Strut and prop placement?

The keel is laminated with 1" White oak bottom side and 3/4 " Mahogany inside with a toe of carbon fiber between. I can epoxy additional wood internally. Internally I can make any modification needed. Very open minded to any good ideas. Everything is glued with G -Flex epoxy and screwed. Two layers of 1/4" marine plywood over battens and frames. External surface of plywood was 1st given 3 coats of epoxy, then covered with carbon fiber cloth saturated with epoxy. Frames are laminated White Ash and Mahogany with epoxy and 4 coats externally. Frames are every 11" apart with floors to reinforce.

 

Beautiful work there, thanks for the pictures.

For a metal bracket:
You build a box out of plywood, minimum 1/2 inch, heavily glassed inside and out. It has only one open side, so the strut can be inserted freely but without slop. This box you insert in a cutout in the keel until the edges are flush with the outside. You glue it to the keel with thickened epoxy, then apply a glass or carbon patch.
On the inside you double up the keel on either side of the box going from frame to frame. The doublers are the same size as the keel, glued to the remains of the keel, the skin, the box and the frames. In the middle of the box you install a gusset on either side, from the top of the box out to the stringers. Alternatively you can do two gussets at the end of the box, instead of one in the middle. They can be laminated to match the frames, or plywood glassed over.
The strut is bolted trough the side of this box with 4 screws (epoxy the holes beforehand). You coat the strut with your favorite flexible sealant before final assembly.

The whole thing will require a great deal of fitting, and grinding. You make the strut like this: take a suitable cutless bearing pressed into a piece of tube and slide over the shaft. Cut a piece of flat bar to match the angle, insert into the hole in the keel and tack weld. Remove from boat, remove cutless, finish welding. Grind a pleasing profile into the exposed part of the thing resembling the cast one you have.
Bracket thickness should also match the cast, lenght is so that about 4 inches are above the keel doublers so you can bolt it in.

For a composite bracket:
Cut hole in the keel, insert strut, fill the hole with thickened epoxy, apply glass or carbon patch on the outside. On the inside glue the same doublers and gussets directly to the strut.

To make a composite bracket you take a cutless bearing and apply mold release. Then you wind one or two layers of glass over it forming a pipe. Next is a wedge of plywood to make the transition from the pipe to the leg, it gets glued on. The leg can be a piece of 3mm plywood or glass/carbon plate. Remove the cutless, suspend the pipe from a piece of rod and apply many layers of carbon fibre wrapping the pipe and forming the leg. Use approx. 60% uni and 40% biax by weight. Use progressively narrowing tapes so you don't have to grind so much. When you reach the desired thickness grind it smooth, then finish by wrapping everything in one layer of carbon biax followed by two layers of plain or satin glassfibre (the glass is important it electrically isolates the cabon).
Thickness again like the cast bronze one, but it can be shorter, 4 inches above the keel since it doesn't need bolts. It can end up buried into the keel doublers and the gussets can look like an additional frame.

 

Thank you!!!!! I really like the idea of a composite strut. Plus I think I have all the correct materials to make it. Just a couple questions. How long of a cutless bearing do I need ? Because I have 5 feet of exposed shaft, do I need a second support bearing? The current brass strut has two short cutless bearings internally with an overall length of 8 inches. It came with a second 2" long Strut for second shaft support closer to the thru hull hole.

 

Usually the maximum recommended length between two bearings is 40x shaft diameter and the minimum is 20x. Your 5ft long one inch shaft needs an intermediate bearing. If your waterseal is of the type that also supports the shaft (rigidly connected packing gland) you measure from there, if not (connected by hose, and that's what the fitting in your pictures is for) you measure from the next support wich is probably the gearbox. You mentioned the total shaft length is 10ft, so you probably need at least one intermediate bearing inside the boat as well. Arrange them as you see fit, as long as they fall in between 20 and 40 inches from the next bearing.
For the cutless bearing length the current arrangement you mention is fine.

 

Here is an update on my progress. Received a 6 inch cutless bearing. Cut it into three 2 inch bearings. Waxed them up and then rolled them in two layers of saturated carbon fiber cloth. Also glued up a 3/8 inch dowel to a piece of 3mm marine plywood to make the strut leg core.

 

Stop and start over. The first layer around the cutless needs to be fiberglass not carbon, you don't want galvanic galvanic corrosion. Same for the last layer.

 

Ugg! Being this will be a fresh water boat and a trailer queen, is this that critical? Just short times in the water like 4 to 8 hours. The epoxy is rock solid this morning. I'll have to grind it all off to start over. After re-reading the instructions, I see the wrap it in glass first.

 

Your boat, your risk.

You don't have to scrap the part, take it off (that's why you waxed the cutless, bang them out using a wood dovel after you cut the squeezed end) now you have a short carbon tube wich you can use elsewhere.

 

Thanks, I'll see what I can do.

 

Monday August 1st, 2023 I have spent an afternoon plus 2 more hours bringing the cutless bearings and shaft piece back to a clean state to start over. Cut a piece of Fiberglass cloth 6" wide by 10" long to use for the first wrap. I will wax all the pieces completely including the inside of the cutless bearings. I plan to also pack wax into the ends of the cutless bearings to hopefully prevent any epoxy from entering that area. I will make a two inch long spacer for between the two bearings of a thick paper material that will dissolve with water to remove. I plan to use this wax. After everything is wet out and rolled I plan to roll the assembly in another piece of plastic to try to get the assembly to hold it's round shape. I've been learning a lot with trying to make this, so it has been a good experience. Thank you!

 

Second Post for today. I've prepared the back of the hull for adding the doublers. There are two pieces of Mahogany 2" x 4" placed on each side of the keel. Then a piece of 1" x 4" White Oak on top of the keel first. Then two more pieces of Mahogany on top of the White Oak for a total of 6.5 inches of wood to bond the strut into vertically. The forward end of the White Oak piece is captured by the frame on both sides as well as the second piece of Mahogany. After this is all glued up I will add a cross brace to the Stringers.

 

8-17-23 Been a couple of busy weeks. Took in the Travers City and Hessel Boat shows. Some progress made on the interior where strut will pierce the hull.
I decieded to make a form to compress all the layers of fiber glass and carbon fiber materials when all glued up. Each side of the single bearing smaller strut has eight plus layers of cloth and carbon fiber glued in place. Five additional layers rap around the top of the bearing and mixed in with the layers forming the foil shaped leg.
This form got me close to shape with a small amount of sanding.
Let it cure and here is what it looks like.

This end photo has a couple of spots that look hollow but that is just at this very end. The part of the leg closest to the bearing and about 8 inches long is solid. Tell what you think so far. I'd really like to hear any ideas before I glue up the bigger main strut. It will have twelve layers per side of the foil shaped leg. Thanks

 

Put some thickened epoxy in the holes. Next time use a big friggin fillet at the intersection of dovel and spine.

 

9-12-23 Struts are made and fitted into the boat loosely so they can be guided by the shaft. Really happy with how this has worked out. They look really good and seem really strong. I put three layers of fiber glass cloth on for the final layers. This was then fared and given three more coats of epoxy with white pigment. Placed the holes in the bottom of the boat this past Monday and assembled things including the struts. Looks great!