Replacing Keel Bolt Backing Plates

[jigray3]

I have owned this boat since 1993. The keel bolts are actually threaded rod (316?) and nuts (stamped 304), keel is lead made by Mars Metal. There are 5 total keel bolts all centerline, 3 middle rods are 1-1/4", 1 each fore and aft are 3/4", all appear to be in excellent condition.



The backing plates are a different story. They are pretty substantial, the large ones are 220mm x 100mm x 20mm, small ones are 180mm x 100mm x 15mm. Stacked on top of these rectangular plates are secondary plates, essentially very large thick round fender washers, 3 large ones are 80 mm diameter x 7mm thick, 2 small ones are 60 mm x 5mm thick. Unlike the other hardware these are all mild steel, go figure. The large rectangular plates are clearly galvanized and fair to good shape, the small rectangular plates are apparently not galvanized and require replacement. I'll be replacing all of them, but the smaller ones are urgent.


My bilge has always been very dry, and this created a bit of complacency on my part. The plan is to replace all backing plates in electropolished 316 stainless, with chamfered edges, and radiused corners.


Here are my questions. I was hoping switching to stainless might allow me to drop to slightly thinner plates, but a cursory study of strength specs of each seem to indicate I might need to stay with what is there. Seems like it might overkill, but I'm not qualified to determine this. Anybody knowledgeable on this issue?



I have the original keel drawing which specs 316 for the rod, so I plan to move to 316 for the hex nuts as well. I prefer high quality hex nuts, and I hear US made is what I want if possible, maybe Taiwan. Practical Sailor recommends heavy profile, some folks like ASTM certified. Because I only need 5 total and the fact the large ones are fairly big (standard profile are 1-7/8" across the flats, heavy profile even larger), sourcing has been a bit of an issue, particularly with my chosen criteria. Am I overthinking this? Can anybody recommend a better source than McMaster-Carr?


I have been provided torque values for stainless hex nuts/rods, but with rods threaded into cast iron. My keel is lead. Will that make a difference in torque values? I'm told the keel was cast with rod in place and that the rod was anchored.


Thanks

[boatpoker]

I've been in the Mars plant several times and I believe all of their rods in the lead keels are "J' rods. J rods are all I've ever seen in lead keels of any manufacture. GIve Mars a call to be sure. Mars Metal (905) 637-3862.

J rods - The bottom of the rod is bent into a J shape.

[jigray3]

That’s helpful, thanks. I suspected as much, but the builder’s technical drawing of the keel is unclear. I sent Mars an email inquiry, but they did not respond. Seems to be a trend these days. I’m a bit on my own because the model is rare in the US, only a few of those have a lead keel, and because it’s 32 years old.

[boatpoker]

Originally Posted by jigray3

That’s helpful, thanks. I suspected as much, but the builder’s technical drawing of the keel is unclear. I sent Mars an email inquiry, but they did not respond. Seems to be a trend these days. I’m a bit on my own because the model is rare in the US, only a few of those have a lead keel, and because it’s 32 years old.

Can't say about email but they've always answered the phone for me.
What year/model is it ?

[capt jgw]

Originally Posted by boatpoker

I've been in the Mars plant several times and I believe all of their rods in the lead keels are "J' rods. J rods are all I've ever seen in lead keels of any manufacture. GIve Mars a call to be sure. Mars Metal (905) 637-3862.

J rods - The bottom of the rod is bent into a J shape.

My 1969 Columbia 36 had a lead keel, unknown who actually made it. The bolts were all 3/4" galvanized hangar bolts threaded into the lead. I believe a couple other of their models were the same. I would assume they used a harder lead alloy to allow that but that's just a guess. That did make it a lot easier to replace them though. They needed it, they were very rusty and one broke off when I tried to remove it's nut. So not all lead keels have "J" rods.

[User 09]

My keel bolts are only 3/4 stainless J bars into lead. My keel bolt backing plates were ALL originally small 3mm thick stainless washers, maybe 1.5" diameter (see pic). They held up ok for 40 years. They did (some) start to 'cup' slightly and distort though eventually. Just to give you some perspective of how little it takes to have an adequate backing. I replaced them recently with 1/4 thick 316 stainless pieces as you describe above, rounded and chamfered edges. I think i used general purpose 316 from McMasterr. I had it water jet cut but did nothing else special. I did add 1/8" thick stainless fender washers between the backing plate and keel bolt nut, mostly because I already had them and had no other use for them, not because i feel like they were needed. I think even what I did was way overkill, but it was not that expensive and will probably never need replacing ever again.

One thing we did do though, which i think is important was to level the area under the backing plate so it was completely flat, so the backing plate was sitting absolutely flat against the bilge so there are no point loads.

For the mast step bolts, i just used fender washers which are bending a little bit because the slots in the step are a little too wide. I will be adding stainless plates there soon. Hard to see backing plates in pic with messy Sikaflex and grey background.

Torque value for my 3/4 bolts were 95 ft lbs. I coated bolts with Lanocote and torqued over two days to full spec to ~95 ft lbs.

I think McMaster list the compression loads for different metals on their site. Not sure what the difference is between stainless and galvanized, but i have never seen metal backing plates over 3/8 thick on any boat. I cant imagine you would need stainless thicker than that. Boatpoker would know much better though. He has seen a lot of boats.

[boatpoker]

Originally Posted by capt jgw

My 1969 Columbia 36 had a lead keel, unknown who actually made it. The bolts were all 3/4" galvanized hangar bolts threaded into the lead. I believe a couple other of their models were the same. I would assume they used a harder lead alloy to allow that but that's just a guess. That did make it a lot easier to replace them though. They needed it, they were very rusty and one broke off when I tried to remove it's nut. So not all lead keels have "J" rods.

