Probably a simple Question

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Probably a simple Question

Post by newbi2008 » Sun May 18, 2008 3:54 am

If i am building the CS-20 is my thinking correct.

Stitch parts together

Fillet and tape the inside of joins then epoxy them

Tape and epoxy the outside joins

Do i then need to cloth over the entire hull or just epoxy and paint?


Also, i've seen alot of posts about epoxy breaking down in sunlight if not protected. i intend to paint my entire hull, does this eliminate the sun light problem?

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Post by BruceDow » Sun May 18, 2008 5:15 am

Welcome to the forum!

I am not sure what the CS20 plans call for. (That is where I would start)

My initial reaction is that you should glass the outside.

I have built or maintained S&G boats both ways.

Two winters ago, I restored a "Mirror Class Dinghy" that my father built in 1967. Class rules forbid glassing the entire hull, so it was constructed of plywood, taped seams, and paint. After 38 years, there were only two small sections of dry rot. And those were due to improper storage of the boat, and us not maintaining it.

BUT... the Mirror is a sailboat, not a powerboat. AND the plywood thickness was designed to provide adequate strenght without the fibreglass covering.

Clearly, a fully glassed hull is heavier, but it will be more durable, and will require less routine maintenance.

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Re: Probably a simple Question

Post by Jones » Mon May 19, 2008 5:51 am

newbi2008 wrote:
Also, i've seen alot of posts about epoxy breaking down in sunlight if not protected. i intend to paint my entire hull, does this eliminate the sun light problem?
True, epoxy is not UV resistant and yes, painting/varnishing will prevent the damage. As for your question about fiberglassing, it's good to know that it possesses great resistance to abrasion.

Welcome aboard.
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Post by newbi2008 » Mon May 19, 2008 5:55 am

Just on the subject of Fiberglassing. I came accross a website today that suggested to save money on a build, it is ok to use normal Extrerior grade ply and suppliment it with extra layers of Fiberglass.

What is the general feeling about this method, especially thinking of a stitch and glue boat. ?

Thank you

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Post by FDMSIV » Mon May 19, 2008 6:20 am

You can use ext ply, but do you really want to?

Ext. ply will have voids in the inner cores and will have fewer core layers. This creates a situation where you can break or deform the piece you ply as you stitch everything together.

If you are going to paint the hull you can use the cheaper marine ply since nobody is going to see it.

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Post by razopp » Mon May 19, 2008 6:34 am

I just wanted to chime in on the Exterior ply comment as it is posted here a lot. I believe Ray Macke used Exterior on his CS-16 and listed on his website that is one thing he wished he would have changed (i.e. used marine ply). Also, I believe the consensus is the fiberglass does not add much additional strength. The purpose of the fiberglass is primarily to add abrasion resistance, reduce/eliminate checking, and prevent moisture intrusion to the wood.

Also, it is true that exterior grade plywood has the same glue as marine. However, the real differences come from the lack of voids in the inner plys with a good marine grade plywood. Also, I would think that would matter much more in a planing hull than a sailboat. Several authors have commented on the use of Exterior grade plywood. Sam Devlin is basically completely against it as it creates false economy. I have read Jacques Mertens site where he and other designers do not support the idea on a planing hull. Harold Dynamite Payson thinks it is okay as long as you fill the voids with epoxy and a syringe. (IMO, That sounds like a lot of work to save a few bucks.)

Basically, I am just reiterating what I have read here and other places. For my sailboat hull, I am using all marine grade (BS6566). However, I will be using quality exterior for the interior bulkheads and what not.

I hope this helps and please post pics of the CS-20. I have been waiting to see a finished one for scale purpose and see how it compares to another popular S&G skiff.

Last edited by razopp on Mon May 19, 2008 6:35 am, edited 1 time in total.

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Post by newbi2008 » Mon May 19, 2008 6:35 am

A good point, Well made!

Cheers, very soon ordering the CS-20 plans.

