40" BEFU Scale Scarab for sport build thread

[marko500]

Yeah I love flying my hydro around the pond in the 60s. But there is nothing like a big scale offshore boat cruising along busting through the waves. My first RC powerboat was a homemade 66 inch offshore boat with a weedeater type engine, wet exhaust out the transom and all. Used to love pulling up next to the real offshore boats anchored at the beach and then gunning the motor. I had alot of fun with that boat, maybe I should dig that one out one of these days too.

Mark

[ScarabChris]

I have made a decision to pull the gas power out of my 50" Aeromarine Apache and turn it electric. I got so frustrated today trying to get that Zenoah running. After 2 hours of tinkering and tugging on that starter cord I spelled like gas and exhaust.

I figure I am most of the way there since I have the hull and radio equipment already. That Zenoah is a pro mod with clutch, I have at least $700.00 into it not including the exhaust and drive hardware. I think I can sell it for a few hundred bucks to put towards some electrics.

Nw what to power it with. I was thinking crazy like triple Stiletto outboards but those things are huge, I think only two will fit.

[tomstoys2]

I have made a decision to pull the gas power out of my 50" Aeromarine Apache and turn it electric. I got so frustrated today trying to get that Zenoah running. After 2 hours of tinkering and tugging on that starter cord I spelled like gas and exhaust.

I figure I am most of the way there since I have the hull and radio equipment already. That Zenoah is a pro mod with clutch, I have at least $700.00 into it not including the exhaust and drive hardware. I think I can sell it for a few hundred bucks to put towards some electrics.

Nw what to power it with. I was thinking crazy like triple Stiletto outboards but those things are huge, I think only two will fit.

Now see what you guys have started?

Mark, I'm still liking those Stilletto Outboards for our Scarab. We need to pick some motors!
Tom

[ScarabChris]

Looking at the Stiletto outboards on OSE they appear to be 9" tall and 3" wide. Thats pretty big. The beam on my 50" hull is 12". So three of them would take 9 of those 12". They would almost have to be touching to fit three.

I'm thinking 2 will do it on my 50" hull.

I wonder what the biggest most powerful motor that will fit in that?

[marko500]

In the outboard cat thread they are talking about some of the Leopard motors that will fit. After running the Leopard in my Stealth hydro I'm a huge fan of these motors. Maybe we need to get ahold of Darin and see what kind of power (rpms) the outboards can take. I want something that's going to be fairly dependable.

Mark

[befu]

Well, done with this boat for awhile as it is too cold to run here. So now I will start working on the scale aspect of this hull. Add cockpit details, paint, railings, improve the swim platform.

I started laying up a new hull also. White gelcoat this time, going to do some playing around and see how they turn out.

Brian

[marko500]

Yeah we're done for the season here too. Time to repair the boats from last season and let the winter builds begin!

Mark

[befu]

Hmm, never did finish the second hull, been playing around with different surface coats and epoxy.

But, I have decided to put a stearable stern drive on this thing. Not a z-drive, but a flex cable stern drive that looks like a z-drive. We will see how it goes. The scale is off, but since this is a test bed, I will still put it on there. If it works out, I think I will make a smaller version and maybe do twins in it. I think I can find room in the boat for twin motors!

These pictures are the start of silicone molds for pouring the pieces out of a strong urethane resin. Taking the original castings for a z-drive and changing them to my needs with cleanclay and sheet wax. Next couple of days I should get the molds poured. Some of these urethanes are dang strong now.

Brian

[marko500]

I tried something like that years ago using a K&b outboard lower leg on a large gas boat. I think it was a 7.5 outboard with a .250 flex shaft on a gas engine. Worked good but the only problems I had was I think 1) didn't use a strong enough servo, 2)tried too tight a turn radius. Mine would tend to whip the drive hard into a turn if I tried turning to hard under acceleration. Keep in mind this was 25yrs ago and I had no clue on what I was doing or the physics part what I was doing, just a head full of ideas. I think with your knowledge this will work out great. Once I learned from my mistakes and used a 1/4 scale push/pull servo and turned down the servo throw I used it trouble free for years. Looks good keep up the great work. Yours looks great, mine was butt ugly! I'll try to dig the boat out and get a picture.

