View Full Version : Bottom to Garboard Joint

09-09-2004, 07:56 AM
I'm building a Phil Bolger 'Spartina' and am at the stage where it's about to start looking like a boat. The plans are designed for an 'experienced boat builder' which I'm not, but am having a go anyway. The picture below is the bulkhead at the forward end of the centreboard case. The circled area is where I am rather indicisive. What sort of joint should I use? The designer has not responded to my query. Probably because an experienced builder would know.
The bottom is made up of two layers of 12mm ply which have yet to be glued together, and the planking of 12mm ply. The following drawings are the possibilities as I see them, with fillets of course. Any thoughts?

Don Maurer
09-09-2004, 12:03 PM
I would use option 3 with an epoxy and ring nail joint. Pre-drill the nail holes and countersink slightly, then fair the heads with epoxy and sawdust or microballoon filler.

gary porter
09-09-2004, 12:50 PM
Byron, any of the joints you have drawn will work but notice that you've exagerated the angle. It's really a butt joint or nearly so. I'd go with #1 or #4. Note that the top side needs to be filled or layed in so you have a smooth area for water flow through your limbers. The epoxy joint is stronger than the wood around it so any of your joints will work if you eliminate of fillet that top overlap.

Dave Fleming
09-09-2004, 01:03 PM
Since I am NO googe user, I will be guessin' here but, that piece atop the I'll call it 'plank keel' and the lap planking is to me a keelson batten well shaped, with enough surface area and probably bedded and taped and filleted in googe to be plenty strong. Rather than ring shank nails I think I would try those plastic/nylon staples to affix the plank keel and lap planking whilst the googe sets. Bet the exterior of that joint gets a feeberglaz tape overlay set in more googe too.

Just because I don't favour the stuff I cannot deny the strength of well applied googe.

09-09-2004, 04:29 PM

Since I have been for over 3 years building a Bolger boat (Chebacco, sheet ply version), I think I know the answer, but I don't know your boat so I could be dead wrong, too. Here's what I think I'd do: Butt the garboard to the bottom plank and keep them aligned with some of that 'stich and glue' stuff: holes and wires twisted just to keep it all together temporarily. Then I'd epoxy it with a) straight stuff if you've not pre-coated, then b) heavier epoxy with fumed silica/wood flour. I'd probably skip over the wires so I could easily get them out once the epoxy sets. Once set I'd remove the wires and fill those slots. Then I'd apply a straight coat of clear epoxy over the joints with the fiberglass tape(s) immersed. Then you're on your way, mate! That'll keep it, don't you think so?

BTW, Cheers to all of Brisbane and to that super-OK hospital (was it Methodist?)just south of town and near to the railroad tracks. They did good emergency work on my wife once upon a time. Ahh for some bay bugs in sauce and that good wine of Oz! Once fixed up, we had a good time in Brisbane and later in Byron Bay. Cheers! :cool:

09-09-2004, 08:29 PM
Thanks Guys, Was sort of hoping for a consensus. I'll have another look, scratch my backside for a while and procrastinate for a bit longer. I thought that if I trimmed the bottom board back a bit before glueing it to its other half, there would be a ready made rebate for a bit more surface area for fixing.
Re the hospital, that's a cut lunch away on the south side of town. Don't very often get down that way.

Phil Young
09-10-2004, 01:20 AM
Byron. Im thinking that the bit of wood that sits on top of the join and spans the joint gives you your answer. You want a nice clean (flattish)V shape there for that bit to sit in. Which means it has to be option 1 doesn't it?

09-10-2004, 11:11 AM
Phil, I think that's a limber hole, in the form ahead. It is for water to flow freely inside the hull. Right?

Bruce Hooke
09-10-2004, 12:27 PM
Assuming BillyBudd is right that the "shape" above the joint in question is a limber hole and not a piece of wood (I cannot tell which it is from the drawing you posted so hopefully other parts of the plan will answer this question), I like BillyBudd's stitch-and-glue approach. However, if that is the intended solution I am surprised that Phil Bolger did not provide a schedule listing how many layers of cloth of what weight need to be applied to both the inside and the outside. With a stich-and-glue design that information should, I think, be part of the construction spec's for the boat because it is the functional equivalent of the size of wood members.

Assuming you do not get more information from Phil Bolger, what I would do first is make up a sample of the joint that is maybe about 6 inches long by about 18 inches wide (i.e. 6" in fore and aft dimension and 18" athwartship). Use the method you plan to use for the real joint, including as many layers of glass cloth as you plan to use. Let it cure for a week or so and then try to break it. If it breaks in the joint then you need to reinforce the joint more. Actually, what I would do is make up one sample that is maybe 24" long, then once I'm ready for the first test I would slice off a 2" piece. If that sample breaks in the joint then I would add more cloth to the joint on the remaining 22" sample and test a new 2" slice from it. Once everything looks good with a 2" sample then you can cut off a 6" wide sample and test that. This way you do not have to start over and make a new sample from scratch if the first one breaks in the joint. I hope that makes sense. The reason I would make the sample 18" wide (athwartship) is to give you enough leverage so that you can break it to test it. A narrow sample would be all but impossible to break...

09-11-2004, 01:38 AM
Tis a limber hole. There are no construction details included with the three A2 sheets of plans. One of them is just the sail plan options.
It's almost a butt joint for the back half of the boat, but becomes about 45 degrees at the pointy end, which is why I included different options. Not being a fan of fibregl*$#, (sorry, wash my mouth out.)I would prefer to use the minimum amount that is consistent with a good joint. Probably more to protect the bottom from abrasion.

09-11-2004, 06:39 PM
Byron, some additional comments. 1) Phil Bolger is well known for always responding to all letters. Even my most stupid questions have been handled with great tact and wisdom by PCB. I'm sure you'll eventually find a letter in the mail. 2) You might, while you wait for your letter from him, consider joining the Yahoo group that is devoted to Bolger boats. There you will meet many people with extensive experience building and thinking about (some adoring) many of Bolger's boats. Finally, 3) you're right on a good target, I think, regarding a fabric/epoxy protective barrier for your boat bottom. Here in the US, xynole and dynel are favored fabrics by some. They are flooded in epoxy and some, myself included, put on several abrasion resistant coatings of epoxy with graphite added.