Tearing into my Oday's deck joint

Started by rfrance0718, Nov 05, 2023, 08:09 PM

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I brought the Oday back to Columbus a week ago. Over the last 2 years, leakage into the cabin has gone from minor nuisance to big problem, and it was time to do something about it. So on Monday I started tearing off the rub rail. I tried to be gentle but the plastic extrusion that holds the rubber rail just crumbled. The rub rail itself seemed fine. When I bought the boat, it came with a box labeled "rub rail", and now that I was removing it, I thought it odd that the previous owner had bought the rub rail, but not the extrusion. I had talked to Rudy at DR Marine and he said that there was no problem ordering new extrusion. ($300 plus) At any rate, it took little time to remove the starboard rail and the extrusion, and I could get my first look at the joint.

It was immediately obvious that there were gaps where the old sealant was missing and that they corresponded with my leaks on the inside. I also noticed that just below the chain plate the deck had actually lifted about a 3/16 of an inch and the wood screws were actually pointed down at a 30 degree angle.

Until that moment, I never had any reason to think that my deck was lifting. There were leaks there, but it was no worse than 2 other places along the rail. The joint was covered by the rub rail, so I couldn't see it,  and the deck around the chain plated wasn't cracked or deformed.

OK, now it was time to go into the cabin and take a look at the whole system. The Oday 240 doesn't have mid cabin bullheads to attach the chain plate to. Instead there is a steel rod welded to the deck plate that extends down though the shelf behind the settee, where it enters a substantial, short hallow bulkhead. There is an access hole where nuts can be threaded on the rod, so that the pressure from the shrouds is transferred down  to the hull. Inspecting this required removing the settee back rest and the shelf, and I'll plead laziness.

Once the little bulk box was uncovered, I reached up, expecting to find the nuts to be loose enough to allow the deck to heave a fraction of an inch. But that wasn't the case. Instead, there were no nuts there at all! I immediately tore into the port side and found the same answer. No nuts! So I have been sailing this boat, in considerable wind and seas, with chain plates relying on the wood screws holding the deck and the hull together, along with some 35 year old crumbling sealant. Amazing.

I went out and pulled down on the deck and I was able to pull the deck down most of the 3/16. I'm thinking that I should be able to remove loose sealant and torque the deck all the way down with the new nuts. I'm thinking that I'll replace the wood screws with through bolts in the area of the chain plates. I'm hoping that I can scrape out old sealant by the other gaps and seal it all up.

And then yesterday I looked into the rub rail box and found that I had both the rail and the new extrusion. I'm feeling very optimistic at this point but I'm sure that there will be more surprises. I'm feeling stupid and lucky at this point.
Oh, and what happened to the nuts? There are supposed to be 2 on either side. The second one, locking the first into place. The bulkhead box is open at the bottom, so it is possible that the nuts worked their way down the threads. If they did, they would have ended up in the compartments below the settees. I don't recall finding any 7/16 inch nuts laying around, but who knows? Another peculiarity is that there were nuts threaded down from the top, holding the rod down onto the shelf. That wouldn't have done anything and they weren't supposed to be there. I just never thought about it.

Finally, today I went over and peeled off the port side rub rail. There, the deck wasn't pulled up, but there were more gaps where sealant had crumbled away. You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.     


Wondering if an oscillating multi-tool would be a good choice for digging out the old sealant?
What sealant will you use to renew the joint?

Big dreams, small boats...


Two great questions. I thought about the multi-tool, or even a Dremmal.

What do others think about sealant? I have very little experience with 5200 type stuff. I think that getting it up into small gap will be difficult. Ideas?


The multitool might be less prone to digging in or zipping out than a Dremel (rotary) tool.

I had a conversation with a seasoned boatwright over the weekend. He is a fan of using a putty knife heated with a plumber's torch on 5200 to remove it. I have only applied 5200 once and it was summer and the joint was open until I closed it. 3M (I called tech support) recommends 1/8 to 1/4" thickness [3.2-6.4mm] for 5200, above and below that it does not cure to its full spec.
Big dreams, small boats...

Charles Brennan

rfrance and Spot, I've achieved near-Elder-Statesman status on this board, by virtue of having made nearly every mistake on a sailboat, it is possible to make! :'(

On your deck joint, you saw "gaps"?
HAH!! I saw DAYLIGHT!  :o

Still had a lot of sealant to remove.
The biggest problem with power tools, either rotary or oscillating, is that they "gum up" pretty much instantly.
After I had exhausted all the tools in my inventory, it was time to start inventing them.

You cannot view this attachment.
The one in the center, is the one I made.
It started Life looking like the one on the right, with teeth and whatnot.
In fact, I started with a toothed blade which promptly clogged up and was useless.
So I ground off the teeth of a toothed blade, as shown at center.
On my next trip to a Big Box store, I discovered they already sell oscillating multi-tool blades with an edge.   >:( 
As  you can see I bought one, but then discovered the tool I had invented, was superior.

That slight curve of the blade tends to gouge the hull a little, going down the length of the boat, since the most cutting force is at the center of the blade and the center sticks out past the hull-deck joint.  And it is so wide, that the main cutting force (center) is only taking slices out of the gel-coat.  Holding the tool upright and going vertically, from under the deck joint to the top; it only cuts the sealant loose on center and the the sealant on either side of center doesn't get cut evenly, or uniformly.  Trying to hold the tool in the vertical orientation and apply horizontal lateral force to move down the length of the boat is very tiring.  It's far easier to hold the tool horizontally and just push the tool down the length of the boat. If the old sealant is sufficiently elastic, you can hold on to the end of the sealant in one hand and keep a slight pressure (not enough to snap it) on the old sealant and allow the multi-tool to do the cutting.
If I had to do it again, I would have ground the blade width down to only slightly wider than the hull-deck joint.

