Increasing spreader length and adding sweeping aft - Anyone done it?

MiddayGun

Super Anarchist
1,178
442
Yorkshire
I'm thinking of increasing the 'sweep' on my spreaders as well as lengthening them to move the shrouds outboard and I'm looking for some input from people that have made some big rig modifications to their boat, or understand what they're about when it comes to rig dynamics.

So this is purely in the theoretical stage at the moment, and I don't have any concrete measurements as of now as I'm just bandying ideas about as a way to pass the time. (Working offshore)

One problem I've always had with this boat is the mast panting in the midsection in any kind of seaway (or indeed large gust of wind), no matter how the rig is setup or how tight the lowers are, now I already have to replace the chain-plate arrangements this winter as the hull is oil-canning in way of the shroud anchor points. So since I"m going to all the trouble of building a new bulkhead and structure, I don't want to end up in the same situation with the same problems after doing a metric shit tonne of work. 

So this image is the current arrangement, the arrows represent what the rig does when I'm beating in a heavy sea. 

MGC 1.png

As you can see there is minimal sweep on the spreaders, I won't have the exact figure until I can measure the distance across the spreader tips + the length & do some trig, but its not that high. The boat was never built with runners or checks & I've no interest in adding them if avoidable. 

So my idea (which isn't exactly a new one) is to increase the angle of the sweep on the spreaders (to an angle yet to be determined), and increase the length to bring the shrouds as far outboard as possible, moving the chain-plates to suit. To my simple mind this will:

  • Increase the pre-bend induced by the caps due to the added sweep
  • Give the lowers a better angle to stop the mid-sections panting forward
  • Improve forestay tension
  • By moving outboard it should also decrease the rigging loads

Downsides would be inability to use a large Genoa, which we never do, we have a 110% that sheets inside the shrouds (they only came with a self tacker as standard anyway), back-stay won't be able to induce as much bend to flatten the sail, will need new spreaders & mast fitting, its a shit load of work. 

So the rig would look something a bit more like this: 

MGC 2.png

Maybe not as dramatic as that, its just a rough sketch. 

I know a lot of people have done 'IRC Conversions' on old IOR yachts with a lot of success, this is nowhere near as dramatic a change as the boat never came with runners at all, I'm looking to add a bit of stability. This is the boats 3rd mast! The previous two were both lost when racing and beating to weather in rough conditions, I'd rather avoid becoming the 3rd statistic. 

Rough thoughts for the process are to carefully measure the current geometry, settle on how much extra sweep I want on the spreaders, draw it all out so that I can accurately work out the position of chain plates, talk with the mast builder to work out the spreader & bracket choices  and go from there.

So has anyone done this?  Am I in the ball park with my summations so far?
Thought I'd float the idea before I went near the angle grinder. (I do realise it would be far less work to buy a different boat)

 

Irish River

Super Anarchist
1,203
131
BC
In my in law has taken his t-bird to this config. No genoa just jibs. Same main. Has same speed but better point the a stock tbird. 

I think he has 15° sweep of spreaders.  The lowers control mast bend. 

 

mgs

canoeman
1,119
251
maine
I know of an Alerion Express  40 something that added more spreader angle. The chain plates stayed where they were though I think. The owner wanted to remove the backstay. There was a long paper trail with Hall Spars about the whole project, since it was their mast and they were making the spreaders. 

If you already are redoing the chainplate set up, now certainly would be the time. I’d ask someone who builds spars what they think while I was at it. 

 

longy

Overlord of Anarchy
6,733
1,113
San Diego
Keep the lowers inboard. This makes walking past the mast easier and allows a 130% or so to still sheet inboard of the uppers.

 

MiddayGun

Super Anarchist
1,178
442
Yorkshire
Keep the lowers inboard. This makes walking past the mast easier and allows a 130% or so to still sheet inboard of the uppers.
I noticed they did this on the Django 9.80 and I thought it was a good idea. 

The only issue with it I have is that it will increase the loads in the lowers as it will be inboard & aft, so will have more of an 'aft' then a sideways component.
Also the plan had been for the bulkhead that takes the chainplates to be aligned with the load from the shrouds, i.e. pointed towards the mast. 
Which would make the lowers further forward than the caps. 

I managed to get hold of the guy who built the mast and he's going to send me through the drawings & designs specs if he can still find. It was built by Atlantic Spars & Rigging who have since gone kaput, hopefully he still has them. 

