1/8 scale Apache 47' design and build

[chrispellegrino]

I'm at the tail end of completing this in CAD (I use SolidWorks for those who are curious). The proportions are bugging me because it's real close but I still find areas that don't quite line up with images. It's difficult to get the angle and perspective right though to make a good comparison. Trying to go back in the CAD history and tweak something creates errors that can take a few hours to fix. I think I'll leave this where it is and start cutting the plugs. LOA is 70.5", 12.7" beam. The beam is too big (from what I've found these were 8' in width), but I'm not going back at this point. This is one of the things that is really bugging me.

I have a smaller sized CNC router so I'm going to have to make the plug in sections.



Perspective is wrong in these next ones because it's actually at 1/8 scale in CAD at this point and the perspective doesn't work well. The center drive is supposed to be shorter and they're a little fat in proportion simply to get gears in there that will hold up.




This was a portion of the first layer for the plug but after going back into CAD and updating a few things this will change.


The beginnings of an outdrive. Again, proportions are off but I have no choice. I'm going to see about making gears out of stronger material to get the proportions closer.


I do have a family and of course a job, so I can't guarantee frequent updates. I am itching to get this going though.

 

[john v]

Looks nice
Please keep us posted

 

[Mike Bontoft]

Nice work! I think she looks good.
As you mentioned they list the beam on a 47 at 8’2”. All the Cigarettes I have measured are slightly wider mid ships than the transom, most likely carried over to the Apache hulls also.
I can probably get more measurements on the Apaches if needed.
A few I have done over the years, 38 Bertram, 35 Cigarette.

 

[chrispellegrino]

Nice work! I think she looks good.
As you mentioned they list the beam on a 47 at 8’2”. All the Cigarettes I have measured are slightly wider mid ships than the transom, most likely carried over to the Apache hulls also.
I can probably get more measurements on the Apaches if needed.
A few I have done over the years, 38 Bertram, 35 Cigarette.

Thanks Mike - nice work! I actually looked at the beam measurement again and originally I had taken into account the bonding lip that goes around the perimeter of the deck lid. Not sure if this is accounted for in full size boats. If I only look at the hull itself, the beam works out to 8'3".
One detail I did miss is the transom being a bit narrower. I had a feeling that might be the case and thought I had it in my model but missed it. If it really starts bugging me enough I might go back and take that into account.

 

[chrispellegrino]

I'm getting a bit ambitious with the drives. (By the way - I made a mistake earlier, the outer drives have the shorter lower units on the full scale boat. I think they are the #5 drives and the center drive is a #4.)

The plan is to have trim capability on its on channel, but haven't worked out a nice way of doing that yet.







The drives can be built for either rotation direction.

 

[chrispellegrino]

Does anyone have access to and/or have overall dimensions for the Mercruiser M6 drive? I want to make these as well for this boat. I know Arrow Shark has a version of these, but they seem much bigger than 1/8 scale.

 

[chrispellegrino]

OK, yet another correction. Both the #4 and #5 drives were shorter. The #3 drive was used in the middle with a shorter skeg. (There was a III and a IIIa drive. The IIIa drive handled more power.) This was the case at least on some boats. On this model, I really don't want to have to make two versions but I may have to. I can't get all three drives to have the same prop submersion without things looking way off where they mount on the transom. As you can see, the outer drives are much lower relative to the hull bottom than the center drive. When it comes to these models, I don't know how much of a difference this will really make on the water. I could make them a little shorter then lower the center drive a little more and raise the outer drives a little bit.



Still working on the details and internals of the drives. Looking bulky but I need to so the gears can hold up. I'm not planning on these holding a lot of power since there are three drives. Hopefully 4 or 5hp each will suffice.



The other issues regarding the vertical positioning of the drives is the connection to the engines. I could put one or two higher power engines in there with a gearbox. Then I might be able to better control the height of the engine crankshafts relative to the drive input shafts better, but I don't want to do it that way. It's actually not a bad thing to run the shafts nominally at a slight angle. That way they don't wear at spot. I'm planning on making dodgone shafts. The real boat has three engines, so I want this to have three engines. These are very crude Zenoah 23cc engine in this image. I've had this engine since the early 90's and never used it. Shorter spark plugs will be necessary, not to mention Zenoahs are larger displacement now so not sure how much height they require.



Hope this piques your curiosity. It's a little slow going at the moment working these out little details, especially the drive internals. I still don't know how to incorporate the drive trim. I think I'll just settle for manual adjustment while it's out of the water. Trim tabs have not been designed yet. I'd really like those to be trimmable by R/C.

I'm planning on beginning the machining of the hull plug this weekend. That will take a while.

 

[ACTION JACKSON]

I'm watching your build closely in anticipation for the first model to come out

 

[chrispellegrino]

Ok, making the lower end of the drives around the prop shaft (the "torpedo" portion) a bit narrower (smaller diameter). May need to thicken the walls a tiny bit from where it is now, but it's a big improvement. The photos are of a 3D print I made last night before making the lower unit narrower. I bought a cheap 67mm prop for reference.



Lower unit much narrower. Less blockage in front of the prop. May be a little difficult to notice, but the prop drive dog is much smaller now.


My goal today is to machine out the first part of the hull plug. Due to limitations with my CNC router table and tool length, I need to make it in thin pieces (3/4" thick). Piece #1 is highlighted here. The very bottom piece is one piece that isn't getting machined. This will be made out of MDF.