Help with 90 SprintCat

[BradV]

Took delivery of the new 90 Aerormarine SprintCat today, CMB 1.0 Evo and Speedmaster hardware. Exciting stuff...

Just a few questions I have, hopefully someone has put one of these together and can help.

1. The Speedmaster combined rudder/water pick-up combo, though well engineered, looks to me marginal in water flow capacity for this size motor running a high nitro blend. Was thinking I would need to run an additional water pick-up on the transom. Ie use the rudder pick-up for header and an additional pick-up for motor. Agree or disagree?

2. Smaller radio box than what I was expecting. Haven't put together a boat before where I had to lay servos on their side. What's the best method of mounting them? I was thinking of fabricating an L shaped saddle from aluminium, but does anyone know of an outfit who sells them ready made, or is there a better method?

3 I purchased Octura 460/3 and 462/2, and Prather S-265 props to teeth on. Did I go too small?

4 No pipe mounting bracket came with the kit. Was thinking of fabricating an O ring brace to go on the stinger end and mount to transom with wire and a neat bracket. Does anyone know if these can be purchased ready made?

Cheers guys, any help be appreciated...

 

[Don Ferrette]

Hey Brad-

Since I've built & sold ( I'm a dealer for Aeromarine) a good number of A/M cats here goes-

Took delivery of the new 90 Aerormarine SprintCat today, CMB 1.0 Evo and Speedmaster hardware. Exciting stuff...

Just a few questions I have, hopefully someone has put one of these together and can help.

1. The Speedmaster combined rudder/water pick-up combo, though well engineered, looks to me marginal in water flow capacity for this size motor running a high nitro blend. Was thinking I would need to run an additional water pick-up on the transom. Ie use the rudder pick-up for header and an additional pick-up for motor. Agree or disagree?

Single pickup in rudder will work great. Been there, done that, many times with CMB big blocks. The water jacket is rather large on those motors. Open up the two scoops on either side of cockpit area also & you'll be fine.

2. Smaller radio box than what I was expecting. Haven't put together a boat before where I had to lay servos on their side. What's the best method of mounting them? I was thinking of fabricating an L shaped saddle from aluminium, but does anyone know of an outfit who sells them ready made, or is there a better method?

The L shaped aluminum saddle type bracket is the ticket. The stock Aeromarine ones flex too much.

3 I purchased Octura 460/3 and 462/2, and Prather S-265 props to teeth on. Did I go too small?

Nope. Another good prop is the Octura X465

4 No pipe mounting bracket came with the kit. Was thinking of fabricating an O ring brace to go on the stinger end and mount to transom with wire and a neat bracket. Does anyone know if these can be purchased ready made?

Speedmaster pipe mounts are nice.

Definitely a fun boat, you're gonna enjoy it!

 

[BradV]

Cheers for that Don.

Since my post I found a pic of Speedmaster's 2 types of pipe brackets - transom mount and deck mount. They are neat looking units aren't they. Running a CMB non-silenced pipe that is pretty short (compared to MACS), so will have to size it all up and see which one I need.

 

[Don Ferrette]

No problem, glad to help!!

 

[[email protected]]

Brady,

it looks as though all the radio boxes of today are getting smaller. Here's what I do for servo mounts:

I take two pieces of wood, make them just a little bit taller than the size of the servo laying down. Cut a groove into them. I glue my blocks down into the radio box, after the glues dried, Slip the servo into it. Cover w/a thin piece of plexi glass and screw them down. Now you have quick and easy servo removal should you need to change them.

The beauty of cats is they don't require these fancy props for sport running. I think the props you got are good eough.

As for the water, the one pick up like Don said is good enough, but CMB love water, use large fuel tubing or you'll run the risk of over heating.

Make sure you get a pipe bracket that removes at the tip of the pipe or you'll have a tough time getting in-and-out of the radio box if you don't.

