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Re: Tahoe 23 project, Norway

Posted: Mon Sep 11, 2017 6:43 pm
by Bill Edmundson
I'm with TomB.

Bill

Re: Tahoe 23 project, Norway

Posted: Mon Sep 11, 2017 6:59 pm
by PeterG
Yup, I agree with what TomB said too. I'm just really reluctant to say plywood is suitable to substitute where solid wood is called out for a structural member. At least not without a design analysis showing the plywood is acceptable :D

Re: Tahoe 23 project, Norway

Posted: Tue Sep 12, 2017 4:56 am
by DrBryanJ
I don't agree that plywood is weaker. Look at the wooded I beams being used for construction now. They have less spring than dimensional lumber and can span longer distances without deflection. The grain running in different directions helps, not hurts.

Re: Tahoe 23 project, Norway

Posted: Tue Sep 12, 2017 6:20 am
by TomB
Toivo,

With respect to the motor stringers, we have been writing about strength and economy. Durability/abuse and rot is another important consideration.

Mark Bonkalla built and documented his mahogany runabout build about 15 years ago. He used redwood stringers and uses his boat for waterskiing. Anchors, water skis, other toys bounce off the stringers and dent the encapsulated wood. The epoxy flaked off and water infiltration became an issue. Quoting Mark, “The redwood simply coated with epoxy looked terrible after only one season.” He added a layer of fiberglass to protect the stringers from abuse.

The spruce/plywood idea might need some added protection.

Tom

Re: Tahoe 23 project, Norway

Posted: Tue Sep 12, 2017 6:47 am
by TomB
I don't agree that plywood is weaker. Look at the wooded I beams being used for construction now. They have less spring than dimensional lumber and can span longer distances without deflection. The grain running in different directions helps, not hurts.
Ah, well, not exactly, wood I-beams are highly engineered products. The top and bottom flanges are made up of a glue lamination of long oriented plies all running with the length. The web is "beaver barf" also oriented with the length. As the beam is loaded and bends, the flange plies go into tension/compression using long wood strands to provide resistance to deflection. The web to a lesser extent is in both tension and compression serves the primary function of keep the flanges apart. So all three components work to provide stiffness in one direction. Flip it the side and the I-beam becomes a fragile noodle since non of the wood fiber is oriented in that direction.

I wouldn't be afraid of using plywood in the stringers as long as the wood strands oriented in the weak direction are discounted.

Tom

Re: Tahoe 23 project, Norway

Posted: Tue Sep 12, 2017 12:34 pm
by Toivo
TomB wrote:Toivo,

With respect to the motor stringers, we have been writing about strength and economy. Durability/abuse and rot is another important consideration.

Mark Bonkalla built and documented his mahogany runabout build about 15 years ago. He used redwood stringers and uses his boat for waterskiing. Anchors, water skis, other toys bounce off the stringers and dent the encapsulated wood. The epoxy flaked off and water infiltration became an issue. Quoting Mark, “The redwood simply coated with epoxy looked terrible after only one season.” He added a layer of fiberglass to protect the stringers from abuse.

The spruce/plywood idea might need some added protection.

Tom
Good point Tom. But how did he manage to dent the stringers in the first place? He didn't cover them with the floor?

Btw i checked with the guy that built the baby bootlegger. He used two 38mm plywood laminated together for stringers. That motor produces 2000Nm

Re: Tahoe 23 project, Norway

Posted: Tue Sep 12, 2017 2:49 pm
by TomB
But how did he manage to dent the stringers in the first place? He didn't cover them with the floor?
Good questions.

Kids, water skis, anchors, fish guts, dropped tools :arrow: dents. With a little luck, a good boat gets used. :D :D :D :D

I don't think he documented the floor. His website http://www.bronkalla.com/index_boat.html for his Riviera is still up and goes through his build step-by-step.

Re: Tahoe 23 project, Norway

Posted: Wed Sep 13, 2017 12:14 am
by Toivo
TomB wrote:
But how did he manage to dent the stringers in the first place? He didn't cover them with the floor?
Good questions.

Kids, water skis, anchors, fish guts, dropped tools :arrow: dents. With a little luck, a good boat gets used. :D :D :D :D

I don't think he documented the floor. His website http://www.bronkalla.com/index_boat.html for his Riviera is still up and goes through his build step-by-step.
I have other boats for that kind of use ;) My Tahoe is gonna be for cruising, and boat gatherings :)

Re: Tahoe 23 project, Norway

Posted: Tue Aug 28, 2018 11:17 pm
by ALR
Toivo,

Will you be treating the spruce with pine tar to help preserve the wood?