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

[Chotu]

Originally Posted by rslifkin

Using just the center sheet near the centerline won't be optimal, but it's not a big loss. Going to a double mainsheet or a short traveler and then the downhauls for when you get the boom further out will give you more control, but more complexity.

I agree with your analysis. It also surprises me how quiet this thread is. my standing rigging thread had all sorts of opinions on what I should do.

with this topic, people don’t seem to have strong opinions

[rslifkin]

Originally Posted by Chotu

I agree with your analysis. It also surprises me how quiet this thread is. my standing rigging thread had all sorts of opinions on what I should do.

with this topic, people don’t seem to have strong opinions

I think there are a lot more workable or "correct" options for the running rigging. And also a lot more ability to make adjustments later.

[catsketcher]

Okay - I'll bite

Although I have had my say so far, in reality, I can't believe Chotu can be making such humungous errors after building a boat.

A boat is a series of intersecting design choices that affect one another in multiuple ways, so popping a cockpit cover on or dinghy davits and then wondering how the mainsheet system is going to work is so silly I can't believe anyone could do such a thing. This should have been thought of years ago, say with a backing plate inside the aft beam and threads spaced to take the track you bought almost when you built the boat. All built in before you even started building the hulls. Then you stick to the plans, or at least ensure that any modifications don't bite you in the bum, like yours have done. Your have made some pretty bewildering choices.

The mainsheet system may take a load of close to half the boat's displacement or even more. I am guessing this means about 7000kg and at angles ranging from straight up to mostly sideways. A bit of spectra or some alloy tube just aint going to cut it. For a cat of any decent size this means some really serious engineering, to ensure the loads can be brought safely down from the boom to the beam, or whatever strong point you have, integrated into the boat in a stress reducing way. This is the job of a good designer who can obtain an intuitive and mathematical sense of load paths, not something you can get from people who have never seen your boat. Cut the davits back and the cockpit cover as well, back to something that allows the designed system to work. Or worry every time you sail with a botched together system and watch it break and snatch away your roof during a gybe, or even worse watch as it breaks and kills someone like has happened on large monos with mains not much bigger than yours. As talented as the guys on this forum are, we don't know your boat, we don't know the loads, we don't know your reinforcing and we don't know the angles of loads and due to this, we don't know what we are talking about - follow the plans.

[Chotu]

Huh. That wasn’t a very good response. Not what i was hoping for. Participation was what i was hoping for.

The plans have the load going to the main aft structural beam.

It still does, via the huge columns and some guy wires we have discussed.

No difference.

And you really think a piece of dyneema, (why are you talking about spectra??) adequately sized, isn’t going to hold up to the loads of… ANOTHER PIECE OF DYNEEMA??? That’s dense. Illogical thinking.

Let’s refrain from put downs and attacks in this thread please. it’s not productive and makes you look like a not very good person, imo

Honestly, this seems kind of uncharacteristic of you.


You made plenty of errors building your boats. don’t even begin to say you didn’t. everyone does, even big manufacturers. we correct them as we go. only difference is i’m not trying to pretend i didn’t make mistakes. i’m not afraid to show them, bring them into the light and fix them rather than burying them. no one has ever built a boat without errors. i’m making sure my errors are fully addressed. this was my big error. the davits. i’m not afraid to admit i painted myself into a corner so i can expose the problem and address it. BUT… i don’t need unhelpful criticizing posts.

i need help

PS: there ARE HUGE composite backing plates in the main beam. also the load path is a straight line either up or at the max angle as boom eases all the way out. ridiculous

[Chotu]

Throughout my build people have made posts like this. and you were wrong EVERY SINGLE TIME. EVERY TIME!

everything i’ve done works perfectly. the boat is amazing.

you’re just projecting your own fear and that’s not needed in a design brainstorming thread.

please save your fear for your own boat

[Chotu]

1/2” dyneema.

34,000lbs breaking strength. My boat cannot displace more than 18,000 lbs and currently is more like 15,000.

that’s just 1/2”. one piece could pick up 2 of my boats and you say it can’t handle the load from the main?

https://www.westmarine.com/samson-ro...-11097458.html


would love to see the logic behind this

[s/v Jedi]

Let’s look at the error with the davits. Can it be fixed instead of working around it?

I think may be it can. The beams you have on top of the roof, I think they can be moved down under the aft structural beam and mount chocks on top the beams that the dinghy can sit in securely. I’m sure you have seen this arrangement.

This leaves moving the dinghy in/out the water which I like how they do it with a large hinged arm (Chris White did that) but I also saw cats that can extend a lifting point from the aft end of the boom.

If you would do all that, would this allow a regular main sheet system or is the roof still in the way?

[rslifkin]

Originally Posted by s/v Jedi

Let’s look at the error with the davits. Can it be fixed instead of working around it?

I think may be it can. The beams you have on top of the roof, I think they can be moved down under the aft structural beam and mount chocks on top the beams that the dinghy can sit in securely. I’m sure you have seen this arrangement.

This leaves moving the dinghy in/out the water which I like how they do it with a large hinged arm (Chris White did that) but I also saw cats that can extend a lifting point from the aft end of the boom.

If you would do all that, would this allow a regular main sheet system or is the roof still in the way?

Looking at the pictures a mainsheet on the beam would clear the roof in the center, but it might need the roof trimmed a little bit further outboard.

[s/v Jedi]

Originally Posted by Chotu

1/2” dyneema.

