Darin's RECOIL 26 "N2-Offshore" Modiciations

[Darin Jordan]

Well, in traditional form, I can't leave well enough alone!

Received my Recoil 26, took it out of the box, and started the modifications.

The Plan: Setup the Recoil 26 to be a legal NAMBA N2-Offshore Racer.

NOTE: "Self-Righting" hulls are legal in NAMBA, but using the Self-Righting feature during a race isn't. HOWEVER, As I'm finding out about some hulls, like this one... Often, Self-Righting hulls have another feature: They don't tend to go UPSIDE DOWN in the first place! So, on we go with the transformation!

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First Order of Business, Add some control surfaces to stabilize the hull at speed. I added a second set of Trim-Tabs by taking another stock set and removing the turn-fins from them. Pretty basic.
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[Brushless55]

That should be a fun little bugger !

[Darin Jordan]

Knowing the NAMBA rules as I do, I recognized that the strakes were not technically legal. They were quite concave, and there are limits to how much concavity they can have. Plus, in my experience, concave strakes make for "silly" handling at speeds. So, I filled them in using some lightweight, water-resistant Featherfill, carefully applied with a flat blade to get them leveled out. Took about 20-minutes to apply and another 30-minutes or so of careful block-sanding once set, and they were pretty much ready to go.

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Another thing I've learned about Monos is that running the strakes all the way to the back, on a smaller boat that is likely way over-powered, tends to lead to a boat that is way too light on the water. Ray Fuller used to say, when referring to the handling of a Mono, that "part of the hull MUST stay in contact with the water". In order to keep the last couple of inches of the keel in touch with the surface, I removed the lower strakes approximately 4" forward. This is as far forward as I could without having to redo too much on the interior.

BEFORE removing the strakes, I filled in the recesses on the INSIDE of the hull with Epoxy and Milled Fiber, then laminated some light glass over the top of that to hold it in place. You WILL break through the hull when removing these strakes, and this prevents a hole.

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Once that was set, some simply sanding in my disk and belt sander, followed by some finish-up hand sanding, and they were removed.

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[Darin Jordan]

With the hull ready, I decided I wanted more turn-fin, so I took a set of IM31 turn fins and some L brackets I had from another project, and simply bolted them on. Removed the original fins, of course.

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You'll note that I replaced the rudder as well. This was NOT necessary, but I screwed up the stock one trying to modify it to get a better pin-fit. Ended up putting an assembly together from spare parts I had laying around from other development projects, etc. Still has slop, and has WAY too much Wedge angle, but for now this will work.

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[Darin Jordan]

That pretty much takes care of the hull. I'm going to just run the stock strut and bracket. I did replace the flex cable with one I made. It's a .150" cable, but the propshaft length doesn't allow for the range of props I wanted to try, so I built my own. Again, not necessary, but I'm looking ahead.

Now, onto the power system.

First, I replaced the Radio System with, what else, Spektrum. Put in an MR200 and am using my DX4R-Pro. Boom. Done.

Also, replaced the steering servo with a stock servo out of my Zelos 36. The Zelos Servo is 148 oz-in and is digital, and is also a bit faster. A little bigger too. Can't have too much servo, in my opinion.

All just drop into the stock locations.

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[Darin Jordan]

For power, I pulled out the stock outrunner, which really helps the self-righting feature work, as well as the stock ESC. Might find their way into another project at some point.

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I replaced the ESC with a stock Dynamite/Pro Boat 120A unit out of the IM31. To fit this, note that I had to remove the lip at the front of the stock ESC Tray. Just broke off the edges using some pliers.

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[Darin Jordan]

For motors, I selected the TP 3630 in an appropriate KV for N2-Offshore (2S, up to 10,000mAh). I'm retaining the stock weighted coupler, as it'll help the self-righting feature continue to work, hopefully, with the in-runner motor and an appropriately sized set of batteries (the weight on the left side is what helps in this regard.)

Simply bolted the motor to the stock motor mount, attached the flywheel, and reinstalled.

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That's about it. Bolted everything in place, installed a 2S1P 6600mAh pack, and she's ready to test.

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[Darin Jordan]

First test was successful. Took the boat, as pictured above, to work yesterday and gave it a shakedown. I wasn't able to video it actually running, as I was alone, but I did capture the self-righting tests. It's not quite a slick as the original setup, but it does flip over:

[Darin Jordan]

Another try:

[Darin Jordan]

That's it for the moment. I'll try to get some video of the boat running.

I'm happy to report that it does run VERY well. With the smallish X537/3 on there, it was hitting a legit 40mph or so and was rock stable. Turns VERY well to the left. To the right, if you turned too hard, it would pop the prop out of the water and hook a bit. We'll work on tuning that out.

[arrover]

Cool project!!!

[T.S.Davis]

Good stuff Darin.

What did you decide to try for KV on the TP motor? I have a couple options I've been tossing around but nothing that I think is great. Mostly too hot. haha I can't run my 1515/.5y in offshore. A tic much.

[Darin Jordan]

Good stuff Darin.

What did you decide to try for KV on the TP motor? I have a couple options I've been tossing around but nothing that I think is great. Mostly too hot. haha I can't run my 1515/.5y in offshore. A tic much.

David Newland formula for Offshore... ~3600KV-ish... Mine is a TP 3630-3Y, which is 3480KV. There is a little bit hotter one, the TP 3630-5D, which is 3861KV, but I wanted to keep it a bit mild, not knowing exactly how the hull would react to 2S2P 10,000mAh. Also like the way the power systems react on Y-Winds vs. D-Winds.

I'm hoping to get buy with a little less battery. Also, I'm hoping that the hull itself will just run and run, and could make up for lack of shear speed with handling and staying upright in questionable water.

I'd rather be able to PEG the throttle and just steer the boat at a reasonable speed, than overpower and have to manage both a throttle AND navigation at the same time. Lap times improve when you can do that. There IS the concept of having TOO much power and TOO fast of a setup.

[T.S.Davis]

With the lower KV you'll be able to put more blade in the water too. With all the turns in offshore getting out of them matters.

[Darin Jordan]

Finally got some real testing on my modified Pro Boat Recoil 26. This is a TP3630 motor on a 2S 5000 mAh Thunder Power 65C pack. Pack is old and was pulling down in Voltage pretty bad, so speeds aren't where the will be with better cells.

Still, the boat rips and is seriously difficult to get to go upside down.

Need to give it another go with better cells. There is another 1,100 RPM or so I'm missing with these old batteries. New ones should liven it right up.