From Archive: XL Marine Plywood bottom by Randy Vanoff

[Club Archivist]

Tom,

Fellow CCABC'er here. I'm putting a new bottom on my 1948 18' Utility, so I'm fascinated by your method of using the XL Marine Plywood. I saw the 16' Riv photos on your ebay store. The construction looks nice and tight. I gather you use the plywood for both the inner and outer layers?

Is this a modified "Dannenberg" type bottom with 5200 between the layers and 1/16" gaps between the planks? How do you address the portions of the chine strake and bottom planks that extend above the waterline?

Do you have experience with some of these bottoms that have been in use for some time? I'd love to hear more about this if you have the time to respond. Thanks for your time and consideration,

Randy Vanhoff

http://home.earthlink.net/~rvanhoff/serenade/

[Club Archivist]

Ok, here is the story on the XL cca treated fir plywood we are using. We are only using this plywood for the inner layers of the bottom, sides, and top. The outer layers are still real mahogany. The bottom is done exactly like Don Danenberg recommends in his book, but we use 1/4" thick not 1/8" thick as he uses on the smaller runabouts. We are also using cca treated fir instead of okoume (okoume is not considered very rot resistant, by the way). These XL panels are designed for the boat industry and arrive kiln dried after cca treatment with no additives like paraffin (to shed water) like you have when purchasing "treated" plywood at Home Depot. It is the wet wood and paraffin and other additives which limit adhesion, not the cca.

We have no trouble whatsover conforming the 1/4" ply on the bottom, sides or top even on the 16 foot Riviera that is pictured. As far as the sides and
top, just consider them a "Danenberg Method" done just like the bottom. A couple of years ago I asked Don about putting plywood on the sides as an inner layer. He commented, at the time, (Don are you here??) that he really saw nothing wrong with shrouding the boat in plywood like the bottom but he simply did not do it. I do know of other restorers who do this and have had, I presume, good luck with it since they are still doing it. This is our first boat with 1/4" ply on the whole boat then planking. So we have had no field experience yet, but others that have done the same say you can expect the outer layers of mahogany to be very stable and not move.

It is also possible to use thinner planking on the outside as long as the total thickness as original is maintained. In reality you end up with slightly thicker sides and top as total thickness since you can only go so thin and have room for a sufficient amount of "meat" under the countersunk screw and bung in the outer mahogany layer. That said, I'm sure some purists would be appalled (at both the increased thickness AND method) while others simply would not want the additional weight, though small IMHO. However, we are repowering this boat so we are happy to have the extra strength afforded by the plywood and the extra weight simply is not an issue with the larger engine.

I hope you don't mind I sent this to the list. We need a good spirited debate these days.

Tom Lang

[Club Archivist]

I think this is a great way to go, as long as you soak everything in Clear Penetrating Epoxy Sealer [CPES], naturally.

Please tell everyone what supplier you found that provides CCA-treated plywood without the paraffin treatment. That is a valuable resource. CCA treatment makes the plywod really rot-resistant, and without the paraffin it can be painted, glued, etc.

Steve Smith

[Club Archivist]

Steve, I'm glad we rehearsed this <NOT>. Your check is in the mail

Actually, I have started to supply it. I buy the the more common sizes (1/4", 1/2") in pallets, other sizes by the sheet and sell on ebay at

http://www.stores.ebay.com/vintageboathardwareandsupply as well as using it for restorations here locally.

For vendor info go here:

http://www.greenwoodproducts.com/xlpanels.htm

For a great article on it go here:

http://www.boatingmag.com/article.asp?s ... icle_id=69

Hopefully you all can find somebody that carries it in your part of the country.

However, I am making a run to deliver (and also pick up a boat) the first week of December (next week) and can take sheets of plywood and drop them off from Georgia to New York. Normally they have to be shipped freight due to size. I'm also headed to Michigan from GA for the Christmas holidays and could deliver plywood along I-75 at that time. Prices are:

Size Price$ Approximate Weight
1/4" above 24 lbs. per sheet
3/8" $38 31 lbs. per 4'x 8' sheet
1/2" $40 43 lbs. per 4'x 8' sheet
5/8" $45 54 lbs. per 4'x 8' sheet
3/4" $50 64 lbs. per 4'x 8' sheet

Tom Lang