Also, is the front bulk head tall enough to slide a fuel tank up into the nose if you cut out the center bulk head? On my cats I cut out the center bulk head and put my tank up there. Provides for a much better and more stable run.

 

[Don Ferrette]

Actually, if you take a 24oz. Sullivan tank & notch the wedge area of the deck underside in front of cowl opening, the tank will fit perfectly between there & front bulkhead. Put your 1 or 2oz hopper tank on the other side of bulkhead just forward of the motor. B)

 

[BradV]

Thanks Rodney. Yeah still umming and arring about the water scoop size, as Don say's it's adequate, but here where I live water is warm and the air very hot, so I might yet run an auxillary as well.

With the cowl type I've got I can access in front of the front bulkhead, and this seems best place to mount the tank. These boats sure have a lot happening at the rear part of them, so I can see the advantage in trimming them not so loose with tank placement up front.

 

[Don Ferrette]

Brad-

It gets pretty hot here in Virginia too. And mix in that late summer humidity .... yuck! :blink:

 

[BradV]

Thanks Don. What do you mean about a hopper tank exactly? Hear of a few guys running one but not sure of the exact purpose. Spent the last few hours going through all the hardware, the Sullivan Oz tank fits just nice where you say..

:unsure: Got some hassles with the stub shaft being a tad too short. I'm using a square drive, and because I'm mixing Speedmaster and Aeromarine gear, I'm left with not enough extension on the stub shaft after all thrust washers and 1/4in drive dog installed, to secure the 1/4 to 1/4 ferrule properly.

Seems to me the best way around it is to go for a 3/16in drive dog. Would have preferred the additional strength of a 1/4in drive dog, but it solves the problem and just leaves me just enough length to fit the biggest pitched prop I've got. Been through the Aeromarine catalogue and they don't have a longer 1/4 to 3/16 reduced stub shaft, so there's not really any easy alternative. Guessing that the Speedmaster strut must be a bit longer than Aeromarine's...

Gee what's your trick with getting those lead teflon bushes in without use of a hammer or press? I've used needle rollers in the past on the mono's and they weren't that tight! Heat the strut and freeze the bushes I suppose?

Other minor issue is though I've got the right Aeromarine mount pre-drilled and tapped to suit the CMB (according to the Aeromarine packaging), bolt holes through the CMB crankase are too small. Small oversight by Aeromarine I suppose. Will have to give the engine lugs a drill out.. Going to use longer bolts than they supplied too - they only go 1/3 way into the mount. I'm fussy hey..

This time of the year out our way we reach 37-43 deg C (98-105F) no kidding, so I'm going the careful route and fitting that auxilary water scoop... Reckon it will look trick too.

 

[Don Ferrette]

hopper tank- 1 to 2oz tank between main tank & remote needle or carb. This tank stays full even as big tank empties so you don't suck up an air bubble & quit. Anything bigger than 2oz isn't really a hopper as it is big enough to develop air pockets defeating reason for hopper in the first place.

I don't use sq drive. standard 1/4" Aeromarine collet, 1/4" shaft with step down to 3/16" at prop.

I used a small vise to press in the led tef's & both nose & tail pieces on the Aeromarine strut. I have since gone to using only nose & tail piece, drilling out them & passing brass tube all way thru. Then flair & flatten end against tail piece & use the Speedmaster strut bearing sleeve. The brass tube size thru strut will be 5/16", Speedmaster bushing acts as bearing & makes up the rest. If this is a Speedmaster strut blade then you just heat up the strut blade & push the 5/16" tubing thru it, as it cools it tightens around tubing. When you pull the cable to grease it all the grease goes in the tube, not off the end of the strut when you slide shaft back in. Properly set up this is virtually bullet proof. One tip, be REAL careful where you start your tubing bend up to hull. Too close to strut & you'll overheat the solder joint between cable & stub shaft.

I always drill out the holes on my motors, they're always on the small side. Plus it gives you room to shift motor a little. you want the bigger bolt size anyway.

