[SkipperKnut]

How much would drag be reduced if you reduce keel bulb volume by 40 % ?

[Marmot]

Maybe the reason you haven't got an answer is because it is one of those "it all depends" things.

What shape is it? How do you plan to reduce the volume? Are you going to reduce the frontal area? Are you simply scaling down the same shape? Is the bulb a cylinder that you plan to shorten, a foil you plan to alter the aspect ratio?

Make a scale model and drag test it before and after the tweaks is the simple and cheap way to find out.

[AMG]

You are right Marmot, there are too many "it depends". I was thinking of basic things like if the weight is also reduced by 40%, what will happen with waterline length and with healing? Or is it iron being replaced by lead? And naturally, it all depends on the shape, before and after.

[Capt J]

Originally Posted by SkipperKnut

How much would drag be reduced if you reduce keel bulb volume by 40 % ?

I thought Naval Engineers designed the keel bulb at a certain size to displace water and not only make the vessel ride better, but to make it more efficient as well? I don't think that making it smaller would increase efficiency, otherwise the naval engineer would've designed it that way in the first place. I may be totally wrong, but doesn't the keel bulb break up the waves so that the vessel maintains a higher average speed in a sea?

[Marmot]

"I may be totally wrong ..."

Keel bulb:





Bow Bulb:

[Capt J]

Ok, got it. But aren't keel bulbs usually found on sailboats and designed to produce as little drag as possible and it allows one to run more sail area in order to increase speed, by reduce keel length while still retaining great counterbalance?

[PropBet]

Originally Posted by Capt J

Ok, got it. But aren't keel bulbs usually found on sailboats and designed to produce as little drag as possible and it allows one to run more sail area in order to increase speed, by reduce keel length while still retaining great counterbalance?

You bring up the critical point here.

Drag in keel bulb is one thing. What the bulb actually does, and modifying that is a whole new scenario. Unless you have the hydrodynamics of a 55 gallon drum as your keel bulb, why and or who are you wanting to reduce its drag by 40%?

Keel length is going to be directly proportional and critical to mast height and sail size / square footage at its greatest efficiency.

[SkipperKnut]

To clarify - what if a leadbulb was replaced by a gold bulb ? It could be 40 % smaller keeping the same weight and righting moment, but less drag. (It would cost 470 million Euro for an AC boat, so the advantage better be great !)

[Marmot]

" ... gold bulb ..."

Now you are being ridiculous. Everyone knows boatyards are full of crooks, that's why depleted uranium has replaced gold everywhere except the Middle East.

[FISHTIGUA]

Bulls-eye Marmot.

[NYCAP123]

Originally Posted by SkipperKnut

To clarify - what if a leadbulb was replaced by a gold bulb ? It could be 40 % smaller keeping the same weight and righting moment, but less drag. (It would cost 470 million Euro for an AC boat, so the advantage better be great !)

Back in the day I saw the lead replaced with cocaine, but never gold. Let me know when you need a diver.

[PropBet]

Originally Posted by SkipperKnut

To clarify - what if a leadbulb was replaced by a gold bulb ?

Yes.
That should work fine.
We'll obviously need to test.
PM sent with our Captain's name and our dock GPS cord's.

Next Tuesday works for us, if that is OK with you.

K-Thanks.