Replies to This Discussion

Permalink Reply by Richard on October 24, 2009 at 3:37pm

When you are talking side panels to the main hull structures like frames, stems posts and transom I would suggest permanent adhesion. Remember the bow of the boat can take some pounding and ask yourself how often do you plan on removing the side panels or stem? I reccommend sticking with a polyurethane adhesive/sealant to maintain structural integrity for the hull like 3M5200. Your polysulfide works well for the rub rails, outside chine and structural items that will need replacement over a regular maintenance schedule, etc.

Hope this helps. Perhaps others may have varied suggestions as well.

• ▶ Reply

Permalink Reply by lhedrick on October 25, 2009 at 8:09am

The boats I build are all stitch and glue type with lots of epoxy/glass over the chine.

I have a question for the framed builders. When the bottom is attached the end grain of the plywood faces out and then is covered by the chine cap. Do any of you do anything to seal off the end grain before the cap goes on like epoxy it or, do the sealants do this job?

---

Another question about sealant and wood. Before attaching the gunwale on the boat how do you treat the wood which faces the plywood? Is a removable sealant used for that or do you just oil it. Same for the chine cap. I always worry about rot on untreated wood parts especially when moisture can get between wood surfaces and never dry out.

• ▶ Reply

Permalink Reply by Randy Dersham on October 25, 2009 at 11:15am

" bottom end grain"
At our shop all end grain is soaked with a thin epoxy to penetrate and seal the ends before a bedding compound is used.

"treat the gunwale"
We epoxy the inside and outside rails at the shear to the side panel (outside rail) or the frames (inside rail) for a permanent instillation. The gunwale is changed much less often than a chine cap and it adds stiffness to the boat. A stiff boat transfers energy from the oars to the water more efficiently. 3M5200 in these locations will add a little flex. We are not talking about much difference here, remember that the frame has a bolt from the outside rail though the frame and the inside rail at each frame joint and several at the transom and stem. These bolts maintain a tight stiff gunwale.

Our general attitude is that the boat should be build to be permanent rather than have removable parts. The two exceptions are the chine batten and the boat bottom to the frames. These two areas need the flex of the 3M 5200 as well as the adhesive properties. Many prefer to use a bedding compound such as 3M101 for the chine batten. It beds just as well and will be easier to remove if you choose to replace the chine batten or re-bed that joint.

Sanderson and I argue about if epoxy or 3M5200 should be used on the stem cap and on the frame joints to the inside of the hull. I prefer epoxy ( so that's how the manual is written); he prefers 3M5200. The 3M5200 has less tendency to crack when stressed but is harder to work with and clean. The epoxy joint can accept a slight fillet and will blend when a clear finish coat is applied.

• ▶ Reply

Permalink Reply by lhedrick on October 25, 2009 at 1:17pm

Randy,

Thanks for the reply. On the subject of 3M5200. I have a sit on top kayak made from some type of roto molded plastic. It has developed a crack on the top. I have found no epoxy which will stick to the stuff. Plastic welds just open up again in short order.

3M5200 has sealed it up and is working great. I am just amazed how that stuff sticks to things and flexes.

• ▶ Reply

Permalink Reply by Joe Dengler on October 25, 2009 at 2:51pm

Thanks everyone for the input. It looks like 3M5200 is the stuff. Do you guys drill pilot holes, then add sealer and put back together? Or seal, clamp, drill pilot holes and screw/nail?

• ▶ Reply

Permalink Reply by Dave Z on October 25, 2009 at 7:06pm

5200 or Sikaflex 291 on all of my boats up there at the stem. As for the bottom end grain under the chine cap. On my boats, I smear on the sealant (no epoxy) pretty thick when installing the chine battens. My interior is 100% oiled, so I believe that water that gets in can evaporate out. I am also using a plywood skid shoe on the latest boat, and no issues, although it is only a season old. My boat is Meranti on the sides, but fir on the floor.

Yes, pre-drill before using the ring nails. These take a bend rather easily and once bent, they crack. A trick I use is to nip the point off the nail, hammer it into the pre-drilled pilot hole. Especially into tough wood like white oak. Learn to hammer those babies in gently, squarely and you will be fine. They like a "push" rather than a "pound". You'll get the feel of it soon enough.

Good luck!

• ▶ Reply