So you really need to use a blade that is straight, not curved, and not too wide.
If you're concerned about hull cosmetics, another thing that helps is a 2" strip of masking tape, run the length of the boat to rest the tool against, as part of the tool extends below the hull-deck joint.
You can still gunk up even a smooth edge, but a little WD-40 and a paper towel makes short work of that problem.  IIRC, I had to -resharpen the edge twice for each side of the boat and probably should have re-sharpened it for the transom, but it was so short comparatively, that I just toughed it out.

If you observe closely, you'll notice that the blade is slightly angled.  It started out straight, but wore down over time on the side closest to the hull-deck joint.  I honestly didn't notice much difference in keeping it straight, versus slightly angled.

But a rotary tool makes horrendous digs and should be ignored out of hand, and an oscillating toothed blade, does nearly as much damage. With something moving back and forth 11,000 times a second, an obvious problem is heat. A little WD-40 sprayed directly on the blade when you hear the tool "lugging" a little, worked wonders. 

Hope this helps,
Charles Brennan


Big help! Both of you. Charles, we're you able to remove all, or nearly all, of the old sealant? Seems like that would be required to get the kind of thickness that 3m calls for.
I haven't removed the wood screws yet, so it will be interesting to see the separation when I get there.

Thanks again!

Noemi - Ensenada 20

I'm sure I've heard of people using a pair of screwdrivers or putty knives to pry the gap open as they apply the new sealant.  Might take three or four hands, though.

Charles Brennan

rfrance, For whatever reason, (possibly surface area) the sealant on my hull-deck joint adhered more strongly to the hull, than to the deck flange.  So the first pass, had the cutting edge of the modified multi-tool against the hull and got out most  of the sealant.  The second pass consisted of simply inverting the multi-tool and running it along the inside flange of the deck-joint to clear out the remaining dregs.

A word about separation of joint:
All Things In Moderation. 
In a burst of enthusiasm, I uncoupled all the through-hull fasteners (screws and nuts) and the deck and the hull, just sitting on the trailer in my driveway, shifted enough that I went nearly insane, trying to get the holes to line up again.  If I had it to do again, I think I would unfasten a few feet at a time, remove the sealant and clean out the joint, apply the new sealant, and then put the screws through the rub-rail into the hull-deck joint, for alignment purposes.   (The nuts went on inside the cabin, later.)

To Noemi's statement, I really had little problem with separation near the mid point of the hull, it was the ends that required judicious prying.  You may have seen those door framing "shims" that they sell in the Big Box stores.  I used a pack of those with the thick end of the shim stuffed in, to hold the hull-deck joint open.

Hope this helps,
Charles Brennan


I did (most of) the deck/hull joint on my Mac 25 earlier this year. Macgregor used a foam gasket instead of sealant, so I don't have much to offer on removing the old stuff.  But some general things I found:

1. When I removed the hardware, much of the joint opened up enough on it's own to fit the nozzle of a caulk gun.  The areas that didn't could be pried open without much effort and held open with shims for working.

2. I assumed I would tighten the hardware on the uncured sealant to close joint.  Really this would just pull closed a couple inches or so right around the screw (like your fourth picture), and the deck flange would have this wavy appearance when you looked down the length of the boat.  I ended up using the aluminum extrusion like a giant washer to avoid this.

3. I started with 5200, but quickly switched to 5200 Fast Cure.  I was doing this outside in the spring (cool to warm days, cool to cold nights), and 5200 cure time was measured in weeks.

4. With both 5200 and FC, I found I had to tape the bottom of the joint to prevent it from oozing out.  It wasn't obvious by eye, but given an hour or so without the tape it would bead up at the bottom of the joint and even start to run out.


So much good info! Very good warning about not removing all of the fasteners and having the whole deck shift. Seems like the screws should go in just tight enough? Not wanting to squeeze the sealant out. Maybe just tight enough and a little harder after it cures?

And Wyb2 was happy with the 5200?

Thanks to all.


Quote from: rfrance0718 on Nov 08, 2023, 06:07 PMAnd Wyb2 was happy with the 5200?

So far so good.  No leaks from the rain (there were a couple before).  Sailing has been tame so far on account of having a three year old on board, so it will be some more time before I can report on how it does with the rail buried.


Yup, that's the tool! I had a thin blade with the teeth and ground them away. I was amazed how I could work the blade all the way up so it was obvious that I had removed all of the old stuff in that section. I also noticed that once the old material was gone I could press in on the hull a bit and create a wider gap for putting in new sealant, when I get there. (Turns out my Harbor Freight multi too was missing 3 of the 4 little pins that hold the blade. So I had to fork over the $ for a new one. $19.95! You can spend that much on lunch at Wendy's)You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.     

Charles Brennan

rfrance, I can't tell you how gratified I am, that things went so well for you!  This is the essence of what the TSBB is all about.  Something I think we could all do better at, is acknowledging and reporting on the results of given advice.  So I appreciate your time (and pics) in following up with your project.
If there are any more mistakes I've made  ???  that I could help save you from in the future, please let me know.  ;D

Charles Brennan