Structure in stitch and glue build

[Nomiddlename]

Ok so maybe this falls into the composite section but my questions are regarding wood so I'll put them here. I am building a stitch and glue boat of 14 feet in length and about five feet in beam. I built the hull using spreader boards to give the shape desired. I have placed in three frames along with some ply on one where I plang to hang seats.
As you can see I have only tacked the sides of the centre frame in place. I did this in anticipation of perhaps cutting out the bottom and running stringers through to the forward frame to support a floor. Bottom panels are 3/8" marine fir ply.
My question is, are stringers necessary in a boat of this size running at generally low speed albeit in moderate chop? Or are frames enough to offer stiffness? If anyone out there has an opinion on sealed floor vs floorboards my ears are open as well. Seats and bow will have floatation foam. Attached a crude photo of proposed stringers and cut out as well as a picture of forward section.

 

[rwatson]

Three stringers are cheap insurance, although you may get away with none. Don't forget, its not just pressure of running in water, its loading you and your gear and beaching and launching and trailering, over years etc.
As far as flooring, permanent flooring runs the risk of moisture entrapment, and you will want as light as possible for a 14' boat.

 

[Nomiddlename]

Three stringers are cheap insurance, although you may get away with none. Don't forget, its not just pressure of running in water, its loading you and your gear and beaching and launching and trailering, over years etc.
As far as flooring, permanent flooring runs the risk of moisture entrapment, and you will want as light as possible for a 14' boat.

Thanks for the reply. You know what I never even thought of the stresses besides running it I will certainly put it under. Will definitely throw stringers in.

 

[Milehog]

Sealed compartments in wood boats scare me. Not only moisture entrapment but the impossibility of visual inspection for moisture intrusion and, if you trailer the boat to different elevations, pressure differentials damaging the joints.

 

[fallguy]

Sealed compartments in wood boats scare me. Not only moisture entrapment but the impossibility of visual inspection for moisture intrusion and, if you trailer the boat to different elevations, pressure differentials damaging the joints.

They can utilize air only vents.

 

[Nomiddlename]

Sealed compartments in wood boats scare me. Not only moisture entrapment but the impossibility of visual inspection for moisture intrusion and, if you trailer the boat to different elevations, pressure differentials damaging the joints.

Yes that worries me quite a bit. Be a headache to restore when moisture inevitably gets in and causes a headache.

 

[Nomiddlename]

They can utilize air only vents.

I was thinking of this. Say I have sealed benches filled with some foam. Is it common practice to drill vents near the top to allow air in but hopefully not water?

 

[philSweet]

Stringers are necessary anywhere you don't have floor boards and if you are trailering the boat. I recommend long carpeted trailer bunks with a hull stringer over the bunks. The stringers don't have to be tall and thin here. If trailerable, I like to use 1/2 ply about 3" wide glued down on the flat and beveled at least an inch at the top. You often don't have the freeboard aft to have both floors and seats. I like a floorboarded section in the middle of the boat to keep stuff dry, but would normally not have floor boards front and back on a 14'er. A drop-in floor board grid is my preference. It can be held in place by one simple pin and makes cleaning the boat a lot easier. A white oak 4 x 4 ripped to 3/8 + makes good floor boards for a 14'er. Support with a frame every 12 inches.

So floor frames on 12" centers between the forward and aft main frames, and stringers for foot rests and trailering aft of that.

 

[Nomiddlename]

Stringers are necessary anywhere you don't have floor boards and if you are trailering the boat. I recommend long carpeted trailer bunks with a hull stringer over the bunks. The stringers don't have to be tall and thin here. If trailerable, I like to use 1/2 ply about 3" wide glued down on the flat and beveled at least an inch at the top. You often don't have the freeboard aft to have both floors and seats. I like a floorboarded section in the middle of the boat to keep stuff dry, but would normally not have floor boards front and back on a 14'er. A drop-in floor board grid is my preference. It can be held in place by one simple pin and makes cleaning the boat a lot easier. A white oak 4 x 4 ripped to 3/8 + makes good floor boards for a 14'er. Support with a frame every 12 inches.

So floor frames on 12" centers between the forward and aft main frames, and stringers for foot rests and trailering aft of that.

Wow thank you for the detailed reply. So if I'm understanding correct you would have your floorboards and frames joined together and simply lock it into the hull when in use? That's very sharp. I might go with that.
I'm having trouble picturing your stringer system though. You would only have them aft, and place them where the trailer bunks would land? Is that correct?

 

[philSweet]

Yes. Exactly that. The floor frame at 12" centers are plenty for the trailer bunks.

<edit> sorry, the floor frames are permanent but only go part way across. They need to go as far as the bunks. The floor boards are tied together with light cross pieces that sister to the frames. I used a tang on the front that fitted into a slot in the forward frame and a pin in the Back to hold the back in.

 

[Milehog]

I was thinking of this. Say I have sealed benches filled with some foam. Is it common practice to drill vents near the top to allow air in but hopefully not water?

My 2¢ on foam filled stitch-n-glue side benches after considering a build with them.
Forget the foam and install deckplates. The dry stowage is invaluable, they allow ventilation, inspection and no air pressure induced stress.
I like DPI pull-up deckplates as they don't get sticky like screw in versions.

I have a fiberglass day sailor that was built and lives at sea level. When I took it to a mountain lake, I was unable to insert the daggerboard because of the trunk and hollow daggerboard swelling.
I did drill ventilation holes with my smallest drill bit in out of the way, dry spots.

 

[rwatson]

Not a big fan of foam filled plywood. In a small boat, it adds a whole lot of weight, and it can swell the sides as it expands on placement. Also, it always leave voids, especially near angles.

 

[Milehog]

Good point. If you must utilize foam go with sheet foam or foam packing peanuts put in place before final assembly.
That way, when sanity comes knocking, you can cut the hole for a deckplate and remove it.

 

[Nomiddlename]

Yes. Exactly that. The floor frame at 12" centers are plenty for the trailer bunks.

<edit> sorry, the floor frames are permanent but only go part way across. They need to go as far as the bunks. The floor boards are tied together with light cross pieces that sister to the frames. I used a tang on the front that fitted into a slot in the forward frame and a pin in the Back to hold the back in.

I see now. So there is still structure going across bunks. I really like this idea. And love the idea of white oak boards. But might go with cedar since it's much easier to source for me. Thanks for your insight

 

[Dave G 9N]

Sealed compartments in wood boats scare me. Not only moisture entrapment but the impossibility of visual inspection for moisture intrusion and, if you trailer the boat to different elevations, pressure differentials damaging the joints.

Yes that worries me quite a bit. Be a headache to restore when moisture inevitably gets in and causes a headache.

I had similar concerns about venting a flotation chamber on a stitch and glue sailboat so I installed a hatch similar to this one. It is an Amazon generic. It is large enough to reach in and sponge out the cavity if needed. It sat under several inches of rainwater for several days without leaking.

The screws that came with it were not quite right. Either the hatch was designed for oval heads and they supplied dome heads or it was the other way around. I replaced them with the correct type and added a bead of silicone between the gasket and hatch, which may or may not have helped seal it.