Rigger design question

[Simon.O.]

I am now designing and building my own hulls. I have the Hybrid hydro,

http://www.rumrunnerracing.com/feforums/showthread.php?t=25047

A little 21” development hull that I have had a lot of fun with a learnt a lot.
So much so that I built another one that is a little bigger to take 8 cells. That is undergoing refinements and may get some serious mods soon.
I use the little one to test ideas then implement these changes into the bigger one.
Swapping out straight shaft for wire drives is next, now that I have worked out how to make my own for very low cost.
I am still a Nickel and brushes man for now and am having a lot of fun with this hobby, my wife thinks I am nuts.
I do not race or even see other boaters (motorised) at my local pond, so I have no other speed target than “ that looks good” and a rooster tail helps !
I am now keen to go for a rigger again. My last one was a disaster for many reasons.
I have enough design tips from here and the other forums to go ahead with a design and build.
One option is for a traditional Predator / Blizzard type, the other idea that I have is for a longer narrower SAW type. Remember this is not competing straight line speed is all I am after with a moderate turn 05 motor and 6-7 Ni cells.

So for those of you who are still awake after such a long read here is the question.
Long, narrow and flat saw type or conventional “blizzard” type

I have the pencil and paper on the bench and wood ready to go !!

[Mich. Maniac]

I am not "into" riggers but, if I had the water to run one on it would be "blizzard" type. Saw racing is awesome and im glad alot do it but a challenge is what I like and that challenge looks like getting one of these speed rockets to stay balanced and corner at full throttle like a F1 car. Again that is where the challenge would be. Since they are soo fast and light, carnage is a given I imagine. Good luck and hope you start a build thread here for us to watch!

[Simon.O.]

I am now ready to design the sponsons.
There seems to be 2 popular styles for rigger sponsons, one is the more traditional shape with a flat top, flatish sides and a forward rake in the transom.
The second type I have noticed is much curvier with a sort of step at the rear similar in side profile to a cat overhang ( does that all make sense ? )
i know that the rinning surface is the important part and i am all happy with my concept so far, all I need now is to decide if I go with a "traditional" rigger or for a more modern "space age" look like the pic here of the Xzess hulls.
Of course I will not end up with one like that, it will be sort of a blend of old and new.

[NorthernBoater]

For your first boat I would just go with the Blizzard style of hull. It would be simpler to make. I am working on setting up a Blizzard Rigger this weekend and I can give you some input on the design.

[Simon.O.]

This is certainly not my first boat. I have one nice classic hydro running now and my smaller hydro that is used as a test rig. It gets mods every other day to trial new ideas. I had arigger last year but that was not a success for a variety of reasons that I have now overcome.
Don't get me wrong, I do like the Blizzard and actually have a set of plans for the Predator too. I am wanting to make this boat "mine" so it will be a little different to those two.
Naturally it will look a little like someone else's boat but that is unavoidable. I mean a rigger is a rigger and they all have some similarities. Look at the blizzard and Joerg's monster, to the casual observer they are the same "type" of boat.

I now have another question....hmmm should really have the title "Rigger design questionS"

Regardless of the sponson shape I am inclined to put the water pickup in the rear of the sponson. This will mean running the water to the tub across or through the spar.
I see some riggers have round alloy or cf booms / spars and some have a wing / foil shape spar.
Pro's and cons of each please.

Always keep in mind this is not a "class" boat or a record hunter.

[J Solinger]

Having the water pick up in the sponson doesn't work very well. The idea is that the sponsons rarely touch the water and can leave your esc and motor dry long enough cook them. I'm speaking from experience.

Here is a photo of my personal favorite sponson type. I like them because they make for a flex free fin mount and it functionaly adds floatation. You can see the threaded hole inserts for the turn fin in the photo.

[Simon.O.]

Joe, you have put up some of the most valuable info for me so far, thank you.
The sponson shape you have is clearly a sucess so I will most likely use that style of profile with a little more downwards sweep at the back. I fully agree with the logic of the design for the tf mount, that is if I actually run a tf.

