Hydrofoil operated heeling system for a solarboat

Hello all!

I'm new on this forum. I'm a student from the university of applied sciences in Amsterdam. Me and several of my colleagues are currently working on a prototype heeling system for an exteremely lightweight boat(solarboat). We have little experience in this field and we were wondering if you believe this concept to be feasible. If you do what kind of hydrofoils would be best suited for this purpose?


The main purpose of the hydrofoil would be to create a lift on either starboard or portside and utilizing this we think it should be possible to create a lift resulting in a continuous heeling moment.

Any tips, suggestions or advice would be appreciated!!

 

I don't understand what your point is -or maybe I do and what you are considering is commonly done. Appendages can and are used to generate rolling moments on boats. DSS is used on monohull sailboats. Active stability fins are used on power boats. The latest IMOCA boats have 'moustach' shaped foils that provide substantial righting with passive control.

This moment is proportional to velocity squared. There are passive control schemes where heel increases area or angle -generally the cost is drag from piercing the surface and angled faces. A T foil loses less to surface piercing but you will need to control it. I recall Tom Speers did a theoretical comparison on the merits of V and T foils. If this boat is so light, why not go completely hydrofoil? That way you don't have waves inducing roll to start with.

 

You are students. What is the specific thrust (thrust/weight) of your drive and what is the payload? Then you can figure out if it is more efficient to float or fly.

 

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I'm not sure that I understand what a "heeling system" is supposed to do? Not sure this will help,but this is a picture of a sailboat that uses foils on either side to lift the boat and increase righting moment:

 

Dear Skyak and Doug Lord,

Thank you for your reactions.
sorry for the what late reaction from my side, I've had a very busy schedule lately.

I'll make some remarks regarding my first post, since it's indeed a bit vague.

First of all the solarboat has to join a race, in which flying is prohibited. So unfortunaly it has to float.

Secondly the purpose of the "heeling system" is to create a lift into a requested direction. This should result in a greater surface for the solarcells towards the sun. So more energy can be generated, which will lead to a possible increase in speed.

I'm currently a bit in doubt.. Should we be using V or T type foils? and would it be better to use one or multiple fins? and on what part of the boat are the foils commonly placed?

any tips, sources or so are welcome!

 

I suspect that you will be prohibited from using any foil that is not vertical. Are you allowed to use lifting foils at all? I have no idea how they could allow lifting but prohibit 'flying'. Vertical is the only orientation with no lifting component.

You will need to have the sun tracking on the panels and the vertical fin can reduce roll. The size would be based on the sensitivity to small angle error. I think optical panel coatings might cut sensitivity to roll angle and eliminate the need for fin stabilization.

 

If the requirement is to tilt the solar panels, why try to tilt the whole boat? Just tilt the solar panels, and run the boat in it's most efficient attitude.

 

In order to tilt the panel (and keep it dry) it will have to be a good distance off the water, so if you want it light it will either have to be a multihull or it will need a ballasted keel to deal with the weight being up high. Assuming it is a monohull then why not use a swing keel to heel the boat? That way you can keep it light, use a circular cross section on the hull for minimum wetted surface and the mechanics used for tilting are at the lowest possible CG - and complexity is kept to a minimum.

A hydrofoil used to maintain a certain heel angle will need to be constantly adjusted, which uses power, both electrically and via water drag.

 

Well, that was what I thought, but was scared to mention, thinking I might have been dealing with some new-fangled principle that was beyond my ken ! Not to mention that tilting the boat will reduce the righting ability underway in a sea.

 

Tilting the panels means more weight. Instead of the panels being part of the deck you will need a regular deck plus you will need a framework and tilt mechanism above that to move the panels - and a corresponding amount of ballast to keep the boat right side up. Then you will also need something to mount the cells to (a panel) - or use a heavy off the shelf panels - more weight.

If you are going for minimum weight then you can attach the cells directly to the deck - the deck is the solar panel, rather than something like attaching a commercially available panel on top of a deck which is adding unnecessary weight. Then a swing keel to heel the boat +/- 30 degrees. Righting ability is retained, weight is absolute minimum and with the right hull form, efficiency minimally impacted.

The other thing is, will the improved panel angle yield faster speeds considering the other compromises? There are always trade offs. Using a MPPT charger can significantly increase the amount of energy harvested from the panel. If that is not already in the plan then I would first focus on that.

 

Righting ability has to be reduced, you have already got it over to 30 degrees with zero righting moment at that angle.

 

Why would it be zero? With the keel center mounted any amount of additional heel will serve to lift the keel higher. Additionally, any amount of heel will move the bulb laterally opposite the direction of heeling. Both of those contribute to righting moment, neither take into account hull shape - which would further add to righting moment.

 

SIB, it would be useful to provide a link to the race rules, in order to assess the best solution within the rules framework.

At first I thought it was this one: http://www.dongenergysolarchallenge.com , but it doesn't forbid flying on foils. So I guess it must be another race you are involved in.

 

Thanks for laying out your reasoning and expectations. I still think that I could make an aiming mechanism on top of the boat that is lighter and more efficient than tilting the boat. My first point would be that tilting the boat is limited to one axis but you need the two axis aiming that can be done above the hull. Second, the moment below the water must offset what is going on above so at best moving a keel would take equal energy and that would be for the case of zero stability standing still. The mechanism below must be sealed (friction) and pushed through water (drag) which has greater density and viscosity -you have a lot working against you. the last point I would make is that the keel bulb is all wasted capacity. Do the calculations I think you will find that you can add a hull for the same or less weight than you need in the keel. It will be much easier mounting and aiming panels on a catamaran

If you want to do something tricky consider that the solar boat has constant weight since it doesn't burn fuel. You would get more out of managing the waterline of two hulls than managing the heel of one.

 

It would definitely be good to know what the rules are for this race...

Two axis aiming is more complexity than I would be comfortable with. I am skeptical that the performance of the system would see significant improvement on this (what I assume is a) small autonomous vessel - and it would add more failure points.

I'm pretty sure that adding another hull would add more weight, windage and wetted surface than adding a bulbed keel to a monohull. This bulbed keel would not have as much mass as a sailboat keel, it does not need to provide as much righting moment. Maybe this solar boat already has two hulls so this could be a moot point.

Energy to move the keel would be insignificant. You move it, and it stays there for a while. Sealing it would be an issue for sure, but manageable.

As to the original question - I think that aiming of the panels via hydrodynamic foils would use far more energy than a gear motor. The hydrofoil idea sounds like it would have to be in the water (absorbing energy) at all times whereas a motor would only be using energy when repositioning.