CD 27 mast compression

[mikebikeboy]

Hi everyone, my first post here. Looking forward to engaging with the community.

I have a CD 27 I've been sailing for a couple months. I stepped the mast and tuned the rigging myself, so have been fiddling with it. I noticed the jib sail would "pump" sometimes when heading close into the wind so I thought perhaps the fore / back stays were too loose. I tightened them. A few weeks later I was in the cabin and noticed a bulge behind the interior liner ceiling, just aft of the doorway going to the head. Seems that tightening the backstay has caused mast compression enough to push the deck down. I've since loosened the entire rig in the hopes that the deck will return to normal.

Any other CD 27 owners have this issue and if so, is it simply because I had the rig too tight?

I hope I didn't damage the boat!

[csoule13]

http://capedory.org/board/viewtopic.php?f=1&t=37538

Give this thread a look. I certainly haven't had that happened and given the engineering, hoo boy, that would take some doing.

[mikebikeboy]

Thanks for sharing that thread. Helps to understand how it's constructed.

Out of curiosity do you know the tension settings you use on your CD27? The manual doesn't mention a % of breaking point for the wires, just says to tighten them so they have 1 inch or so of play when you pull on them with "some force". I thought I was within that, that's why I didn't worry about it when I tightened it.

Will go to the boat in a day or so to check if the deck has remembered it's old shape.

[fmueller]

FYI The mast step plate in the 27 is not aft of the door between the cabin and the head space. It is more or less centered or maybe slightly forward of center overhead in the head space and aft of the opening to the v berth. So hard to imagine over tensioning of the stays would create a sag in the location you mention, but who knows. Water ingress under the mast might do two things, corrode the steel member that is glassed into the cabin trunk to spread the compression load to the 4 mahogany posts that form the door opening, and/or rot the core of the cabin roof - both of which would compromise the strength of the cabin roof and therefor its capacity to support the mast.

I owe this thread and the previous thread some pictures of the access panel I cut over my head just to be able to see the structure up in there and more easily service the wire harness that come thru the deck by the mast. I'll try to get on this this week and post here and in the previous thread.

It's a trivial matter to cut the liner and fashion a panel to cover the resulting opening so you can investigate. I made mine about 8"x10" and off to the port side where there is a gland that allows wires to pass thru. When I bought the boat that fitting leaked just a little. Thankfully it had no effect on the core of my cabin roof and did not cause any rusting of the encapsulated mild steel support that I can see. To casually check the core of the cabin roof or any cored deck space you can just tap lightly with a screwdriver handle. Dry deck will have a high pitched tapping sound, while wet core will generally have a lower and more muffled sound. You can also get a moisture reading device and scan your deck surfaces.

When I bought Jerezana I borrowed one from the yard she was in and she scanned bone dry all over - and all else equal, that is why I bought her, even though she had lots of crazing in her topside gelcoat.

https://www.tequipment.net/FLIR/MR160/B ... boQAvD_BwE

[mikebikeboy]

FYI The mast step position in the 27 is not aft of the door between the cabin and the head space. It is more or less centered or maybe slightly forward of center overhead in the head space and aft of the opening to the v berth. So hard to imagine over tensioning of the stays would create a sag in the location you mention.

That's true! A previous owner had cut out a circle in the head lining where the wires come out of the mast boot. So I am aware of the location of the mast. Why would the bulge be appearing aft of the doorway? Up top on deck I saw no new crazing in the gelcoat, and nothing seemed to be depressed up there.

What in the world

The mast is raked aft a little bit, could that have caused the support system the mast is held up by, to tilt and cause that bulge? Maybe I need to make sure the mast is perfectly vertical.

[fmueller]

Mike,

Also - I've got my backstay at about 900 pounds (if I'm remembering correctly, I'll check) with a Loos Gauge (the forestay is not measurable under the furling blade, but it would measure a little higher due to the more vertical angle compare to the backstay), but if you get the backstya correct ... the forestay is by default correct. I got tired of guessing so I bought the gauge. Same for the upper stays, port and stbd. Lowers are at about 450 - 500. The forward lowers should be a little tighter than the aft lowers - and that will limit pumping just a bit. Also rule of thumb if you don't have a gauge: leeward shrouds when close hauled should be tight enough to eliminate any visible looseness in fairly heavy air. If you can see movement, they are not tight enough. That gives you a way to incrementally add correct tension. Most people under tension if working by "feel". When you do get the tension right the rig just looks and feels good. One of my aft lowers is a wee bit loose now, but after a summer of sailing often in some righteous breeze, which we've had a lot of this year.

Fred

[mikebikeboy]

Mike,

Also - I've got my backstay at about 900 pounds (if I'm remembering correctly, I'll check) with a Loos Gauge (the forestay is not measurable under the furling blade, but it would measure a little higher due to the more vertical angle compare to the backstay), but if you get the backstya correct ... the forestay is by default correct. I got tired of guessing so I bought the gauge. Same for the upper stays, port and stbd. Lowers are at about 450 - 500. The forward lowers should be a little tighter than the aft lowers - and that will limit pumping just a bit. Also rule of thumb if you don't have a gauge: leeward shrouds when close hauled should be tight enough to eliminate any visible looseness in fairly heavy air. If you can see movement, they are not tight enough. That gives you a way to incrementally add correct tension. Most people under tension if working by "feel". When you do get the tension right the rig just looks and feels good.

Fred

Fred,

Excellent data, thank you. I have a Loos coming tomorrow so will definitely use that from now on.

