Thru-hulls above props on Hatteras MY

Hi,

The name is a "P Bracket" as far as I know, it looks like there has been some fairing around the aft edge fall out in the first photo you posted.

That is sort of what it looked like to me. But I can't understand why they didn't fill it in before they painted the bottom.

Great info! I had never seen this before. If I understand correctly, it's a patch to deal with insufficient blade tip clearance. Or - if you want to look at it in a positive light - a technical innovation allowing you to use a bigger propeller or smaller shaft angle with the same noise levels. Pressure pulses on the hull from the propellers are a major source of onboard noise, and I can see how a layer of air can counteract this.

A few more questions:
1. are the holes connected to a pipe above the main deck (atmospheric pressure), to a compressor or to the exhaust system?
Edit: just read in one of the posts above that they are connected to the transom, which seems logical.


2. aren't there any negative side-effects from the ventilation? We usually try to keep the underwater exhaust far away from stabilizers, props and rudders, because they loose efficiency when ventilated (except for surface-piercing propellers, which are specifically designed for this).

3. does this really help at all - given the more recent models don't seem to have it?

Bruno

No, consider it more of a patch to fix a screw up.

I meant to answer Brunos' question, but I've been playing catch up all week. Took off yesterday for the funeral of Clarence Clemens, a long time friend of the family. He's on his way to see the 'real Boss', bringing heaven a good dose of soul.

CaptJ, how do you surmise this system is a patch?

If the hull was designed with more space above the props, I don't think it would be added. The few existing thru-hulls that are filled in, indicate that it was more of a trial and error process that was incorporated after the boat was launched. Sort of like the first 1/2 dozen 63 MY's had to have that 1" lip added into the tunnel so they'd get more stern lift, then after that it was incorporated into the mold. Same with the 60' SF that had a lip or hump on the bottom at the transom, that they ground down on the first few because it ran too flat, then incorporated the change into the mold.

My 1989 65MY stretched to 78' has this as well. Right behind strut. I was told that is was exhaust that was plumbed to the thru hulls. They said it was to reduce rumble. I believed them and never thought of it again. I have never been under the boat while engines running, for obvious reasons, but I think I have seen bubbles coming from under boat while engines running. Now I am curious and will see if I can find plumbing to substantiate this.