Tahoe 23 project, Norway

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Toivo
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Re: Tahoe 23 project, Norway

Postby Toivo » Sun Sep 10, 2017 10:47 am

What would be the preferred way to make the stringers? I have the opportunity to use 2x6 spruce logs, and I think I can get them in 15' witch is what the pattern says. However, I'm a bit concerned that the log might warp over time. Should I use plywood instead? Laminate of 3/4'' plywood with butt joints and sufficient overlap.

DSR
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Re: Tahoe 23 project, Norway

Postby DSR » Sun Sep 10, 2017 11:26 am

Hi Toivo,

I would do a lamination of both. Use the Spruce and laminate plywood on both sides of each. That would give you the best of both. It would increase strength and reduce warpage and the possibility of the Spruce splitting.

Thanks,
Dave
DSR Performance - Home of yet another jet TNT build :D
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Toivo
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Re: Tahoe 23 project, Norway

Postby Toivo » Sun Sep 10, 2017 11:31 am

DSR wrote:Hi Toivo,

I would do a lamination of both. Use the Spruce and laminate plywood on both sides of each. That would give you the best of both. It would increase strength and reduce warpage and the possibility of the Spruce splitting.

Thanks,
Dave


Good idea. Can I still use butt joints?

EDIT: And still 3/4'' plywood?

DSR
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Re: Tahoe 23 project, Norway

Postby DSR » Sun Sep 10, 2017 12:27 pm

Butt joints on the plywood lams shouldn't be an issue, I would just keep the joints from being directly across from each other. If you need to do butt joints on the Spruce, I would split the 2" thickness into 2 lams and spread the butt joints from each other between the lams (doing it that way would be more work of course, but it would make the stringer even stronger and more stable also)

Thanks Toivo
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Toivo
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Re: Tahoe 23 project, Norway

Postby Toivo » Sun Sep 10, 2017 12:43 pm

Ripping 6" wide is too wide (or tall if that make sense) for my table saw.
Is this type of scarf joint an alternative? And of course cut the joint so its longer than 6''
DSC_0773.JPG

DSR
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Re: Tahoe 23 project, Norway

Postby DSR » Sun Sep 10, 2017 1:26 pm

Scarfing the stringers would work great. A lot of people don't have the capability to resaw 6".
I wouldn't be comfortable with doing a joint like you're showing though. It's more of an edge lamination than a scarf. Doing a scarf across the 6" width and 12-16" long (6:1 to 8:1 ratio) would be better in my opinion. It gives you much more glueing surface.
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Toivo
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Re: Tahoe 23 project, Norway

Postby Toivo » Sun Sep 10, 2017 1:50 pm

DSR wrote:Scarfing the stringers would work great. A lot of people don't have the capability to resaw 6".
I wouldn't be comfortable with doing a joint like you're showing though. It's more of an edge lamination than a scarf. Doing a scarf across the 6" width and 12-16" long (6:1 to 8:1 ratio) would be better in my opinion. It gives you much more glueing surface.


Thanks. That make sense. I managed to get my hands on Edgar's email. So I'm gonna try contacting him, and see what happens :)

TomB
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Re: Tahoe 23 project, Norway

Postby TomB » Sun Sep 10, 2017 2:40 pm

A few things. First, the stingers are 16' long, with a minimum net dimension of 1 1/2"x 5 1/2".

I agree with Dave, laminating is a good idea. A 2"x6" - 16' will tend to "wander". Straightening stringers with the form and frames and clamps is a pain. Lengths of plywood will be stable and straight. After glue-up, with a 1"x8" and two 1/2"x6" strips of plywood, you can cut down to a straight stringer.

On the issue of scarfing, I maybe agree with Dave and maybe not. If you use two layers of plywood widely staggered butt joints would probably be OK. If you are using one layer of plywood, scarf the joint.

Tom

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Bill Edmundson
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Re: Tahoe 23 project, Norway

Postby Bill Edmundson » Sun Sep 10, 2017 2:58 pm

I laminated the stringers on my Tahoe. I used 2 1x6. I had to scarf each one. I cut at 60* in the wide direction and 45* cross way. The joints for the 2 laminates do not line up with each other. None of the scarfs are under the engine.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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Toivo
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Re: Tahoe 23 project, Norway

Postby Toivo » Mon Sep 11, 2017 12:51 pm

TomB wrote:A few things. First, the stingers are 16' long, with a minimum net dimension of 1 1/2"x 5 1/2".

I agree with Dave, laminating is a good idea. A 2"x6" - 16' will tend to "wander". Straightening stringers with the form and frames and clamps is a pain. Lengths of plywood will be stable and straight. After glue-up, with a 1"x8" and two 1/2"x6" strips of plywood, you can cut down to a straight stringer.

On the issue of scarfing, I maybe agree with Dave and maybe not. If you use two layers of plywood widely staggered butt joints would probably be OK. If you are using one layer of plywood, scarf the joint.

Tom


Yes, my bad. Didn't have the patterns in front of me. But this sounds like a plan. Laminate to pieces of plywood outside a core of spruce. Scarf joints, but not where the motor is gonna be.

