Twin Outboard Vs Single Outboard Efficiency

[Sims]

Here's a few pictures from the build. My inspiration came from what i remember of watching off shore power boat racing as a kid. Once a year they'd all converge on Taupo –which was heaven for a petrol head father and son.

I decided from the get go that i wanted a boat that would run in all conditions, so the bow is a very deep vee, that gradually softens as it runs towards the transom. I built in a hefty reverse chine, to help her rail around corners –It also seems to add stability. Finally i added two steps into the hull, with side cuts on the chine to allow the air in.

I built the whole thing to scale out of cardboard first to help visualize the shape. Then it was straight into the real thing. Its all built out of balsa, because thats all i had at the time. Consequently it is pretty light, but structurally i think it'll need some work before re-powering. At this stage I'm considering a very light layer of fi-glass on the outside, just to beef things up.

[Avanti]

very nice

[Sims]

Yep, another kiwi by the name of Simon too! – I'm based in Auckland
I'll attempt to answer your Qs now. :)

The boat is 33-inches long, and fairly light. In its current form it runs an Aquacraft ep1 outboard, powered by a 27t 550. Powering that is a 6-cell NiMH battery, and a traxxis ESC capable of running 7-cells. Given that everything currently runs cold, or just warm i'd say its very under driven. Radio is basic futaba kit.

At present I'm probably more interested in the 'project', (hehe) but more speed is the new project quest. Given the Ep1 was a very modest pace, i was hoping phase 2 would get me to around 40~50kph. There is a little bit of sibling rivalry, with my brother building a nitro jet boat, but given his boat is looking more like a dingy, i think i've got this one in the bag.

I don't mind spending a bit of coin, but i prefer to spread it out. For example, i was considering getting all the drive hardware and rudder setup, while still running my current ESC and 550 brushed electric motor. Then once the bank balance is up again, investing in a brushless motor and brushless ESC.

The only combo i'd thought of at present was the SV27 twin battery brushless setup. A) because i have two batteries and don't want to buy Lipos. B) because it seemed to work well, and i didn't know what other options where there!

My first problem is deciding what to do with the back end of the boat. You can see in the photos it has a nice little motor well in the back. However this doesn't leave much room for bolting on s rudder, and it creates a massive bottle neck for fiddling with nuts and bolts on the inside...

[Stealth Assassin]

I say If you like outboards and don't want to mod a lawless or k&b then buy a rek ob lower unit from fullers that Is ready for a brushless motor. They don't cost much... Then you will see her get up.

[ED66677]

Very nice boat!

[Sims]

The outboard is now repowering a tiny childrens toy boat. :D
Should be entertaining.

Brushless power for the other one, once i get around to rebuilding the transom to take a rudder (fabricate or purchase hrmm). Thinking maybe a Feigao 540 XL, not sure on ESC yet. Will run dual NMiH batteries to begin with –*Means i don't have to invest in lipos and new charger just yet.

[j.m.]

Try these:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4936&Product_Name=KB45-10XL_1200kv_Brushless_Inrunner

That motor is rated for three times the power of the XL feigao's, and it's cheaper.

Here's a descent ESC:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=3728&Product_Name=TURNIGY_Plush_100amp_Speed_Controller

Hardware package:
http://www.offshoreelectrics.com/pro...?prod=sol-mono

You'll also need a flex cable and stuffing tube.

No need to buy lipo batteries. Plenty of boats go REALLY fast with "regular" cells.

But 12 is kinda on the low side. i would do at least 14 cells, but i don't know if you want to buy any 7 cell packs. You could go all the way up to 24 cells if you want to stay with 6 cell packs.

If you went the 24 cell route, then you would need to upgrade to this hardware:
http://www.offshoreelectrics.com/pro...od=ros-monosys
and this esc:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=4691&Product_Name=TURNIGY_Sentilon100A_HV_2-12S_Speed_Controller

[Sims]

Thats just the sorta info i'm after! Nice work J.m.

The boat is quite big, so i was thinking about the stinger strut hardware package. What else would i need to complete the hardware – bushings, motor coupling, prop, stuff tube? Is strut assembly very complex? Once i've got a tray of all the right bits it should make sense, right? (I tend to be a hands-on thinker)

I'll keep an eye out for some 7 cell packs locally, as i will be able to use them on other gear. There's no reason to purchase an ESC specifically designed for twin packs is there? (eg proboat or aquacraft) I could just use an adaptor cable to run them in series. And cheers for the heads up on the motor and ESC. Just what I'm after, i'll keep those in mind.

Time to re fab the back of the mono this weekend. The outboard motor well in the transom, creates a major bottle for fitting gear on the inside. So the thinking is to trim off the whole transom, rebuild it in light ply and reshape to provide enough room to mount the rudder.

POWER!

[j.m.]

Yeah. The KB45 XL has (at it's maximum power) a little more than 4 HP! It'll make that hull fly.

Here's all the other gear you'll need/want to complete the hardware setup:
http://www.offshoreelectrics.com/pro...rod=ose-str-ci
(6mm to .150)
Select the .150 cable size in the drop down menu for the hardware.
http://www.offshoreelectrics.com/pro...od=ose-drmount
http://www.offshoreelectrics.com/pro...prod=aero-2010
http://www.offshoreelectrics.com/pro...-jacket&cat=66
http://www.offshoreelectrics.com/pro...=ose-wide-tabs
http://www.offshoreelectrics.com/pro...d=ose-monofins
fool around with these to find the right one,
http://www.offshoreelectrics.com/products.php?cat=58
then get one of these that matches the dimensions of the plastic one:
http://www.offshoreelectrics.com/products.php?cat=45
http://www.offshoreelectrics.com/pro...od=oct-oc6pnmm
http://www.offshoreelectrics.com/pro...dh-ks-brass-tb
get the 1/4"

[Sims]

Well i've now cut off about 2 inches off the back of my boat... (eek!) As that was the easiest way to get rid of the low transom and outboard motor well. As its turned out, its been quite beneficial because i've rebuilt a lot of it in light ply, rather than balsa.

Seeing as our exchange rate has been quite stuffed against the US, i've opted to temporarily re-power it with bits from my parts box... and i managed to scratch build an alloy rudder than buying a new one.

Finally coming together again, :)

[Sims]

Just a little update:

The inboard setup was rubbish - terrible hole shot and a similar top speed. So it was back to the drawing board.

I decided if I was going to step it up, it needed to be a big step. So off we went shopping. Now its got a big XL brushless can driven by 16.8v, pushing a 68mm triple blade prop. There's still a little bit of trim work needed, but I'm very happy with the result and speed. Finally feel like I've got the hull working how it was designed too. I've run it in some fairly choppy water water with great results.

http://www.youtube.com/watch?v=03wjXgKXIB8