Hinged Thwart

[Toxophilite]

I see some members here have hinged center thwarts on their small boats for more comfortable camping(sleeping) on the boat.
This looks like an excellently practical idea
I haven't looked at them all but most seem to be glued lapstrake designs though I could be wrong

Is this something that could safely be done to a traditionally built boat like my Gartside 130?
Or would I want to?
I wonder about athwartship hull strength, while having the thwart up, especially if you happen to be tied up somewhere and moving against a dock at all.

Problem is it that would give me the willies to do

I can sleep under the thwart but it's pretty snug and I have a thing about my legs being held down...( 6 older siblings torturing me when I was little )

I guess on my boat I would have to make it VERY strong or relocate my main sheet bridle as it's fastened to the main thwart

Like this (AJZimm's):
hTrjHIf.jpg

[wizbang 13]

You gonna be counting zeeez while banging against a dock rough enough to buss it?

[jpatrick]

Stop thinking about it and take the boat into your shop and remove the thwart. Then do a bunch of push/pull tests to experience just how flimsy the shear really is. Because right now, you likely don't know how rigid your boat is. Some experiments will give you more insight than three hundred posts to this thread.

Once the experiment is done, ask your question again if you need to.

Jeff

[Edward Pearson]

I wouldn't cut a thwart...but it's your boat.

Forces up through your keel, pass up through your case, along your thwart to your sheer inwale/ outwale via the knees. And in the other direction: gunwale down to keel.

It's a structutral triangle with the planking. Even if you never sat on it, it would still be needed. Without glued in tanks like with glue lappers and being trad clinker with less innate stiffness, you need all the structure you can get. Centrecase-keelson junction needs not to be moving and stressed. Beside the sailing there's a fair bit of banging around on trailers.

On some designs like Ilur, there is a large fore and aft semi bilge bulkhead which stiffens the fore and aft centercase, which with fore and aft bulkheads and longitudinal stringers can get away without a central thwart - its removable (though it's still probably a bit dodgy long term).






There's space for those bilge bulkheads because the design has more freeboard and the seats are higher - its prolly got two strakes over your Gartside.


A couple fo guys in the PNW Tim and The James, modded their thwarts to hinge but added fore and aft frames during the refit. One of the advantages of 6ft beam sailing dinghies is there's space, with 5ft beam sail and oar boats it's tight unless you're super skinny and make the floors shallow and curved to the hull and not flat floored.

Foils in a side tank clears the central area and it puts your sleeping center of gravity low and central - if you look at John Welsford's Walkabout that's why it's how it is. Ideally you want to arrange it so your heads as close to the center of pitch as possible. It is on the Ilur.

[Edward Pearson]

I'd fill in that rear cockpit level to the seats accross with some boards that roll up. Inflatable mats on that. It's 5'9" 'ish from your transom to the front of the thwart. You'll roll more but you're out of the dirt.

[Toxophilite]

Thanks very much Edward. As usual you provide a lot of insight and useful information. I didn't know those boats had extra frames to accommodate for the thwart modification. So far when I sleep on my boat I've put my legs under the thwart and my head roughly at the start of the stern sheets, so the opposite of what you've depicted.
As I said I was loathe to cut my thwart but the idea seemed like a good one on those forum members boats

Probably what I was asking was the difference between glued lap and traditional construction in this regard. It would seem glued lap would be easier to modify

IMG_1706.jpg

[Priscilla]

Maybe the Smart car is the giveaway as it appears to me you would have to be a Leprecian to comfortably lie in a supine position on that sole.
What will support the side seat at the thwart junction if you hinge it.
AD122C25-2EC7-4176-8C62-FA34DFBAEB94.jpg

[Yeadon]

I've hinged thwarts on both traditional cedar lapstrake with steamed oak frames as well as glued plywood okume lapstrake. It's all good man.

[stromborg]

I may as well chime in too

That thwart, on your clinker-built boat, is the main bit of structure holding the two sides in place. You could probably cut it out and hinge it sitting on the dock/trailer just fine but as soon as it goes in the water the beam will close up and the thwart will be too long to fit in the hole you created, anything more than the saw kerf and you'll be out there leg-pressing the boat apart to put the thwart back in place. This might even tweak the CB case enough for it to start leaking.

I think Ed is on the right track for this boat.

[John Meachen]

If the thwart is cut,give serious thought to adding some kind of mechanical lock to tie the sides of the boat together.Dovetailed ends and doorbolts perhaps so that the thwart drops in and is locked in place against all forces.Ideally the dovetails would taper from top to bottom too.

[Yeadon]

I need to add a short video explaining how these work. If done right they are absolutely bomber.

[Toxophilite]

Not a leprechaun 5'9" 175 lbs. Big in my family, smallish in the world. Smart cars are much like regular cars inside room-wise actually. They have inner bigness.

I believe one makes a small lip to support the thwart on both sides likely.

[Toxophilite]

That would be cool and very appreciated.

I need to add a short video explaining how these work. If done right they are absolutely bomber.

[Ben Fuller]

The locked in thwart at the forward edge of the CB case will take most of the load of the board sailing since that is the part of the trunk loaded up. Think about it as if a daggerboard, which in my boat is locked in with a thwart at the headledge only. My center of the boat thwart is completely removable like a dory's. My side benches have a piece of wood glued under them to give them some beam strength forming a T beam with the thwart being the top and a short vertical. I've done this to my dory benches as well to control flexing. If you pull the after thwart you might need some stanchions under the side benches. The hinged thwart still works in compression. Be interesting to see what Yeadon has done.

[Edward Pearson]

The Gartside 130 being fairly recent and clinker probably has it's centercase bedded down with a Sikaflex product and some screws through the case logs. That will take some movement.

It's below the waterline there though all the way along the centercase to keel join. Water is under positive pressure trying to come in. Get a leak, and you're in for a world of pain sorting that out even if you'd previously built it and knew how it went together, which isn't the case.

[timo4352]

If the thwart is cut,give serious thought to adding some kind of mechanical lock to tie the sides of the boat together.Dovetailed ends and doorbolts perhaps so that the thwart drops in and is locked in place against all forces.Ideally the dovetails would taper from top to bottom too.

plus one...
my first thought was dowel pins in the thwart, and it drops down into the corresponding holes.... hardwood dowels may be strong enough, but bronze pins may be better....they won't swell like a wood pin would when soaked.