back to ribs

This is a clarification of my initial post. I greatly appreciate all the responses to my question, but when I spoke of laminating 3/4 ply for ribs my intent was
to cut two pieces of ply to the specified shape then stack them to achieve the one and a half inch thickness called for. This approach would also facilitate the simplest half-lap joint for the rib base to vertical. The plans call for using pressure treated pine so I wonder how much of a factor weight would be. Thanks again for all the great advice.

 

ribs=frames?
or
ribs=ribbands?

what are you building?

 

Pressure treated pine (really low quality lumber if from the LowesDepot) once dry (it comes very wet) will be much lighter then the 2 layer lamination you've suggested.

Ply can make a good framing stock, but the design must have this in mind when the thing is drawn up. The typical half lap joint is a poor joint when compared to others. The kink in the lap creates a stress riser and this is the place it will break. The half lap with a heavy rounding over of the laps will cut this down a great deal, but now you'll be performing as much "joint tuning" as you would in a scarf, so way bother with the weaker of the two.

Why are you re-engineering this aspect of the design? Designer's use lumber types, joint types, materials, hardware and the rest for many reasons, but mostly because of the known quality of the unit, piece, gear, or other, selected for a design.

Substitutions can be made, but should have near the SAME qualities of the item it will replace. Framing material accounts for a substantial amount of the bare hull's weight. Going heavy in this area isn't recommended. You gain nothing by using plywood, but possibly a joining method you like to do and a bunch of extra weight.

If you want to kill the performance of small craft quickly, add a bunch of extra weight. This is one of the most common mistakes the backyard builder makes. The thinking is usually based in "so I'll make it stronger, what will it hurt?" Well, in the case of a local, who was building a skiff rated for 20 HP outboard max, the added weight of the 3/4" bottom (he had a bunch of it and figured it would be stronger and longer lived) rather then the 3/8" specified in the plans kept that boat from getting up on plane. He was right, it was stronger.

Lets make this simple, what design are you building? Of the thousands of us around, surly several of us will have built one.

 

Thank you for the interest and help with my questions. I am building a carolina skiff, the darkwater to be specific. I am modifying the plans slightly, and will be using it for a small hunting and fishing boat. When I speak of ribs I am referring to frames. I plan on using about a 15hp, design is rated up to 20. As a master carpenter I refuse to use pressure treated on any project of any quality ( other than basic framing), and for this reason want to substitute it. Poor quality, excessive movement, and poor if any glue,paint adhesion are my primary reasons.

 

Excellent answers for the most part, Daniel K. PT is real junk, if you want something other then a deck behind your house.

The Carolina Skiff is a fine little boat and will serve you well for the use you've intended. I'd strongly recommend you stick with the plans as set forth by the design team. Southern Yellow pine is hard to find in grades that will tolerate much moisture, probably the reason for PT. I come across it several times a year when an old building is torn down (it's called Dade county pine down here) and the structure is available for cheap. Long, clear old growth stuff, known for it's ability to shed water and rot. You may want to check out the back of the news paper (they still print those things) for building materials. It'll turn up sooner or later.

You can treat good lumber with a number of products currently available, to stem off rot and moisture invasion. A good grade of Doug. fur or Western larch will serve you as well. Stay away from the oaks and other hard woods as they'll be too heavy, though quite strong.

If you are selective and willing to go through several stacks of lumber, PT can yield some good stuff, but you WILL go through many stacks of lumber before you find three or four pieces you can live with.

This is a boat that is intended to go together fast, live hard and die quickly (the life of the fast lane) but you could build her to better standards then the designers intended, which should bring longer service and pleasure.

Stick with the solid lumber for the frames (ribs are typically bent) and the more effort you place in the materials the better the craft will be in the long run.

 

a quick question for PAR
i've read alot about 'yellow pine' (heard it referred to as longleaf..)
never had the pleasure of using it here in the west
but i've come across some old beams of 'ponderosa pine'
is it or would it be the same or similar

~poetprince

 

PAR Thanks for all the help, I really appreciate it. It was suggested to me that I look into sitka spruce, what do you think? Also what can I do to give this boat the longest life? Thanks again for all your help!

 

Sitka spruce is a light weight, straight and tight grained lumber typically used for spar construction (masts and booms) and would be a poor choice for framing material.

Again, typical framing material is dense, holds fasteners well, has natural rot resistance (this can be gotten around if necessary) straight and tight grain. The folks who gave you the advise about spruce for framing can't be relied on for reasonably reliable information.

Yes, there can be many names for lumber types, I was speaking of long leaf yellow. In the south it's reasonably plentiful. Some really fine stuff can be found in old buildings about to be torn down. A friend of mine owns a restaurant, built in 1923. The rafters and floor joists are old growth SYP and rough cut into 4" x 14" beams, some over 50' long, perfectly clear, straight grained stuff. I have a standing order with him for those pieces if the need arises.

The little experience I have with ponderosa pine is a knotty, weak grained, kind of stuff, that doesn't make a good table top without warping badly if wet.

Your best bet would be to pick the brains of some of the local boat builders. Another option would be to check the properties of lumber types easily available in your area with the forest service. They have a large data base on the qualities of the lumber in your area. The local university may have an agriculture department that can help you as well.

Your looking for a good substitute for the framing stock asked for in the plans.

As far as long lived . . . Seamanship . . . It's the only true way of keeping a craft of any type or construction for a long time.

Being one of the few civilians allowed in the bilge of the USS Constitution, I can attest to the value of the care, good seamanship can provide. That ship was built in 1797, has the bulk of her framing, knees, deadwood and keel assembly as built, over two hundred years ago. This, despite some years of neglect, is a testament to good seamanship.

Seamanship is about boat handling. Not only the steering, docking, launching and other duties, but the upkeep as well. Washing sails, dock lines, fenders and running rigging, cleaning, lubricating, tuning, scrubbing, and all the things that come with good boat handling.

Planking is considered consumable, being that it will need renewing after a period of time. The structure may require repairs, but can remain intact long after you're dead, if provided with the care necessary. It isn't hard, but can get away from you very quickly if you lay down on the seamanship job.

Wooden boats cost no more to own then any other hull material. On the other hand, wooden boats can not tolerate much neglect, before major issues start cropping up.

I have several wooden boats and a few of other materials. One is a show winner, others work boats, projects or sentimental sore spots on my other half's mind. They all look good to the casual observer, but the skilled eye will note the slight rust stains around the bolts on the chain plates or the sag I forgot to sand out of the varnish in the port cabin side, or . . . the list goes on, but I'm not dead yet and I'll get around to it eventually, long before they become a bigger issue of a different color.

Good Luck,