The water pickup idea still needs further investigation for this design / build.
Here is some of my logic.
Running the water forwards all the way from the stern may not be as efficient as running it sideways from the sponson.
The sponsons on my test hull do spend enough time on the water to provide a fairly steady flow through a variety of pickups.
The ram fed water pickups on my home-brew hydro do a splendid job.
I think the reason for this is that I am running brushed can + Ni cells + plastic props so am not really getting world class performance with a flying sponson.

With a j-tube pick-up taking prop blast can I expect to flow enough water 12+" forward to the motor?
If so, then I'll do that.

I am not trying to re-invent any wheels here, I just want to build a rigger that I understand why it is built that way............................and run it !!!!

[J Solinger]

I am not trying to re-invent any wheels here, I just want to build a rigger that I understand why it is built that way............................and run it !!!!

I understand completely. Thats alot of the fun part.

With a j-tube pick-up taking prop blast can I expect to flow enough water 12+" forward to the motor?
If so, then I'll do that.

Oh yeah. You will have plenty of water presure and volume from a J tube. But, it's good to see you thinking about alternatives to the common methods. WTG

[Simon.O.]

We are getting closer.
I have the sponsons made and am now working on the tub.
The hardware is coming along well too.
I am using the Balsa Hydro as a test rig to try a few weight and balance ideas.

Here is the big one for my rigger project.
What is the common distance between hull and sponson.
Is is a function of length ?
It is tub width plus "X" ?
Is is it "that will look cool on the water" ? That is how some of my designs happened
Any tips for this one.

This is for pure amusement at the pond !.....no saw records for me.

[J Solinger]

A good balance would be any where between 25% and 35% of the over all length measured between the inner edges of the sponsons.

[Simon.O.]

Joe, as always you come up with some gems.
I am trying to picture this, let's see if I have got it right.
Take the outside of the tub to the inside of the sponson and we are looking at 25-35% of the LOA ( length-over-all )
If this is correct then my guestimate of "that looks o.k" is very close to the mark.

I have these questions here and over at rrr to spread my feelers as such.

I am begining to think that I may have a fairly usefull design that is ready to to be built, well completed as I have the sponsons made already.

I am trying to source a 17-19t brushed can as I have had a lot of success with my latest 23t can in the hybrid-hydro running 6 cells and a 531 prop.

I'll get some pics up of this latest mad machine when I can.

Thanks you everyone for the help so far.

[J Solinger]

I accually mean the distance from sponson to sponson is about 25%-35% of length over all. They can be made much wider but that creates other possible problems. In your case, where you are designing for a brushed car type motor, keeping it in this narrower range will provide better stability. It will be easyer for the hull to stay fully air born on three points.

[Simon.O.]

Here are a few pics of a possible layout.
The sponsons are at 240mm inside to inside
Sponson to tub gap is 90mm
The LOA is 630mm
So we are near the reccomended 30%

Next question is regarding attaching the sponsons.
Do I go for the traditional Tube type or for the more modern (xzess ) mini wing type, with a foil cross section?
Pros and cons of each please.

[J Solinger]

It's taking shape, looks good. I have only used the round tubing for sponson booms so I can't tell one is better than the other.

One thing that I noticed is that the sponson angle of attack looks low. When the AOA is to low the sponsons will suck onto the water and your boat either won't plane or have a very hard time planing out. In this perticular case I would use 4 1/2 degrees.

[IMG][/IMG]

[Simon.O.]

I agree that the AoA looks a little flat. This was only laid out on the bench to get an idea of what the little bugger would look like.
In my notes I have AoA angles ranging from 2.5 to 5 degrees.

I have not decided on sponson attachment at this point but am leaning towards a symetrical airfoil high aspect ratio wing to do the job.
Either way I go I am keen to make the front boom / wing adjustable so that I can play with AoA adjustments My reason for this is I am now at the point where I understand a lot more about altering the hull AoA on my hydro to alter the lift in the front.

If I can alter the AoA of the tub and the sponsons independently then I will have a far better chance of fine tuning this hull.

On that note I have taken the advice of a senior FE boater and am now keeping a diary of changes and alteration especially for the Balsa Hydro so that I can track progress.
One tiny tweak means the difference in launching out of the hole and a prolonged tail drag before the plane.

I really anticipate a lot of adjustments in this boat before I am done.

I wonder if I will be able to scale it up to a 700 12cell beast.