Reducing weight by using Kevlar or carbon

Or

Put in several interlocked VERY thin & narrow plywood frames. Also known as eggcrateing. Car people call it monocoupe framing.
You have learned from the first boat where more bracing is needed.
In sharp turns the motor is really trying like crazy to cause the boat hull to lean / bank into the turn. The rear of the hull is taking the full twisting force of the motor trying to lift the outside corner of the boat.
Unfortunately the tunnel hull shape is great for speed. But the weakest shape for withstanding cornering stresses.

More beef & diagonal bracing in the rear. Maybe you can shave the weight gain in the back from somewhere else. Like in the center area?

Strength in the bow for waves. Strength in the rear for the motor trying to twist the transom right off the boat.

Remember the stern is twisting in one direction. If you hit bow waves that try and twist the opposite way................Bad things can happen.

Also. If you are worried if the hull is going to survive......You are not fully concentrating on the race as a driver.

You need a attitude of " Screw the chop! My boat is tough. Lets race. "

 

so kind of like an arch in an aquaduct?

well i have been known to brake motor mounts in the past the weakest point breaks first eh! it is a famous stunt boat after all.

The center panel is where I sit and it all ready has more flex than I like.

 

Those FG Flivers are some of the most wastefull uses of hull space.
Is there ANY solid reason why a simple board / brace cannot be Epoxied to the very back ends of the flotation hulls? That would be simple & Spread the motor twisting force over a huge area.

 

There are several loadings taking place here. The first is the local pounding on the bottom resulting from hitting waves. For this you want panel stiffness that results from a sandwich construction. A few layers of glass on each side of a foam core will give you much better strength to weight than solid glass for the bottom surfaces, and it will be a lot stiffer too.

The second is the overall twisting and bending of the structure. As noted above, depending on the geometry of the hull, it may require bulkheads that can be made from thin plywood, which will provide siffness with a minimal weight.

If you are careful you should be able to end up with a boat that one person can easily load and unload. My first boat was almost the same dimensions as what you are building, and it flew with a 16 hp Merc, (literally). My boat was made from 1/4 inch plywood with 1X2 framing and it took basically two sheets to make the whole thing. It only weighed a bit over 65 pounds including glass on the seams and a coat of paint.

You should be able to make something that light with foam and glass without too much trouble. And yes someting that light will fly very easily with a 25 hp outboard on it.

 

Would v shaped ridges on the bottom of the center panel increase the rigidity and also break up the surface tension of the water as it hit?

I also have the original that I would like to firm up.

 

Tunnel shapes are not weak in construction or there shape !! Far from it !!
They are stronger than a mono !! they corner at speed faster than you can blink an eye just need pwer trim on your motor to make it tuck and lift the back a little .
Have a look at small tunnels =sst 45 is a fast and very stable strong boat !! theres a new formular 40 some where out there being developed and could even have a class by now !! These boats could be about the same size as what you playing with !!.

I designed and built a sst 45 a few years back and it was a wow machine !!!. would do in excess of 80 mph quicker than you mouth could open and could go round corners like it was on rails and not loose any speed once the young guy got the hang of it after a few hours a of seat time !.
Had problems with G force on his helmet till we changed the cockpit seat to incoparate a fixed and semi solid place for his helmet to fit snuggly and was totally enclosed like the F I boats .
The motor sst 45 is a special motor based on the 2 cylinder 50 omc with all the factory goodies and a racing lower end .
Nice wee motor and strong !!.
Merc make or used to make a racing 20 you should look at !!!!.
If its you own design i hope you done you home work and got your head around aerodynamics because you could fly litteraly !!!!and because a lot of the older tunnel boats were going so fast and aerodynamicly unstable they took off and went sky wards with disaterous results .
Its not only hydrodynamics you playing with ,but aerodynamics as well !! and another thing you may never heard of called surface effect !!! a cood place to be but if you get out of it your in trouble sort of !!
Welcome to my world name "TUNNELS" !!

 

Have you ever rubbed kevlar on anything?
Can you now explain what happens?
Do you think the kevlar is now weakened?

Biax over the top for abrasion resistance is to protect the kevlar so as to prevent it from losing strength and to prevent it from furring when abraded.
Better to sacrifice some sacrificial Biax than the kevlar which provides the strength.

 

We are wandering away from his problem.

He has broken engine mounts.

He & tunnels should design this improved boat.

They both want maximum speed at any price.

I design & modify for safety first. Then speed gets what is left.
Everyone laughed at a turn fin I designed for a 5.0L hydro. Until the old boat passed everyone in every turn. One driver said his engine was losing power in the turn. Untill he saw everyone else still holding position.

Safety first ALWAYS makes for a huge bar bill & lots of laughs each diner night.

I am wasting my time on this one.

Good luck to both of you.

Rich

 

I value anyones opinion, I am a novice I am here to learn. The more information I have and the more pionts of view the greater the potential of the end product.

There already are braces on the back of the flotation hulls to the transom. Im not only concerned about speed weight was the original issue.

I use it as a stunt boat also eg. jumps, catwalks, doughnuts, handstands, general showmanship ect.

thanks for every ones ongoing input

 

The Dux Superlight Tunnel Hull RD-400X is closer to what im looking for than a sst 45.

http://www.youtube.com/watch?v=4EEQHiqr9gI