Chotu's Advanced Running Rigging Thread (lots of pics)

[Chotu]

Originally Posted by rslifkin

Those pictures (and more that I found) all make me think that if you add support on the top to spread the load and stiffen everything (and tie into the davits so some of the load is spread forward into the roof as well), you'll be fine. Adding some triangulation to the existing supports outboard of them (1 additional leg per side) would add more safety margin. You could probably use dyneema or stainless cable for it, but if you could do it with tubing that would be best, as then it provides support in both directions. It doesn't need to be some massive, ugly brace though. personally I think your existing supports look pretty good, so adding another piece to triangulate them wouldn't look bad at all. They don't necessarily have to angle as far out as the drawing you did on page 5.

yes, the davit beams are through bolted every 24 inches or so. Approximately. And they go all the way up to the forward part of the deck house. I used the beam characteristics to help support the roof and stiffen things up. they are like 20ft long or something


thanks for the compliment on the existing supports. It is nice to get a complement. Lol

from a structural point of view, if I have a diagonal triangulation piece on each side, nothing can go anywhere. I wouldn’t need support in both directions if you did it at the angle I drew with the red line. And I could keep it down to something pretty thin like the dyneema or stainless.

but I see what you are talking about also. you could have a second pole like the ones I already have going at some bit of an angle to act as an anchor that would experience forces that were not directly in line with it, but since there are two of them on each side, they wouldn’t twist out of the main beam as easily as one of them on each side would. difficult to put into words but I think I visually see what you are talking about with a second pole with a slight angle to it on each side.

Kind of like the red line I drew better. Just from a design standpoint. As in aesthetics. A very thin item on that red line I think would look better than to make the supports more chunky or wide by adding a second one at some angle near each one of them. This is personal opinion and into aesthetics at this point on that

[rslifkin]

Thinking of myself working around them, my biggest concern with something thin that angles too far away from the existing supports would be me not noticing it and whacking into it...

[Chotu]

Originally Posted by rslifkin

Thinking of myself working around them, my biggest concern with something thin that angles too far away from the existing supports would be me not noticing it and whacking into it...

valid concern if people went through that area. But look closely. That’s not an area that you move through as a human being lol. On the other side of that is just open water that you would fall into. You don’t go over there. It’s actually unused space.

[rslifkin]

Originally Posted by Chotu

valid concern if people went through that area. But look closely. That’s not an area that you move through as a human being lol. On the other side of that is just open water that you would fall into. You don’t go over there. It’s actually unused space.

I was thinking more of reaching past while tying down the dinghy after hoisting and stuff like that.

[Chotu]

do you know what else is a factor?

The placement of the main sheet on the boom. obviously if it’s one of those boats where it is very close to the centerpoint of the boom getting closer to the mast, the forces are going to be ridiculous.

but if you are holding the very end of the boom like in my case and all of the other cases where people do what I’m doing, the forces are not as great

[Chotu]

Originally Posted by rslifkin

I was thinking more of reaching past while tying down the dinghy after hoisting and stuff like that.

ahh. gotcha.

this is where the Internet probably fails a little bit.

it’s really hard to get the dimensions to look right in the pictures. I actually don’t go over there to do that. I pull the block and tackle (that you recommended and are working great!) for the dinghy from an area in between the two support poles.

everything I do with the dinghy is between the two support poles.

what’s really nice about this is I can just easily lift a bicycle into the dinghy as if I were putting it onto a counter. Same with provisions. same with all of the diesel I have to carry all winter. It’s just really really nice having the dinghy right there. So everything takes place between those two upright support poles.

funny thing also. I go up with the dinghy. I never really thought that it would work but it does. I bring the dinghy to the transom of the centerline of the boat, I connect the block and tackles, and I pull myself up with the dinghy. Lol

[Chotu]

Originally Posted by rslifkin

I was thinking more of reaching past while tying down the dinghy after hoisting and stuff like that.

OK. You’ll have take my word that it’s not a factor. Lol I don’t know any other way to really show you unless you were right here and you saw how I do everything. I don’t go over there at all. all tying of the dinghy takes place between the two columns or lined up exactly with the two columns.

I think you can see in the pictures how I have the dinghy tied up. I don’t go outside the davits for that tie up

[rslifkin]

Originally Posted by Chotu

OK. You’ll have take my word that it’s not a factor. Lol I don’t know any other way to really show you unless you were right here and you saw how I do everything. I don’t go over there at all. all tying of the dinghy takes place between the two columns or lined up exactly with the two columns.

I think you can see in the pictures how I have the dinghy tied up. I don’t go outside the davits for that tie up

If everything is reached between the poles, then yeah, whatever you add outside them isn't an issue. I couldn't tell from the picture if you could reach the drain plug, etc. from the center.

[Chotu]

Originally Posted by rslifkin

If everything is reached between the poles, then yeah, whatever you add outside them isn't an issue. I couldn't tell from the picture if you could reach the drain plug, etc. from the center.

yeah that’s where the Internet fails. It’s hard to see all of that with the picture angles.

to get the drain plug for instance, you have no choice but to go between the poles. You can’t reach it from outside the poles. As weird as that may seem

[Cavalier MK2]

You can find mainsheet load calculators on line which ma help. For example a 20 foot boom and 60 foot luff in 25 knots of wind gives under 5000 pounds of load. Add safety factors in to see how you need to beef things up, or not.

[Chotu]

Originally Posted by Cavalier MK2

You can find mainsheet load calculators on line which ma help. For example a 20 foot boom and 60 foot luff in 25 knots of wind gives under 5000 pounds of load. Add safety factors in to see how you need to beef things up, or not.

Might as well go through the exercise….

only problem is they ask for a wind speed. What do I put? 15 knots? 20 knots? Reefing and easing the sheet will happen.

[Chotu]

so here are the results for the actual mainsheet load:

Foot of sail: 20ft
Luff of sail: 55ft
Assuming attachment point at 20ft at end of boom.

Load @ 15 knots: 1055 lbs
Load @ 20 knots: 1876 lbs

I think there should have been a reef in before I hit 20 knots, but to assume worst case scenario, i put it in anyway.


1876lbs is 850kg. a FAR cry from 7000kg (which is more than my boat weighs)

glad we went through the exercise because this explains why it works on all the boats that have it and why it works on that very skimpy metal in the pic jedi put up. The sky is not falling.

[MicHughV]

Chotu,
You need to factor in some "shock loads" in your load estimates.
ie, an accidental jibe can have that boom zipping across the cabin top lickity split !
'jes sayin'....

[rslifkin]

I think everyone leans conservative on this one because of margin for shock loads or accidental mishandling. And because the result of a failure is really bad.

[Chotu]

Originally Posted by MicHughV

Chotu,
You need to factor in some "shock loads" in your load estimates.
ie, an accidental jibe can have that boom zipping across the cabin top lickity split !
'jes sayin'....

although I have never had one in my life, I agree.

safety factor has to be added.

additionally it’s probably time to figure out when to reef this boat now.

That’s something I have no idea about.