34,000lbs breaking strength. My boat cannot displace more than 18,000 lbs and currently is more like 15,000.

that’s just 1/2”. one piece could pick up 2 of my boats and you say it can’t handle the load from the main?

https://www.westmarine.com/samson-ro...-11097458.html


would love to see the logic behind this

What we don’t know is if the designer meant for a traveler that spreads the load over the length of the aft beam or if the design allows point loading. Now I believe I remember that the traveler doesn’t really spread the load much but I’m an EE not some structural architect wizard

But I feel confident you can reinforce the roof enough for the main sheet, the question is how. I would be tempted to remove everything on top and laminate reinforcement straight on top of it.

Catsketcher is right that it would be better to design the main sheet system first, then the dinghy hoist around it. Of course you can design the main sheet system to accommodate the davits.

[Chotu]

Originally Posted by rslifkin

Looking at the pictures a mainsheet on the beam would clear the roof in the center, but it might need the roof trimmed a little bit further outboard.

this is absolutely correct. An arc would need to be cut out of the roof and the davits would have to go. I’m not really wanting to get rid of the davits. That would be the last choice

[Chotu]

Originally Posted by s/v Jedi

Let’s look at the error with the davits. Can it be fixed instead of working around it?

I think may be it can. The beams you have on top of the roof, I think they can be moved down under the aft structural beam and mount chocks on top the beams that the dinghy can sit in securely. I’m sure you have seen this arrangement.

This leaves moving the dinghy in/out the water which I like how they do it with a large hinged arm (Chris White did that) but I also saw cats that can extend a lifting point from the aft end of the boom.

If you would do all that, would this allow a regular main sheet system or is the roof still in the way?

I would strongly prefer to keep those davits and not introduce another several week project delay things more. I also prefer those types of davits.

finding a way to bring the load from the main sheet down to the beam kind of like we have done already, would be most preferable.

and yes, the roof would be in the way as the main sheet is eased.


Tons of catamarans have the sheet loads on the roof goi through something to the beam.

my last one even had it through an aluminum arch added later. lol

Certainly i have the ability to do this right since i’m starting from scratch here.

I think we were on the right path before. the loads were accounted for.

the issue was the complexity of the sheeting and downhaul with the cabin roof in the way.

i was hoping to perfect that issue, but maybe it’s something i’ll have to live with if i want those davits

[s/v Jedi]

Originally Posted by Chotu

I would strongly prefer to keep those davits and not introduce another several week project delay things more. I also prefer those types of davits.

finding a way to bring the load from the main sheet down to the beam kind of like we have done already, would be most preferable.

and yes, the roof would be in the way as the main sheet is eased.

Would moving the beams take weeks? I would most definitely take that approach (would have done it initially and did recommend it iirc) but of course we all make our own choices. I know you can make the roof strong enough because I see it on many boats.

[Cavalier MK2]

I'm going to have to look at these threads I've chipped in pretty casually. Where do I find a picture of the roof and davits?

For me sailing builds/mods have a list of priorities, it puts needs before wants.
Safety, sailing function, simplicity, whole system integration.

Spending a few weeks to get things right is small change compared to years of a build or (hopefully) years more of sailing so do what you have to to restore primary function.

Everything about boats is a compromise so make them with the emphasis on safety and primary function.

Without seeing anything here are a couple thoughts.
Curves look better than straight lines anyway, if that is all your structure needs to clear the mainsheet and you can keep your davits that is a great way to go.

An issue with dyneema taking the loads down would be creep, you might be creating a convertible with a spontaneous pop top if you go that way.

Walk the deck, practice with lines till you can check the boxes, you have time before building weather returns.

Everybody starts somewhere, Phil isn't wrong about priorities so bear that in mind. As you use your boat improvements will suggest themselves and refinements will come. You are never done with a boat, check the list, safety first.

[Chotu]

Originally Posted by s/v Jedi

Would moving the beams take weeks? I would most definitely take that approach (would have done it initially and did recommend it iirc) but of course we all make our own choices. I know you can make the roof strong enough because I see it on many boats.

definitely. and it’s epoxy work and it would make the boat a lot less enjoyable.

i’m more inclined to move forward rather than backward. and exactly. the majority of cats actually have the sheet on the roof. so…. it’s certainly fine provided the loads have a path to follow to the beam

[Chotu]

Originally Posted by Cavalier MK2

I'm going to have to look at these threads I've chipped in pretty casually. Where do I find a picture of the roof and davits?

For me sailing builds/mods have a list of priorities, it puts needs before wants.
Safety, sailing function, simplicity, whole system integration.

Spending a few weeks to get things right is small change compared to years of a build or (hopefully) years more of sailing so do what you have to to restore primary function.

Everything about boats is a compromise so make them with the emphasis on safety and primary function.

Without seeing anything here are a couple thoughts.
Curves look better than straight lines anyway, if that is all your structure needs to clear the mainsheet and you can keep your davits that is a great way to go.

An issue with dyneema taking the loads down would be creep, you might be creating a convertible with a spontaneous pop top if you go that way.

Walk the deck, practice with lines till you can check the boxes, you have time before building weather returns.

Everybody starts somewhere, Phil isn't wrong about priorities so bear that in mind. As you use your boat improvements will suggest themselves and refinements will come. You are never done with a boat, check the list, safety first.

pics of everything are on the past couple pages. just after your sketch of your system.

sound advice however.

i was really just asking about various sheeting arrangements. figuring out how to best sheet the main and downhaul it. just like the jib talk. your contributions in addition to others seem to make the most sense.

i have dyneema holding my mast up with pretension and nothing is creeping. why would it creep with this? also, i’m sure i’d have a provision to tighten it. turnbuckle probably.

ultimately, i’m trying to figure out how to do like you are doing, but within the parameters of what i have.

there will be trade offs. it’s a boat. lol. but i’m trying to optimize the trade offs and have a little fun discussing the problem publicly.