Electric Foiler(or foil assist)

<<<<<Do your numbers for your proposed foil set up and I will do them for mine and we will see what looks the best. The target is to get an overall L/D of 30 when flying.>>>>>>>

I would love to but i'm still learning how to plug the data into michlet and xfoil FLR5 so i'll come back to you on that once i'm confident of the process.

I think L/D of 30 is quite realistic . Strut resistance is not proportional to wetted area though.

 

The analogy is wrong.

We have a boat doing a leisurely 20kts. I would not expect a planning craft to be destroyed if it hit a log, rock or reef at this speed. Worst damage expected would be a scratch in the gelcoat and maybe a bent prop.

I have seen the aftermath of planing boat hitting a log at 35kts and the only indication was a slight ding in the prop. It was a timber boat with a brass rubbing strip on the keel. The motor certainly bounced out of the water and may have shocked the transom but just lowered back down and away it went.

This is an extreme example but typical of the abuse that you reasonably expect a boat to take:
http://www.youtube.com/watch?v=Zt0eGnu7Sk8&feature=related

If your foil system cannot take a decent knock then it will not be acceptable. That is in the original specification.

Rick W

 

<<<If your foil system cannot take a decent knock then it will not be acceptable. That is in the original specification.
>>>

I agree , but only to the point that one might expect a normal boat to withstand a blow.

I do not expect any small boat to be able to survive falling off a wave onto a barely floating container, for example. It is simply not realistic.

 

And btw 20 Knts is not leisurely. You can pedal your bike at that speed and steer into a parked car say, and you'll know what i mean.

 

Oh, and the video is quite entertaining, and is also a great example of recklessness and the kind of thing that makes boat builders like me cringe!

 

Compared to 800kph of a jetliner 20kts is leisurely, which is what you were comparing it with.

Also I am not saying a sudden stop but something that can be reasonably expected to happen when navigating any river or coastal waterway. For that matter an ocean as well.

One of the advantages of old style long keels is their ability to ride up on a rock or beach to absorb energy. Modern deep keelers just come to a shuddering halt with some energy being absorbed by dipping the bow.

A great feature of an outboard boat is its ability to ride up on sand banks without experience damage.

From my own experience I would say that anyone who has not gone aground in a small boat has led a very sheltered life. If you are building boats that are not able to take a grounding or hit a partially submerged object and remain operable then you are deluded. It is a fact of life and not what I regard as careless operation. I regard someone who designs without that possibility accounted for as negligent.

Rick

 

Ok lets not get worked up here .

Yes you have mostly valid points , but it's a question of degree . As in how much damage.

For example the outboard boat hits a gradual sand bank and it will still function afterwards but it was not a boat improving event.

I guess my point is that at these kinds of high speeds it is not reasonable to expect that your foils should be able to survive a collision with a substantial object , like say a log.

 

LOL, maybe if we made them out of Kevlar-sheathed, hammer-forged Titanium billet they could...but I don't think that'd be very good for our weight considerations. (and, to keep things reasonable, let's just say that we want the foils to withstand the same abuse as the aforementioned fin keel...is that agreeable to everyone?)

 

This is where we disagree. I want to be able to run down a river at 20kts knowing if I hit a log or submerged branch I will not have expensive damage.

I have managed to do this to a reasonable degree with propellers and compete quite well with paddled craft in log infested waters. I expect the same with foils. Anything less makes them fragile and of very limited use.

As an example the mirrors on my car protrude quite a distance and they take regular pumps in car parks and just fold out of the way. They afford protection for pedestrians and cyclists by easily folding to avoid extensive injuries. If I had to replace them every time they took a knock I would carry barriers to sit beside the car each time I used a public car park. In fact I would also need them in my own garage.

Rick W

 

Well i would say if you can design something like that then i want some lessons!

To me reasonable would be if there was terminal damage to the foils it would leave the hull itself watertight. Much like daggerboards in multis.

I think that designing a foil boat for log infested waters might not be the most practical ...

 

No problem. Happy to teach you.

Rick W

 

Thank you.

I will make good on your offer straight away.

I have as shown below the beginnings of yet another design in rhino 4. I also have michlet program with a black window looking at my dumb face....

How do i get that hull's relevant data into Michlet for an analysis?

Would very much appreciate some pointers and can move this to another thread or wherever else.

 

T,Rick: keep it here-please....

 

Crash survivability may be the make-break issue for a commercial boat, although a home builder might be expected to have more caution than the bozo in the video. Since a boat hull is designed to slide through the water it tends to have the right shape to slide up and over a low obstacle. It is also broad in shape which contributes to its durability.

None of that is true of a hydrofoil. Bulk them up and the drag will be unacceptable, use a sweptback strut and the foil will ventilate. Any foil appendage I can think of looks pretty much like a log-fishing hook. If Bozo had been in a foiler with the foil made from infinitely strong unobtanium he would have ended up in the water with his dog, and maybe run over by his own boat.

To expect a foil to survive a collision with an underwater immovable object is like expecting a mast to survive contact with a bridge without damage. It's safer if the foil (and the mast) yield.

That sounds like the answer. If the foil(s) can snap up and out of the way that leaves the hull to plop down into the water from a modest height. However, all the foils need to snap up at the same time, and quickly enough to avoid transforming into sea anchors. I don't think it's enough to let the foil spring back from the strut leaving the strut stationary, the whole thing has got to pop up.

 

The rear view mirror analogy is promising but a rear view mirror is designed to fold back when there is a relatively slow speed encounter. At sixty mph it no longer folds back. It just disintegrates into shrapnel.