Stuck brass center-hull plug

[AirTool]

The explanation in your case of why it was easier at the ramp is the moisture still around the threads is acting as somewhat of a lubricant. By the time you get home it is dried out and harder to remove. The plugs have a "tapered" thread which helps act as the sealing mechanism, there is no need to hulk them down super tight. There will be more water coming in to the bilge from the prop shaft packing gland anyway. It's not the end of the world to have a little water in the bilge. The packing gland on the older boats was designed to leak some, that is the cooling mechanism.

How does the moisture disappear in less than 10 minutes especially when the bilge has water that covers the plug? I've gotten right out of the boat and loosened the turnbuckle and hopped back in and the plug was easier to get out. Remember, my plug is over halfway forward....not at the stern. Part of it is just how the boat sits/rocks on the wishbone trailer.

The taper doesn't just help act as the sealing mechanism....it is the only sealing mechanism. It is true the threads don't have to be leak proof, but the plug needs to be tight enough to not back out due to vibration, etc. It's not the end of the world to have a little water in the bilge. But it would be the end of your boat if the plug came out and wasn't tended to immediately. it doesn't have to be hulked down and I said that in other words. But it does need to be tight enough for the threads to energize for sealing and not back out.

I would find it hard to believe that the hull of any boat, would flex ...

Its call "hog and sag" and every vessel does it. It is inherent in the design. That is why gel coats get spider cracks. The gel has to be flexible or it will crack. When the gel gets too hard, it cracks. The glass was flexible from day one....even along the strong axis of the stringers.

....enough to compress a fairly stout through hull fitting....

You're kidding me? its brass!

[bhectus]

You must be off your meds if you think loosening/tightening up the turnbuckle has ANYTHING to do with how easy or difficult it is to remove the drain plug at the bottom of the boat. Do you realize how much linear expansion must take place for this to even become a possibility??????

[shag]

Thank you Bhectus. Pressure expansion over the entire bottom section of the boat, should not reach a degree of compression of a circular (yes even brass) through hull fitting, to the point where it is keeping the plug from being turned. If so, there has to be a structural problem somewhere. (imo)
I have owned many different CC/Nautique models over the last 20 plus years, and been in countless others, and put in/taken out plugs literally hundreds of times. I have never had an issue surface where the plug could not be removed, because the bow turnbuckle or strap was fastened/pulled down.... This is just my opinion. None the less, using a long water shut off Key was a good idea.... If you can get it in there...

[TxJole]

YOu can i've had to do it when I bought my boat mine was stuck (without the bow strap LOL) I grabbed a slotted meter key from the shop and presto.

Thank you Bhectus. Pressure expansion over the entire bottom section of the boat, should not reach a degree of compression of a circular (yes even brass) through hull fitting, to the point where it is keeping the plug from being turned. If so, there has to be a structural problem somewhere. (imo)
I have owned many different CC/Nautique models over the last 20 plus years, and been in countless others, and put in/taken out plugs literally hundreds of times. I have never had an issue surface where the plug could not be removed, because the bow turnbuckle or strap was fastened/pulled down.... This is just my opinion. None the less, using a long water shut off Key was a good idea.... If you can get it in there...

[AirTool]

Do you realize how much linear expansion must take place for this to even become a possibility??????

On the trailer with the bow tied down with the turnbuckle, the fitting and the plug are in compression not expansion but I understand you even though you are wrong.

The fiberglass in that direction acts as a skin and is incredibly strong but where there is stress there is strain (unless its constrained thermal stress) and the poor Chinese brass thru fitting has to take the squeeze.

If one tightened the turnbuckle down and the back foot of the boat became suspended because the hull rocks forward and the lifted load was 500 lbs ...multiply that times 10 feet would generate a torque of 5000 ft lbs. That would be plenty of compression to incrementally make the plug be tighter and now somewhat elliptical versus round. One could argue that the torque load is even much higher because the engine is behind the center of rotation.

There has been several people on here give warnings about those turnbuckles and when to tighten them versus pulling out of the water. The first few times I launched the boat was on a very steep ramp at Canyon Lake. I put the turnbuckle on snug in the water and when I pulled the boat out it was so tight I couldn't loosen it. It was sprung like a piano wire so I backed it into the water to float the stern and take the load off...and loosened it up and started over. The slop in the swing tongue also causes problems. It is sagging when on the tow point then hogging when on the jack because the jack is behind the pivot. Taking the boat of the tow point also affects the turnbuckle tension and the position of the boat.

Here is a picture of the stern from a previous discussion about wishbone trailers.

