My first design Aubigny 5.5m

The Aubigny Keel/bulb Interface.

History: Lead torpedo bulbs are favorable at the lower end of the keel. Sizing of the bulb can be reduced significantly by bolting vertically into the keel rather than horizontally encasing the keel of lighter density material.

Issue: Lead bulbs bolted vertically at the end of the Keel board snap after bolts are weakened by the bulb racking sideways. Loosened bulbs by hours of use rack sideways in response to the boats motion.

The smaller weight bulbs should be easier to correct.

Solution: Redivert the sideways racking to a almost vertical motion, thus elinimating ageing and weakening of the supportive bolts. How to do this? Propose an interface between the keel board and bulb to redirect the motion. Using carbon fiber flared at the bottom of the keel closely interfacing with the top of the lead bulb. Adding pivot points on each side of each attachment bolt to redirect the sideways motion 90 deg. out of the direction of the bolts to in alignment (0 deg.) thus the motion turns into a thrusting motion.

Summary: The motion racking the bolts into weakness is mostly eliminated and a long term service is gained while reducing drag.

Statistical data collected on the attachment bolts should validate the design.

 

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Looks like you're making progress. Is that green foam polyurethane? I worked with green polyurethane 20+ years ago and it was very nasty stuff especially if it got in my eyes which it would have a propensity to do after I took my goggles off. Also caused my skin to itch(like glass).
Good Luck!

 

Yes it is. It wasn't that bad. A little itchy on the arms but the sanding went quick. I glued some sand paper on a 1 x 4 and started shaving. Kept vacuming up any mess. Rather clean to tell you the truth.

 

The Keel board core out of Western red cedar being cut with a skilsaw,router and jig sled.

 

The keel board filled in two days ago. I had issue with the router on the thick board. I found it best to slit with the skilsaw in 1" increments down to just above the core shape and then use the router. The router bit slipped on me three times. Filling was easy with the Glen-L epoxy and silica. The core almost shaped up to what I expected. It will get a wash dry then sanded with 80 grit prior to laying cf. I will be laying 6 layers a side 2-100%-45 x45deg., 2-68%- vert, 2-32%-vert. I will lay each side, cover with release film, squeege then wrap with elasastic bandage in substitution for vacumn.

 

Here's some info on this boat. I did a comparison to this design to a 6.5m Mini-Transat. I calculated the Displacement/Length ratio on an mT its about 102. The Aubigny 5.5m is approx. 61.24. Then I cal'd the Sail Area to Displacement/Length of both. The mT was about 42.x where my Aubigny was around 44.69. Its all pending final SA and D which is somewhere around 248 sq-ft and 800 lbs.

I was surprised. No wonder the i550 does so well. Its biggest downfall is their in-experienced builders. Some look at their assymetrical bulbs (due to poor build practices) and they say "oh well".

I expect the future Aubigny 55's will be high in build quality if I have anything to do with it.

 

I also have another sailboat parameter to bring up. It has to do with plane-ing hulls. After reading about the difficulties the SB 18 has getting on plane it occured to me maybe it doesn't have enough wetted surface area within a few degrees of horizontal to displacement. I made calculations for some numbers on the A. 5.5m and wondered what the SB 18 numbers were. I'd imagine it would be based on wetted surface area within 5 deg of horizontal. This parameter if it doesn't exist could be a fundamental design goal. Any comments would be appreciated.

 

An i550 bulb from rear view. Take a close look how out of symmetry and alignment it is.

 

While priming the keel bulb I started to work on extending the donor boat rudder castings. My transom is 18" from bottom to top of the cockpit sole. My expert welder said its weldable. The added aluminum up top will strengthen the castings so adding to them tackles two issues.

 

Bulb plug is getting some protective coating.

 

In the midst of glassing the board. I fitted the finished bulb plug and have half the keel strut with cf. The buld looks fairly straight.

 

Did this very creative project continue? Would enjoy watching the entire process and the creative answers to some of the tough challenges that always seem to arise during a boat build. Keep us up to date. Lack of replies does not mean we are not watching intently.

 

In temporary pause. Will continue soon.