skoda450

I am going to compete in the Crackerbox class the summer and I was reading the IMPBA rules for the class. The rules define the ride plate and give specifics about it's proportions. My question is "What is a ride plate and what does it do?" I have designed and built my own boat and I want to konw if this a hull componant that I should incorporate to be more competitive.

CsChuck14

My Feedback: (-1)

what exactly is ''crackerbox class" ?

OLD_SLOW and in the WAY

affectionately known as the Bathtub races

BajaBob-delete

Ask the gas director for your district and/or the CD of your club about the specifics of your boat.The reason being ,not every district/club operates under the national rules,for example some districts don't allow "billet" engines to be used,even though the national rules allow them.

skoda450

Hey...Hey....!!! Us ole farts need a class to run in too. The question was spawned from the section describing the hull proportions, not the engines allowed. CsChuck14; The class is a specific hull design, 1/4 scale of the full size class. It requires a boat 46"to 49" long, 15"to 19" beam with no more than a 5 degree dead rise at the transom, no harware extending more than 4" beyond the transom and two scale passengers weraring helmets and life jackets!! Engines are limited to cantiliver crank, rope start, no tuned pipe etc. All this is easy to understand. I just don't know what is meant by "1/8 ride pad" in the rules.

lawnsplus

The way I understand it the ride pad is a flat surface at the transom and keel. The sharp point of the keel is flattened out starting at the transom say 1/8" wide that tapers to "0" toward the front of the boat. This gives the vessel a "ride pad" at plane with the bow at positive trim. Someone correct me if I am wrong. Hope this helps-John

skoda450

Thanks, That what I thought. The rules further define the maximum width as 52% of the transom at the bottom. I am not sure what affect that limit has on the performance of the hull. Since the hull I run is completely flat at the transom, maybe the ride pad would act like a step and lift the hull slightly reducing drag. I may try it on my next design.

BajaBob-delete

The comment made about the engines was to point out that the rules vary from club to club ,district to district,if you read the entire reply you would have realized that.

The last thing a crackerbox needs is more flat on the bottom ,at 5 degrees deadrise its almost flat as it is,it could use more deadrise if anything.Flatbottom may help with straightline speed ,but you need to get around that corner at the end of the straight,again you questions should be directed to the gas director of you district or local club, just to make sure you don't put a lot of time and effort into a non legal boat.

gashydro

My Feedback: (1)

In IMPBA you can add a sheet of wood 1/8 inch thick to the bottom of the boat up to 52% of the transon width. As far foward as you want?This is what is known as a ride pad in cracker
Email me for a pic
Jerry
[email protected]

gashydro

My Feedback: (1)

Here are a couple of pics of my cracker.
The ride pad is the area in black.
It is a thin coat of epoxy mixed with graphite.The 5 degrees is still maintained.
Jerry

skoda450

Great looking boat. And the pic is exactly what I needed. Do you think that if the ride pad were flat and the original 5 degree hull deadrise was maintained it would still be legal? I haven't done the math but that may be the reasoning behind the 52% max width at the transom and the 1/8" thickness. Interesting variant to play with in any case. Do you race your boat in IMPBA races? The motor looks to be a Zenoah which would not qualify in the rules I read requiring a cantilever crank. There must be "local" rules for your class if thats the case. What kind of MPH do you get from that setup? With my McCulloch 32cc dead stock and the right prop I'm at a disappointing 24.5 MPH max according to my GPS.

BajaBob-delete

Should be getting more than 24.5 with a 32 MacCulloch

skoda450

I have been "stabbing in the dark" so far, in that, the boat is my original design and one off construction. It may be heavier and wider than others and I made no attempt to consider speed in the design. I managed to keep it within the parameters of the IMPBA Crackerbox hull requirements but I did not go to the fastest minimum dimensions. It was "that looks about right" engineering that generated the boat. Number two will take advantage of the lessons learned and tricks of the trade. We will see what happens next year. Mean while, I am going to compete this weekend for the first time. I will not be the fastest but I will be there for the finish. Even if I am last, I'll have fun getting there.

gashydro

My Feedback: (1)

You want to maintain the 5 degrees at all cost .They slide in turns enough with 5 degrees. Flat bottom will be harder to turn.
Also by IMPBA rules any engine that is piston ported up to 30cc can be used. You can use a quickdraw if you want. No tuned pipe.
The only class for cantilevered engines only is the SLS mono class.

skoda450

Gashydro, Thanks for the refresh on the rules. The boat I built does have a flat bottom and does slide a lot. I added trim tabs that work well keeping the turn fin in the water but that slows the boat some. Since I dont have a Zenoah to drop in it, I will compete with a 25cc Hommie this weekend. I just have to stay out of the way and try to finish with out getting run over. I have lots of improvements to consider in making my next design. Let's see, 49" long, 15" wide, ride plate at 52% with 5 degree deadrise, surface prop and, oh yeah, a G26PUM.