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post #1 of Old 01-26-2010 Thread Starter
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chainplates>>inboard vs outboard

This question may have been answered elsewhere but I couldn't find it. Which is better for a crusing boat? Inboard or outboard chainplates. In general it seems to me that chainplates that are bolted through the hull would be stronger and easier to replace and maintain than those that go through the deck and are bolted to a tabbed in plywood bulkhead with possible water intrusion at the deck. Plus, the shrouds may be in the way while going forward some stormy night. So, what are the pro's and con's of each?
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post #2 of Old 01-26-2010
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Inboard chainplates—

May leave the sidedecks free, don't have to pass under them to go forward.
Allow for tighter sheeting angles on the head sail, allowing the boat to point better.
Probably require more tension on the rig to support the mast properly.
If not properly installed and bedded—can lead to water intrusion into the deck or cabin—can lead to deck delamination/core rot or bulkhead rot and create an expensive repair.
Possible risk of crevice corrosion where the chainplate passes through the deck

Outboard chainplates—

Requires wider sheeting angles for genoa, reduces ability to point. May allow an in-board set of tracks for a jib fairlead, which would negate this problem for the most part.
Usually lower rig tension than if mounted inboard.
May obstruct passage forward, as you have to duck the shrouds when going forward.
If mounted to the outside of the hull, can be easily inspected and replaced.
Some risk of crevice corrosion if not bedded properly.
More vulnerable to damage in the case of a collision or allision.
Rigging is further outboard and more liable to be damaged.

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post #3 of Old 01-26-2010
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I think SD pretty much nailed it. It's really about what factors are more important to you. And of course, the chainplate positioning doesn't "make the boat"--there are many other factors. I like having inboard chainplates because I like to be able to beat upwind (tighter sheeting angles). Since we cruise on weekends mostly, being able to get where we want to go while still sailing is nice.

But if we were cruising long-term, then the tighter sheeting angles might be less important to me. For that lifestyle, timelines and "needing to get there" would be less prevalent.

Of course, as I mentioned, chainplate position by itself is just one of a thousand factors in which boat is better for a specific usage (and owner) over another.
-J

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post #4 of Old 01-26-2010
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I agree, SD covered most of the pros and cons succinctly. And as josrulz added, much depends on how you weight those individual factors. After a decade of owning boats with near maintenance-free outboard chainplates, and constantly reading about headaches associated with the higher stress and leak-prone inboard chainplates, it would be tough to go back. Your mileage may vary.

However, I did want to elaborate a bit on the question of sheeting angles. Because some less obvious variables are in play, there is a tendency to make generalizations that overstate the correlation between inboard and outboard chainplates, sheeting angles, and pointing ability.

Sheeting angles do have an affect on pointing ability. Many boats with outboard chainplates sheet their genoas outboard of the shrouds to a track on the caprail. Intuitively, this would seem to lead to a wide sheeting angle. But not necessarily.

The actual sheeting angle is determined more by the geometry of the foretriangle, than the placement inboard or outboard of the chainplates. To envision this, consider two boats: A traditional narrow-beamed cutter, and a more modern, relatively beamy, fractionally rigged sloop. With its mast stepped farther aft, and possibly a short sprit, the cutter has a long foretriangle. The fractional sloop, with its mast stepped much farther forward, and the tack at the stem head, has a short foretriangle.

Next draw a centerline along the decks of these boats, extending it forward to the tack of the headsail. Now measure the respective sheeting angles, from that centerline to their lead tracks.

You might be surprised that, due to its large foretriangle and narrow beam, the cutter with the outboard chainplates and tracks has tighter sheeting angles than the frac sloop, with its short foretriangle, greater beam, and with tracks outboard of the inboard chainplates.

I am not trying to open a debate about whether the cutter rig is more weatherly than a modern fractional sloop -- I only use these two examples to point out the danger of over generalizing.

Another factor that SD mentioned and worth elaborating on, is the placement of inboard vs outboard jib/genoa tracks. Some boats with outboard chainplates, have both inboard and outboard jib/genoa tracks. Some have ONLY outboard or ONLY inboard jib/genoa tracks. An example of the latter is in some modern fractional boats that compensate for the short foretriangle (and associated wider sheeting angles) by putting the chainplates completely outboard and sheeting the headsails inside of them (best of both worlds?)


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post #5 of Old 01-26-2010
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Some pretty much pure race boats like Corby are built with outboard chainplates and a rig that matches

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All excellent points...

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post #7 of Old 01-26-2010
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All good points another thing to keep in mind is: If the boat is desigined for inboard chainplates you have to really build up the inner hull to take the stress and distripute the load into the hull. Some boats nowadays are built real thin on this part of the hull and you may wind up with a weaker solution.
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post #8 of Old 01-26-2010
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I'm just halfway through inspecting and restoring my 12 exterior chainplates on my 37 year old Morgan....


This before and after condition is so much more difficult with the embedded interior chainplates. I have a friend with a Hardin that has bleeding from embedded plates,- I would dread the complexity. I've owned my vessel for 25 years. It's an important factor if you plan longevity. 'take care and joy, Aythya crew
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Glassed in chainplates are a real nightmare in terms of inspection and replacement. First, being glassed in means that crevice corrosion is usually a major factor, especially if the deck is leaking at all. Second, visual inspection is basically not possible with glassed-in chainplates... Really hate when boat builders do that.

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—Cpt. Mal Reynolds, Serenity (edited)

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post #10 of Old 01-27-2010 Thread Starter
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Thanks to all who responded to my question. I have a much better understanding of the forces at work here. I hadn't really thought much about sheeting angles, so now that is another matter to study in my search for "the perfect boat" although I know there is no such animal. Right now it's about 60/40 in favor of outboards due to ease of maintinance.
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