12" scratch built cat

[Dr. Jet]

A New Dilemma....

I ordered this strut/rudder assembly for the cat: https://www.offshoreelectrics.com/pr...prod=ose-80972

It's a nice unit and it fits the transom, but........

The strut won't go low enough. It needs to go about 1/4" lower. I have two ways I could solve this. The first is to cut the adjusting slot in the strut all the way to the top of the strut blade. That would work, but then I wouldn't have a whole lot of material left to grip the strut blade. The second solution, and the one I think I will do, is to mount the strut 1/4" lower on the transom. This would result in the mounting bracket hanging down in the tunnel by 1/4". I would then make a streamlined wood faring block in the tunnel to go up against the flat surface of the bracket.

[Jesse J]

Plan b sounds like a good option, but maybe some pics would help us think up other options.

[Dr. Jet]

Plan b sounds like a good option, but maybe some pics would help us think up other options.

Here's a sketch of my plan. The fairing block (crosshatched) would only be as wide as the bracket on the strut; it would not be the full tunnel width.

[NativePaul]

I have added blocks like that but concave instead of convex to cats that were too flighty before. IMO cat tunnels need some reflex on the wing section, like WIGs and flying wings, as without it a wing's center of pressure will move forward with increased angle of attack, increasing the angle of attack further, cascading into a blowover.

[Dr. Jet]

I have added blocks like that but concave instead of convex to cats that were too flighty before. IMO cat tunnels need some reflex on the wing section, like WIGs and flying wings, as without it a wing's center of pressure will move forward with increased angle of attack, increasing the angle of attack further, cascading into a blowover.

Hmmmm....... That's an interesting thought; essentially a trim tab. I like it, and it's easy enough to do.

Just cut a couple of slits on the bottom sheeting and bend the resulting tab up to rest on the extended transom tab.

[Dr. Jet]

The Wood Is Cut

Well, I got the wood from the laser guy. Photos are of it "Dry Assembled" meaning not a drop of glue anywhere. Other than a couple of slots needing adjustments, it's all good. This is the single-motor version with the rounded ends at the transom. Unfortunately, he cut it before I modified the transom for the relocated strut. No problem though, I can just glue on a piece and a doubler to make it work.

[Jesse J]

Sorry, but I have no tolerance for angles on sponson tips... for me it ruins the lines... makes it easy to build, but not easy on the eyes.

BUT I am soper excited to follow your build

[Dr. Jet]

.... makes it easy to build.....

That was my entire reason for doing it that way......

[Dr. Jet]

Well, I tacked everything together with thin CA, then added a 1/8" square basswood chine piece and sanded the left sponson out. Lo and behold, the angled bow took on a nice curve instead of the angle. It just worked out that way.

[Dr. Jet]

I've made a few revisions to the plans and they are at a point I would call complete and ready to archive for future use. I didn't like the angles on the first two bulkheads and modified them to provide a better curve transition for the sponson bottoms and the gunwales. My original plan was to skin it with 1/32" ply, but for ease of construction and proof-of-concept testing, I think I will use 1/16" balsa instead. It will also give some leeway in dealing with the angles on the first two bulkheads that I didn't like. This boat will never see deck-to-deck racing with a bunch of other similar-sized boats, so I can sacrifice some durability for convenience.

[Dr. Jet]

I started some sheeting, but ran out of glue. It will be a couple of days before I run out and get some more.....

[Dr. Jet]

Just to confirm the twin motor version will work, I dry installed a motor mount and installed the motor through the various openings. Admittedly, everything is TIGHT, but it will work. Using a long ball-end Allen wrench, it is possible to reach the motor mount screws (that's why I put them on a 45° angle). The motor is installed/removed through a deck hatch in the sponson.

[Jesse J]

I didn't like the angles on the first two bulkheads and modified them to provide a better curve transition for the sponson bottoms and the gunwales.

Good, I didn't like them either! Nice work senyor!!

[Dr. Jet]

Nice work senior!!

Senior, (as in meaning "Old Fart" in English)?? Or Senõr (as in meaning "Mr." in Spanish)???

I respond to both.......

[Jesse J]

Senior, (as in meaning "Old Fart" in English)?? Or Senõr (as in meaning "Mr." in Spanish)???

I respond to both.......

I meant to type the latter, but recon autocorrect wanted the former.
I changed it back in my post..