chainplate knees??

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chainplate knees??

Postby nhdory » Fri Jul 06, 2007 5:22 pm

I am in the process of cutting knees for the chainplates in my 65 Frisco Flyer. Originally they were layed up in the hull and I removed them because they were 42 years old and showing some signs of corrosion. The plan now is to put them on knees as I have seen on other small boats. I was wondering how thinck should the knees be? I cut up a couple which are 2 inches thick as this matches the other knees in the boat which support the cabin house but I have never seen knees on a 25 ft boat this big. The ones I have seen were approx 1 inch thick and smaller in size. Am I making them too big? Is this overkill??

I would like to put them in asap so your reply is appreciated.
Thanks

Matt

May be some pictures here (under "rigging") of the old chainplate set up and the size of the existing knees, which are the size of the new knees I planned on putting the chainplates on:

http://friscoflyer.blogspot.com/
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Postby CharlieJ » Fri Jul 06, 2007 5:36 pm

lol- too big almost always works better than too small. two inches seems a bit thick to me, but why not? Then you'll not have to worry about them.

Personally I moved our chain plates outboard and put them on the hull side. No more through the deck for this boat. The total distance in my case was 2 inches so had little effect on sheeting. Other boats it might not be so easy.
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Postby Figment » Fri Jul 06, 2007 6:40 pm

The strength of the tabbed connection to the hull will matter more than the thickness of the knee, I think.
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chainplates....

Postby nhdory » Fri Jul 06, 2007 8:31 pm

I'm still in a place where I could easily place them outside as well. It would only be a matter of moving two inches as well. Whats strongest? What is preferred?
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Postby Figment » Fri Jul 06, 2007 9:34 pm

Outboard chainplates are stronger. Direct connection to the hull is a direct connection to the hull, and the rig generally likes a wider base. Less potential for deck leak.

But unless the boat already has a somewhat cluttered look, they become an eyesore I think. One man's opinion.
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potential leaks and chainplates....

Postby nhdory » Fri Jul 06, 2007 10:49 pm

Having them on the outside is a salty look for sure but what about all the through hull holes that it takes to attach the chainplates? About four holes per each of the six chainplates so thats 24 holes instead of six if they were on knees. No concerns about leaks through the hull, not even when heeling?
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Postby Tim » Sat Jul 07, 2007 6:45 am

Any through hole anywhere is a potential leak, of course.

So whether you go through the deck or the hull, seal the openings extremely well. Outboard chainplates through the hull are less likely to leak the way the oversize slots required for through-deck mounting are, though.

A 2" knee is way thick, but as they say, nothing too strong ever broke. Yankee engineering dictates overbuilding, since it's all "seat of the pants".

Personally, I'd go through the deck and to some stout knees. I'm not a big fan of outboard chainplates except on certain boats where they're part of the traditional design.

As Figment said, the strength of the glasswork holding your new knee to the inside of the hull is what matters--far more than the thickness of whatever material you use inside. 3/4" plywood, well and adequately tabbed into the hull, would be adequate for the strains involved here, but there's no harm in using the large material you've come up with.

Good luck.
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Postby Rachel » Sat Jul 07, 2007 1:50 pm

Warning: I'm not a physicist.

However, I think the reason the chainplates mounted to the side of the hull aren't 24 times more likely to leak (even though there are so many more holes) is that those holes are where the plate is firmly mounted. With through-the-deck chainplates, that mounting surface is the bulkhead (and those holes/fasteners don't move either, unless there is something wrong.

But, the chainplates have to pass through something on their way to the inside strong mounting point, and that something is the deck. They can't really be attached to the deck, I don't believe, so they kind of float through and they tend to "work" when you sail. So you have a large slot that you can't totally stop movement in, by design. What you do have is good bedding, good core practice, and attention to maintenance. So I think either method is okay, but with the through-the-deck method you have take a few more precautions (but then if you don't want to take care, you probably wouldn't be a sailor anyway).

Unless you want to have the chainplates on the outside (I like them outside sometimes, but it depends on the overall look of the boat), I would keep them inside, but be sure to reef out the core around where they pass through the deck (then when they leak, the water comes into the boat but not into core) and where their bolts go through your bulkhead. I've seen people use fiberglass custom "tubes" around the plates, or you can make little "platforms" of glass around them to discourage casual water flow/standing water. Cover plates give the caulk more surface area.

Someone on a certain boating group wrote that the knees have to butt up against the underside of the deck to keep them from rotating up and pushing through the deck (I let it go), but I would leave a gap like the original Triton method, I think.

As an aside, and although I'm not sure a lot of design planning went into it on many of our boats, I suppose the chainplates on the bulkheads does spread the load around, via the bulkhead tabbing. I'd think that if you were moving them to the hull you'd want to build up a load-spreading areas around them, so they didn't just stress one little part of the hull.