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Jimbob
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Re: Tahoe 23 project, Norway

Postby Jimbob » Mon Sep 11, 2017 1:44 pm

On my boat I made my motor stringers by laminating two 4/4 pieces of mahogany. I scarfed each of the individual pieces before laminating them together. I laminated them together on a flat 16' long table. (a 4/8 sheet of plywood ripped down the middle placed end to end. see pic). I also used a jig to align the scarf joints when they were glued together. As others have said, place the scarf joints staggered and where they won't be under a load. I made my scarf joints using a router which allowed me a long ratio in the joint. You could make your scarfing jig as wide as you want (I think mine would accommodate up to a 6" wide board) , just make sure you mount your router to a clear piece of plastic so you can see what you are doing when you cut the joint. When I made my battens, I cut the scarf joints on a wide board, and then ripped those boards to the finished width. The pic below shows multiple battens being glued up at once. Pics below of the scarfing jig and the assembly jigs.
Jim
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P1010060.JPG
The scarfing jig. Make your ratio whatever you choose.
P1010061.JPG
The router on the plastic piece that rides on the jig
P1060095.JPG
The glue up table with alignment jigs (make sure to use wax paper)
Jim Neeley
Sacramento, CA

PeterG
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Re: Tahoe 23 project, Norway

Postby PeterG » Mon Sep 11, 2017 2:01 pm

Sorry, I have to step in here and say I believe laminating stringers to the plan dimension from a plywood sandwich is not a good idea for strength, especially for an inboard of the size you are building.
Check your plans for the stringers, they specify wood (not plywood) for a reason. Plywood has alternating grain directions with each layer and only half of the wood grain will be going the lengthwise direction that you need for strength. The plans may specify laminating thin plywood to one side to stabilize the wood from possibly splitting lengthwise. But the wood is the primary structural piece. The stringers on the Barrelback and Key Largo are made this way. Roberta's Torpedo does have plywood laminated to either side of the stringers but that is in way of a major step or discontinuity in the stringers near the bow. The wood in those stringers is sized for the loads, the plywood reinforces the joints like the corner gussets of your frames.
I strongly recommend building your stringers per the plan dimension with wood. Replacing wood with plywood will weaken the stringers. Laminating them in two or three layers of wood will be great for dimensional stability and strength. Scarfing pieces to make a full length layer is the best method, butt joints are weaker. Make sure you alternate the scarf joints in each layer so none will be in the same spot on the stringer, and don't place a scarf joint under the engine.
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

Toivo
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Re: Tahoe 23 project, Norway

Postby Toivo » Mon Sep 11, 2017 2:33 pm

PeterG wrote:Sorry, I have to step in here and say I believe laminating stringers to the plan dimension from a plywood sandwich is not a good idea for strength, especially for an inboard of the size you are building.
Check your plans for the stringers, they specify wood (not plywood) for a reason. Plywood has alternating grain directions with each layer and only half of the wood grain will be going the lengthwise direction that you need for strength. The plans may specify laminating thin plywood to one side to stabilize the wood from possibly splitting lengthwise. But the lumber is the primary structural piece. The stringers on the Barrelback and Key Largo are made this way. Roberta's Torpedo does have plywood laminated to either side of the stringers but that is in way of a major step or discontinuity in the stringers near the bow. The wood in those stringers is sized for the loads, the plywood reinforces the joints like the corner gussets of your frames.
I strongly recommend building your stringers per the plan dimension with lumber. Replacing lumber with plywood will weaken the stringers. Laminating them in two or three layers of wood will be great for dimensional stability and strength. Scarfing pieces to make a full length layer is a good idea, so long as you alternate the scarf joints in each layer so none will be in the same spot, and don't place a scarf joint under the engine.


Hmm. The guy who built this
Image

With a v12 Rolls Royce Merlin engine used plywood for the stringers. That said, It may be a bad idea anyway, haha. I've always thought that plywood is stronger, just because the grain goes in different directions... But as we concluded, I will make the stringers according to the plans, but if I'm going to use a log, I'll have to make one scarf joint/butt joint to avoid warp. For extra stiffness plywood will be laminated on each side of the stringer.
At least the added plywood can't make them weaker right? :)

PeterG
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Re: Tahoe 23 project, Norway

Postby PeterG » Mon Sep 11, 2017 2:47 pm

That is a great looking boat! He may have used a laminated beam for the stringers? That is different from plywood, the grain of the thin layers of a laminated beam all go lengthwise, not alternating. That makes a very strong, very stable stringer.
You can certainly add plywood to the sides of your stringers if the stringer is per the plan dimensions. You are adding some weight but not a lot and should have a dimensionally stable stringer. If you are scarfing the stringer itself, you could use thinner plywood like 3/8" (9mm) and have butt joints in the plywood.
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

TomB
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Re: Tahoe 23 project, Norway

Postby TomB » Mon Sep 11, 2017 4:50 pm

I spent most of my career designing things and I wasn't the first to say "the design documents are just a vague representation of what might get built". So let's circle back to the Instructions. "Motor Stringers: ... Although they can be cut from nominal 2"x6" stock, they can also be laminated and/or scarf joined from shorter, smaller members. This latter method may be preferable to maintain a true edge along the set-up level and to prevent twist and defects."


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