Simon's Balsa Cat

[domwilson]

I think the main point of the steps is to reduce the "wetted" area of the hull. The step introduces a "bubble" under the hull to reduce contact with the water which in turn reduces drag. From what I've read, you will need sharp edges on the steps to have a clean break in the water. Rounded edges will create a vacuum which will increase drag. I think "b" will cause the bow to ride a little high and may require a little negative degree on the prop angle. Not neccessarily a bad thing depending on water conditions. But I could be wrong.

[crabstick]

other thing to consider is these steps are used on full size race boats where drag is a major issue, Water does not scale down so steps may or may not be a waste of time on a boat this size. just food for thought.

[Simon.O.]

I considered running it as a 3-pointer but decided that I have enough of those already. 2 riggers and a hydro.
I can always cut/sand this build back off and go for a 3-point if it is a pain with the steps.

Today we have flattened the front steps and built up some new middle and rear steps.
I know this is a very different looking bottom to most cats and that is because the design is constanly changing.
I can build this back to a fairly normal looking bottom quite easily but I am keen to have a play with this step setup first.

The steps ar made out of 4mm thick sheet and are this way so I can sand them down to change the ride attitude if needed. I can alter the AoA and flat ride area of each with a sanding block. Worst case is they come off and I am back to the begining.

I can see also that I may have some high speed cornering issues with the flat sides to the middle and rear steps. This can fixed by adding sheet to the outer half of that rear area and clever sanding.

It should hit the water in a few days as soon as the weather is better.

Todays work.

[peells]

That looks nice I was thinking of doing an all wood look if I could get all the prefect wood and grain structure to my liking, I was thinking of adding a few discreet pin stripes maybe a couple of cool decals and that would be about it. (old school) I really like the look of your work and you did not cheat.

[Simon.O.]

Peter, thanks for the compliments. PM Graham Doggett and he will tell you what my hulls really look like.

This is as good as a new hull, so I had to treat it as such.

First run. Shaft a little above the sponson line and neutral. 540-8S fed with 2S to a 432 prop.
I put my old “test” pack in, this is a near rooted polyquest pack and has no punch off the line and not a lot to offer on the straight. I use it to see what a hull will do on low power.
It ran wet and I was not impressed at all.

Second run. In goes my Zippy 5Ah 20C pack. O.k that wakes it up a lot. It is still very wet at the nose and well planted on the water. In for a strut tweak to give a little positive (bow up) and out it goes again. That is better. Now it looks like it may loosen up a bit. 3 good passes and in for a prop change.

Third run. Now sporting a 632 in it went for another run. Now THAT was a difference. It now ran nose up and on the last of the ride pads. There was no skip, hop, jump, or any of the craap that I have dealt with over the last year with this hull.
Into the wind ( enough breeze to lift at least 2” chop) and this Cat was a beautiful thing. Running on the rear step and a very slow nose up/down motion as it was trying to find a balance. It looked like many of the big Euro cats that I love to watch.

No sign off blow over yet, these conditions would have blown the old design over well before now.
I will now refit the 12S motor and give that a run. The numbers are very similar to a 8S but the higher wind on bigger volts has the grunt to throw this Cat around. I have a few proven power setups that I can try.

I did not GPS it today as it was a quick run just to see if the new pads work. They do !!

[peells]

Well I can almost see it running in my minds eye, now for a short video Simon and all will be as it should you just have to take a video come on please for all of us (But you do have very good commentaries I must say.

[Simon.O.]

A few more runs today and one thing was apparent, I have lost a lot of the lift in the rear and this is a problem.
I tried two different power setups and the results were similar. 540/8S on 2S and 540/12S on 3S. These are two well proven setups and usually spin a 632 for speeds in the high 60 - low 70kmh. About 42mph.
It was not so today. The strut went here there and everywhere but the speed was not there.

I believe the steps were too big. I have now filled in the steps to reduce the step size and will try them in the morning if the weather is good.

Here is what I have now. Remember, I have a lot of wood and a lot of time.

[CornelP]

I would also be tempted by the addon in the pic... It just feels right...

[Simon.O.]

I would also be tempted by the addon in the pic... It just feels right...

Cornel. I had to look twice to see the additions that you made, thin yellow lines are not easy for me to see.

I like your line of thought, and if I need to add more hull to the rear then I will do it the way that you have drawn.

Thank you again for your input.

[CornelP]

Sorry for the color, same here with yellow, I only spotted it after posting. It looked right in Corel Draw... This could bring it closer to the sort of rounded section I've seen on some big cats...

[Simon.O.]

Cornel, do not worry about the colour.

I will run it as is and see how it goes and then if I need to add to the rear I will be going the way that your "yellow lines" showed !! That way is a lot easier than the later black lines with curves.

I should get a run to the Quarry in the morning for test time.
The big rigger is coming too......70 may happen

[Jesse J]

I was fixin to comment along Cornel's lines, and like the drawings, both yeller and black, but I would not do rounded. It would pull water up and possibly along the sides = rots o drag. Instead I would angle them back to horizontal or maybe a tad neg, like a true spray rail. I think all that angle next to your deep step might cause some suck-shun. I would probably fill in most of that space... but that's just me.

lookin good Simon -

[peells]

you should run twin power you would fall in love with it, I have one little cat I made with single motor setup and it tends to pull to one side but it is fun to run, the twin drive setup it just works real nice and I do mean REAL nice the handling is right there turning is great in either direction, and the single likes to run counterclockwise the best

[Simon.O.]

you should run twin power you would fall in love with it,

I am already in love with twin power and still plan on doing a twin cat one day. I am considering a pair of 400 or 450 outrunners 3000-3500 kv on 3S to 430 L/R props for this hull.

That shopping spree is on hold until I save a bit more for the boat fund. I need a new 4S pack for the big rigger first.

I ran this one today with the new steps as seen above and it is a big difference.
It is much lighter in the tail and will run on the rear step alone.
I got 4 passes at or above 66kmh (40mph)
No blowovers and will change direction like a pinball.

I am very happy now.

[peells]

That is just about the exact same set-up we run look around on ebay for motor and ESC combos it will be more affordable, get the ones that have a fan on the back that seems to really help keep things a bit cooler, I got a couple of those 400 out runners with no fans but they were really inexpensive like $10.00-or $11.00 USD each but no esc's with that price, if you click my blog link under my signature you can see a video of my yellow cat which has one of those motors in it, it is a 3200 Kva running an x430 prop.