Suggest you read my post again. Nowhere did I say all lead keels used J bolts and we were talking abour Mars keels ... your keel was not built by Mars.

[Bowdrie]

Originally Posted by capt jgw

My 1969 Columbia 36 had a lead keel, unknown who actually made it. The bolts were all 3/4" galvanized hangar bolts threaded into the lead. I believe a couple other of their models were the same. I would assume they used a harder lead alloy to allow that but that's just a guess. That did make it a lot easier to replace them though. They needed it, they were very rusty and one broke off when I tried to remove it's nut. So not all lead keels have "J" rods.

Haha, old times for sure.
Your keel would have been made by a, (long out of business,) company named "Keelco".
They started out in a dirt lot in Costa Mesa, Ca. furnishing lead castings for the burgeoning SoCal yacht building industry.
Yes, they used a high antimony content in the lead for bolted-on keels, this made them suitable for holding threads.
When struck with a hammer they had a "ring" to them that soft lead lacks.
Side note; Today many would be amazed at the "back yard" businesses that grew-up and supported the glory days of SoCal boat building.

[barnakiel]

Strange ...


In our boat the washer is a huge double unit spanning the whole width of the bilge and hosting two adjacent bolts ... say 1 inch by 4 inches, maybe 4mm thick. Or so.


Why such weeny washers under those bolts. Is SS so expensive out there where this boat was built ???


barnakiel

[Bowdrie]

Originally Posted by barnakiel

Strange ...
In our boat the washer is a huge double unit spanning the whole width of the bilge and hosting two adjacent bolts ... say 1 inch by 4 inches, maybe 4mm thick. Or so.
Why such weeny washers under those bolts. Is SS so expensive out there where this boat was built ???
barnakiel

The op said the backing plates were 220mm X 100mm X 20mm, and 180mm X 100mm X 15mm.
That's hardly "tiny".
The washers used between nut and backing plates are simply used to reduce friction when tightening the nuts, the load is carried by those quite large plates.

[jigray3]

Originally Posted by Bowdrie

The op said the backing plates were 220mm X 100mm X 20mm, and 180mm X 100mm X 15mm.
That's hardly "tiny".
The washers used between nut and backing plates are simply used to reduce friction when tightening the nuts, the load is carried by those quite large plates.

I believe barnakiel is referring to User09’s photos of his keel bolt backing washers, which are small compared to my plates, but in my case the hull is only 1-1/4” plus maybe an additional 3/8” from the liner sandwiched on top, and I have only 5 keel bolts attaching 2400 lbs of ballast. In my case it seems apparent they wanted to distribute the load. His photos look like the keel bolts are passing through a pretty robust structural area, and he may have 2-3 times as many bolts as I do. Horses for courses …

[jigray3]

Originally Posted by boatpoker

Can't say about email but they've always answered the phone for me.
What year/model is it ?

I had planned to call, but felt this thread may answer some questions and prompt others, and it has.

It’s a 1994 Beneteau Oceanis 300, hull #134 out of the Marion, SC plant. They took a First series go-fast hull (Figaro, First 310), added water tankage, a roller furling main, wheel steering, and the aforementioned keel, and called it a cruiser. We saw it at the ‘93 Annapolis show, and purchased it 3 weeks later. She’s been very good to us, but with retirement looming within the next 18 months, we’re looking for a larger, more capable, more comfortable alternative.

[User 09]

Sailing UMA on Youtube recently sistered new bolts into their lead keel. Theirs were 1" diameter but the bolts were just epoxied and threaded directly into the keel. Im pretty sure from the video they used standard torque values for old and new bolts. Not that they are the be all/end all source for exact specs. Maybe reach out to them and ask if they found any particulars on torquing j-bar -vs- threaded if you cant find a difinative answer from Mars or another source?

[boatpoker]

Never given much thought to drilling and tappin lead for an ss bolt and don't have much faith in AI but ...

google AI To determine the correct torque for a stainless steel (SS) bolt into lead, you must first identify the bolt's preload (the desired clamping force), then use a formula like T = KDF, where T is the torque, K is a friction coefficient (unique to the stainless steel/lead combination), D is the bolt's nominal diameter, and F is the target preload. Experimentation, using a calibrated torque wrench and potentially a Skidmore-Wilhelm device or Direct Tension Indicator (DTI) washer, is the most reliable method to find the correct K-factor and avoid galling or over-torquing.

[jigray3]

Originally Posted by User 09

Sailing UMA on Youtube recently sistered new bolts into their lead keel. Theirs were 1" diameter but the bolts were just epoxied and threaded directly into the keel. Im pretty sure from the video they used standard torque values for old and new bolts. Not that they are the be all/end all source for exact specs. Maybe reach out to them and ask if they found any particulars on torquing j-bar -vs- threaded if you cant find a difinative answer from Mars or another source?

The specs provided for M30 stainless hex nuts on rod are 325-651 ft/lbs. My 3 large nuts are 1-1/4”, as close as you can get to M30 with almost the identical pitch, but what I don’t know is if those torque values change if the keel material changes. It makes sense intuitively that rod threaded into cast iron would be different than j-rod cast in lead, but not my field.

You’re right, Mars might be a good source. But, there’s 326 ft/lbs of latitude in that range, so maybe it doesn’t matter that much, and just shoot for somewhere in the middle? Makes me consider the risks that may exist at the low end of the range vs. the high end, especially with an older boat?