12ft Cat for Solar Splash Competition - first time tips needed

Hello people with boat knowledge,

I am building a 12ft electric outboard tunnel hull/catamaran for the college event Solar Splash. I plan on using xps foam and 6oz fiberglass with epoxy for the construction. It will go ~5mph for the endurance event and if the power is there over 30mph for the sprint. Since this is my first time designing and building I have a few questions I haven't been able to find an answers to on the forum.

1. I need to mount things like solar panels onto the front deck, what kind of inlays can I use to make mounting points. I thought about an aluminum or hickory frame inside the foam but want your input.

2. I saw a comment saying de-lamination is common for fiberglass and foam construction, is that true? Also how could I prevent that if it is.

3. Is there any glaring issues with my design? I printed off a few models and they seem to work fine but that isn't always accurate. Also in Fusion flow it doesn't show any flow through the tunnel, I would imagine that is an error, but I have no prior experience.

 

Jacob, post some section views of your boat so that we can understand what you have drawn. Put some dimensions on the section views,
perhaps we can then furnish some useful comments.

If you are to cause this 12 footer to go 30 MPH, you will need some real horsepower. You will not get that kind of output power by using solar panels that will fit such a small boat. Why have you chosen to use a "tunnel hull" design? Does the design contest require that you use only electric power? Must the boat be no more than 12 feet long?

 

The electric motor will output about 30hp. The boat only runs on solar power during the endurance event, during the sprint it runs off battery power and the panels are removed. Unfortunately we are limited to lead acid batteries, they go down in the rectangular cut outs. Also we can only use electric. Technically flywheels are also permitted but we are not going to do that.

I chose the "tunnel hull" design because I wanted a wide stable boat with decreased cross section width. Most of the boats in the competition are +2.5ft wide mono hulls that are around 15ft long, my design has a width of 2ft in the water so I thought that would be an improvement. The bit on the back is so that while the boat is submerged in the endurance race the water can re-converge like a kayak. Then the flat part is so that it still has planing capabilities at speed. The 12ft length just happened to be reasonable when we layed out a tape template on the floor, everything fit and we didn't need extra length.

Dimensions:
1= 8in
2=12in
3=18in
4=12in
5= 10deg

 

You have the job ahead to come up for something that will excel at both the sprint and the endurance event

 

Nothing like redesigning the wheel when you have never designed anything.
What actually gives you any idea your shape will work at all?
You have got a huge amount of surface area which will make it slow in the endurance, and bizzare shapes for high speed.

Just make a catamaran shape like a Nacra and move your people to minimize drag.

Fantasies with no engineering will get you an "interesting" failure.

Do you have any kind of a weight analysis?
A filled foam boat will be heavier than a conventional design.
Have you done any tests with foam/epoxy/glass for strength or point loading, etc?

 

The point of the competition is to try new designs. I think my design is going to work because I am using measurements and design methods from existing hulls in the competition and elsewhere.

Could you elaborate on the increased surface area, I know the rear fin will be added surface area during endurance, but it seems better than a squared off back.

A teammate is currently doing a weight analysis. The fiberglass and epoxy have not arrived yet so we cannot do tests.

One of the rules states that the boat must float even if it overturns or fills with water, so the solid foam areas are necessary, unless there is a good way of making a sealed chamber that is strong. I would imagine a hollow part would ruin the strength of a fiberglass-foam sandwich.

 

Can you calculate surface area? You really should.
Then compare to a simple circular section with a keel shape that comes up to the waterline at bow and stern.
There is no problem with a squared off back, so long as it is kept at the water surface. Such a design straightens out the flow lines aft, which would be better for higher speed.
Solid foam is never necessary, it is a lazy man's way of providing flotation.
Wooden kayaks are usually made with an enclosed bow and stern chamber for flotation when inverted. Never seen one have a strength problem. 1/8" plywood is usually sufficient.
Fiberglass catamarans (daysailors) are a single enclosure that is sealed (the entire hull).

If you are going to design a boat you really ought to look into how boats are made.

Additionally, if you are going to make a 2 hulled boat, there is no need to connect the hulls with anything but two crossbeams. Solid structure is much heavier.

 

I have surface area of the whole boat, but will find the wetted surface area later today.