@mgs, I'm in contact with the original mast builder. Definetely want to keep the backstay, on my boat it really makes a difference. 

@irish. I've seen various figures thrown around, this article: https://www.aes.net.nz/info.html
Seems to suggest 30 degrees. I'll have to measure what I have now and go from there. 

 
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The mast would need some solid engineering on the new spreader brackets to hold the new longer spreaders in line.

The hull would most likely need substantial beefing up at the outboard location. Lots of load on hull/deck joint due to more leverage.

Again, more engineering translating to more expense.

Why not just add a babystay up forward? Make it adjustable in case you are off a bit on the geometry.

Should solve the mast pumping and you retain ability to use larger jibs/genoas. Cheap solution too.

 

MiddayGun

Super Anarchist
1,178
442
Yorkshire
Don't think I've ever seen a baby stay on a fractional before. 

Anyway it wouldn't work, the problem isn't inducing bend, I can do plenty of that using the backstay, the problem is that even with the lowers on ultra tight they still don't stop the mid section of the mast pushing further forward. 
The cheap & easy solution would be check stays, but I'd rather not go down that route. 

The chainplates need substantial beefing up as it is as the hull is nicely oil canning around the current attachment points when the tension is wound in, I've already got a lay up schedule to build the chainplates, but since I'm going to all that trouble, it makes sense to look at the whole equation. 

Anyway I'll get it planned & priced up and see if its worth the effort. 

 

Rushman

FIIGS
2,493
247
Melbourne, Aust
Take a rigger for a sail, see what they say before doing anything.

lowers on ultra tight.... This sounds wrong to me

shrouds and spreaders to control mast location and forward bend, lowers to control sideways and forward location

babystay to control backwards inversion which leads to mast pumping/breaking

 

MiddayGun

Super Anarchist
1,178
442
Yorkshire
I've had plenty of people who should know come to look at the setup and I'm not totally ignorant myelf, had several rigs with this setup, (Single spreader Fractional) and never encountered one that I couldn't tune out before.  However they all had much greater sweep on the spreaders and with the further aft chainplate position consequently a more favourable angle for the lowers to support the midesction from moving forward. 

I've no idea why people keep mentioning a baby stay, that's a mast head rig thinking, if I want bend I wind on the backstay, if I want more bend then I can wind on the caps more or ease the lowers (to a point), the issue is the midsection of the mast going too far forward, not back. No one even mentioned inversion. All a baby stay wil do is pull it futher. 
As I said to the other guy, check stays would probably work, but I want to avoid them if possible. 

 
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Joakim

Super Anarchist
1,468
102
Finland
This the same Contessa 27 that was discussed a few months ago about chainplate structure reinforcement?

Since you don't use a larger than 110% headsail, why don't you move the chainplates all the way to freeboard where the deck-hull joint is a naturally strong point anyway. This is common practice for most new builds.

I had a similar size boat from 2000 with a deck stepped mast and chainplates at the deck-hull joint. There was quite minimal reinforcement, but the setup was very stiff and no problems with loosing tension or panting in heavy weather. The chainplates where just bolted to hull and deck with a bit thicker solid local laminate just at the chainplate (cored hull elsewhere). 

It didn't have excessive spreader angle. The rig was 9/10 with very nice forestay control using backstay. I think my current boat with inboard shrouds has bigger spreader angle. The top battens look quite bad when the boom is all the way out on a run. The earlier boat didn't have this issue.

A rig designer can give you the correct chainplate location, spreader angle and length.

 

MiddayGun

Super Anarchist
1,178
442
Yorkshire
This the same Contessa 27 that was discussed a few months ago about chainplate structure reinforcement?

Since you don't use a larger than 110% headsail, why don't you move the chainplates all the way to freeboard where the deck-hull joint is a naturally strong point anyway. This is common practice for most new builds.

I had a similar size boat from 2000 with a deck stepped mast and chainplates at the deck-hull joint. There was quite minimal reinforcement, but the setup was very stiff and no problems with loosing tension or panting in heavy weather. The chainplates where just bolted to hull and deck with a bit thicker solid local laminate just at the chainplate (cored hull elsewhere). 

It didn't have excessive spreader angle. The rig was 9/10 with very nice forestay control using backstay. I think my current boat with inboard shrouds has bigger spreader angle. The top battens look quite bad when the boom is all the way out on a run. The earlier boat didn't have this issue.

