Keel design

[Perm Stress]

Originally Posted by Michail

Unidirectional fiber available locally is a 2200 g/m2 which is used for heavy piping. No lightgweight unidirectional is available here.

It should be possible to "rip" it and use the fibers...

[Paul B]

Originally Posted by Michail

I have three major problems with plywood-fiberglass:
- I pretend to use vynilester resin and not epoxy for sheathing (due to local costs). If the sheathing is structural (such as is the case with plywood), a delamination issue is probably very dangerous.
- The original design has already a rather thick profile. Since I am increasing loads, the resulting profile would have to be even more thick. In fact I estimated that I need to have about 45 x 9 cm profile (20 %) to be in the same strength range. I can make the keel longer (i.e. not 45, but 55 cm.) but that would change lateral plan, so I would have to adjust rudders plus the whole structure

Just FYI:

Here is a photo of my keel. It is more than 20 years old. Still looks and functions as if it was built yesterday. It is 1.6m span, approx 200 kg lead, and almost half the thickness you are considering for your keel.

The volume below the red line is lead. The keel above the red line is Honduras mahogany. The whole thing is sheathed in glass. There is no steel plate or any unidirectional glass or carbon.

You might want to consider building in this style rather than using plywood, steel, etc.

[water addict]

One thing to think about-
It sounds like you will be adding a substantial amount of righting moment by making the keel deeper and heavier than the original design. This imparts more load on the rig and hull structure all over the boat. Be careful. The support structure for the entire boat may not be able to handle it.

[xlr8]

I prefer using solid wood rather than ply for keel fin. Fiber orientation of solid wood doubles the strength than ply. If you are using metal, consider hollow aerofoil welded keel fin, this is commonly used for small boats.

[Michail]

I am progressing well with the mold but it takes considerably longer than I thought…

Next week we are going to weld the keel from normal steel. I decided to go with steel rather than with fiberglass-plywood because it is much slicker (6 cm. versus 9 cm.), and only marginally heavier. (The keel without ballast would weight about 70 kg. versus 40 kg. of the fiberglass, but because it will be deeper, I can save on the ballast the same 30 kg.).

The keel will have four 10 mm x 50 mm. stringers, welded in two pairs (could not find 20 mm x 50 mm.) and covered by a 4 mm. plate. Total keel length including bulb - 200 cm. Keel part inside the hull when fully lowered – 65 cm. Keel length in water from bottom of the hull when fully lowered - 135 cm. Ballast – 120 kg.


I have one doubt and would be grateful if anyone can help me in this:

How often would you expect the keel to be removed completely from the hull for maintenance-inspection?

I plan to use a 6 cm. wide blade (00 series at about 14%) for the part which would be in the water and 10 cm. wide square cage which would run in the rectangular shaped well with four guide rollers. This design would reduce the weight of the keel in the upper part (by about 15 kg.), where it is obviously not needed. The problem with this design is that to remove the keel from the boat, one would have to remove the ballast bulb and hoist the keel upwards. Is this OK?

The other option would be to build a 6 cm. wide blade for the whole length, but that would increase the weight in the upper part. In that case, however, the keel can be removed easily through the bottom just by lowering it. I also have another problem with this idea, namely, that one can accidently loose the keel, since there is no.safety stop to prevent the keel from dropping out if not secured. There is also the problem of the roller guides which would not go through the bottom opening… Any suggestions which design is better?

[Michail]

Keel Profile