Photos Dumas SK 2 build as a FE

[oldbikerarlo]

OK I guess photos will help. I'm building this as a FE and need some help now, as you can see I have the motor mount in. I have a Leo 3650 1840kv, and a HK 90 amp speed control also. The boat is 27" long. could use some advise on running gear, like what size flex cable, offset, or inline, strut, and rudder? I have an idea in my head, for a one piece hatch, and silicon gasket, that will seal the top side. My aim is to make this a cracker box, that is why the transome was redesigned. I just put on the first coat of finish epoxy, love that mahogany.

100_0026 (2).jpg100_0035 (2).jpg100_0033 (2).jpg

[Moonie]

Vary nice!

[oldbikerarlo]

Now I'm thinking piano wire drive.

[srislash]

Now I'm thinking piano wire drive.

You need to keep a wire drive clean. If a speck of rust forms it will drastically weaken it. So depending on how much maintenance you want to do....
A .150 flex cable do the trick, Teflon liner keeps it quieter and lubed longer. You have a wide transom to work with so offset rudder would be best. To set the Center hole for stuffing tube a rule of thumb is to have 35-40% of the prop in the water below the keel.

Love a wood boat, Shawn

[Fluid]

These models did not use a surface drive but rather a fully-submerged drive like the originals. That said, it may work well with a stinger. I know that the actual Crackerboxs run faster and are more stable with a stinger. Obviously an offset rudder would be required. A 0.150” cable will work well with or without teflon, lube is required either way. I assume this is a 4S build.

And as for the hatch - don’t reinvent the wheel. Use tape to attach/seal the one-piece hatch. Proven seal, plenty of holding.


.

[oldbikerarlo]

Thanks for the reply Shawn,
A .150 cable, with offset rudder, I understand. The center hole has me confused.

Fluid, just cleared that up for me, as I was asking Shawn. The hatch sealed with tape is the way I'm going. the silicon seal was my mind making things over engineered. yes 4S.

[srislash]

Center hole meaning the propeller shaft Center. A lot of trepidation in drilling/setting up that hole through the transom.

[oldbikerarlo]

Doing a little templet, for the hatch.
100_0038 (2).jpg

[srislash]

I like that, ‘ I have power tools, it will fit’! Must’ve worked on custom Harley’s, haha.

[oldbikerarlo]

Well, things are coming together. Went with a TFL stinger, OSE rudder, and .150 flex cable. The hatch is also under construction
.100_0044 (2).jpg 100_0040 (2).jpg100_0041 (2).jpg

[srislash]

Looks good. I like that stinger on there.

[oldbikerarlo]

I need to make a decision on a prop. would a x440 or x438 be a good starting point with my Leopard 3650 1840kv on 4s?

[Fluid]

Depending on your speed and run time expectations, I would consider an x440 a minimum. For higher but reasonable speeds you could go with an x442, m445 or perhaps an m545. But, larger also means less runtime, depends on the packs you use. The boat will need to be set up to run loose to minimize heat.

Where in AZ are you located?


.

[oldbikerarlo]

Thanks Fluid,
I'm just north of Tucson, In Marana.
So a x442 is kind of in the middle. I'm looking at 2-5000mhp 4s packs in parallel to start with. I can enough run time, to warrant the 20+ miles to the lake.
I want enough speed to be able to dial it in but not so much I have to rescue a upside down boat the first time out. I did run nitro boats in the 80's, but things have changed a lot since then.

[Fluid]

It is tough to estimate the amp draw because your setup (flat bottom + stinger) is not common. The last similar hull I ran was a much smaller CBox over 15 years ago but it ran a straight shaft submerged drive and small brushed motor on 7.2 volts. The most common FE monos are deep vees which ride on the narrow surface near the keel rather than on the entire width of the bottom. If the SK boat is set up to run on the last few inches then amp draw will be minimized.

If you ran at the top end of your ESC rating (90 amps) your safe run time would be around 5-1/2 minutes at full throttle. In reality you seldom run at full throttle all the time unless you are racing, so actual run time can be much longer. But....we don’t know for certain what your amp draw will be because it depends on trim and prop size. You should be safe with an x442, but the only way to know is to test it.


.