Transom Drifts...Threaded?

[DanO]

A search through old posts failed to make something clear. Should transom drift bolts be threaded or solid rod? My guess is that the threads would help with epoxy gluing. Any thoughts?

This transom is for the L.F. Herreshoff Buzzards Bay 14 I'm building. My New Year's resolution is to step up the progress a bit. So far, with almost all molds made and lofting complete, I can see the life-size beauty in this design. It's gonna be a tough one, though.

Dan

[JimD]

No doubt threaded would give the epoxy more to grab on to. I've recently set up the molds for an 11 footer. Nice to stand back and admire one's efforts, eh? smile.gif

[Jon Etheredge]

Should transom drift bolts be threaded or solid rod? My guess is that the threads would help with epoxy gluing. Any thoughts?
In traditional construction, galvanized rod is used for drifts. The roughness of the galvanizing and the inevitable rusting of the surface of the rod are what hold things together. They are driven in to a hole that gives a snug fit. It is not usual to apply glue.

Modern builders sometimes substitute bronze rod. Bronze rod usually won't hold as well as galvanized rod since the bronze doesn't rust. One technique that is used to increase the holding power of bronze rod is to nick the surface of the rod with a cold chisel (or your tool of choice) to create barbs on the surface of the rod. Bronze rod drifts are also installed in a hole that gives a snug fit. They can be installed without glue but epoxy probably wouldn't hurt since the holding power isn't influenced by rusting like it is with a galvanized drift.

[Jack Heinlen]

Basically what Jon said, though I'm wondering about the utility of epoxy here. I've never seen it used with drifts, and I can see how it might cause problems, such as not being able to drive the pieces together because of hydraulics at the bottom of your holes. Not to mention making things a slippery/sticky mess during assembly. But I'm not terribly familiar with many epoxy techniques...maybe someone else who has used it for this will chime in.

[windfall]

-DRiving a drift right is a tricky buisness...sizing the hole being the most criticle part. Too big no grab, too small split timbers. Another option that gives good holding power is to use threaed rod, slightly taper the point and grind a three sided tip on the other end. Then you can run the rod in using a large elcetric drill just like a long lag. The hole should be slightly undersized, and you might want to lubricate with oil. When done cut off the top and grind it flush.

-I think you might get into trouble with drifts and epoxy. the drifts are going to resist the woods movement and may cause the joints to crack open.

[Jon Etheredge]

I'm wondering about the utility of epoxy here. I've never seen it used with drifts, and I can see how it might cause problems, such as not being able to drive the pieces together because of hydraulics at the bottom of your holes.
Jack has an excellent point about potential problems due to hydraulics. I have not used epoxy with drifts myself having only driven them in dry. Given more thought, I think my statement "epoxy probably wouldn't hurt" is not correct.

[NormMessinger]

Yahbut... If one were using threaded rod for drifts set in epoxy one would drill the holes 1/16-1/8" over size to be sure there is plenty of goop to set the threads and to grip the wood, eh?

[Jack Heinlen]

Yahbut... If one were using threaded rod for drifts set in epoxy one would drill the holes 1/16-1/8" over size to be sure there is plenty of goop to set the threads and to grip the wood, eh? Possibly so. But you're now talking a different system of fastening, one I'm not familiar enough with to comment on, but different.

My inclination is that it doesn't improve much on the original, but I don't know.

[DanO]

Sounds like there's more of a debate on the issue than I first thought! The "How to Build the Haven" book by Maynard Bray suggests the glued drift approach. I've used epoxy and Honduran mahogany in the past and there's been no sign of any problem. On the other hand, galvanized rod costs peanuts compared with silicone bronze, and this boat will largely be used on a fresh water lake...hmmm. Now there's more to think about!

Dan

[Jack Heinlen]

I, personally, would use galvanized rod and drift it together in the tried and true fashion. I might substitute bronze rod, but in this piece the steel would work fine for many, many years.

The other, the buttering with epoxy, seems silly or worse, damned difficult to accomplish. It's hard enough to get everything lined up and ready to go without worrying about the cup of slime, and then when the drifts are almost home and the pieces almost together to discover the drifts acting like a syringe, and refusing the final omph.

