Holiday Build Hydro and Marine Intruder MK II

[megalops]

Ok I finally have some time to post my first ever build and Christmas is fast approaching. I looked around to find a hull that IMO would handle well in turns and still have good top speed. So being the Software Nerd I started a spread sheet with some of the most popular MFGs and their cat offerings. In my mind a wider beam to length ratio should equal better stability and thus handling. So in early November after a lot of "analysis" i went with H&M Intuder Mk II. Its specs are 950mm or 37.4 in Long and 305mm or 12 inches wide. The other factor is I dont think there is another full build example of this model here on OSE.

Anyway this hull has an extrmely low CG from top to bottom. So it should not be easy to roll. When I received it and pulled the hatch I was suprised to see how tight it was. Like most other newbies before I got my hands on it was TWIN. Oh well, i mean it can be done but i opted for simnplicity and went with a single engine setup. Here ae some of the main items i purchased.

First the ever popular Leopard 4082 1600 kv motor. After talking it over with some of the pros mainly the "Teakman" I figure it will be a mainly a 6s boat. Seaking 180 esc. FDM all-in-one 21EGSRA Hardware. I was looking for an strut rudder combo where the rudder was offset and FC was "out of stock" on the offsets. Again the FDM was a little pricey but it looks like its real top notch hardware. It also has a real nice "break away/pop up" rudder and a "lifetime" warranty. hmmmm i guess I'll see. I live down here is south central florida and we have some huge live water hazards here. So here are some pics of the hull to start with. Got the CF FC motor mount that is designed kinda for the Leo 40mm Long body. Got the OSE CNC Aluminum servo mount and a few other items and surprises. More to come.

photo1.jpgphoto2.jpgNew Intruder MKII Top better.jpgpreBuildRear.jpg

[megalops]

Like i said this Hull has a super low profile, so before I ordered the motor and mount I had to take some careful measurements. There was only about 76mm of clearance on the inside between the tunnel top where you would mount the motor and the Highest point on the inside of the cowling. while I was at it I measured to find some critical marks for the centerline and horizonal cg. The CG of the clean hull is forward of the traditional 30%. Its a 37 in hull where the CG is at about 13 - 14 inches from the transom almost exactly where the H&M sticker/logo is under the cowling. After some careful calcs using the specs of the motor mount on the FC site It looks like the Leo and the mount should fit.. Barely.CGTape2.jpgcgTape.jpg

[megalops]

Next I had an idea to create a mount "adapter" that sits between the rudder mount bracket and the transom. The idea is if I ever decided to change out the hardware with different mounting hole specs i could simply use the same mounting holes in the transom instead of filling and redrilling. Of course you have to have a second blank bracket to get it done. Anyway I decided to use Aluminum to add some "bling" as well. So next I embarked on a three day exercise in learning to use Freecad and designing a usable bracket drawing that a machine shop could understand. the attached photos are a screenshot of the design and some exported design pics.

ScreenShotBracket.jpgfinalFrontHoledems.jpgfinalAxioWdems.jpg

[megalops]

So after the drawing I decided to make a mockup of the transom adapter before sending it to be made. Cut out some cardboard and used some good ole two sided tape to secure the whole setup to the transom to get a feel for placement. Its a good thing i made the mockup. Turns out it was a couple MM too tight. I wasnt concerned with the thickness since I was using a a 3/8 in piece of aluminum stock roughly 9.5mm.

tmockWide.jpgTMockPropDepth.jpgtransomMock.jpg

I also wanted to reinforce the transom with a piece of Hobby plywood. I knew going in that just getting to the actual transom was next to impossible so I decided to cut an access hole in the bump so i could at least get my fingers in there to do some work. I made yet another template as a guide to cut the transom out just in case. Used the dremel with a drill bit to cut a bunch of holes around the perimeter then put in a GP cutting bit to finish the hole. Used the small sanding drum to clean it up.
PretransomCutout.jpgtransomCutout.jpg

[CornelP]

Excellent hull, very stable at high speeds and nice careful work so far...
Just one word of advice: H&M quality is not what it used to be: my Intruder broke open in a crash because the joint was not done carefully. The FG strip inside did not have enough epoxy in a couple of places and this is exactly how it broke... Do yourself a favor and reinforce the seam with another layer of glass and epoxy. See the attached pics.
Another thing: it really likes to have the weight far forward, it's much more stable at speed. With a Leo 4074 on 5S and X442 I got a 105km/h.

[megalops]

Hmmm, wow i see! Yes I am going to reinforce it a bit. The hatch lid seems kinda thin as well but it fits really nice and tight. I will try to reinforce the seams but as you know you can only get a little way up the hull.

[megalops]

Now i have the transom reinforcement in. The pic is kinda bad. If you look down in the "hole" you can see the plywood.

transomReinforcment.jpg

[megalops]

Next on the list was to create a sort of Motor mount reinforcement. Again I first thought about using aluminum in some sort of rail system. Nah, too much hastle. I am in a hurry to get her on the water. I then decided to use some of the thicker hobby plywood to create some pads that are groved to allow the CF rails to slide into and give the setup a better "footing". Here i used my table saw to make the "slotted slats". I went ahead and glued in and secured the slats. For now The Motor is still able to be taken out but is lined up well.

MotorAndTubeBrace.jpgCenterAlignment.jpg

[megalops]

Meanwhile while the bracket is off getting done I moved on to mounting the motor and stuffing tube and support. Since this boat has a way forward cg I figured the motor should be forward as well. I made numerous measurements to be sure is was close. I got a great tip from Tiqueman to assist i getting the hole for the tube in the right spot. He suggested using a straw slid over the motor shaft. I set the motor in my "best" location. Cut the straw a little long to the approx spot where it touches the hull. Then made my mark. I used the smallest straw you can find that just fits the shaft. It keeps the straw closer to true.

