View Full Version : How do I build this shaft log?
01-17-2006, 08:48 AM
I am at a pretty exciting milestone on my 23'...but need advice here.
Frames, transom, stem and keelson are in place on the jig, and I am ready to get out my keel now. I sure do need advice from those in the know concerning the assembly of the wood skeg/shaft log. I am a bit stumped. The designer recommends splitting the skeg horizontally along the shaft centerline, to avoid “boring the skeg”. Fair enough, two-piece shaft logs are shown in books and discussed here on the forum, and I think I’m ok with that.
But I do not know how to incorporate the shaft log as shown. Typically (from what I can glean from reading), the wooden shaft log (split horizontally), would be built into the outboard part of the keel, and run into the boat to just aft of the engine, where the stuffing box would be mounted. On the lobster boat Lowell writes of and depicts in “Boatbuilding Down East”, the “horn timber” sits on the shaft log, and is essentially the aft continuation of the keel. But in my boat, the keelson as shown below is a one piece, 6” wide member that runs the whole length of the boat. However, the keel, and hence shaft log are sided 3”. And therein lies the rub.
This may be dumb, but: Do I “mortise” out the keelson (at the shaft angle) for the 3” sq. shaft log, so it runs all the way to the stern bearing area, and is part of the skeg? Or would the shaft log be limited to just inside the boat, and sit on the keelson? The latter would not be unlike the one piece bronze shaft logs one finds in smaller boats, bolted directly to the keelson, and does not go outboard at all.
Note that a stern tube is employed between stern bearing and stuffing box, which is tapped to receive each. Galvy pipe is called for, but if I use one, I will go with copper or bronze.
01-17-2006, 11:30 AM
Dunno but can add to the confusion. My guess is to split what you can, and bore through what you can't, or split the horn timber, use that as guide to through bore the keelson and reverse through the keel or skeg. Navy brass would be good tube and you might consider a cutlass bearing outboard with stuffing box inboard.
01-17-2006, 12:54 PM
Harry - The way I read your plan, the shaft log and skeg, whether split or not, are two seperate pieces above and below the keelson and only the stern tube penetrates the keelson. Whether you split the log and skeg or make them one piece depends on your confidence in drilling that bore for the tube. Either way, plenty of bedding and the pairs of bolts p/s of the tube will pull everything up tight and the tube will minimize the possibility of leaks through any of the joints. One thing you might consider is slightly hollowing the joining surfaces of the skeg and log except for 1/2 inch or so around the perimeter of each joining surface. This creates a shallow pocket in the interior of the joint to hold a reservoir of bedding compound and keep it all from being squeezed out when you tighten up the bolts. Some builders also like to wrap a bit of cotton string or wicking around the stern tube ahead of the stern bearing and behind the stuffing box when installing those as an additional seal. I've used an o-ring for the same purpose with the edges of the opening of the shaft bore relieved around the circumference to create a sealing surface for the o-ring. Either serves, along with bedding compound, to keep water out of the shaft bore on the outside of the tube. Jim
01-17-2006, 09:14 PM
Thanks for the replies...good point on the naval bronze, '77. Do you have a source perhaps?
FSF172, if I understand your scenario, the shaft log would consist of only the inboard portion (that which the stuffing box is attached to, and is cut to bed on top of the keelson). Then the outboard portion of the keel would consist of 4 pieces (if split horizontally): the two major long pieces of the keel proper, the tiny "jib" piece above the outboard part of the shaft, and the end piece which is apparently to avoid attaching the stern bearing to end grain. Is this the way you see it?
I appreciate your tips regarding the o-rings, wicking and such. Any suggestions on a tube source?
Many thanks for the tips...this is an area where I could really benefit from the experience of others.
01-17-2006, 09:29 PM
Alignment depends on where the shaft is mounted at each end. Do you have the skeg and know where it will be mounted? Do you know where the shaft comes through the keelson and where the coupling is to be?
01-18-2006, 07:13 AM
Engine, prop, shaft angle and shaft hardware locations are given on the plan, Gary. My question relates to the conventions used for putting together the keel components.
As a comment on stern tube material ('Navy brass' being suggested). Years ago I was in charge of the constructions of some small inboards at a yard I worked at. Per the yard owner (and designer) we were to use 'Navy brass" for the stern tube on one boat. literally within 24 hours of launching the stern tube was leaking like crazy, when we got it pulled we found that it had split lengthwise. We replaced it with another new piece & the same thing happened again. I forget what we changed to (maybe even plastic) but we did solve it. The feeling was that the Navy brass tubing didn't like the salt water & for whatever reason it was the seam from forming the tubing in the first place that split. So you should research the material you choose quite well. - Just sharing some experience that may save you some grief.
What's the design?? (Looks like it may be similar to a Crosby Striper??) Looks nice from what we can see.
