thus, the H377 will not distort or break even with a 3:1 cunningham or 1:1 outhaul!

As a general word of advice, start not by brand (even if you are "predisposed to Harken") but with your control line system design and the resulting loads on each block. Determine your minimum SWL requirements for each block, and then consider which blocks will do the job before optimizing for weight, length, sheave diameter, etc.

Specific examples of such custom control sytem designs are provided in the drLaser web site article "Designing Custom Control Systems".

Shevy

PS. For a comparison of how much higher your control line will lead into the camcleats when you use the H377 versus the H376, check out:
http://www.drLaser.org/images/parts/H376377.jpg
(soon to be uploaded -- having FTP problems right now.) I will ask HARKEN to confirm or correct the estimated dimensions in that figure.
 
> For a comparison of how much higher your control line will lead
> into the camcleats when you use the H377 versus the H376, ....

Dan Rondeau of HARKEN just gave me some exact dimensions to compare.

The relevant distance is from the bearing point of shackle to the sheave - measured to the "root" or smallest
diameter of the sheave. These distances are:

376 16mm Forkhead - 10 mm
377 Micro Forkhead - 13.5 mm

So, the photographic evidence based guesstimates were off! There is a difference, but not too much.

Nevertheless, it still looks like the H377 is only appropriate for the few who might want to use 6 mm control line ends. HARKEN notes that the 377 was not sollely targeted for the Laser.

Dan also emphasized that the 376 is the HARKEN block of choice for attaching to the double bail mastbase
fitting. In fact, he claims (and he should know) that it is the block that is now included in Vanguard's "new and improved" Upgrade Kit.

I am always amazed with Vanguard! They change the components of their Kit, and never bother to let their customers know. Last ununnounced change was the move from 4:1 to 6:1 power ratio in their outhaul kit. The Vanguard outhaul kit now includes an additional Harken H225 block, plus an additional 3' of 3mm Spectron.

I will post these details of that on the website, too.

Shevy Gunter
Editor, drLaser
 
You must log in or register to reply here.

Back
Top