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FiremanFil
07-18-2014, 08:49 AM
I am building a Spira 14' dory. The plans call for the keelson to be a 2x4. I gave a 16' clear mahogany 1st that I would l I've to use. Will that be a problem? Also the plans call for using epoxy on the frame but joints. Can I use Gorilla glue or Titebond III as a substitute? Any thoughts would be welcome. I'm a newbie and need some guidance.

thanks.

James McMullen
07-18-2014, 09:01 AM
The mahogany is certainly a vastly better piece of wood than a construction 2x4...but you might want to save it for the next project, honestly. It'll be kinda wasted on this, and you're going to have a hard time replacing it down the road. Hoard that mahogany for a project where you'll be carefully crafting a delicate shape. A 2x4 is perfectly appropriate and ideal for a Spira dory.

Use epoxy. There is nothing more forgiving of a newbie boatbuilder's mistakes than waterproof, gap-filling epoxy. Neither Gorilla nor Titebond are actually gap-filling in any meaningful structural way. You need to learn how to use epoxy anyways, so just get started.

My best advice to you is don't change anything from the plans on this, your first build. You really ought to gain some practice and experience with what is known and proven to work before you head off into uncharted territory. Make this first boat a success, and you can build on from there on your next boat.

Of course there's a next boat. Don't be silly. :D

David G
07-18-2014, 09:05 AM
What James said - and adding only that Titebond II or III would be an acceptable substitute... but only in well-crafted, tight, clampable joints. The Gorilla Glue? Don't buy it. If you've already bought it... give it to a neighbor or relative you dislike.

Oldad
07-18-2014, 09:10 AM
No on the glue. IMHO there is no substitute for epoxy. Unless you are a qualified MA or designer, build according to the plans. If you have questions about changing or substituting items on your plans, ask the designer, that should be part of the service. If you want advice that is all over the place, some from people who never built a boat or have any expertise with the design you are building, ask your questions here.
P.S. I just read James and Davids posts which were posted while I was writing—now there's examples of the good advice you might find on this forum.

JimD
07-18-2014, 09:53 AM
Let's keep it unanimous. Epoxy yes, mahogany no. Don't forget a thickening agent for the epoxy such as fumed silica or wood flour.

Lewisboater
07-18-2014, 10:31 AM
Let's keep it unanimous. Epoxy yes, mahogany no. Don't forget a thickening agent for the epoxy such as fumed silica or wood flour.

I'm with that... and no... sawdust isn't wood flour... too coarse. You can use baby powder if you want something cheap... smells good when you sand it too.

FiremanFil
07-18-2014, 11:30 AM
Bad typist. The mahogany is a 1x4. My real question is whether I can sub the 1x4 for the 2x4. The butt joints are flush and tight and will be secured with four deck screws. Hence my question about the glue. I fully intend to use epoxy elsewhere where it is appropriate. When I posed these questions to Spira, I have received no response.

Thanks again for all your knowledge and help.

Oldad
07-18-2014, 11:38 AM
Bad typist. The mahogany is a 1x4. My real question is whether I can sub the 1x4 for the 2x4. The butt joints are flush and tight and will be secured with four deck screws. Hence my question about the glue. I fully intend to use epoxy elsewhere where it is appropriate. When I posed these questions to Spira, I have received no response.

Thanks again for all your knowledge and help.

No, for all the reasons listed above. Stick to the plans. Why second guess the designer? Really, why? Realize, that when you change the plans in any way, you own the design and its success or failure. No longer Spira's. In the words of Jacques Mertons, "You have epoxy, use epoxy."

James McMullen
07-18-2014, 02:18 PM
No. You cannot substitute a 1X4 for a 2x4. Ever.

I wouldn't recommend you use deck screws either. Use marine grade stainless or heavy galvanized. Deck screws are for structures that won't drown you if it comes apart.

Breakaway
07-18-2014, 04:00 PM
Its exponentially weaker and less stiff. I forget the actual ratios, and they vary by species, but in general, half the thickness is less than half as stiff or strong. Don't do it.

Kevin

FiremanFil
07-18-2014, 06:11 PM
Thanks everyone. The 2x4 and epoxy are in...along with proper wood screws. Learning a little (a lot?) more with each post.

Thanks again

Lewisboater
07-18-2014, 08:17 PM
Its exponentially weaker and less stiff. I forget the actual ratios, and they vary by species, but in general, half the thickness is less than half as stiff or strong. Don't do it.

Kevin

I believe twice the thickness is 8 times as stiff... but I could be mistaken. Seems I read it in one of my bow making books.

David G
07-18-2014, 08:39 PM
Yes. In general terms - the stiffness increases by the cube of the increase in thickness.

So - if you multiply the thickness by 2... the stiffness increases - not times 2. Not times 2, times2 (or times 4). But times 2, times 2, times 2 (or times 8)

JesterGrin
07-19-2014, 02:29 AM
I'm with that... and no... sawdust isn't wood flour... too coarse. You can use baby powder if you want something cheap... smells good when you sand it too.

Sorry to jump in on this but does one need to thicken the Epoxy for Glue Joints?

James McMullen
07-19-2014, 07:14 AM
Sorry to jump in on this but does one need to thicken the Epoxy for Glue Joints?
Yes. Pro practice is to wet out both of the faying surfaces with thin epoxy, then add some thixotrope to your cup and butter it up again with thickened before assembling the joint. This eliminates any risk of a glue-starved joint and makes sure you get maximal penetration into the porosity of the grain coupled with best gap-filling for any irregularities in the joint surface. You also increase the strength and reduce brittleness of the cured resin with the right thixotrope.

LittleGoat
07-21-2014, 12:42 PM
For those out there who are wondering, getting equivalent amounts of epoxy is price comparable to 5200, Sikaflex, etc. I'm talking about Marinepoxy (Duckworks or Bateau), AeroMarine, Raka, etc grade. While it doesn't have the convenience of a one part, it is stronger and longer lasting. I for one charge myself nothing when it comes to building boats (since my time is worthless... ;)) so the only advantage of a one-part system is moot.

Stick to the plans. Epoxy is your friend and is like Earth: Mostly Harmless.