Thread: Rabetting a keel

Howdy ... If you are going for a glued hull construction most of us these days use an inner keel that aligns with the rebated face. You glue the ply skin the the face of the inner keel.

Then flatten it all off and glue the outer keel on top of the lot.

This method is becoming particularly relevant in medium sized boats where it is hard to find timber big enough for the traditional one piece keel with rebate and more frequently are being laminated out of smaller pieces. This makes it almost crazy to laminate up a bigger bit then cut the rebate. Easier to go with an inside and outside as above.

MIK

Thanks Boatmik,
I think i might go with that idea as the keel has been laminated of many pieces and like you said it would seem a big waste of time to spend all the time laminating then have to cut a rebate into the lamiations i have spent many hours preparing. So i guess i will attach the keel as a cap after the ply is on with silicon bronze screws and epoxy. Thanks for the help
Archie

Don't need the screws if you don't want to put them in there archie.

MIK

Originally Posted by Boatmik

Don't need the screws if you don't want to put them in there archie.

MIK

The wood will work and glue lines crack over time ,depending on the choice of wood . Better to put in some mechanical fixings to be sure and stop large movements.

I'd recommend you don't glue the "false keel" on over the plywood planking. Instead, just bed it in your underwater goo of choice. My preferred sealant/adhesive for underwater wood joints is polysulfide. Fasten this cap or false keel with screws to the keel batten.

This will permit you to remove and replace it easily when it gets torn up on rocks, hard landing on the trailer, etc. A glued on cap will make removal much more difficult. On most small to mid size craft, this piece is considered "consumable" or sacrificial in nature. Meaning it will have a limited life span and require replacement.

With smaller boats it is OK to glue it on ... as you can simply plane it off and glue a new bit on.

It doesn't need to be removed in one piece. With bigger boats that sit on the affected part then planing it off is going to be problematic, so Pauls suggestion makes more sense.

Remember too that whatever external keel structure goes on the bottom of the boat ... maybe only a small thickness will ever get damaged. So a lamination of harder wood that is 6mm thick for a dinghy or 12 or 25mm thick for a bigger boat could be worth considering if the built up keel extends a fair distance from the hull.

In this case I would look at gluing to the plywood directly in every case, but have a sacrificial piece either glued or gooped on depending on the size of the boat.

Best wishes
Michael Storer

Originally Posted by Boatmik

With smaller boats it is OK to glue it on ... as you can simply plane it off and glue a new bit on.

Originally Posted by PAR

I'd recommend you don't glue the "false keel" on over the plywood planking.

I'm going to set PAR against MIK on this one ... in a nice way because I respect you both and am looking for specific answers ... as much as are possible in this game

My thinking, based on long hours over a coffee cup and buggerall experience, fits with Mik, that it's relatively easy to plane off the old timber and the old glue line and hence I have gone with gluing the false keel on. Same thing with the rubbing strips on the bottom of Redback (she's got both an outer keel and rubbing strips - no fasteners).

However, thinking about the removal process, planing off is easy when the surface you're planing to is raised and harder when it's a wide flat area (such as the rubbing strips on Redback's bum) ...

Then there's the thought that removing sacrificial strips isn't something I intend to do very often anyway so does a bit of extra effort really matter?

Is this a big boat vs small boat vs tiny boat thing?
Does it make a different if you're an occasionaly user like me vs someone who's using the boat all the time and hence will face this sort of repair more often?
Should I get off this forum and go do those two uni assignments that are due on monday?

Richard
so many decisions, so little time and no flamin' water to float the results in

I'm always thinking about future repairs and maintenance when I design, assemble or perform a repair. On boats (like Michael suggested) that you can easily flip on their deck, whacking down a gouged up rub or false keel is relatively easy. I still don't like it because I seem to always find the one temporary screw, they forgot to remove after the glue sets. Not much pisses me off more then having a nicely sharpened blade get a good ding. I'd much rather remove a few screws, scrape the goo off, cut a new rub or keel strip and bed it down again. I know this will come off without fuss and it can usually be used as a template to make a new one.

On bigger boats, ones that can't be turned with free beer and BBQ, I like to see some metal down there. It's not as common a practice as it once was, but a metal keel "shoe" can take a lot of abuse, before it needs to be replaced. Bronze or stainless are the usually choices, but I've seen aluminum and recently HDPE and ultra high stuff, screwed to keels to offer some grounding protection. I don't much care for aluminum, but HDPE or the other high density plastics have amazing resistance to abrasion. Goos and adhesives don't stick well to this stuff, but they can be mechanically fastened in a good bedding.

Hey Daddles,

Maybe this is partly because I don't build many boats these days. So I do even fewer repairs and I never work with other people.

The plane blade thing is pretty painful for me too (sigh) but I only repair boats I have built recently and I know there are no fastenings in them (except for one gunwale of one of the qld pdrs when the wrong filler powder got put in the epoxy!!!

So it is pretty easy for me to follow the plane-off method.

Also another difference is that I only really use epoxy. Paul uses all sorts of sophisticated glues and goops and knows different ways of using them too ... something I don't have as much experience with.

So that would be a factor too.

Michael

Wow All valuable information here, I think i will go with the epoxy keel method without the fixings. I think still thinking about this one, thanks for all the info guys