Athwartship Stringer Replacement
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Hi all,
I need to cut out and replace the #1, 3 and 4 athwartship stringers in my Olson. The #1 is especially mush and has to go immediately. The #2 main mast step stringer support was previously rebuilt by the prior owner and does not need attention at this time. My question is what is the best material to build the new stringers out of? Thanks!
-Jon
My professional boat building friend used mahogany. It is easy to shape and is very strong. Coat in epoxy 100% and it will last a hundred years. Remember to sand the epoxy coat when tabbing it in.
If the mast step is not 2 1/2″ wide 90% down into the sump..tear it out too. It needs to be built up very strong.
Thanks Bruce. I see your pics from your repair. That should be helpful. On closer inspection the main beam was simply widened with the original left in place. This has now compressed almost a centimeter and needs to go as well. Fun times and a delay to the start of racing season [supposed to kick off Saturday…].
Bruce when you laminated your beam with 1×3’s I am assuming they were stacked? Or were they vertical?
Slabs..glued up with 3″ top (2.75 actual) Does that make more sense? Make a rough pyramid, then use a band saw to the rough oversize shape. In the boat..take a hand grinder/sander to make the custom fit with about 1/8th” gaps to the hull. Thick epoxy fills the gap..then tab it with heavy cloth after putting in the fillets. Then cover it all with cloth and epoxy. Before gluing in…wet/seal the whole piece with straight epoxy, then glue in right away. Then tab right away…let that get tacky and then cover the whole thing with cloth. ( this avoids having to sand to remove blush )
PS: Can be done in a weekend.
Hi,
I did very similar replacement on other boats and I’m getting ready do do this on my Olson. I’m using Divinycell and unilateral fiberglass. Its easier to work with and allows you to shape the foam to the hull quickly. Tack glue a piece of sand paper to the hull and shape final touch on the stringer by sliding it back and forth. You’ll get perfect fit. Make sure you add a radii on the top edge to allow thick glass to wrap around it.
Your original stringers were made of foam core.
Whatever you end up using the key is to grind off all the exterior paint to get good bond between the new glass and hull. Epoxy is the easier way to go. Lay up a lot of glass on the top and side(3-5 mm) and make sure you will bond all of that to the hull. Ultimately that is what gives you strength.Good Luck!
The original frames are wood…most likely Douglas Fir. I agree that other than the mast step, the foam could be fine…but I worry that foam won’t take the compression load of the mast.
Please post pictures of your progress!
Stringers #1 and #4 are foam. Mast step [#2] and #3 are wood. It is my feeling that foam is not up to the task for the front stringer. Mine had lost most of its structural integrity. Removing the old glass a foot on either side of 2 and 3 was the hardest part of the demo I found. Though once the beams were removed I found the resin in the blankets had become quite brittle. Enough to simply use a chisel and hammer to separate the layer from the hull. Once this is done some sanding and cleaning gives a large clean bonding area for the new glass and resin. I haven’t been the best with pictures along the way but will post what I have when done.
Fabricating the beams out of Mahogany to fit the hull is quite time consuming due to the hardness of the material. Though the material really is quite light for its strength and I would think far superior to foam.
It really wasn’t hard to shape the mahogany. You make a cardboard template first, maybe a fore and aft pair. The bilge is fairly square, so it is easily fine tuned with a belt sander. Just take some time. Remember the epoxy needs a small gap to glue properly. You fill that gap with epoxy that has silica made into a real thick mix..at least peanut butter. You don’t want it to sag. Put in fillets; tab it; wrap the whole thing in a glass coat and call it good.
If the others are foam…hmmm….I might replace them all some day.
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