daggerboard case/hull join

I picked up #61545 for free and am embarking on an extensive restoration/rebuild, which will involve replacing almost all of the hull shell panels (following, as best I can, the pictures and rather telegraphic instructions posted at http://www.ukmirrorsailing.com/index.php?option=com_content&view=article...), and much else besides. So far I have the aft portside bottom panel replaced successfully. I've already found many useful points in the forums here, but there will probably be many more questions!

I'm toying with the idea of a centreboard (and will contact curlew for plans, I think?), but for now I'm puzzling over indications of an alternative way to join the bottom of the daggerboard case to the hull as compared to the original build instructions:

"The daggerboard cut-outs in the aft bottom panels may be enlarged to accommodate the daggerboard case side panels if these extend past the daggerboard case bottom battens" (International Mirror Wooden Hull Specification 2017), p 13). I can't find any information about this--whether it is preferred, and whether you'd still glass over the corner on the outside of the hull and into the daggerboard slot, for example. It seems like it would be a strong join overall ...

While I'm at it, two other questions:

1. Are the nails the original build instructions call for through the bottom of the hull into the bottom daggerboard case battens really necessary, or are they just to keep things in place while the glue set? They seem unnecessary to me, and I'm trying to use as few metal fasteners as possible.

2. I see some have reinforced the dagger/centreboard case to hull area with another layer of plywood. I think perhaps the idea is to prevent flexing that will weaken the joint? Any thoughts or advice on this? I might as well do things right given that I'm doing a pretty deep dive with this project.



PuffinInTegel's picture

Welcome to the forum, I hope we can help.
I am one of the folks who have reinforced the hull around the CB case. But I have no aspirations to keeping "Puffin" class-regulations-conformant, I just want a reliable hull to take me out on the lake for an afternoon or perhaps on a multi-day cruise. My reasoning and what I did are outlined from page 3 on in https://mirrordiscussforum.org/documents/stories/jf2012english.pdf .
So the major question is: do you want your boat to meet regatta measurement inspections or do you need a boat just to mess around in? In the former case, you need to read the class rules and specifications carefully, in the latter, you are free to follow advice and common sense.
Wishing you success in the restoration work!
Gernot H.

Thanks, Gernot. I somehow find it hard give up the idea of conforming with the class rules, but I think that I've already ruled this out by using batten joins for the hull panels. Also, there are no active class associations/regattas out this way (Pacific Northwest), to my knowledge. And I don't race in any case. So I guess I'm free!

Two questions about your project: did you shape your plywood "keelson" piece to the curve of the hull (i.e., fore and aft, and/or port/starboard sides) at all by chamfering the edges of the mating surface (not sure of the correct boat building terms!), or just clamp it in place as is? And do you recall what the thickness of the plywood was?

Red Kite's picture

Hi Jeremy, If I may add my “two pennorth” to this, I spent a lot of time trying to work out how to chamfer the undersides of the centreboard case battens accurately to match the hull around the slot. It wasn’t easy and eventually I didn’t get quite accurate, but I found that that the hull itself gives a little when screwed to the case. I therefore epoxied the case to the hull with thickened epoxy and then screwed them together until the epoxy oozed out of the joint. It has held together very well over the past three years with no signs of leaks or rot.
Red Kite 43814

Thanks, John. Good to know. Replacing the aft bottom panels has taught me that there are few straightforward angles in boat building--all curves, in every direction! This particular problem will give me plenty to puzzle over during the slow hours at work. But as you point out, epoxy joins are pretty forgiving in this regard.

#61545 (in progress)

PuffinInTegel's picture

The "keelson" bit was about 10 mm (guessed by memory) taken out of the odds and ends at my local chandlery. I cut the slot first and then planed around it carefully until it fitted as snugly as possible into the hull curve.
I cut three solid V-shaped bocks to fit the hull on the outside and used these with some long bolts to clamp the keelson in place while the epoxy set.
I then fixed the CB case in with the aid of two of the V-shaped bits and ropes ("Spanish windass") while the epoxy set there. The thwart was screwed into place to make sure the case was aligned vertically. Unfortunately I was too conservative and made the slot a bit too thin. My daggerboard can only have a minimum amount of varnish and has to be banged down, but the upside is that it stays down without needing a bungee or similar to hold it.
Clamps 1
the bits and pieces
Clamps 2
Spanish windlass hoding the CB case in position. Note battens to distribute forces and polyethylene bag to prevent sticking the battens.

Thanks, Gernot. This solution is going to come in handy. I find the problem-solving element of all of this pretty engaging, to be honest. I

'm considering how thick to make the CB in relation to the slot. Too tight and I imagine that it will have a tendency to get stuck with sand and things; but too much play doesn't seem good, either. On my GRP Wayfarer, it seems to be pretty tight, but I've never had it stuck yet.

#61545 (in progress)

Red Kite's picture

Jeremy, my centreboard case slot is 17mm wide. The board is 12mm wide. By the time you’ve undercoated and put two coats of topcoat on both the board and the inside of the c/b case, I found it worked fine. The board stays either fully or partly down without it slipping up or down.
Red Kite 53814

curlew's picture

I remember I put a board as thick as the gap into my case when I was working on it to ensure it did not close up during the work. I made the gap 17mm for a 12 mm centre board.

PuffinInTegel's picture

That is something I should have done!
The little mistakes one makes, as an amateur "wood butcher".
Thanks for passing on your tips and hints ... here's hoping that we all have an enjoyable season!
Gernot H.