Douglas Fir vs. Plywood for Stringers
08-02-2012, 12:28 PM
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Douglas Fir vs. Plywood for Stringers
This seems like a well-worn topic here, but I bring it up again with a "small boat" twist. Here are a few other posts on this, but none were conclusive.
http://www.offshoreonly.com/forums/f...ine-grade.html
http://www.offshoreonly.com/forums/f...vice-guys.html
I'm starting to repair (I won't say restore yet, but that's what it will likely be) my 88 Seebold Eagle 21 I/O.
It has the usual rotted stringer and bulkhead problem, most severe around the gas tank which was foamed in and held water around it. Under the floor, its completely rotted, and that's what I'm working on now...scooping it out by the handful.
Trying to decide what wood to use for the stringers and bulkheads...
The original build used some flavor of 2x dimensional lumber. It does not appear to have been pre-coated, and from the looks of the remaining glass, there was minimal resin penetration on the original layup. Most of it peeled from the wood perfectly clean.
Of course I will soak the new wood with resin and wrap it with cloth before installing. I assume that will take care of water intrusion no matter what wood I use.
So the question is...Douglas Fir or laminated 3/4" plywood (with 1.5 oz cloth between)?
Seems like most would recommend plywood. However, being a light build boat (similar to a Checkmate), I'm concerned about changing the flex properties of the hull and creating a "hard spot" in the middle of the boat.
The wood in the bow area is dry and seems fine, so I'm not ripping into that yet. Aft in the bilge area, I have not found any rot in the transom or stringers by percussion testing, but no core samples yet. It seems solid so not in the scope of the repair at the moment (motor's still in it).
The Seebold family knows a lot about building light weight wood construction boats. They have been building Champ O/B racing boats for decades, and are known for their use of exotic woods to balance strength and weight.
I'm leaning toward using Douglas Fir lumber for the repair. My current thinking is to repair using the same materials as the original build, but with better glassing practice to avoid future rot.
However, I could be swayed by the deep experience here...what are your thoughts? Cost is about the same either way, and not a big concern.
BTW...pics coming soon...and I may start a restoration thread to capture all the fun.
http://www.offshoreonly.com/forums/f...ine-grade.html
http://www.offshoreonly.com/forums/f...vice-guys.html
I'm starting to repair (I won't say restore yet, but that's what it will likely be) my 88 Seebold Eagle 21 I/O.
It has the usual rotted stringer and bulkhead problem, most severe around the gas tank which was foamed in and held water around it. Under the floor, its completely rotted, and that's what I'm working on now...scooping it out by the handful.
Trying to decide what wood to use for the stringers and bulkheads...
The original build used some flavor of 2x dimensional lumber. It does not appear to have been pre-coated, and from the looks of the remaining glass, there was minimal resin penetration on the original layup. Most of it peeled from the wood perfectly clean.
Of course I will soak the new wood with resin and wrap it with cloth before installing. I assume that will take care of water intrusion no matter what wood I use.
So the question is...Douglas Fir or laminated 3/4" plywood (with 1.5 oz cloth between)?
Seems like most would recommend plywood. However, being a light build boat (similar to a Checkmate), I'm concerned about changing the flex properties of the hull and creating a "hard spot" in the middle of the boat.
The wood in the bow area is dry and seems fine, so I'm not ripping into that yet. Aft in the bilge area, I have not found any rot in the transom or stringers by percussion testing, but no core samples yet. It seems solid so not in the scope of the repair at the moment (motor's still in it).
The Seebold family knows a lot about building light weight wood construction boats. They have been building Champ O/B racing boats for decades, and are known for their use of exotic woods to balance strength and weight.
I'm leaning toward using Douglas Fir lumber for the repair. My current thinking is to repair using the same materials as the original build, but with better glassing practice to avoid future rot.
However, I could be swayed by the deep experience here...what are your thoughts? Cost is about the same either way, and not a big concern.
BTW...pics coming soon...and I may start a restoration thread to capture all the fun.
08-02-2012, 07:42 PM
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Any dimensional Doug Fir is going to warp, twist, cup..you name it..it's shape will change over time causing all of your pretty glass work to crack eventually. The strength of the Plywood is comparable and it will stand the test of time if you're going to coat it. (I'm a Wood Guy) have you looked at Composite Lumber?? It's heavier than standard plywood, but not by too much?? It'll never Rot..glassed or not.. it won't twist, warp, or cup, and you'd save the next 10 future owners of the thing a headache??
08-03-2012, 05:07 AM
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Use plywood.
Lb per LB it's stronger than almost anything especially for skin. The fast tunnel boats have been 90% plywood (as were almost all race boats) for eon's until just recently going to exotic ($$$$) composites. Most of what you're reading about also are tiny stringers and not close to what you're thinking. Where the Seebolds and the like, use Spruce and similar are small, typically 3/4" X 3/4" stringers run the length of the boat, parallel w/each other and 4" - 6" apart to support the outer skin's of the deck and bottoms. The main uprights or coamings that provide the cockpit sides and what the motor boards are attached to are almost always plywood and that is the back bone of that style of boat. That is way closer to what you're thinking of as a stringer than what your seeing in your research.
