Here is how John Fisher built two Star45 keel trunks. First he make a aluminum mandrel that is the same size and shape of the top of his keels. Next he waxed the aluminum and then put a single layer of wax paper over the mandrel.
He used a light spray of 3M 77 to stick the ends together on the second one. The first one had a pc of tape, which is now a part of the trunk.
The mandrel with waxed paper is wrapped with glass which he again used 3M 77 to hold in place. He has not verified that this doesnt have any long term effects to the glass so use at your own risk. John used 2 layers 3.2 oz glass with glass tape on the top and bottom edges to help add some stregth. Usually he would add kevlar, but that is not allowed in the stars. One the glass was in place John wet the whole thing with resin. If you dont have any way to vac bag the trunk, just let it cure and remove the mandrel. The trunk weighted in at 1 oz.
John has a food vacuum sealer so he put a release paper over the top (wax paper with holes in it), then breather cloth (he hasused paper towels in the past), and then into a food saver bag for the night.
To remove the mandrel he used a hammer and a vice. He knows that sounds severe, but that is what it took to get the mandrel back out. He started by placing the mandrel into a vice with smooth jaws. The jaws were just far enough apart that the aluminum would fit between them, but not the fiber glass wrap. Then he tapped the mandrel out. He points out how much force it took for him to get this apart so you can design your keel top with this in mind.
Photo 01- mandrel before prep
Photo 03 -mandrel with glass, ready for resin
Photo 04-keel trunk in food saver bag. You can see the resin going into the breather cloth.
Photo 05 - keel trunk off the mandrel, note the tape. 2nd trunk used3M 77 instead.
Photo 06 - Trunk on the keel.
The following picture shows the way that John aligned the keel on his second boat.
Since the keel is plate and 1/8" thick I laid a straight edge on it and
aligned it with the pc at the center of the transom. I did this on both
sides to make sure it is centered as well.
To capture the top of the keel box he added 2 1/8" X 3/8" spruce blocks
to the top of the keel trunk and glued them to the king plank. The photo also shows the glass tape He used to reinforce the
radio tray.
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here is an alternative keel trunk (from Uncle Dave)
I poked my camera down into the Sirius 45 and snapped a couple of pictures showing how the keel is attached to allow it to be removed and another installed.
The keel is a aluminum fin with my flat bottomed bulb. The keel trunk is assembled over the keel fin before mounting the trunk in the hull. The trunk is pretty simple. Two pieces of 1/8 ply on either side of the fin. Cut flush across the top of the fin. Height is determined by the amount of the fin to extend into the hull. Length is determined by the shadows or braces to support the fin. A filler pieced goes between the sides so that fin can be slid own and out of the trunk.
Before gluing the trunk up it is very important to coat the insides of the trunk to make the sides of the trunk as water resistant as you can. The the fun part is placing two mounting bolts through the sides of the trunk and thought the keel fin. I think the two bolts in the picture were 1/2 long 3/8 inch dia.
I placed a heavy wire through the both the bolt heads so I could turn the nuts on the other side.
With the nuts removed the two bolts simply push to one side and the keel fin mounted or removed as the case may be. In my models the height of the fin inside the model is low enough for a swing arm sail control to fit properly. I use Probar (now Dumas) SCUs.
Before building the deck I simply dropped the trunk (with keel fin) through the slot in the bottom of the hull so the trunk rests on the keelson. The hull being fiberglass the trunk if filleted with the bottom using some auto body resin-paste. I think I also used the resin paste to mount the keel trunk in my wooden models (memory escapes me its been years). The ends of the trunk are braced to the chine to with stand leverage forces from the heavy keel bulb and sailing stresses.
When the two bolts are tightened they not only hold the keel in place they also pull the sides of the of the trunk tightly together. With the tight fit one should expect the keel fin may stick in the trunk if some sort of lubricant (silicone) isnt used.
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