On the subject of bilge runners, when building my little 6 m catamaran the design called for a dagger board, the case of which intruded quite considerably in the accommodation. I asked the designer for another non-intrusive option. He came back to me with a design for an inward angled bilge keel on the inside of each hull. These were very small, .9 m in length and about 95 mm depth at the forward end, and 60 mm at the aft end. I was a little bit skeptical about their effectiveness, but thought they were worth a try. They were very quick and easy to construct, and I have to say I am very pleasantly surprised at how well they work. The boat goes to windward just fine. The keels don't start working until the boat speed is at about 2 knots, but then any leeway disappears and my little catamaran goes to windward as well as any cruising boat I have owned. There is apparently a lot of science involved in the design of leeway prevention devices, and different devices are suitable for different hull shapes. Chine runners being suitable for flat bottom hulls, and the bilge keels I have fitted being suitable to single chine, v shaped hulls. I wonder whether such an unballested bilge keel which does not protrude below the bottom of the hull would be an option for the SibLim hull shape. From my perspective I have effective leeway preventers which are as simple as is possible, add almost no weight, and do not add to the draft of the hulls. After all my worrying about the construction of the dagger boards and cases, and their effect in the interior of the boat, I am now very pleased to have come up with such a simple and effective alternative. Image below

Graeme wrote:

I am interested in your chine runners. They look tiny to me. I put somewhat more substantial ones on my scow, horizontal fore-and-aft, at 45 degrees, so they do not follow the line of the chine, rather they run out at each end as dictated by the bottom planking - they came out looking quite different to yours. I have absolutely no idea if they will be a help or a hindrance, but keeping my fingers crossed they will do no harm at any rate. Mine are integrated with the bottom planking, so they are probably going to be permanent whatever the result! All I know is, they do work on the Paradox, I've seen it with my own eyes. I am not sure if the concept is transferable, however, so lets both keep our fingers crossed - yours at least will do little harm.

On the subject of bilge runners, when building my little 6 m catamaran the design called for a dagger board, the case of which intruded quite considerably in the accommodation. I asked the designer for another non-intrusive option. He came back to me with a design for an inward angled bilge keel on the inside of each hull. These were very small, .9 m in length and about 95 mm depth at the forward end, and 60 mm at the aft end. I was a little bit skeptical about their effectiveness, but thought they were worth a try. They were very quick and easy to construct, and I have to say I am very pleasantly surprised at how well they work. The boat goes to windward just fine. The keels don't start working until the boat speed is at about 2 knots, but then any leeway disappears and my little catamaran goes to windward as well as any cruising boat I have owned. There is apparently a lot of science involved in the design of leeway prevention devices, and different devices are suitable for different hull shapes. Chine runners being suitable for flat bottom hulls, and the bilge keels I have fitted being suitable to single chine, v shaped hulls. I wonder whether such an unballested bilge keel which does not protrude below the bottom of the hull would be an option for the SibLim hull shape. From my perspective I have effective leeway preventers which are as simple as is possible, add almost no weight, and do not add to the draft of the hulls. After all my worrying about the construction of the dagger boards and cases, and their effect in the interior of the boat, I am now very pleased to have come up with such a simple and effective alternative. Image below

Well done Frederick. Beavering away there quietly and making good progress. I should learn from you.

I am interested in your chine runners. They look tiny to me. I put somewhat more substantial ones on my scow, horizontal fore-and-aft, at 45 degrees, so they do not follow the line of the chine, rather they run out at each end as dictated by the bottom planking - they came out looking quite different to yours. I have absolutely no idea if they will be a help or a hindrance, but keeping my fingers crossed they will do no harm at any rate. Mine are integrated with the bottom planking, so they are probably going to be permanent whatever the result! All I know is, they do work on the Paradox, I've seen it with my own eyes. I am not sure if the concept is transferable, however, so lets both keep our fingers crossed - yours at least will do little harm.

Best wishes on your build, keep up the good progress and keep us all informed.

Ignore the water line - she's currently floating in 7" (just immersing the chine runner), you can see where the coppercoat has turned muddy-blue. The draft will increase a bit later, of course, when topsides, internals, rig etc are in place. 5 or 6" more I expect - nothing like the line of the coppercoat indicates. I hope.

The hole is for the internal off-centreboard pin, and leads only into the case. It will be bogged up later.

The reason for the white paint is, the tops of the chine-runners were sheathed after the boat was turned over (I could not do that part upside down.) They are ferrocement sheathed, like the rest of the hull, and the white paint is water-borne epoxy resin as a water-curing membrane, and sealer. I hope I've got enough coppercoat left to do them. Its expensive stuff and I have some misgivings about using it over ferrocement, relying on a good primary layer of epoxy sealer to keep it isolated. Time will tell.

Anonymous wrote:

Great progress Frederik, I'm also watching very closely. Are you glueing the two layers of plywood together with (lots of) epoxy? I've wondered about using a PU (D4) glue for this, it's cheaper and gap filling and it's probably what the ply is made from but it may be impossible to work with big sheets of ply fast enough and it won't seal the ply as well as epoxy. Anyone else have thoughts on this?

Also, I'm intrigued by Chris Morejohn successfully going against all advice I've ever seen (including his friend Reuel Parker) and using polyester resin over plywood. Any thoughts on this?

I've used Collano Semparoc 60 between the layers of ply. In case you don't already know, it's a PU expanding, waterproof adhesive categorised as C4. As I understand it, C4 is probably more suitable than D4 as the C group are thermosets and the D group are thermoplasts.There is no problem time-wise with gluing up big sheets; the working time is perfectly adequate.

Anyhow, so far, I'm happy with the results - it certainly seems to stick well!. Unfortunately the boat isn't in the water yet, so I can't tell you anything about long-term performance...