A bit of light reading

Here is a paper that investigates the operation of the bailers and in particular, the Anderson bailer found in the V12.
There is a couple of surprise conclusion here if you enjoy reading through a lot of technical stuff.
It also proposes and tests some novel types of drains and attempts to modify the production bailer for better draining/ lower drag.

It is carried out in relation to racing sailboats, but the speeds and head of water are directly translatable to surfskis.

Very illuminating actually.
Fairly long read and the best bits are a fair way in, and if you don't like techy stuff, then you may want to just paddle the boat you got without worrying about this crap.

Jeez, amazing what you can forget after varsity maths!

Um... so how would this relate to using bullet bailers vs non-bullet bailers of the older school (non Andersen) variety?

Have I got it right that the increased draining of bullet bailers leads to a bigger underwater vortex, and therefore slows the boat down?

In regards to bullets, I think that one of their custom streamlined things is the closest, it had much lower drag but drained very poorly.(it could be made bigger and better optimised)

Obviously this was written back in the IBM 486, maybe early Pentium days, so not a lot of computing available to optimise one like today.

But I think that it does show that simply plonking a bullet there may not work as well as you hoped.

What I really found interesting was the 300% increase in flow as well as a lower draining speed that happened when they removed the sides of the bailer.

I wonder if I forgo having a backflow door, if cutting away the sides and locking down the opening height to a few millimeters would drain as good as current as well as have lower drag and also be a simpler thing to custom design for a surfski market.

Just a simple trapdoor in the bottom.

Imagine a plastic/composite moulded trapdoor with a spring loading and a string/cable to the middle of the footplate to an operating mech.

Cheap, lower drag, as good as or better draining and remote operation at the footplate for on the fly action as well as universal fitment for all surfskis.


I don't know if bullets actually increase draining speed much, I think their biggest gain is lower speed operation and less drag if properly designed and executed.
The bullet blocks less of the output area of the drain than a circulating vortex, but not a lot less, it mainly smooths flow and promotes better mixing I think.

You could probably design a bullet system with less overall drag for the amount of flow, but it's always in the stream.

That's why I like the trapdoor idea, when it's closed it's drag neutral.

But in the end, we are talking about percentages of a percentage with the general agreed drag figure of a drain being around 1% of total boat drag.

Does show how bloody complicated and difficult to measure everything about water dynamics is.

Sure I totally agree on the amount that this doesn't really effect me at all being that I'm nowhere near the front... For me I can improve my time much more with a bit more paddling.

That said, I am one that has an abstract interest in the technical details - hence the interest.

...likes to think he knows how stuff works...

So I took the door of my bailer to try it out.
Needs to open about 4mm for any appreciable draining to happen and it leaves a small amount of water in the bottom up until just under where it would normally start draining when the flap opened if it was still in place.

I did the tennis ball thing with the handle, but also added another cable tie to keep the ball from flopping around and to make it a positive opening action just by kicking it with my heal.

I just put another tie through the holes in the tennis ball and then out through the bottom cut and around the grating in the bailer.
This gives it a great action.

Also, by removing the flap and then filing a contour on the back of the trapdoor, I made a tight spot in the middle at about the place where the flap would be fully open.

So now I have a nominally three position position bailer, fully closed, kick it once and it opens to the normal drain position, kick it again and it opens all the way up to what I have dubbed the surf position.

It's still quite easy to just kick it softly and open it up a few mm to allow for continuous bailing with very little drag, but I found it was simply better to close it and only open it when water collects in there for small stuff and only open it up for when waves break into the bucket.

The standard bailer without the flap and fully open, will empty the bucket from sitting still equilibrium to dry and gurgling in 6 good paddle strokes.
If there is a huge speed benefit without the sides as suggested in the artical, I was wondering about cutting the sides away from just where I have it sitting in the middle position to fully open and try and gain draining speed for going out through surf, without a drag penalty when in the half open normal drain setting.

As soon as I get a hold of a spare one to use in case I make a mess of the original, I shall try.

Ric, have you read this?

Great bullet article hosted here on this site

On my V12, I cut/filed off the flanges of the trap door of the bailer about a year ago because it just seemed "obvious" (obvious in common sense only) that a reduction in surface area of the trap door would result in a lower drag when the bailer is all the way open. I didn't know what would happen to the draining rate or min speed for draining though.

I can tell you that the bailer still works and seems to work about the same. I can still feel the extra drag when the bailer is all the way open, so if drag was reduced by grinding off the flanges, then the reduction probably wasn't much in the overall scheme of things. The footwell drains very well - but alas, I can't say that it drains better or earlier because I didn't take any measurements beforehand. Erik

So, do you mean you cut away the sides of the trapdoor so that it is a U shape and not a fat inverted T shape that sticks down into the flow?

If so, does it still seal when closed?

Yes the shape is more like I_I as opposed to _I_I_ now. Seals the same as before. Not sure what the flanges are for and I couldn't figure out what they were saying in that article you posted regarding whether or not what I did is was the modified "sideless bailer" but upon further reading, what I did is different.

I was going to post a short article with pics on this site last autumn but got busy with life . . . I might do so soon but I'll get some flow numbers beforehand regarding min speed of draining first. Erik