We see 90- 100 degree weather all the time in the summer. You'll do fine with just the rudder water pick up & large size water line.

 

[nitrotoys]

For servo mounts, I would go with the aeromarine servo mounts.

get them from aeromarine, or rocketcityracing.

for the 5 bucks, it makes it much easier to mount and they fit nice.

you can mount them standing up or laying down.

put a sealer on the threads going through the box.

Hope this helps you.

Tom

 

[Don Ferrette]

For $2 worth of aluminum angle you'll have something 10 times as strong. Like I said, the A/M mounts flex too much & will eventually break. I'm even a A/M dealer but I'd rather be honest about it ..... B)

 

[BradV]

Yeah was going to custom fabricate the servo brackets, but today will also check out what the car guys are using on the 1/8 and 1/10 scale racers.. Might get some ideas..

Don one more question, with the square drive I'm using I see after your explanation the obvious differences between standard drive and square drive.

Went for the square drive because thrust is taken up on the strut and not motor, flex bind not an issue and if you break a shaft you don't lose all the gear.

However I see that the stuffing tube with square drive will be just "hanging in the breeze" at the strut end, and not solidly connected to strut like a normal set-up. Doesn't sound too robust to me

 

[Don Ferrette]

Brad I've always been a firm believer of the KIS principle- keep it simple. I have never seen a properly set up conventional collet arrangement fail, and it's set up is pretty **** simple. Now brain farts like forgetting to tighten the collet ... well that's another story in itself.

 

[[email protected]]

Bradv,

the car guys will tell you to double stick the servo down and run a bead of Shoe Goo around it.

As for the hot water and air where you live, could you freeze a small block of ice into a tupperware container attach inlets for your water pick up to run through to cool the hot water before it gets to the head? Crazy idea but I love to experiment w/things like that.

 

[BradV]

Yeah car guys are like that! LOL B)

They didn't have anything decent in the servo mount department but I bought some heavy duty car ball links that I liked, much heavier duty than the generic dubro etc stuff.

Now definately going to fabricate the servo mounts, though the best I could find today was 1mm (3/64inch) thick Aluminium angle. Would have preferred twice as thick but will shape one up and see how it feels for strength and flexing. Not sure of the rudder loads on these cats, but bought the Futaba S9402 super high torque servo for the job, pulls 89oz/inch @4.8V & 111oz/inch @ 6V. Few years ago you needed a 1/4 scale servo for that type of torque...

Like to experiment too, always run a lot of water through my motors, would rather have too much cooling than too little. But I'm a maniac on saving weight in my boats, couldn't justify the weight of the ice cubes..

 

[BradV]

:angry: :angry:

I was just about to begin the build and start with the strut install when I noticed that the back of the SprintCat didn't look symmetrical.

So I've taken some measurements:

Left hand hull corner to centreline - 84mm.

Right hand hull corner to centreline - 94mm.

So a noticeable drift of 5mm to the centreline, not acceptable to me as it will affect the tracking of the boat. Also where do you hang the strut? In the middle of the friggin' boat and it's off the 'v' point by 5mm looks stupid.

Hopefully it's not an issue with all the 90 Aeromarine cat hulls and it's just a one off error AND the supplier will promptly deliver me a new one... Will find out Monday.

Don or others, have you seen this before with Aeromarines products, is this a common problem with them?

Cheesed Off

 

[DaveMarles]

1mm aluminium angle is definitely not stiff enough for rudder servo mounting.

 

[Don Ferrette]

Brad-

It's supposed to be that way. Put the strut in line with the V in the tunnel & keep building, she'll track straight as an arrow. B) B) B)

 

[BradV]

You serious Don? I did check the plans, centreline or 'v' of hull is dead smack in the middle on the plans.

If I put shaft on the 'v' the prop will be 5mm to one side, you telling me that's been done on purpose by Aeromarine???

mmm