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Shipyard Memories #16: Boring Bars and Custom Castings

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Blog entry by shipwright posted 02-21-2011 06:42 AM 2589 reads 2 times favorited 6 comments Add to Favorites Watch
« Part 15: Rolling Hulls Over and Pouring Lead Keels Part 16 of Shipyard Memories series Part 17: Keel Bolts »

One of the interesting tools that find a regular use in building boats is the boring bar. After the hull is finished and the time comes to install the engine and associated equipment one of the first jobs is to install the stern tube, the passage through which the shaft will penetrate the hull. It must be perfectly aligned with the output shaft of the engine but often must be drilled at an oblique angle to the skin of the hull. This challenge is overcome with a boring bar. It is simply a piece of bar of sufficient diameter to maintain stiffness over the required length but still be narrow enough to be significantly smaller than the required hole. A hole is drilled transversely through the bar near it’s center and an adjustable fly cutter is installed and locked in place by a grub screw. One end is then turned down to fit in a drill chuck.

The boring bar being used here is 1” dia. stainless steel about eight feet long. After hacking a rough hole big enough to pass the bar through, bearings are set up inside and out as close to the eventual shaft line as the rough hole will allow. A few passes with the fly cutter will allow the bearings to be moved closer and soon they can be set up exactly on the shaft line with a string stretched from the center of the engine output to the center of the propeller position. These bearings are usually just holes in blocks of wood but they serve just fine.
Once the bearings are in final position inside and out the bar is re-inserted and the cutter is advanced slowly in fine cuts until the desired diameter is reached. The photo below shows the the bar and the inside bearing position in Olfara. You can even see the string that was used to set up the bearings.

This is the outside position. It’s a very simple setup but would be difficult to do any other way.

Once the hole is cut the shaft tube(stern tube) is glued in place with epoxy and the shaft and it’s water sealing gland are fitted. In this case the tube was ABS pipe and had no bearing in it. The outer bearing was in a cast bronze strut and the inner bearing was on the bronze casting you can see here.

Another way this can be done is with a bronze tube with the stern bearing installed in it’s outer end and the gland mounted directly on the inner end. This photo is of the inside shaft tube in Friendship.

When building custom yachts , you can’t always find all the hardware you’d like to use. I used to make patterns and send them to a foundry in Vancouver and get castings done in aluminium bronze. This is a toe rail chock that I designed for Olfara. It’s advantages are that it is closed so that your line won’t slip out of it if you’re rafted next to a higher vessel or dock, but the hole is big enough to pass your hand through with a line. Sailors will understand the advantage. There are mortises in the ends to accept the toe rail tenon ends and fit the toe rail flush and fair.

This one is a double headstay + anchor roller casting for Olfara. Two headstays can be an advantage at sea, particularly for running with twin headsails, but even just for redundancy.

This one is a backstay tensioning lever. For the non-sailors an over center type tightener sort of like the chain tighteners truckers use except for sailing. I managed to get my company name on this one.

The last one I have a photo of is this custom stanchion base for the lifelines , again on Olfara. It’s not easy to find something off the shelf that fits the angles and style of a custom boat and if you make do with the store bought parts and make adjustments to account for them it always shows.

I guess that’s it for tonight. Next time I’ll show some finished shots and the few sailimg photos I have of these boats.

Thanks for following and keep the questions coming. I’m happy to answer them.

Paul

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/



6 comments so far

View HalDougherty's profile

HalDougherty

1820 posts in 1989 days


#1 posted 02-21-2011 12:29 PM

Very interesting details. Thanks for sharing, now for the sailing photos.

-- Hal, Tennessee http://www.first285.com

View SPalm's profile

SPalm

4939 posts in 2634 days


#2 posted 02-21-2011 03:07 PM

Fascinating. Just fascinating.
There is so much talent and knowledge here. I can tell you are only scratching the surface with us, but dang, you gotta know a lot about a lot to pull this off.

Steve

-- -- I'm no rocket surgeon

View antmjr's profile

antmjr

262 posts in 1936 days


#3 posted 02-21-2011 04:06 PM

yes, interesting and fascinating. I never read of this method (I mean, the bar with the fly cutter).
...
Are you thinking (I hope :-)) to show us how to drill the keel and install the bars that fasten the lead ballast?

-- Antonio

View shipwright's profile

shipwright

5315 posts in 1550 days


#4 posted 02-21-2011 04:32 PM

Thanks all.

Hal, don’t get your hopes up to high. The only sailing photos I have of these aren’t much.

Antonio, The drilling is so critical, ( two 3/4” bolts with washers have to hit an area only slightly larger than the two washers at the front end of this keel and then hit a very specific spot on the inside of the boat) that drilling would be REALLY difficult so we cast 3/4” copper pipes in exact positions in the lead. You can see them in the last blog entry. The holes are drilled in the wood guided by these pipe holes but the lead is not drilled. the bolts simply slide into the pipes.

I have better photos of this with Friendship. Maybe I’ll do an extra blog entry to show it better.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View antmjr's profile

antmjr

262 posts in 1936 days


#5 posted 02-21-2011 05:07 PM

aha, I haven’t noticed it! I didn’t read of this one either. But that way, the heads of the bolts stay under the ballast, don’t they? (in some details, in some books I have bought, there is a recess in the ballast for the nut).
I like your method, thank you.

-- Antonio

View shipwright's profile

shipwright

5315 posts in 1550 days


#6 posted 02-21-2011 06:22 PM

I’ve posted another blog entry to clear this up, thanks for asking about it.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

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