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Old 13-06-2016, 15:15   #1
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lash small block to pulpit base?

Hi:

I want to attach small blocks to the base of my pulpit to turn my preventer lines. In the past on my other boat, I have installed a split (hinged) rail mount to which I shackled the block. The block, once located, really does not need to move or swivel in this application more than a very nominal amount. Seems about two rail mounts, two shackles, and $40 extra cost if instead I could use 3/16 line to lash the block directly to the pulpit instead.

Would a double constrictor knot lead through my block loop work and be reliable long term? Some other technique?

Thanks,

Boulter
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Old 14-06-2016, 10:40   #2
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Re: lash small block to pulpit base?

Tried a constructor knot with the block loop embedded in the knot. This looks like it would pull the knot apart.

Next I tried attaching the block with a bowline, and then I tied the line to the pulpit with a constructor knot. This seems promising as now pull on the block just acts to tighten the constructor knot.

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Old 14-06-2016, 14:08   #3
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Re: lash small block to pulpit base?

You could try actually lashing it to the pulpit rather than tying it like you are now. A traditional lashing would keep it in place an prevent it from flopping around depending on the block configuration. You can look up a spar lashing on YouTube to see what I mean or if you need more details you can let me know.
I use lashings all the time, they are quick and easy (once you know how) and offer a lot of flexibility.
Good luck!
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Old 15-06-2016, 05:03   #4
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Re: lash small block to pulpit base?

Thanks Shoalcove. That is what I want. I think my initial Google search was "lash block to post" or something like that, but nothing turned up.

So what I want is a round lashing around a single spar,
with the block loop embedded in a loop, or something else?

Thanks,

Boulter

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Old 15-06-2016, 05:18   #5
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Re: lash small block to pulpit base?

Are you talking about blocks for a mainsail preventer? As if you are, "small" shouldn't be characterizing any part of the system. Nor should they be lashed to the pulpit. Because the loads on a mainsail preventer can exceed those seen by the mainsheet, during an accidental gybe.
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Old 15-06-2016, 05:32   #6
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Re: lash small block to pulpit base?

I'd take about 6' of small line and double it in half. Then pass the 2 ends through the shackle or loop on your block and then through the loop in your line to form a cow hitch with two equal legs of line.
Place the block on your pulpit and ( in opposite directions) wind each leg around the pulpits trough the shackle loop a few times. The actual number of turns will depend on the strength of your line and will be a judgement call.
Once you get your turns, cross your lines and wrap them in opposite directions around your turns between your pulpit and the block, pulling your lashing tight. Make a couple turns that way and finish with a reef knot.
Of course there is a good chance that, like I sometimes do, you will discover you needed a longer piece of line about halfway through the process but that is part of the learning process!
I hope this helps. Preventer lines can take a lot of strain so I'd be sure to check your lashings to make sure they are in good shape. Also, it is possible for them to slide on stainless tubing depending on where they are placed. Of course, you could also bend your pulpit! Have you considered putting the blocks on your toe rail? The lower angle might be helpful and they are much stronger.
Best of luck!
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Old 15-06-2016, 05:36   #7
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Re: lash small block to pulpit base?

Quote:
Originally Posted by UNCIVILIZED View Post
Are you talking about blocks for a mainsail preventer? As if you are, "small" shouldn't be characterizing any part of the system. Nor should they be lashed to the pulpit. Because the loads on a mainsail preventer can exceed those seen by the mainsheet, during an accidental gybe.
I must have been typing when you posted. I agree 100 percent. I would not use my pulpit that way. A lashing can be plenty strong though depending on the material used and the skill with which it is made imho.
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Old 15-06-2016, 07:18   #8
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Re: lash small block to pulpit base?

Thanks guys. Just to be clear this is for a Tanzer 22 with 100SF main. The pulpit has backing plates and will have reasonable chances with a moment arm of about 2 inches as opposed to catching me at 250 pounds 18 inches away. I agree, I would not do this on a say over 30 foot boat.

The blocks are rated at MWL 550 pounds, using 1/4 inch braid which has breaking rating of about 2000 pounds.

Surely what I propose is not unreasonable?

Boulter

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Old 15-06-2016, 07:25   #9
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Re: lash small block to pulpit base?

Shoalcove. Thanks for the detailed description. I don't have any line in stock small enough to give it a try other than whipping twine, which might be too small, and in any event perhaps not rated as to strength.

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Old 15-06-2016, 08:00   #10
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Re: lash small block to pulpit base?

When I first read your OP I immediately thought of the huge sudden force which could hit your block and the pulpit, especially if the block were able to move up the pulpit tubing. You are probably looking at putting it on a support on the tubing base where it can't move. But the force on a bigger boat could rip your pulpit up from the deck.

If it were me though, I would think that a pulpit with a strong backing plate would be able to handle the likely forces from a jibe on a Tanzer 22. A preventer should have a small amount of slack but should never have a large amount of slack. A lot of slack will allow more momentum to build up and be a much larger force trying to pull up your pulpit.
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