Chainplate clearance/tolerance

[galleywench]

I am beginning to see the light at the end of the tunnel for my recore (very distant, faint light) and while I'm not quite ready yet, I am thinking ahead about the clearance tolerance for the chainplates as they pass through the deck. I know it needs to be tight enough of a fit to allow for sealant to keep the water out, but how tight should it be? Right now, the chainplates are hammer tight (I need a hammer to pull them through the deck) and I'm wondering if this will lead to the area around the chainplate to crack if/when the chainplates move while sailing? I know that they probably shouldn't be moving much, but experience tells me that Everything on a boat will eventually move.

Any thoughts would be appreciated.

[Hirilondë]

If sealing them were the only consideration then a bevel in the deck around the chainplate into which sealant could by placed before installing the cover would be sufficient. It is also important to have a little wiggle room so that when put under load the chainplates don't transfer this load onto the deck in any way. I don't think any more than 1/8" should be necessary. A bevel in the deck around the hole, or in the down side of the cover also around the hole through it, or both, will help with sealing.

[galleywench]

It is also important to have a little wiggle room so that when put under load the chainplates don't transfer this load onto the deck in any way.

Excellent, thanks for the feedback, this is what I was worrying about. When I pulled the chainplates prior to recoring the deck, they were really tight, but I figured that it was due to the rotting, swollen core that was my entire deck and I just wasn't sure how much tolerance they need.

I don't think any more than 1/8" should be necessary. A bevel in the deck around the hole, or in the down side of the cover also around the hole through it, or both, will help with sealing.

Do you mean a 1/8" gap on each side or 1/8" total (ie 1/16" for each side)?
I do plan on beveling the top of the hole for sealant purposes and I'm considering adding risers to keep them slightly above deck level, but thats another topic.

[Hirilondë]

You need just enough room that the chain plate does not work against the deck. So I figure there is no need for any more than 1/8" all around. They should not really move when loaded, but the small gap assures that any slight movement does not interpret into pressure against the deck. It is just a safety margin.

[Drew]

I used a big (~1/4") chamfer in both the deck and the fiberglass cover-plate. I had about 1/32" to 1/16" clearance between the deck and the chainplate.



They don't leak a drop and I could not be happier with the installation.

drew

[galleywench]

Cool, I like those risers. Are they molded in place or are they covers held in place by sealant?
Also, is that photo of your a35? If so, it looks like the toerail is a bit narrower than mine (maybe it's the photo), I'm not sure if mine is the original or not but mine is ~3 inches wide. I'll be replacing mine once the decks are done and that's another thing I am beginning to worry about doing.

[Drew]

The "risers" are not molded, they are covers held in place by sealant.

I believe that the best way to prevent leaks is to have sufficient sealant thickness at the gland or sealing area. A thin layer of sealant is not nearly as flexible as a thicker layer and cannot withstand as much movement without failing. I cut a substantial bevel in both the deck and the cover so there is a large triangular cross section that is full of sealant.

That way there is a large surface area to bond to the chain-plate and sufficient thickness to accommodate any movement without compromising the seal.

Yes, the photo is of my A35. She was built in 1966. I do not know the hull number.

Drew

[sscoll]

Timely topic, I'm learning, thanks. I'm thinking of moving my chainplates to the outside of the hull and am looking for suggestions regarding the structural requirements for doing that. Any thoughts or suggestions where I might look for information along those lines would be appreciated.

Steve

[Rachel]

Steve,

This is addressed in Dave Gerr's book "The Elements of Boat Strength: For Builders, Designers, and Owners." I think it's a great book to have for reference and just reading. If I remember correctly, he gives a thickness and height/width of reinforcement that one should add to the hull. I'll see if I can look it up for you and post back in a while.

Edited to add: Here is what Dave Gerr says in the book mentioned above:

Where [chainplates are bolted to the hull topsides], the topsides laminate must be increased as follows:

Chainplate-Region Topsides Laminate = 1.3 x topsides laminate thickness
Fore-n-Aft Length of Chainplate Region = beam overall at chainplates
Height of Chainplate Region = from sheer down to lowest chainplate bolt, plus a distance equal to 20 times the lowest bolt diameter down beyond the lowest bolt.

elements.jpg (56.19 KiB) Viewed 2572 times

[sscoll]

Thanks Rachel,

I think I'd best get the book. The reference "Fore-n-Aft Length of Chainplate Region = beam overall at chainplates" sounds like I need to spend a bit of time digesting what it may mean.

I appreciate it.

Steve

[Rachel]

The reference "Fore-n-Aft Length of Chainplate Region = beam overall at chainplates" sounds like I need to spend a bit of time digesting what it may mean.

Hmm, I think that was the right wording, but my guess is that either he or I left out an "inches" symbol.

The way I would take it would be that if the beam of your boat were 8 feet at the chainplates, then the "width" of your hull reinforcement for the new outboard chainplates would be 8 inches. In other words, if you were laying in cloth to make the boat thicker in that region (in order to meet his scantlings), then the cloth area would be 8" wide (as you stand in the boat facing outboard/athwartships at the chainplate region).

I will double check what it says in the book though.

So running through it all (and assuming for now that an inch mark was left out):

Chainplate-Region Topsides Laminate = 1.3 x topsides laminate thickness

Let's say your topsides are 1/2" (.5") thick, so now the area of topsides where the chainplates will go should be 1.3 times that much, or .65" thick.

Fore-n-Aft Length of Chainplate Region = beam overall at chainplates

If beam there is 8', then the width of the new "patch" will be 8"

Height of Chainplate Region = from sheer down to lowest chainplate bolt, plus a distance equal to 20 times the lowest bolt diameter down beyond the lowest bolt.

If it's, say, 10" from the sheer down to the lowest chainplate bolt, then the first figure for this reinforcement patch would be 10". If the lowest bolt diameter is, say, 3/8", then you add twenty times that, or 7.5" more, for a total of 17.5"

So (again, if I have this right), if you were going to reinforce the topsides in the way of your new outboard chainplates with fiberglass according to Gerr's book, you would add a "patch" in that area that was 8" wide, about 1/8" thick, and 17.5 long (or tall).

I would think there are other acceptable methods for making the new chainplate area strong enough. And indeed, Gerr says in his book that there are many ways to go about things, and that what he's trying to do is share at least one of them in facts and figures, so that builders have some numbers to go on should they want them.

Rachel

PS: His book also has interesting information on things like the advantages of biaxial +/-45º fabric (and when you can use those advantages vs. when they are not adding anything), and other such scintillating topics. There are also sections on steel and wood, although I have not read them (yet).

[sscoll]

Thanks Rachel,

James Baldwin just directed me to Fernando's Pajero pages on this same topic. Between the two of you I think I've got it figured.

Steve
#532

[Rachel]

http://www.pajaroweb.com/refits-en.html

By the way, I checked Gerr's book on that chainplate formula, and I had typed it just as it was in the book (page 58). Although I think most people would presume a change from feet (beam) to inches (chainplate reinforcement area), it would probably have been a plus to have added "in inches" to the text.