StuffingTubeAlignment.jpgStuffingTubeMotor.jpgStuffingTubeMotorSupport2.jpg

[megalops]

I finally got the new bracket adapter in just in time. I had 2 made. One that is drilled and tapped for my current FDM strut/rudder combo and the other has the transom holes drilled but the bump is blank with no holes. I guess this adapter has a couple of benefits. The biggest is strength. Second is the ability to change the hardware without having to fill in the old holes and redrill.

Man installing this bracket with 7 mounting holes in this super tight space was an excersize. I designed it to use 7 4-40 cap heads bolted thru the transom. I bought both self locking and blind nuts not knowing which would be easiest. Turns out the blind nuts won out after i figured how to install them.

I used double sided tape to preset the bracket in place. then i unbolted all the harware except the "T" that holds the strut and rudder. Made drilling a lot easier. With the adapter in place I drilled the pilot holes. Then i removed the setup and drilled them to size.

After pulling my hair out for an hour with the blind nuts and hemostats and everthing else i could think of - I took the dremel and from the inside i widened out the back of the hole so I could press the blind nut in the hole with my finger. Then i gently slid in the bolts and bolted her up..

New Bracket.jpgtbracketPartialInstalled.jpgtbracketInstallPic1wDSTape.jpgbracketHolesDrilled.jpg

[CornelP]

I found another decent solution: the transom was doubled with a piece of 4mm aluminum cut to shape. I then drilled and tapped it from the outside... very easy to install / remove now.

[megalops]

I found another decent solution: the transom was doubled with a piece of 4mm aluminum cut to shape. I then drilled and tapped it from the outside... very easy to install / remove now.

Hmmm - what a great idea!

[properchopper]

I found another decent solution: the transom was doubled with a piece of 4mm aluminum cut to shape. I then drilled and tapped it from the outside... very easy to install / remove now.

That's a technique I have used before. Good stuff - easy to do and eliminates the problem which occurs when the bolt seizes in the blind nut and causes the nut rotate with the bolt. ( once that happens you're in a bad spot - if you absolutely have to use a blind nut, go stainless with the nut and bolt, put some anti-seize on the joint and use a lockwasher).

[megalops]

I finally got the "Rear end" installed with the adapter and bracket mounted up. Final Pic with bolts in. It turned out good.
FinalBracket.jpg

Next on the list is the stuffing tube/drive line. At this point the CF motor mount is still loose so I go ahead and set/expoxy in place in the slots on the already installed ply "feet". The hole is drilled for the stuffing tube. On the advice of my expert source I went ahead and made the hole sorta oblong oval about 3/4 to 1 inch before bending the tube. The dremel made short work of that.

I searched the OSE forum for advice on how to correctly bend the tube. The problem is there is no real answer. You see some that use the "anneal" method by heating the brass till pink then cool it in a cup of water then bend. You see people who have dont it for years and never had a problem bending the tube as is. Then there is the "sand" and "sugar" methods to keep from kinking the tube. Oh well - i choose the anneal method and after it was cool I just inserted the Liner before bending and didnt have a problem. It was suprisingly easy after heating it up. I'm not gonna lie I did by not 1 but 2 extra 1/4 brass tubes for a total of 3. Just in case and since Im total green to this. I did clamp down a 2.5 lb weight and another smaller Jar cap to use as a bending tool. This allowed me to make sure i didnt end up with the beginning of a spring or something. I left the cutting of the tube to the very last bend near the strut. Basically worked from the motor back. Once I had it close I started to fine tune the bends using the flex cable as a guide.

When it was near "perfect" I installed the Kintec stuffing tube bracket. Left that unglued but still in place. I then ran the uncut flex shaft into the motor collet, mixed up some glue and glued it in. At this time I also installed the CF ESC mount in front of the motor.

tubeHole.jpgTubeHoleandTubeb4Glue.jpgTubeHoleandTubeGlued.jpg

[megalops]

Well I can see the maiden run coming up. On to cutting the flex, Steering and Plumbing. So next i cut the flex shaft to length. Again I had no idea on what was required on this crucial peice of the project so again I researched OSE and the web for some clues. On OSE there were some who recommeded either tinning (soldering) the area to be cut to prevent fraying or unraveling. Others used epoxy and I think at least one member welded his. So to the phone again to talk to "Tiqueman". He suggested to just cut it to length with a High end dremel metal cutoff wheel and then carefully bevel the cut end to remove any snags and to ensure that it slids smoothly and easily into the collet. So first I setup my strut and rudder combo to a "best" postion and tightened it down. Then i slid in the flex cable with washers into the drive line and into the collett. I did it in two cuts to make sure I didnt mess up since I did not have a spare. The first cut was intentionally a half inch too long. After that I re-installed it - measured again with the Micrometer and made the final cut. All good!

Next was steering. I already had the rudder on so using a blank steering rod I found and marked the transom hole location and the servo location. Before continuing I set in the aluminum servo mount. For this application i used a laydown type mount. I drilled a pilot hole for the steering boot. As luck has it the hole was directly over the seam in the transom and the drill would not cut straight. It would hit the seam and then wander either up or down. i decided id better use a rat tail file to finish the job before the hole became a problem.

While i was busy drilling holes in the transom i went ahead and drilled and installed the water inlet.

steering 2.jpgsteering 1.jpgsteering and water.jpgwaterInlet2.jpg