A rig designer can give you the correct chainplate location, spreader angle and length.
Yeah same boat. 
Not much happened this year yet because I had to take a contract working in the Netherlands & when I'm back since its summer I'd rather sail the thing. Just trying to get a solid plan in place before the end of the season so we can carry out all the work before the spring series next year. 

The chainplate reinforcement is definetely happening, but while I'm doing that, it makes sense to me to look to see if other modifications are required. 
I quite like the idea of moving the chainplates outboard, however given that I've got an aluminium extruded toe rail then I'd need to cut a section of flange off to get the angle for the lowers on the chainplate. Since all stiffness of that toe rail comes from the flange it seems silly to cut a section out in the one of the highest loaded points of the boat. 

I did speak to a company that does this kind of modification & Irc conversions that sort of thing, however the price wasn't justifiable coming to about 10% of the value of the boat. 
I have managed to get in contact with the guy who designed the mast when the previous owner ordered it, his current thougths are that its possible that the spreader tips are not correctly positioned in relation to the chainplates. 
I can't make any real decisions until I've got some extensive measuring done and drawn it all out. 

@gewoon ik, that's probably what a smart person would do. 

This is the best picture i have of spreaders / caps / lowers angles. Took some time last year.. 

resize.jpg

 
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MiddayGun

Super Anarchist
1,178
442
Yorkshire
Did you ever make any progress on this?

Yes, ultimately we were never able to set up the rig satisfactorily, in typical SA style some people just assume you don't know what you're doing regarding setup, but we knew we'd tried all options.

I managed to get in contact with another owner in Poole that said it wasn't uncommon for them to drop the rigs, I also spoke with the original designer Rob Humphries (was actually surprised when it was the man himself who picked up the phone) and he said that the spreaders only came with 10 degrees of rake, which with no runners is very much borderline. Apparently he'd wanted to go more, but apparently Proctor didn't want to, I can't remember the details and it was nearly 40 years ago so by the by.

Anyway he kindly sent me across some dimensioned drawings and I got John Corby to design me a rig, and chainplate attachment system, he's done a lot of these recently, very successfully in some cases.
Not only did he provide the drawings and the layup schedule, he talks you through the whole process, a really nice bloke.
I carried out all the work myself between 2019-2020. Covid led to delays in the new mast so it wasn't until summer 2020 that I was out sailing.

Ultimately we went full width spreaders, 21 degrees of rake and outboard chain plates.

1666252967010.jpeg


1666252981014.jpeg


1666253022602.jpeg


1666253065914.jpeg

1666253079825.jpeg


1666253373924.jpeg


Overall I'm very happy with it, the rig feels solid now, but can still be tuned on the backstay, visually the taper that Z-Spar put on it wasn't as nice as the original but it seems to work.
In terms of the rig size, its a little taller 11.48m overall, the forestay moved up making it closer to 19/20 than the original 7/8ths.
Since overlapping sails are a no with this rig, the extra height and foretriangle area makes a difference, it feels like a powerful rig and I can get some nice forestay tension as well, especially with the backstay wound on.
 

KGB-224

New member
39
0
LIS
Yes, ultimately we were never able to set up the rig satisfactorily, in typical SA style some people just assume you don't know what you're doing regarding setup, but we knew we'd tried all options.

I managed to get in contact with another owner in Poole that said it wasn't uncommon for them to drop the rigs, I also spoke with the original designer Rob Humphries (was actually surprised when it was the man himself who picked up the phone) and he said that the spreaders only came with 10 degrees of rake, which with no runners is very much borderline. Apparently he'd wanted to go more, but apparently Proctor didn't want to, I can't remember the details and it was nearly 40 years ago so by the by.

Anyway he kindly sent me across some dimensioned drawings and I got John Corby to design me a rig, and chainplate attachment system, he's done a lot of these recently, very successfully in some cases.
Not only did he provide the drawings and the layup schedule, he talks you through the whole process, a really nice bloke.
I carried out all the work myself between 2019-2020. Covid led to delays in the new mast so it wasn't until summer 2020 that I was out sailing.

Ultimately we went full width spreaders, 21 degrees of rake and outboard chain plates.

