Chesapeake File bottom

[Bill Perkins]

This is a 24 ft. V bottomed outboard launch I'm working on designed by Pete Culler.
http://www.imagestation.com/picture/sraid67/p4ec0c29e042bc82fcce7d1a6b2406ba6/fbd6232b.jpg

She's a Chesapeake file bottom and will have frames only from chine to sheer.

http://www.imagestation.com/picture/sraid67/p7bca4fa526ace9c59b39b2bfe86d3484/fbd623d6.jpg

About 3/4ths of the way to the bow the 1by4 planking will no longer make the required twist and thicker stock must be shaped to fit .I had a power plane and used Cedar .Hats off to the stalwarts on the Bay who hand hewed these bottoms out of Southern Pine .

http://www.imagestation.com/picture/sraid67/p0164871e8320fcdde95b38c812758827/fbd62056.jpg

http://www.imagestation.com/picture/sraid67/pa3afee10c056348b6b604437e2a26175/fbd61ff7.jpg

http://www.imagestation.com/picture/sraid67/p1e142ad6f08ec35a0220448e4f383bb9/fbd61e7d.jpg

More at

http://www.imagestation.com/album/?id=4290208883

[ 06-27-2003, 11:55 AM: Message edited by: Bill Perkins ]

[Thad]

Good stuff!!

[videoguy]

You do nice work thats going to be a pretty boat when shes done kee the pictures coming. smile.gif smile.gif ...Phil

[SailBoatDude]

This is a tried and true building method, saw a lot of it as a kid on the bay. Isn't very good in power boats though. Small boats don't need the typical framing, but the larger ones have frames, stringers, cheeks and the whole lot.

Looks to be a good job of it on your end. Keep it up.

[Bill Perkins]

I've been intrigued by this type since I first read Chapple's Boat building .Culler drew 15 16 and 18 footers too if someone else would like to have a go at a smaller scale .The 30 footer has all the pieces you mention.A number of these 24 foot launches have been built and held up OK as far as I know .Word would have gotten out in New England if the boats had fallen apart .The chine logs are 1 1/2 in. thick clear Fir and the keel will finish out at about 6 by6 .The topsides will be glued lapped ply .I'm not worried about the boat breaking in half (in either direction ).

I set the planking at 20 deg. to the keel as recommended by one author .I may have carried this planking angle a bit too far forward as when the dead rise gets quite steep the rake in the planking produces a slight convexity athwartship .The bottom doesn't touch that second mold back from the stem .Instead it has about a 3/8th in. crown there .

Wether this is typical, good ,bad ,or indifferent I don't know .Any theories ?Chapple recommends setting the plank at 12deg. to the keel .Maybe this is why . The less the rake the less the camber produced .If he'd known the reason for that spec it seems he would have said so .

As the deadrise diminishes aft the camber disapears .As the staveing comes perpendicular to the keel at the base of the stem it likewise goes to zero .I'm adding a second diagonally opposed layer and I have enough thickness to plane out all or part of the convexity forward if it's a real detriment .Everything has faired in nicely and looks OK so I won't mess with it unless there's a real problem .I think keeping the two sides as identical as possible is probably more important than pursuing the theoretically perfect shape at this point .

[ 06-29-2003, 12:28 PM: Message edited by: Bill Perkins ]

[SailBoatDude]

I too have used the multiple layers of file planking in my boat. When doing this technique of bottom construction, you must "adjust" the planks every so often to keep them in the same plane. As you get away from amidship the dead rise changes the angle and the rake of the planks. I, typically have used a "cheater" plank every ten planks or so to get the angle right or close to. This slightly tapered plank lets the next ten or so fall where they want to be, close to the angle designed. Mine were more like 30 degrees to perpendicular, but this was found by bending stock over the toughest part and settling on an angle that would work (my hull has a slight bit of shape in the bottom) I let them stand up more vertical as I got to the ends with cheaters. The final product has plank angles approaching 20 degrees in the ends and 30 amidships.

If everything is tight and fair, no worries. Typically this construction was the "down and dirty" way of getting it done fast and with little waste. I had very little waste in the bottom planks, being able to figure to a few feet in plank stock.

Powerboats racked the hell out of this construction style (single layer) and fore and aft planking held up much better. I'm not sure of Chapple's reasoning, but from what I've seen most all file planked boat bottoms fell between 10 to 35 degrees. This may be more a function of the bottom shapes used and the ease to plank them then reasoning. My hull has quite a bit of dead rise (by modern standards, a whole lot), yours seems much flatter. Possibly deadrise being the only difference in angles needed.

[Bill Perkins]

I'd be interested to know what type and thickness of planking layers you used.

For ease of building it seems most logical to me to use the maximum rake selected untill you reach the point where the plain sawn plank will no longer take the twist and you have to start shaping thicker plank to fit. The point of the rake , I think , is to push the practical limit of the sawn plank as far forward as possible . As you say , the more deadrise the more rake . Next time I'll start the tapered planking at this juncture ,the taper set to gradually bring the planking perpendicular to the keel at the base of the stem .

This is not so very different from what I've done . As you suggest ,if all is fair and firmly fastened these nuances may be academic . The bow shape of these boats was not expected to be fully determined by the molds.Both Chapple and Culler mention bringing the staves vertical at the bow if you want a sharp entry though, which I now better understand and am glad I did.

[ 06-29-2003, 12:26 PM: Message edited by: Bill Perkins ]

[Bob Smalser]

How are you handling the seams?

[Bill Perkins]

Bob the double diagonal planking will have epoxy in all seams and between the layers .