[ 01-18-2006, 07:38 AM: Message edited by: nedL ]
01-18-2006, 09:58 AM
Hmm, I bought a nice hundred dollar piece of navy brass pipe for rudder shaft log, the pipe I used was a salvaged piece of copper, works fine! What am I gonna do with this nice useless piece of pipe, thought I might use it on the Crosby Striper who needs her skeg and keel replaced.
01-18-2006, 10:04 AM
Hi Harry - Yes, your description fits how I read your plans. As for finding tube, check with builders in your area or you might give the folks at Gannon and Benjamin out on the Vineyard a call. Sounds like a dandy excuse for a ferrry ride to me. Or check the Boston yellow pages. If you can't find what you want locally, or if you just want to order it and be done, try - National Bronze (http://www.nationalbronze.com/bartube.php)
01-18-2006, 01:39 PM
Originally posted by HarryH:
Engine, prop, shaft angle and shaft hardware locations are given on the plan, Gary. My question relates to the conventions used for putting together the keel components.Welll... I spose there are a lot of ways to do that, but here is what I would do.
I would mount the skeg in the proper place on the boat.
I would then bore the hole in the boats bottom, and keelson and everything else in the shafts path.
After that is done, I would make a bracket to hold the shaft in the proper place so the coupling would be in the proper place for the engine to align.
Now I would make the keel in 2 pieces with the shaft hole being cut with a ball nose router bit. If it's a lot larger than a router bit's radius, I could use a table saw or a skill saw with changing the depth and finish up with a curved scraper blade. If you dont want a 2 pc keel, cut the slot deeper in the one pc keel and then make a filler strip to cover the slot. Spose there are ways to drill that hole straight and then fit the keel, lotsa ways to skin the cat.
But then, someone else can tell you of another way, no doubt there are several.
01-18-2006, 03:57 PM
NedL, regarding those stern tubes you mentioned: how were they affixed at either end? My design calls for a pipe, with ends threaded into stern bearing and stuffing box respectively. I am fairly well committed to bronze for the tube if possible ($$), but am open to other materials if serviceable. Appreciate your story…and yep, this boat has some similarities to the Crosby Striper in lines, but is round bottomed unlike the hard-chined Striper, and is 23'. A nice little cruiser, powered I hope with a small deisel. It came off the drawing board of Fred Bates of Damariscotta in the mid sixties. He called it "Pogo". I purchased the plans in ’73, and just got underway with lofting about 15 months ago. Here is a rendering from Sport Fishing Mag back then:
Seayou77, do you have a Striper? Nice vessel…
FSS172- I do have G&B in mind for a visit. And I made that ferry trip last year to check out their shop…was on a Sunday, did not get to speak to many folk, but man, that is a pretty heady atmosphere; right in the heart of what wooden boat building is all about in many ways. Brad Ives, who supplies those guys with stock from Suriname, sold my wana to me…affable guy, nicely portrayed in the book Wooden Boats by Ruhlman. A wonderful read about G&B, building, wood boats and those interested in them. But I digress…thanks for the tip on National Bronze.
Gary..I had forgotten the option of cutting a slot and covering it. Indeed, there are a variety of ways to tackle this and I appreciate your input. I'll be sifting all this input before I start cutting up the oak I've been drying. Time spent in head scratchin’ and pondering pays off. In my younger days I would be foaming at the mouth to make chips fly.
This forum is a great resource.
[ 01-19-2006, 06:45 AM: Message edited by: HarryH ]
01-18-2006, 04:04 PM
OOPS!..posted thumbnails by mistake...these are a bit more sizeable...
Harry, Very nice & capable looking design. I'm sorry to say that I don't remember all of the details of how the stern tube, cutlass bearing, & stuffing box were installed as that was more than 20 years ago :( . Also, the boats were very different (not that it really makes a difference), the boats I was building were replicas of late 1800's launches (available gas, electric, or steam) with glass hulls, finished off with wood. As I remeber, the stern tubes were about 3' long & basically slid or pressed through the hole bored in the F.G. hull through the 'dead wood' area, the tube extended forward through a bulkhead about 2' forward (for two points of support). A sealant something like '5200' was used in the 'deadwood' area. An inch or so was left extending aft out of the hull (enough for the set screws for the cutlass bearing). A piece of flexable hose was used on the the inside end to transition from the tube to the stuffing box. So you can see the set up was quite diffent than yours. What yor design calls for is certainly more robust.
01-19-2006, 12:32 PM
I have the pieces of a Striper; some assembly required.
From this discussion I picked up that Navy Brass may be too brittle. And be aware there are two thicknesses of two inch pipe and the inside measurement changes accordingly.
I would get acquainted with a prop shop and buy all components in one place. Scandia in Fairhaven Ma. are salt of the earth folk and worth my drive even though they honored me by asking if they could hang my mangled prop on the wall.
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