But going to modify it slightly.

I'm going to try to bring the roof of the cabin up front out to meet the hull side at the sheer. (i'm new with the terminoligy, bear with me!)

I'll step the hull about half way along, so i'll lose the walk around at the front but gain a deck space for sunbathing etc, (for the misus! apparently now its 'our' project!)

So the hull with have a colvic style shape to it.

Hands up who thinks i'm insane! Will it work. Who knows!


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Post by Jones » Mon May 19, 2008 12:32 pm

newbi2008 wrote:
Cheers, very soon ordering the CS-20 plans.

But going to modify it slightly.
I'd encourage you to order and read Glen's Boatbuilding With Plywood text before making modifications. Certainly, they are yours to make, but you may gain a few insights about proportions.
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Post by leakcheck » Mon May 19, 2008 5:10 pm

The absolute best move you can make is to get your wife involved and thinking that all the ideas are when the wallet starts opening up for those tool purchaces just say: "Honey, look what I got you for your anniversary !!!"


PS..Let me know how that works out for ya ?? :roll:

And oh yes...marine substitutes.

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Post by Falcon » Tue May 20, 2008 2:37 am

>>>>>>>>>And oh yes...marine substitutes.<<<<<<<
I LOOK AT IT THIS WAY, The plywood is the bace. That said ,do you want a bace that "MIGHT" have voids? I think marine ply is a very good investment.
Be who you are, say what you want those that mind don't matter an those that matter wont mind.

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Post by basilkies » Tue May 20, 2008 9:16 pm

I bet it costs more to put one extra layer of fiberglass on your hull than it would to buy marine plywood. The other nice thing about marine ply is that it just seems to be more supple and bend around things better that outdoor ply.

On my boat the plans called for outdoor plywood wood on the transom. The transom is completely framed and reinforced so the voids that go all the way through the plywood from edge to edge (that's the trouble with voids the run the whole width of the board) are beefed up by the frame job.

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Post by raymacke » Tue May 20, 2008 9:43 pm

When it comes to comprising on building materials, everyone has their own opinion. For what it is worth here is mine on using exterior ply.

From what I have read the main reason that voids in ply are to be avoided is that the air in the voids tend to absorb moisture from the the water. With enough moisture the ply can start to rot from the inside. I believe this is a serious concern on a boat sitting on the water 24/7 but to a lesser degree on an occasionally used trailered boat. Still the fewer the voids the better. I did use an good grade of exterior for all but the bow section of my Cabin Skiff and have experienced no problems.

BUT I probably wouldn't do it again. The reason is there is next to no "good grade" of exterior ply available these days. At least in my area. Check your local lumber yard. Look down the edges of a stack of exterior ply. Look at the number of voids. Some skids are better than other but most all are just full of voids. The best grade is B-C and most of it is junk.

On my True Grit I have used all Douglas Fir marine ply for the hull. I paid the price and have no regrets. But for the topsides I have again compromised. After a fair amount of research I decide to go with MDO (medium density overlay) This is an exterior ply with a resin coated fiber surface. It is available with both or just one side coated. A common usage is exterior signs and some local lumber yards may stock it. My experience is the the number of voids are very low (again look at the edges) but the surface quality will vary. Get a sheet out in the sun and look across the surface. The lesser quality sheets will allow the grain to print through the coating. The better stuff is very smooth.

The thinnest I have found is 3/8" and thickest is 3/4". Some boat builders have used this for hulls and just painted without glassing. I guess that might be workable for some but running rivers my hulls tend to take a lot of abuse hitting debris in the water (not to mention the dock now and then). I would be concerned with scraping the paint off and exposing bare wood. Glass and epoxy lend a lot of abrasion resistance. Also the MDO is softer than DF and I feel it would dent easier when the hull impacts something. Not a huge concern on the topsides.

My advice is if you can find GOOD exterior it can be considered but you won't find it at Lowes are Home Depot. All in all marine is usually a better choice.

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