Mark

[befu]

I had a 55" scarab with a funcraft outdrive that worked the same way. With the gas engine turning a 70mm ish size prop, it took two 1/4 scale servo's at the time to control it. You do not need much deflection to get a good turn radius either, it would turn either direction great.

I figure I will be using a 42 to 47mm prop, so it should be easier to control this time, maybe just one 1/4 scale servo or one newer servo that is stronger. This boat with twin outrunners turning some 37 to 40mm three blade counter props would be great I am thinking and very scale looking.

We will see.

Brian

[marko500]

I was worried the constant back and forth of the flex would cause it to fail between the hull exit and the outdrive. But that was the one thing that never broke. I ran the same flex cable for years, never had to replace it once.

Mark

[befu]

Molds for new outdrive

OK, finished up the masters, made the mold boxes and poured the silicone tonight. Hope this works! Spent about three nights prepping everything and pouring. The dang silicone sitting there is almost $50 worth, plus the mold release and what not pretty much wipes out a $50 bill. We will see.

I am excited about this. Next year I may do my 54" scarab build with twins and twin outdrives! Gotta get this one going first!

Problem is, I will get the outdrive poured and machined, then have to wait for the water to get soft again to see if it works....

Brian

1-8-11 Update: All of the masters came out of the silicone just fine. Cleaned out the clean clay and trimmed up the silicone. Now they are in the oven post curing at 150F for 4 hours. I may get to do the first cast tonight, maybe tomorrow! I also made a new mold for my crackerbox rudder pieces.

[befu]

It worked

OK, silicone is really expensive, super goey and not the easiest thing to work with, but once you get it done, it is way cool!

Pulled out the first cast tonight. This is just cheap resin as I wanted to do a test casting. Not the strongest stuff, but it works.

so here are the pics of them, for the first pour it went pretty well. I am going to make these out of a strong urethane resin, but I do have a concern. The middle piece on these seems to be the weak link. They are thin and have a large hole drilled in them to allow the drive to pivot up and down. This causes a weak spot and I have seen the aluminum ones broken here. I tried to make this one thicker, but I am limited on room. So a few options:
1: I use the model and make one that has more material on it by making it taller. Another words, bring it out from the transom.
2: Glue the outdrive portion and the middle portion together. This will take the trim adjustment out of it, but you could still trim it out by shimming the transom plate or sanding the transom plate to an angle. Transom plates are easy to pour and different angle plates could be made. Not as nice, but it is an option and would be really strong.
3: Try making this piece out of a different resin. I can try this with the silicone mold, and/or couple it with option 1. Epoxy casting with kevlar pulp or carbon fibers would be an option. Will have to experiment. which brings me back to the problem of frozen water and testing.....

Well, this test turned out, so time to cast one with the better resin.

Brian

[marko500]

I think option 2 would be the easiest, but I would try option 3 with some kind of filler and see what happens first. Having a quick way to adjust the trim would be nice. Besides you have time to experiment and I've never seen you take the easy way out. LOL Me and Tomstoys2 still have the 40" Scarab hulls and where going to do outboards on them but due to other projects they got put on hold. If these work out they may be a serious option for us in the future.(if they work and you'd be willing to sell a couple in the future)

Mark

[befu]

Outdrive progress

OK, did some cast of the outdrive. The first two I am still learning. having an issue with airbubble entrapment, so I need to work on that.

Also working on the weak gimble. I made up a new model and working on finishing it off so I can cast it in silicone soon. It is MUCH beafier than the original and I think it will work just fine as it was designed to. Also doesn't look bad. The one picture shows the original sized one with the new model which is primed in red.

Check it out.

Brian