[Keith]

Mike,

Also - I've got my backstay at about 900 pounds (if I'm remembering correctly, I'll check) with a Loos Gauge (the forestay is not measurable under the furling blade, but it would measure a little higher due to the more vertical angle compare to the backstay), but if you get the backstya correct ... the forestay is by default correct. I got tired of guessing so I bought the gauge. Same for the upper stays, port and stbd. Lowers are at about 450 - 500. The forward lowers should be a little tighter than the aft lowers - and that will limit pumping just a bit. Also rule of thumb if you don't have a gauge: leeward shrouds when close hauled should be tight enough to eliminate any visible looseness in fairly heavy air. If you can see movement, they are not tight enough. That gives you a way to incrementally add correct tension. Most people under tension if working by "feel". When you do get the tension right the rig just looks and feels good. One of my aft lowers is a wee bit loose now, but after a summer of sailing often in some righteous breeze, which we've had a lot of this year.

Fred

I believe that the rule of thumb is that the leeward shrouds should start to show slack at 20 deg of heel. I'm trying to remember where I read that. If I do remember I will post it.

Keith

[fmueller]

Went back to my sheet I kept with the Loos gauge.

I have been using 15% of breaking per the Loos reference charts as ballpark. I have my 7/32 backstay at about 900 pounds - “30” on the gauge I wrote down.. and my side stays a notch under that - “29” on the Loos PT 2. I parsed about 500 pounds on my 5/32 lowers by reading 5-6 notches down on the chart ... I did not want to buy two gauges - at “12” on the PT 2. I added one turn to the forward lowers and slacked 1/2 turn on the aft lowers after setting them all the same. Sailing in very heavy air will show just occasional “dancing” in the off wind shrouds, usually the aft lower first. It looks like a plucked guitar string. They are never visibly slack. Most days I don’t see any movement.

If you read the Loos site, they caution that shock loading is more detrimental than slight over tensioning. So I have gone on that advice especially since I can have high confidence that I am not significantly over tensioned. I also had a well respected rigger on my boat two years ago who tunes many boats in the Newport racing scene and he was pretty clear that he did not like to see any movement in standing rigging excepting back stays and running side stays. Especially on cruising boats he said.

[mikebikeboy]

Went back to my sheet I kept with the Loos gauge.

I have been using 15% of breaking per the Loos reference charts as ballpark. I have my 7/32 backstay at about 900 pounds - “30” on the gauge I wrote down.. and my side stays a notch under that - “29” on the Loos PT 2. I parsed about 500 pounds on my 5/32 lowers by reading 5-6 notches down on the chart ... I did not want to buy two gauges - at “12” on the PT 2. I added one turn to the forward lowers and slacked 1/2 turn on the aft lowers after setting them all the same. Sailing in very heavy air will show just occasional “dancing” in the off wind shrouds, usually the aft lower first. It looks like a plucked guitar string. They are never visibly slack. Most days I don’t see any movement.

If you read the Loos site, they caution that shock loading is more detrimental than slight over tensioning. So I have gone on that advice especially since I can have high confidence that I am not significantly over tensioned. I also had a well respected rigger on my boat two years ago who tunes many boats in the Newport racing scene and he was pretty clear that he did not like to see any movement in standing rigging excepting back stays and running side stays. Especially on cruising boats he said.

Fred, thank you very much for this! Getting my PT 2 in the mail today, will check on boat in the next couple of days and report back. I'm crossing my fingers that the bulge has gone away and I've not actually damaged anything permanently.

[mikebikeboy]

Hi Fred and everyone else,

I've gone back to the boat with my new Loos PT-2 gauge. The bulge had not completely popped out but had receded a little. I tuned the rigging, however once I got to 25 on the backstay I stopped. That was about as tight as I had it before. Same with cap shrouds. I stopped at about 26 on those as that was about how tight it was before, when I noticed the bulge in the cabin. I've also attached a few pictures here with notes, as to what I found upon closer inspection and taking measurements. What I'm deducing is this was most likely an issue long before I bought the boat, and the previous owners lived with it. So I can choose to also live with it or try and fix it.

[mikebikeboy]

A few more pictures. I've put a couple concepts here which might be completely wrong as I've never installed a compression post before. Any tips very much appreciated.

[mikebikeboy]

Another idea:

[fmueller]

Mike ,

I think you may know more about this than I do ...

I thought it was more like this. (see pix) ... either way I think you've got to discover if your support structure (which I have read is embedded mild steel) has not rusted due to water incursion. Or do you have rotted core in your coach roof.

If it was my boat I'd remove a very large section of the hull liner (ceiling) on the assumption that it can be replaced easily enough with a slightly larger piece of suitable material; just so you can see what is going on ... I would not want to "live with" a rig that can't be properly tensioned and I'm ptrtty sure that our CD 27 backstays want to be at 800-900 pounds for 7/32 wire. The liner itself is not structural I don't think.

One of the crits about Cape Dorys from would be open ocean sailors is that the hull lining in Cape Dorys really inhibits inspection and care of the hull or in this case, your coach roof. Fat chance of anyone plugging a hull breach on a stock Cape dory.

I'll be sure to look carefully up into the opening I do have on my boat just to verify where I think the support structure is ... I'll report back here later in the week.

cheers

Fred

[mikebikeboy]

Hi Fred,

Thanks for the info. I'll look forward to hearing back about what you find on your boat.

Looking at your drawing of where the steel members are, makes me think that the steel member spanning the aft bulkhead has failed and needs supporting. There is no sagging under the forward bulkhead.

Here is a picture I found from the Minimus refit, where they added a support beam. I think their boat is the 25, also no compression post.