The squared off back would be below the water surface during the endurance race, that's the issue and why I chose to forgo it. I get what you are saying about it not mattering during the sprint, that makes sense. This competition just requires two completely opposite uses from the hull so it is hard to make it specialized for one.

Making the front hollow seems like a difficult construction challenge. What do you think about using two densities of foam? Use regular XPS for the exterior sections in contact with the frame and fiberglass, but then some low density foam to fill in the hole and make it easier to build.

 

Jacob,

Welcome to the Forum.

You've done a good job on your first design, I can see what you're trying to do.
I suggest you post the rules and guidelines for the competition as these are your constraints and your SOR (Statement of Requirements).

I've responded to your queries, below.

 

7.2.1 Length – The overall length of the craft may not exceed 6 meters (19 ft, 8 in). This does not include the boat number sign.

7.2.2 Width – The maximum allowable width, including the solar array, is 2.4 meters (7 ft, 10.5 in).

7.2.3 Height – The maximum allowable height above the waterline is 1.5 meters (4 ft, 11 in). This height can never be exceeded during the events. This does not include the boat number sign.

7.2.4 Depth – No restriction. An excessive depth may make the craft awkward to handle near shore and may increase the likelihood of encountering underwater obstacles.

7.2.5 Cross Sectional Area – In profile, the fixed area (such as the hull) is unrestricted. The solar array may be fixed or may be in the form of one or more movable panels.

7.5 Visibility – The skipper must have unobstructed vision forward and at least 100° to either side.

7.6 Stability – The stability of the craft will be tested by placing 10 kg at the sheer line (outer edge at the beam) with the skipper stationary in the normal operating position. Craft must not heel more than 15°. Skipper must remain centered with hands/feet in normal position.

7.7 Dead-man’s Switch – It must be functional at all times when the skipper is in the boat and must be demonstrated in an egress test during Technical Inspection.

7.8 Circulation – Fresh air must be provided for the skipper if the cockpit is enclosed.

The people on the team in charge of solar decided on some big solid panels, so that is what I have to work around.

7.9 Ballast – The ballast must be placed in a manner such that the ballast will fall out of the craft if it capsizes (turns over 180º) or adequate flotation must be provided for the ballast.

 

Jacob,

Those aren't all the rules.
I know because I designed the winning boat a few years ago.
You need to post ALL the rules, limitations, circumstances, conditions, cautions, equipement, everything.
And it has to be current for 2022.

How much does the pilot weigh?
Where did you get this outboard electric you speak of?
And the batteries?
What panels do you have?

Is this it?
Rules http://solarsplash.com/rules/

 

Yes that is the link for the current rules.
I have to get the other info from another group member.

 

From section 8.3 in the rules that BlueBell posted:

"The only two components that may be removed from or added to the boat for different configurations are the solar panels and the batteries. However, the boat configuration may be modified by replacing or exchanging other individual components (motors, propellers, drive train components, rudders, etc). All components (other than solar
panels and batteries) that will be used in any of the configurations must be safely secured within the boat for all configurations and all competitions."

(note section 8.3 is continued on page 18 in the PDF)

If i read this correctly you are allowed to remove the "flat part" or "rear fin" to improve planing characteristics for the endurance race. As long as you store them inside the boat when not in use. The rules also allow for a different rudder for the sprint and slalom course, something you will probably need.

I do like your original design approach to combine a planing hull with a displacement one.

 

I like that idea a lot! It would be more efficient and easier to construct. I could make the fin on our CNC machine rather than hand forming it with foam.

 

Pilot weighs 150lb per the rules, for anyone under weight weight must be added to the boat.

The outboard is custom using this motor: https://www.kit-elec-shop.com/gb/di...eur-courant-continu-48v-200a-saietta-119.html

Batteries: Odyssey extreme PC 1100

We ordered two different panels and will pick one of these after testing them: 175 Watt 12 Volt Flexible Monocrystalline Solar Panel (pre-order) https://www.renogy.com/175-watt-12-volt-flexible-monocrystalline-solar-panel/?gclid=Cj0KCQjwqp-LBhDQARIsAO0a6aLhP8UwyXa0vXidg9vWC1S8dawDcEZHwSuUTUAftt6pzDYa1-dx5VUaAudVEALw_wcB https://www.newpowa.com/products/20...NO3G1TCt0TTQQSpYZSgxQmRwMEzvSIvoaApEiEALw_wcB