laying up glass bottom on boat...??

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Permalink Reply by AJ DeRosa on December 2, 2009 at 5:19pm

Mike,

Glassing the bottom is not hard. A roll of 20 oz cloth and some epoxy is all you need. I like the "wet" method which starts with a coat of epoxy on the bare wood. A 9" foam roller lays it on nice and evenly but you can also pour out a batch and use a plastic trowel push it around to cover the bottom panel. Let it sit for an hour or so and then roll the cloth on. A plastic trowel will help lay it smooth and get the bubbles out. Now pour on a batch of epoxy on to the middle and use that trowel or big plastic putty knife to work it out toward the edges and into the fabric. The trick here is to saturate the fabric until it is transparent and then scape the excess to another area. The first coat will leave the fabric transparent but the weave of the fabric will be apparent. A foam roller can be used to add flow coats, usually two or three thin coats to get it smooth. Many folks, myself included, add some graphite powder to the flow coats. The bottom then is black and slick. I then cut the excess glass from the edge to create a smooth transition from side panel to bottom end grain. The end grain of the bottom panel should be sealed with epoxy. The chine joint, where bottom panel meets side panel is then covered by the chine cap. The cap should be bedded with 3M 101 or similar bedding compound and held in place with screws or ring shank nails. The bedding compound makes this a removable piece. If you bed with and adhesive like 3M5200 it is there forever.

Side panels can be glassed the same way but 4 oz cloth is most appropriate here. You can also just paint the bare wood but the light glass gives a very nice base for paint or varnish and will prevent checking if the panel is fir.

I am of the school of thought that neither bottom glass or side panel glass be wrapped over the chine joint. There are others who will differ and hopefully they will jump in and explain their preference. Either way seems to work but after 35+ years of success I still prefer the traditional way.

As far as oil is concerned there are several good oils out there but a 50/50 mix of Boiled linseed oil and turpentine works fine and is at least half the cost of Seafin Teak Wood Oil which is very good. I add a little pine tar and Jap dryer to my blend.

I look forward to seeing this boat on the McKenzie in April and this is where you might get a good idea of age and maybe even builder. The Rapid Robert is a wonderful boat, not as sexy as the full rockered McKenzies but much more versitle.

Good luck on your project and we'll see you in the spring.

AJ

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Permalink Reply by lhedrick on December 5, 2009 at 8:39am

Like AJ said I don't think you want to wrap glass around the chine on a framed boat. Some things need to be replaceable. I say this because just the other day I had to take something apart on which I had used 3M 5200. I delaminated some plywood. I only needed a seal not a glue bond. If you used that stuff on a chine or glassed over it at repair time you would need a grinder to get it off.

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Permalink Reply by Randy Dersham on December 6, 2009 at 5:07pm

Thanks for the invite A.J. I've attached an image of the two methods to show how similar they are and point out the differences.

On the left is the method that A.J. describes. On the right is the method that we use for glass bottoms in our shop. The dark black line is the fiberglass cloth. Notice that in both methods the chine batten is bedded last and the edges of the fiberglass cloth are protected.

I forgot to say that these images are of a cross section of the chine area of a drift boat that is upside down, in the position that it will be when you put on a bottom. It does not show the side or bottom frame for simplicity.

Rather than get into a lengthy discussion about pro's and cons I will make a list of methods to always or never do.

Always soak the end grain of the plywood with epoxy before either method.
Always protect the edges of the fiberglass cloth at the chine. Notice that on the left the fiberglass edge is covered by the cine batten, on the right it is tucked under the chine batten.
Never run the fiberglass over the bottom of the chine to the outside edge of the chine batten
Never wrap the fiberglass over the chine batten
If you are fiberglassing the sides of the boat with a light weight cloth then protect that edge under the chine batten.
Never attempt to wrap fiberglass over a sharp corner, especially on a boat's chine.

Today most west coast boats protect their chine batten with either a strip of UHMW or a stainless steel half round. Either of those two protectors prevent rocks from chewing away at the chine batten, so the battens are replaced less often. It is my opinion that replacing a chine batten today is usually because of rot or leaks caused by failed bedding.

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Permalink Reply by lhedrick on December 6, 2009 at 6:12pm

That make a lot of sense. For some reason I had it in my mind that people were talking about glassing over the chine cap.

I think I like the idea of glassing over a rounded chine edge then adding the chine cap.

But, help me understand this point from the frame builders point of view. By glassing over the chine it's kind of like the stitch and glue method. It seems a few layers of heavy tap could be added and just skip the chine cap.

Or,,,,,,, perhaps I should consider trying a chine cap on a stitch and glue boat. The chines are always taking a beating and I am always looking for a why to make them less maintenance and easier to repair. So far when they get soft I just grind them out and build them back up with new glass and epoxy.

Seems there is some cross over possibilities between the stitch and glue/framed methods of building

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Permalink Reply by Randy Dersham on December 6, 2009 at 8:52pm

If you wanted to you could build a framed boat without a chine batten. On our lava rock rivers the chine without a batten would likely need constant repair. In fact a protective layer of stainless steel or UHMW over the chine batten is the norm on our boats in order to cut down on the repair to the oak chine batten.

You could add a chine batten to a stitch and glue boat. You might need to add a chine log on the inside to attach to or attach it with fasteners to available bulk heads.

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Permalink Reply by Jeremy Christensen on December 7, 2009 at 7:01am

I am interested in the idea of adding a chine batten to a S&G boat. I wonder how it would have affected the outcome when I hit a rock broadside mid-chine, ferrying to the beach in Westwater? Put a large hole in the chine requiring immediate repair, maybe this would have lessened the damage.

I am soon adding a plascore & biaxial glass shoe to my boat, which has a 3/8" marine ply & woven glass bottom, not stout enough for the use it gets. I am taking the boat down the Grand Canyon in April 2010. I am now toying with the idea of a chine batten as further reinforcement, both from rock hits and surging beaches. Thoughts?

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Permalink Reply by michael burke on December 7, 2009 at 7:48am

thanks for all the insite this info is greatly apreciated and i thanks you all for the discussion. i will be glassing over chine and then installing the chine battens over the glass for protection.

what is the prefered bedding compound that you like to use and am wanting to use coat-it as final coat for bottom...??

thanks again....this has been a really fun project..well now that the major sanding is done...!!!

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