Lb per LB it's stronger than almost anything especially for skin. The fast tunnel boats have been 90% plywood (as were almost all race boats) for eon's until just recently going to exotic ($$$$) composites. Most of what you're reading about also are tiny stringers and not close to what you're thinking. Where the Seebolds and the like, use Spruce and similar are small, typically 3/4" X 3/4" stringers run the length of the boat, parallel w/each other and 4" - 6" apart to support the outer skin's of the deck and bottoms. The main uprights or coamings that provide the cockpit sides and what the motor boards are attached to are almost always plywood and that is the back bone of that style of boat. That is way closer to what you're thinking of as a stringer than what your seeing in your research.
08-03-2012, 08:53 AM
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Plywood it is...
Thanks for the feedback!
I hadn't considered the warping and twisting aspect...and now that you mention it, I may have seen some evidence of that on the original build. The original tabbing came loose in a couple spots, and this could be an explanation.
Also the background on the light build race boats is helpful. The more I read, the more I see that most folks use plywood. Its awesome that this forum exists with all this info readily available.
Sounds like there's reasons not to use Doug Fir, and no reason not to use laminated plywood, so that's the way I'll go. I've considered LVL as an alternative, but I've got a sheet of plywood I can use, so that's the ticket...
Thanks again...and look for a restoration thread by me coming up in the next week or two. I'm sure there will be more questions!
I hadn't considered the warping and twisting aspect...and now that you mention it, I may have seen some evidence of that on the original build. The original tabbing came loose in a couple spots, and this could be an explanation.
Also the background on the light build race boats is helpful. The more I read, the more I see that most folks use plywood. Its awesome that this forum exists with all this info readily available.
Sounds like there's reasons not to use Doug Fir, and no reason not to use laminated plywood, so that's the way I'll go. I've considered LVL as an alternative, but I've got a sheet of plywood I can use, so that's the ticket...
Thanks again...and look for a restoration thread by me coming up in the next week or two. I'm sure there will be more questions!
08-03-2012, 08:38 PM
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I used Douglas Fir marine grade ply when I built my stringers, bulkheads and transom! 2pcs laminated together and screwed every 4" those stringers were as straight and solid as a rock!!!!
08-04-2012, 02:00 PM
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fleg, I think Doug Fir plywood is what I will use.
The original wood was dimensional lumber, probably some kind of pine, maybe just spruce. I was considering Doug Fir dimensional lumber, which a yard stocks locally. But the marine plywood they have is also Doug Fir in plywood form.
Seebold used marine plywood in the transom, and also used 2 laminated plywood cross members to hold down the belly tank (probably scraps). It was uncoated...just 2 3/4 pieces glued together. That wood still looks like new, and the stringer it was screwed to is rotted completely to powder...
I assume the best way to laminate them is to coat both sides with resin, let cure somewhat, then add a layer of mat with more resin and clamp?
The original wood was dimensional lumber, probably some kind of pine, maybe just spruce. I was considering Doug Fir dimensional lumber, which a yard stocks locally. But the marine plywood they have is also Doug Fir in plywood form.
Seebold used marine plywood in the transom, and also used 2 laminated plywood cross members to hold down the belly tank (probably scraps). It was uncoated...just 2 3/4 pieces glued together. That wood still looks like new, and the stringer it was screwed to is rotted completely to powder...
I assume the best way to laminate them is to coat both sides with resin, let cure somewhat, then add a layer of mat with more resin and clamp?
08-04-2012, 03:28 PM
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fleg, I think Doug Fir plywood is what I will use.
The original wood was dimensional lumber, probably some kind of pine, maybe just spruce. I was considering Doug Fir dimensional lumber, which a yard stocks locally. But the marine plywood they have is also Doug Fir in plywood form.
Seebold used marine plywood in the transom, and also used 2 laminated plywood cross members to hold down the belly tank (probably scraps). It was uncoated...just 2 3/4 pieces glued together. That wood still looks like new, and the stringer it was screwed to is rotted completely to powder...
I assume the best way to laminate them is to coat both sides with resin, let cure somewhat, then add a layer of mat with more resin and clamp?
The original wood was dimensional lumber, probably some kind of pine, maybe just spruce. I was considering Doug Fir dimensional lumber, which a yard stocks locally. But the marine plywood they have is also Doug Fir in plywood form.
Seebold used marine plywood in the transom, and also used 2 laminated plywood cross members to hold down the belly tank (probably scraps). It was uncoated...just 2 3/4 pieces glued together. That wood still looks like new, and the stringer it was screwed to is rotted completely to powder...
I assume the best way to laminate them is to coat both sides with resin, let cure somewhat, then add a layer of mat with more resin and clamp?
