Ken,
US ships all squat when the rudder is laid over, especially at slow speed with a large rudder angle. The rudder acts like a brake and the hydrodynamic force makes the stern drop, or appear heavy. A little tweak of additional throttle will counter this and tighten up the turn considerably.
Take care,
Bill
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Groton was the first time I ran the Skipjack for any significant time. I'll describe any issues that I had. Surfaced trim was good. Submerged trim, I need to remove some above the waterline foam. Submerged, the waterline is at or just below the fairwater planes. The few days before leaving for Groton I spent trimming the boat and checking out the Marlin. The seemed to be enough friction with the fairwater planes that the pushrod would separate the magnet connection. Did not have enough time to figure this out so I locked the fairwaters and hoped that boat depth adjustments can be made with the aft planes.
Saturday
Surfaced, the aft end of the boat was porpoising. I changed the sensitivity of the pitch controller from I think 3 to 1. Much better with the sensitivity at 1. Next, not sure if this is typical of a Skipjack model, going into a turn, the aft end would dig in. Will have to see how this goes once the boat is running better.
Submerged, the boat was hard to control with only the aft dive planes. Could not get it running level or have decent control. These dive planes were controlled by the knob on the top of the transmitter. Using these to control your depth and pitch seemed to not be the easy to go, even temporarily. David suggested to switch the aft dive planes to the right stick which should give better control to the aft planes. So I did this on Saturday and would test it on Sunday.
The water level of the pond was low. Where we launched the boats it was shallow and sandy. At one point the aft planes locked and would not move. A few of us could not figure out why this was. I removed one of the shafts and found a few particles sand had gotten between the fin and dive plane casing the planes to lock. Once the sand was removed all worked OK.
Sunday
Surfaced was fine.
Submerged, for me it was difficult to control the depth and have the planes keep the boat level. Iâll have to work on getting those fairwater planes working properly.
Another thing that occurred. One of the magnets that held the top of the sail down separated from its mount. I thought using G-Flex would have solved that problem but oddly it did not. Will now have to figure out how to keep those magnets attached.
Again, had a problem with sand getting in the slot in front of the dive plane. Cleaned this out once I got home.
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This is for Ernie. He asked about the magnets I used to hold the sail top down. I purchased the magnets from K&J Magnetics. They are 1/4x1/4x1/32. I did not use the stock sail as I made my own. You will have to fill in the stock sail to make a mounting surface. The mount area on the sail, since it has a slight angle to it, I carved that angle out so the surface was flat so the magnets seated flat together.
I bought my G-flex years ago, but this is what I would by today, same thing. My hardener tube is getting thick with age but still works. GREAT STUFF!
https://smile.amazon.com/WEST-SYSTEM...s%2C181&sr=8-4
Last edited by Ken_NJ; 05-25-2022, 02:13 PM.Leave a comment:
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At the center of gravity remove a small hunk of buoyant foam from above the models surfaced waterline. This will not change surfaced trim, but will bring the submerged trim down a bit more than what you have now. Keep removing chunks of foam till you have about an inch of sail sticking into the air in submerged trim.
Almost there, Ken!
David
Task Master extraordinaireLeave a comment:
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Experimenting.
I added a very small weight at the aft end and added a small block of foam under the bow. Now the boat submerges and surfaces level. But in this configuration the submerged WL is below the sail planes.
Yes i know the weights go low.
Last edited by Ken_NJ; 09-19-2021, 06:28 PM.Leave a comment:
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Did as you said. As the boat submerges it goes down bow heavy then levels out. As it surfaces, it comes up bow heavy then settles with the bow slightly down and aft end slightly high above the WL. You can see the engraved WL in the pictures. Seems like it's unbalanced, the bow needs to rise as much as the stern needs submerge.
I played around with different combinations, couldn't get it right.
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Move the after pieces of foam up above the designed waterline and check that the boat assumes the correct waterline with the ballast tank empty. If need be, cut off portions of the next-in-line set of foam blocks and mount them above the designed waterline. Keep doing this till the boat assumes proper trim when on the surface.Boat is submerged with 1" of the sail above the water. And level.
If I blow the tank surfacing the boat leaving the foam exactly where it is in the picture, same place as submerged. The boat is slightly down at the bow and slightly up at the stern. What should I do to get both ends at the waterline? I did not move the foam vertically, didn't have to.
DavidLeave a comment:
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Boat is submerged with 1" of the sail above the water. And level.
If I blow the tank surfacing the boat leaving the foam exactly where it is in the picture, same place as submerged. The boat is slightly down at the bow and slightly up at the stern. What should I do to get both ends at the waterline? I did not move the foam vertically, didn't have to.
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I'm notorious for not reading directions. Aren't most guys? My girlfriend always chides me for not reading the directions. Maybe I should start.
In the case of the Marlin, probably didn't do it right from the start, but I got it. The second time with the SJ, didn't do it right, but I'll get there. Hopefully when I get to the XXIII I do it right from the start.
David is always right! Listen to David! Read and understand the procedures that David wrote! Do not deviate from David's directions! Do not do anything to be punished by David!Leave a comment:
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You ****ed up.
Submerged trim first -- ballast tank fully flooded. That way you have firmly established the amount of fixed lead weight AND amount of buoyant foam to make the boat neutrally buoyant and statically stable about the roll and pitch axis. After that, to establish the designed waterline, all you have to do is empty the ballast tank and move the foam vertically -- above or below the designed waterline -- till the boat floats at the correct surfaced waterline.
Just the vertical position (above an/or below the designed waterline) of the foam is changed between the two conditions of trim.
You people!
David
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