Bustle Ahead of Rudder Turbulence

[silverp40]

Our IOR era boat has a deep bustle just ahead of the skeg hung rudder. Designers of the the era used it to reduce girth (it was quite popular ) and obtain a more favorable rating for the boat. These days they are not seen on modern boats much to the best of my knowledge...

I know that it cause turbulence, especially at higher speeds. I am thinking of fairing/flattening it out (hollow inside not full of material) to remove it. (Also thinking of filling in the "frown" just ahead of the skeg).

I am really curious if anyone has done it on their boat and the results, before and after the bustle?!

Any opinions or suggestions are also welcome....

[Benz]

It seems a shame to ruin that fine finish by grinding and glassing and fairing. Why not sell that boat to someone who wants that particular design (there are those who do, I'm sure), and then get a boat that is designed the way you like? there's something to suit all tastes out there. What you speak of doing seems terribly expensive and difficult.

[silverp40]

What you speak of doing seems terribly expensive and difficult.

Doing it myself about 10-12 hours total over a few days(my work is really cheap) and about $100 in epoxy, cloth, etc.

Now boatyards....hmmm I think you are right..

[donradcliffe]

I'm not sure exactly what you are asking, but you could fair the gap between the skeg and rudder with plastic or rubber flaps which are attached to the skeg by a thin stainless strip. It may make you look faster, but probably won't do much.

[cal40john]

If you fair from in front of the skeg to the transom, won't you have to modify the rudder?

[S/V Alchemy]

How do you know that the "bite" in front of the skeg is that which is causing turbulence? Perhaps there is simply excessive play in the rudder post due to worn bearings which is only revealed at speed.

Would you fair that bite flat to the leading edge of the rudder or below that edge?

A diagram of what you want to do and why you think it's a good idea would work.

[silverp40]

Quote:
I'm not sure exactly what you are asking, but you could fair the gap between the skeg and rudder with plastic or rubber flaps which are attached to the skeg by a thin stainless strip. It may make you look faster, but probably won't do much.

THe original racing form included rubber flaps which worked and fouled and once in a while lost. I think the gap makes a little difference in avoiding turbulence, but pls see the bustle pic.

Quote:
If you fair from in front of the skeg to the transom, won't you have to modify the rudder?

The modification would only be in front of the skeg. (Good observation, though John - I modified the rudder from swept back to semi balanced and it is an incredible improvement).

Quote:
How do you know that the "bite" in front of the skeg is that which is causing turbulence? Perhaps there is simply excessive play in the rudder post due to worn bearings which is only revealed at speed.

Would you fair that bite flat to the leading edge of the rudder or below that edge?

A diagram of what you want to do and why you think it's a good idea would work.

The rudder post is not loose , I made double sure. I would fair the "bite" to the back edge of the skeg.


Here is a photo of the modifications made by a friend but has not tried it yet. The boat still is a bit away from sea trials.

[Blue Stocking]

I'm curious--what do you wish to gain from this redesign? If speed, surely newer designs are available to answer that need.
Not being judgemental, just interested in your motivation for a lot of work.

[silverp40]

Buying another boat would not be an option for me. I would like to know though if I delete this design quirk, would it help the efficiency of the aft end of the boat??And how much (although this might be hard to quantity, but a general idea would be nice to have)

[Blue Stocking]

Originally Posted by silverp40

Buying another boat would not be an option for me. I would like to know though if I delete this design quirk, would it help the efficiency of the aft end of the boat??And how much (although this might be hard to quantity, but a general idea would be nice to have)

OK--I see. I know what its like when some brain cells get "antsy"

[foggysail]

Years ago I filled the joint that existed between the hull and keel along with the hull and the skeg on my Hunter 30 with epoxy. My goal was to eliminate any unnecessary drag on the boat. What a waste of my time and effort although the bottom looked much nicer than it did when the boat left Hunter's factory.

[minaret]

Easy-peasy, and probably worth doing. The angle at which the buttock lines intersect the CL is critical in the run of the boat, and yours is presently less than optimal. Your friend is on the right track with his forms, I would expect this to take 2-3 days of working time at most, including coatings. If your already out of the water, why not? It can't hurt....

[S/V Alchemy]

Originally Posted by silverp40

Here is a photo of the modifications made by a friend but has not tried it yet. The boat still is a bit away from sea trials.

OK, that's not remotely what I assumed you meant, so this picture is indeed worth a thousand words.

I have no honest idea if that would work, but it's a interesting mod, that's for sure. The phrase "tip vortices" comes to mind, as if it's in the same school of thought as the winglets at the end of most modern jets having a significant drag reduction. Or, to bring it back to boats, how the "foot plate effect" (I think it's called that) of deck-sweeping genoas is more efficient than the same sail area, but off the deck.

It's the sort of job I would run by a naval architect, frankly...looks like something you could figure out in a test tank.

I would say that this issue must be important to you to go to this much potential effort to remedy it.

[Cheechako]

I really wonder if you will see any appreciable difference. Cant hurt though I suppose. At least your rudder is partially balanced, rudders with a full skeg seem to have such a hard feel to me. Let your friend try his first!
Is that boat similar to the old Pearson 39? I liked those boats....

[malbert73]

Originally Posted by S/V Alchemy

OK, that's not remotely what I assumed you meant, so this picture is indeed worth a thousand words.

I have no honest idea if that would work, but it's a interesting mod, that's for sure. The phrase "tip vortices" comes to mind, as if it's in the same school of thought as the winglets at the end of most modern jets having a significant drag reduction. Or, to bring it back to boats, how the "foot plate effect" (I think it's called that) of deck-sweeping genoas is more efficient than the same sail area, but off the deck.

It's the sort of job I would run by a naval architect, frankly...looks like something you could figure out in a test tank.

I would say that this issue must be important to you to go to this much potential effort to remedy it.

Those vanes were forms on which to fill the void. End result is in the picture of the painted hull. That looks like a nice improvement and I think will make a speed and turbulence difference.

Don't listen to the naysayers- this is easy to do and cannot hurt. The IOR bustle didn't help performance, only ratings. Generally, smooth, fair, and tapered ends of boats work better, and your friend improved his stern end a lot.