90 rigger questions

[TonyKilbarger]

I am setting up a 90 rigger and have a couple of questions. First for background, this is hull built a couple years ago by Dave Showers. Don't think there are many out there. It came from Dave with the tub already skinned, all sponsons built, front sponsons have stubs glued in. I am putting a CMB 90 orange head in it with CMB Big Belly pipe. I likely will use an add on muffler once I get it going.

Questions:

1 - What pipe length would be a good starting point.

2 - What would be a good target weight for the boat? Feels pretty light but wondered how much others weigh. Completely assembled without fuel it is about 8.5 lbs.

3- Front Sponsons - The tub is 3.75 wide inside, sides I believe are 1/4 ply. How wide should I space the front sponsons from the tub. If I shove them all the way in the sponson tubes, it is 7 1/4 inches left, 6 7/8 right. I'd have to cut the boom tubes to go narrower, wondered if wider or more offset would be a good idea.

Thanks

 

[dr gary turner]

I am setting up a 90 rigger and have a couple of questions. First for background, this is hull built a couple years ago by Dave Showers. Don't think there are many out there. It came from Dave with the tub already skinned, all sponsons built, front sponsons have stubs glued in. I am putting a CMB 90 orange head in it with CMB Big Belly pipe. I likely will use an add on muffler once I get it going.
Questions:

1 - What pipe length would be a good starting point.

2 - What would be a good target weight for the boat? Feels pretty light but wondered how much others weigh. Completely assembled without fuel it is about 8.5 lbs.

3- Front Sponsons - The tub is 3.75 wide inside, sides I believe are 1/4 ply. How wide should I space the front sponsons from the tub. If I shove them all the way in the sponson tubes, it is 7 1/4 inches left, 6 7/8 right. I'd have to cut the boom tubes to go narrower, wondered if wider or more offset would be a good idea.

Thanks Pipe lenght, 11 3/4 to 12 1/4 depending on the motor, Prop and amoujt of nitro. The weight is good. The off set is plenty. Many hulls run NO off set. Leave the width as is and try it. If needed then reduce the width. I does not need to be wider. Gary

 

[John Knight]

Tony,

If the boat in question is a Reptile I have raced against them and remember them fairly well. David and Ray (forgot his last name) created the boat and has very similar characteristics with a Roadrunner (RR). The setups were quite similar as well. The sponson spacing for the 90 RR is either 5" for the standard or 5.25 for the Ultralight. The figures you quoted may be too wide. The Reptiles that David and Ray ran were close to those figures. I would be looking at no more than 6" (and probably close to the RR settings) especially with that narrow of a tub.

Pipe length quoted by Doc is also about right. May be going from 11.5 to 12.5" in range depending on the motor and any mods.

Look at a 1667 prop for a good all around 90 prop.

 

[TonyKilbarger]

Thanks for the replies, I have the pipe lengh at 12, the way I have the mount I can easily go from 13 to 11 so that should be ok. I pinned the sponsons last night as they were. I'll try it to see what it does. Not sure what to look for to know I need to go narrower. I know if too narrow they can lift and roll easily.

Plan to run 50-60% nitro. I run 65% in my 21 CMB greenhead Jag 2, 60% in my 45 mac Eagle SGX. I have 60 now so that is likely the blend I will start with.

So far the motor is stock, I plan to send it down to Ernie this fall to have him adjust the rotor clearance ( he checked it before when he was in town for a race and it needs done ) as well as some other mods. He knows how to make the CMB 90's go well and consistent.

I boat with Jim Shaefer so I imagine whatever prop I end up with will be ABC ( but I do have a 1667 for trial : ) ). He threatened to crush my 45 Eagle SG with a sledgehammer when I had an Andy Brown modded Octura on it. That boat now is H18, H22 all the way.....

I'll post a couple pics tonight. The sponsons definitely look RR. The only thing I need now is a cowl. The one provided with the boat was WAY heavy and dead flat on the bottom althought the tub is curved. Not a good fit at all. I'll post dimensions and maybe someone will have a suggestion on one that would be closer. Or I'll dig out some plywood and redo this one.

Thanks again.