Adding bouyancy - retrofit tanks or simpler solution

[PAR]

The center thwart knees can be removed, but a replacement stiffener needs to be figured out, so the wale doesn't want to curl inward, with is a common trait in steam bent ribs.

If it was me, I'd remove the thwart, the knees and the ledger piece under it, on the thwart cleat (stringer looking thing). I'd brace the wale, so it doesn't move during this process, then I'd make a 1"x2" (25x38 mm) beam, maybe on edge to save even more space. This beam would tie the back of the case to the hull shell and extend from the thwart cleats on each side. It would likely land on, or very near the rib at the forward side of the current center thwart. To prevent point loading on this rib, I'd put in a doubler, much like the ledger used on the current thwart and also a knee (each side). The knee would be heftier, but not extend as far out onto the beam as it does on the thwart.

This would retain the athwart stiffness, lost with the removal of the thwart, but you'd gain a lot of usable leg room. This beam would be the forward end support for side seating.

The side seats I'd make very simply with 1x2 legs, landing on ribs, with more reinforcement ledgers, which could be as simple as short length of sistered rib. Instead of dropping these legs straight down, which would require you alter the sole slats, I'd angle this out to the edge of the seat. Again offering more leg room and keeping the slats continuous and clean looking as they are now.

The seat top could be just plywood, but I'd have a 1x2 on edge that served as nailer along the inboard face of the seat. This will stiffen up this edge and let you rabbit the plywood into it, to hide the end grain. It would also make a great place for the legs to land against, triangulating the whole seat assembly, with a minimum of wood. If you used slats like the sole (which would look especially nice), it would be able to drain off water naturally and would fit the style of the boat very well. The slats would need additional support in the form of athwart stretchers, probably at each leg. I'd space the legs on every other rib, maybe every third rib, depending on how stiff and thick the slats would be. A 3/4" (19 mm) thick slat would be about right and you might be able to use the wider leg spacing (use the butt test, to check for flexure). This should all be of softwood, like cedar or fir. Weight is to be avoided in all except the knees, which should be hardwood.

The CatsPaw has a nice, wide open framing arrangement, which is why it looks so nice. Plywood seat boxes will be easy to make, but will also spoil this look. So, think light and airy in regard to the framing for side seats. The seat top cleats pretty much marries you to the seat height available, so adjust the seat width so it's comfortable for you, then work in the position of the legs and slats support.

It'll look great. Additionally, you'll only need seating in the back half of the boat, which is from the board case aft. The thwarts forward of this can remain, as there's no need to modify them.

[b.o.a.t.]

Wot PAR said
with comment that the two outer boards on the rear thwart could be continued
forwards to the #3 thwart (or beam). You need the width inwards in light air to
bring your weight comfortably amidships. In heavy wind, just hook your toes
under the opposite seat.

As whathappened points out, too much buoyancy down low can force the boat
to turn turtle. Ideal place for buoyancy whilst laid on her side is up around the
gunwales, to force righting. Worst place is in her bottom - encourages turtling.

After righting, the ideal pace for buoyancy is in her bottom to lift her up & force
drainage. Worst place is in her gunwales - least 'lift'.

Removable closed-cell polyurethane blocks under the thwarts is probably the best
compromise between the two. Bagging the foam in canvas would perhaps
preserve her open looks & saltiness, but you'd need to take care of the canvas.

cheers

[Clinton1]

Thanks fellas.

I'm going to think on this for a few months, and if I go ahead with it I'll do a mock-up first.

Thank you all very much for the assistance.

[Clinton1]

15+ knots today, with gusts somewhere in the low 20's.

I really got bashed by not having a solid seating postion, and the rear oarlock is right in the middle of my back when hiking.

I had to tension the sprit pole till she hummed, and put a lot of pressure on the downhaul on the sail.


Lots of fun until I turned for home.... wind was almost straight down the bay. Tack, beat, tack, beat.... repeat, repeat, repeat.
Too much wind for that sail.... I can't reef it... but still fun.
Much more confident after clawing my way up into strong wind and a bit of chop.

[tpb03]

Hi Clinton,
I'll come for a sail with you in a couple of weeks. I just became a Dad on Tuesday night so I need to sort things on the homefront first!

Tim

[Clinton1]

Two lots of great news.
I'll pm you.

CONGRATULATIONS TO YOU AND THE PARTNER!

[redx]

Hi Folks,

All this talk of bouancy aand flotation reminds me of an article I read some time ago in a "Popular Mechanics" magazine. I stumbled upon it when I was browsing the internet using Google's BookSearch (something I sometimes do when I'm bored). The magazine was printed in the early 1930's, long before polystyrene was in use I guess, and it recommended you fill all available underfloor cavities with Ping Pong balls! It claimed that if your boat's hull was accidently holed some of the balls would be damaged or lost but there would be sufficient left to keep the boat afloat. I see that packs of 120 balls at 38mm diameter are selling on fleabay for $18.20 AU. Makes me wonder how many thousand I would need to fill my 20 foot hull.

Cheers,
redx

[PAR]

The math is simple enough Redx, have fun. My issue with fixed floatation anything (bags, foam, milk jugs, ping pong balls, pool noddles, etc.) is they cause very small spaces to be contained inside a closed space. These are prime spots for mold, mildew and rot to fester. A dark, closed, low or no ventilation location is exactly what you don't want in a wooden boat. This is why I prefer floatation chambers (boxes), as they can have deck plates that can be opened to permit ventilation and they can be also used a storage, which isn't possible with fixed (hard) buoyancy techniques. A floatation chamber is also lighter then the other methods.