As to drilling oversize, setting the fasteners in epoxy. That would be the way to go if you are set on epoxy, but I really don't see what it buys. It seem born of a fear of drifting planks together, rather than any sound practice.

And if the seam are going to be glued that brings a whole nother matter to the table. Best left to another discussion.

P.S. It's an interesting discussion, and my reactions are just that, reactions. I'm willing to entertain other suggestions, even though I think Jon and I are correct.

[ 01-04-2004, 12:01 PM: Message edited by: Jack Heinlen ]

[Jack Heinlen]

And I'm compelled to ask, does LFH specify drifts in this transom? That would suprise me. Usually the planks for small boat transoms are simply splined and/or glued.

Assuming they are specified, why? Is there intention of an outboard motor?

[Gary E]

Can someone explain what a transom drift actually is and what it does? Seems it's a sailboat thing, and I am from the school of Mo POWER..grunt grunt grunt..

G

[Jack Heinlen]

Can someone explain what a transom drift actually is and what it does? A drift is a blind nail, meaning it hasn't an exposed head either for pounding or threading and bolting. It's naked on both ends, each intended to go into a blind hole.

They are rods of iron or nobler metal, used to hold planks together in traditional construction. See Chapelle if that doesn't quite grok.

P.S. And now that I think on it, I'm incorrect. They can have a headed end, usually fitted with a washer, and hence very much like a common nail.

They're metal rods, used to make up or reinforce plank construction. And a drift never has a thread on the end. Even if driven home, that would be a screw or a bolt. Nup, to be a drift means driven. Look at the word for Christ's sake. smile.gif

[ 01-04-2004, 01:34 PM: Message edited by: Jack Heinlen ]

[DanO]

Jack,

LFH didn't specify the drifts, but the "construction plans" by Robert Pittaway (which came from Mystic Seaport) designates 3/8 bronze drifts, which seems a bit much on this 1" thick transom (which is only 4' wide, 3' tall). This is a 17' 3" full keel (900 lbs) sailboat which is really an "updated" (1945!) version of the 1914 Herreshoff 12 1/2.

I think I'll scout around a bit before ordering the drifts. I wonder if using galvanized drifts would be a problem on the boat if I also used bronze through bolts on the keel, stem, etc.

Dan

[Jon Etheredge]

I wonder if using galvanized drifts would be a problem on the boat if I also used bronze through bolts on the keel, stem, etc.
I think you would be fine in this case since (I assume) you won't have an electrical system on board and the dissimilar metals are well seperated.

I think you might want to consider the wood that you are using for the transom when choosing the drift material. If it were my boat I'd probably choose South American mahogany for the transom because of the good stability of the material. I'll probably catch some (or a lot of smile.gif ) flak for this suggestion but I'd edge glue the seams with epoxy and drift it with bronze drifts. I have successfully used this method on pieces that are similar in size to what you are talking about.

If you are going with white oak for the transom I'd be more inclined to use the galvanized rod for drifts. The white oak will move a lot and the galvanized rod will help to hold the thing together. White oak transoms with galvanized drifts on boats that are used in salt water eventually explode due to the expanding rust but the boat will probably have lots of other age related problems by that time anyway. And no, I wouldn't try to glue the seams on a white oak transom.

WIthout regard to the material, your drifts will hold a lot better if they aren't parallel.

[scepticus]

Originally posted by Jon Etheredge:
[QUOTE]

WIthout regard to the material, your drifts will hold a lot better if they aren't parallel.apparently, this is yet another point of some debate: whether the drifts should be parallel or not. Yes they will hold better if not. However, while building the core sound skiff last summer with Walt Ansel, he had us drift the rudder, transom, centerboard, and whatever else, parallel. I asked him why and I think I recall two reasons. 1) the old "... but if you ever need to get it apart..." argument, and 2) parallel allows the wood to move along the drift without damaging itself.

btw, we used smooth bronze rod (1/4") and nicked it with a cold chisel. We also "pointed" the leading end(s) with a hammer. The wood was white oak.

Walt also told me that some say to very slightly undersize the hole for a tight fit. However, others say to slightly oversize the hole because the act of driving will fatten the drift. We drilled 1/4" holes for 1/4" rod.