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Old 27-09-2011, 09:40   #31
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Re: Deck- vs Keel-Stepped Mast

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Originally Posted by barnakiel View Post
It only depends on how much of a tech freak you are. I tend to spend long moments (ask my first mate and she will tell you 'too long moments') just walking the docks and looking at how boats are made, set up and laid out.

Here a link to what I quickly got off the web:
Sailboat Family: Preparing to Unstep the Mast - Marking the Standing Rigging

In our marina, there is a couple of boats with the same arrangement. The less extreme, and in my eyes still very much desired, solution is to have continuous shrouds even when they end up on the same chainplate. I think when such a twin chainplate is beefy enough this solution is as good or better than the separate chainplates way.

The discontinuous rigging/single chainplate is most common today. It is also the one I like least. In the racing context, I would take it - less weight, less windage, etc.. Yet on a cruising boat, I would always chose the continuous rigging and beefy plates.

b.
G'Day Barnie,

Yep, I agree that the linked boat has a separate chainplate for the intermediate, but I still think that it is an uncommon way to do things. It appears that two of those chainplates penetrate the deck adjacent to each other, and I'd guess that they simply are through-bolted, one on each side of a bulkhead down in the cabin. Seems to me that this results in three deck penetrations with rather slender chainplates (more flex) and is really asking for leakage.

So, I think that having all of the shrouds come to a single, well engineered, beefy plate is the best solution. Oddly enough, that's exactly what we have on Insatiable II: swept back spreaders, continuous intermediate, single chainplate made of 12 mm 2205 duplex stainless (no crevice or oxygen starvation corrosion), tapering in width from ~75 mm at the top to ~150 mm where it bolts to a 25 mm thick structural partial bulkhead.
This plate is stiff enough that the sealant has only required one renewal in the 8 years that we have owned the boat.

I have mixed feelings about discontinuous rigging. There are some potential weight aloft and windage advantages, the chainplate is a bit simpler, etc, but my biggest hangup with it is having to go aloft under sail to tune the rig. I found that to be a big PITA on Insatiable I which had such an arrangement.

And I too spend a lot of time looking at other boats. Sometimes one gets good ideas that way, but sadly, more often I am appalled by the shortcuts taken by some builders.

Finally, for the OP, I've always preferred keel stepped masts because of their better stiffness (as mentioned in a previous post) and the fact that they will stand with little aid whilst doing rigging jobs. I do agree that a well engineered deck step is perfectly seaworthy.

Cheers,

Jim
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Old 27-09-2011, 13:27   #32
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Re: Deck- vs Keel-Stepped Mast

UD has 7 chainplates per side.

Main has 3, 1 for shroud, 2 for intermediate stays.

Mizzen has 4, 1 shroud and 2 for intermediates. Plus 1 for the split main back stay.
Only 1 stay/shroud per chain plate to keep loads in a constant direction...
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Old 27-09-2011, 15:23   #33
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Re: Deck- vs Keel-Stepped Mast

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Originally Posted by Jim Cate View Post

(...) So, I think that having all of the shrouds come to a single, well engineered, beefy plate is the best solution. (...)
G'Day,

You are absolutely right - the separate plates are less common than one plate for both shrouds. Also when the single plate is designed and executed right, it will be as good as separate plates. Probably in GRP or wood construction it is much easier to execute too.

BTW On chainplates: on my boat, the lower screw/fork clearance is about 12 mm, but the chainplate material is only some 6 mm thick ... wondering why the builder did not use thicker material (other than that it is harder to cut and drill). I think when making new ones I will have them made of much thicker plate!

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Old 27-09-2011, 16:20   #34
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Re: Deck- vs Keel-Stepped Mast

Quote:
Originally Posted by Unicorn Dreams View Post
UD has 7 chainplates per side.

Main has 3, 1 for shroud, 2 for intermediate stays.

Mizzen has 4, 1 shroud and 2 for intermediates. Plus 1 for the split main back stay.
Only 1 stay/shroud per chain plate to keep loads in a constant direction...
G'Day UD,

I think we may have a nomenclature difference here. Intermediate shrouds are the ones that come from the roots of 2nd and/or 3rd spreaders... I doubt if your ketch has a triple spreader mainmast! I think what you are calling intermediates are usually called lower shrouds. Some rigs have two per side, and this requires separate chainplates as you describe. Other rigs have but one per side, and this may or may not have a separate plate fitted.

Rigs with two lowers have better fore and aft support of the lower panel of the mast, and boats with single lowers often have a baby stay to help avoid mast pumping and control lower panel bend.

Each variation of the rig has good and bad points, so we all suffer from the usual compromises, tailored to our individual ideas and prejudices.

Cheers,

Jim
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