My business for the last 18 years has been the design of offshore structures....mainly floating ones. I've been to the CC factory and met the gang and I don't think they'll be offended by this comment...because I love them and CC and the 206 in my barn. But fiberglass boats are basically flimsy pieces of marine crap that are designed just good enough to do the job. You can go and read the arguments on stiffness in the 200 open bow versus closed bow threads. In order to make these things more robust, it will just take more fiberglass and money to build a strong boat. This is evident in the G23 and G25. The price is off the map compared to a stripped 196...because it is a completely different boat. Sure there is some hype profit in that price tag, but those boats are expensive to build.

This simple statics and structures class is interesting but costing me money. I've got to get back to work.

[bhectus]

Airtool, don't take my comments as a personal attack as they are not meant to be such, but you are way off base with your logic. I appreciate you need to go back to work, hopefully it doesn't involve anything with statics or structural loads. If you had any mechanical engineering classes you would understand better. But this simple bit should be relatively easy to grasp: Take a look at your trailer and boat, then take a look at the angle of the turnbuckle and the bow eyelet it attaches to. Now take a look at the angle of the nose of the boat. They are almost perpendicular angles. Now tell me how force applied at a perpendicular angle can possibly pull enough leverage to put a high enough static load to pull a cast bronze thru-hull fitting on the bottom of the boat out of round when it is appx 10' away.

[swc5150]

When you guys put the plug back in, how tight do you go? I tighten with my hand had tight as I can get, and this it. To remove, I take a crescent to the T and it only takes a slight amount of force to turn. 11 boats and counting, and no problems with this method yet.

[AirTool]

Airtool, don't take my comments as a personal attack as they are not meant to be such,

I don't take much on this site personal except the "thanks" people have sent me for helping solve their problem.

If you had any mechanical engineering classes you would understand better.

I have a degree in Mechanical Engineering from the University of Texas. So you are wrong again. I also have a Master's degree in an engineering field not mechanical.

Now take a look at the angle of the nose of the boat. They are almost perpendicular angles. Now tell me how force applied at a perpendicular angle can possibly pull enough leverage to put a high enough static load to pull a cast bronze thru-hull fitting on the bottom of the boat out of round when it is appx 10' away.

I'm going to tell you again and for the last time, the fitting is getting squeezed and not pulled. I'm also going to tell you again that there were many occasions where I couldn't twist the plug loose and I took the load off the turnbuckle and I was then able to turn it. I finally figured out to get the plug out before tightening down the turnbuckle and not putting it in so tight. Maybe in the 30 seconds it took to get in and out of the boat the water evaporated losing lubrication as you suggested and then a few drips migrated in as the pitch angle changed.

The perpendicular angle is what pulls the bow down and torques up the hull. 206s and 196s rock on ramlin wishbone trailers and that's the main problem. If the boat sat on a bunk type trailer with a bow roller, the turnbuckle would just load up against the bow stop. Instead, the stern lifts off gradually and compresses the bottom skin. It is pretty obvious if you draw the free body diagram. And clearly there are not structural problems, if there were the strength wouldn't be there to transfer the loads. It would all just yield.

Now I'm going to get back to designing these guided dry tree caissons for offshore Peru.

[shag]

I just put my plug in until it seats. I don't even turn it in tight. Usually check it a time or two while i'm out, never had one come loose at all. Can you really turn a turnbuckle tight enough to raise the back end of the boat off the trailer?

[AirTool]

Can you really turn a turnbuckle tight enough to raise the back end of the boat off the trailer?

You can if the boat rocks forward and aft in the wishbone.

The turnbuckle doesn't have to be turned that tight, it just pulls the bow down because the hull rocks in the wishbone. The bow will hit the v guide in front after a few turns. The rocking and the swing tongue are what I don't like about the trailer. But it sure is nice to be able to load in shallow ramps and be able to see over the boat in my rear view.

For you guys with v-drives that are 1000+ heavier and have deep square transoms that fit snug in bunks, I'm sure it is a different story.

I looked again for the photo in my upload manager but it is gone. I put it on here long ago before the site upgrade for someone else that was having issues with the rocking. I'll just take another the next time I'm there.

[bhectus]

I have a degree in Mechanical Engineering from the University of Texas.

Texas huh? Hmmmm......

[mastercard]

Liquid nitrogen and modeling clay works wonders in situations like this.

[GCSuper]

Interesting thread. We now know the answer to the age old question " How many engineers does it take to remove the drain plug "

[AirTool]

Interesting thread. We now know the answer to the age old question " How many engineers does it take to remove the drain plug "

I thought the age old question was "How many beers does it take...?"

Or maybe that's to put it back in.

[patoloco]

I can believe the turnbuckle theory as I've seen how much the hull flexes even under moderate load. The carpets were soaked once after a rain. There is a little place in the walkthrough where two carpet covered floor pieces come together. At idle the pieces were touching but not tight, when I would accelerate the boat the hull would flex and the two pieces would press together strong enough to squeeze the water out of the carpet at that juncture.