View attachment 547385

View attachment 547386

View attachment 547387

View attachment 547388
View attachment 547389

View attachment 547390

Overall I'm very happy with it, the rig feels solid now, but can still be tuned on the backstay, visually the taper that Z-Spar put on it wasn't as nice as the original but it seems to work.
In terms of the rig size, its a little taller 11.48m overall, the forestay moved up making it closer to 19/20 than the original 7/8ths.
Since overlapping sails are a no with this rig, the extra height and foretriangle area makes a difference, it feels like a powerful rig and I can get some nice forestay tension as well, especially with the backstay wound on.
Very nice looking. A few questions.

1. Do you have any photos of the inside? Particularly the bulkhead you needed to build and install. And the backing plate arrangement?
2. How did this effect your rating, if you have a measure rating. (I understand were in different parts of the world, just curious).
3. Were the chain plates off the shelf parts or part of the new rig build?
 

MiddayGun

Super Anarchist
1,178
442
Yorkshire
Very nice looking. A few questions.

1. Do you have any photos of the inside? Particularly the bulkhead you needed to build and install. And the backing plate arrangement?
2. How did this effect your rating, if you have a measure rating. (I understand were in different parts of the world, just curious).
3. Were the chain plates off the shelf parts or part of the new rig build?

1. See below, the main thing was adding several layers of biaxial cloth on the inside with epoxy. Each getting smaller than the previous one. Backing is just penny (repair) washers. The whole arrangement is in shear so a backing plate isn't really needed. The extra layers of fibreglass are what take the load.
There's a web made from 12mm plywood, up to the deckhead.
Everything done with epoxy.

2. Not sure, I've not re-rated with IRC since I made the change, there's not enough racing to justify it. However my last cert in 2017 I rated 0.878, that was without overlapping headsails. I would imagine it to be similar or perhaps a touch higher due to the larger foretriangle area.

3. Not off the shelf, but a very easy part for any stainless fab guy to make. It's basically stainless plate with a bend at the top and some holes in it.

Hull ground back to bare glass.
1666296832776.jpeg


You can see the anchor point for the old setup. This has since been chopped out.
I was concerned that my grinding may have been over enthusiastic so I put a layer of 600gsm over the whole area you can see, just to be sure. Probably overkill.

The patch:
1666296947211.jpeg


Patch in place
1666296991996.jpeg


The web.
1666297022890.jpeg



1666297064638.jpeg




Chainplates a simple design:
1666297120611.jpeg


Had to move the stanchion as it was right in the place the chainplate needed to go.
1666297158453.jpeg


Measure twice, drill once. (Actually I checked the measurement a 100x at least :D)


1666297197082.jpeg



Bolt on
1666297283157.jpeg
 

KGB-224

New member
39
0
LIS
1. See below, the main thing was adding several layers of biaxial cloth on the inside with epoxy. Each getting smaller than the previous one. Backing is just penny (repair) washers. The whole arrangement is in shear so a backing plate isn't really needed. The extra layers of fibreglass are what take the load.
There's a web made from 12mm plywood, up to the deckhead.
Everything done with epoxy.

2. Not sure, I've not re-rated with IRC since I made the change, there's not enough racing to justify it. However my last cert in 2017 I rated 0.878, that was without overlapping headsails. I would imagine it to be similar or perhaps a touch higher due to the larger foretriangle area.

3. Not off the shelf, but a very easy part for any stainless fab guy to make. It's basically stainless plate with a bend at the top and some holes in it.

Hull ground back to bare glass.
View attachment 547467

You can see the anchor point for the old setup. This has since been chopped out.
I was concerned that my grinding may have been over enthusiastic so I put a layer of 600gsm over the whole area you can see, just to be sure. Probably overkill.

The patch:
View attachment 547468

Patch in place
View attachment 547469

The web.
View attachment 547470


View attachment 547471



Chainplates a simple design:
View attachment 547472

Had to move the stanchion as it was right in the place the chainplate needed to go.
View attachment 547473

Measure twice, drill once. (Actually I checked the measurement a 100x at least :D)


View attachment 547474


Bolt on
View attachment 547475
Thank you for the pics and explanations of the steps.
 

MiddayGun

Super Anarchist
1,178
442
Yorkshire
Thank you for the pics and explanations of the steps.

Unless you really know what you're doing, I would highly recommend getting a naval architect to draw up some plans.
This isn't something to leave to guesswork IMO. Plus your insurance company / surveyor may want that as well.
 

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