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Postby nhdory » Sun Jul 08, 2007 7:01 pm

Thanks for the great response. I decided to use the big two inch thick knees for th middle two chainplates and the other four will be on 1 inch knees attached to bulkheads. Their all cut to butt up against the underside of the deck and cabin house. Should be plenty strong and they look good too. When glassing these in I was planning on using some thickened West System to bond the knee to the bulkhead then glass over that, Should I use the same technique as I would when tabbing in a bulkhead? Large pieces of cloth first then sucessivley smaller pieces on top of that? How far onto the bulkhead should I go? Is there a rule of thumb?
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Postby Tim » Mon Jul 09, 2007 7:35 am

The "largest first, smallest last" fiberglassing technique applies to filling holes, but for tabbing bulkheads it's the other way around: smallest first, largest last, so that each overlaps the one before.
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Postby nhdory » Mon Jul 09, 2007 12:51 pm

I'm glad you cleared that up for me. Looking at the West System "Fiberglass Boat Repair and Maintainence" Booklet it shows using the largest piece down first then succcessivley smaller pieces after that. But in other places such as "This Old Boat" by Casey and "From a Bare Hull" by Mate suggest smallest down first to largest last.
So its smallest first (except for filling holes). Got it, thanks.
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Postby Ceasar Choppy » Mon Jul 09, 2007 3:39 pm

Figment wrote:The strength of the tabbed connection to the hull will matter more than the thickness of the knee, I think.


Can't agree more on this.

You will also need to pay particular attention to avoiding any hardspots or the sides of the hull will dimple if loaded up. This is the case on my Pearson 39 BTW. It appears that whenever I tension the rig (I'm not over tensioning), I get a dimple in the hull between the upper and aft lower knee. An upcoming project I have will be to glass in stiffeners between the knees and possibly replace factory tabbing on the uppers. Not a fun project in the space provided.

Incidently the knees are about 1.5" thick (3/8"" ply surrounded by a little over a half inch of glass on both sides). I did a core sample to find this out.
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Postby nhdory » Tue Jul 10, 2007 7:52 am

I'm placing these knees in the reinforced slots/channels left behind from cuting out the old chainplates. They were originaly layed up in the inside of the hull in long tubes. This system seemed have worked well for the first 26 years the boat was active. There isnt any noticable flexing around this area by looking at the outside of the hull.
The original set up....the "tubes"...
Image
The "channel" left behind. The new knees will be attached here with some thickened epoxy then glassed in.
Image
This is an example of the size of existing knees which I duplicated to hang the chainplates on (mostly for visual asthetic but also for strength)...
Image

Ok, So how do I avoid hardspots?



(This thread started out as a quick question but now I'm thinking it should have been in the rigging section or boat building techniques)
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Postby Figment » Tue Jul 10, 2007 9:00 am

Avoid hardspots by spreading the load out as far as possible.
If you're replacing the knee with something roughly the same size as what was there before, you're off to a good start.
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Postby nhdory » Tue Jul 10, 2007 10:24 am

I'm not replacing any knees. The ones that are there already (to tie in/support the cabin house to the hull) are staying as is. I copied them in size and shape to hang the chainplates on in the same spot they used to be when they were layed up in the hull.

It seeems the load will be spread ou over a pretty wide area because they are really long and there will be just short spans "between the knees".
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About your chainplates...

Postby WayneS » Thu Aug 09, 2007 8:14 pm

Hello, Matthew--

I have a Type II Frisco Flyer, a year older than yours, and have been thinking about putting new chainplates on the outside of the hull. You've written some descriptions on your blog page and on this forum about your thinking about that, so I wanted to ask-- did you do it? How difficult? You mentioned "channel" for the chainplates, and there was a picture of you with a grinder; I might have misunderstood, but if there's metalwork in there, your boat, I'm fairly sure, is different than mine. Mine has backing blocks (fiberglass top-hat sections with who knows what inside) with the chainplates on the inner side of the backing blocks, visible to the eye. The top chainplate bolt is a quarter-inch, and the others, I think (haven't taken them out) are lag bolts.

Getting my boat, "Sumatra," ready for a pretty long cruise to Mexico, leaving at about the same time that you plan to put your beautiful Flyer back in the water. The plan is to trailer it from San Diego to San Carlos, in the Sea of Cortez on the Mexico mainland side, sail around the Sea of Cortez for some months, and then to Puerto Vallarta, where the boat, with its trailer and tow vehicle, will go into dry storage. My wife and I will try to rent an apartment near Puerto Vallarta and spend part of each year there.

By the way-- knees on my boat are about two inches thick, and seem to have facing plates of bronze. Cheoy Lee built these boats well.

Please let me know about the chainplate issue, and thanks--

Wayne
1964 Frisco Flyer "Sumatra"
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chainplate knees.....

Postby nhdory » Mon Aug 20, 2007 8:43 pm

Hi there Wayne,
Theres no metalwork in that photo of me grinding, thats me grinding the head of off of one of those lag bolts holding the Chainplate in the "tube". Your descrpition of your chainplates was the 3rd option I was considering. The real problem with that set up is of course getting the bolts and backing blocks out if they need changing. It can be done, but it's not as convenient and having access to both sides chainplate/backingplate. I debated quite a bit re what to do with mine and in the end decided not to hang the chainplates outside the boat and it wasnt an easy decision. I just wrote about it on the blog so wont really go to far into it here. I will just say that it was more of a challenge to build the knees on the inside than it would have been to bolt them to the outside. Who knows, if the boat goes in and the knees give me any cause for concern, I could always take them out and build up the inside of the hull and hang them on the outside. Its just a boat afterall. Thats been the unexpected lesson of this project so far...that it can all be changed/repaired, its just a boat.

By the way, thanks for all the helpful information re the Flyers on the CL association website. I've seen a couple pictures of your beautiful boat and would like to see more......
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http://friscoflyer.blogspot.com/
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