UL-1 trimming out boat to reduce chine walk and bouncing

[rich.peters]

Hi all,
I recently purchased a UL-1 and it ran very nicely out of the box, with two 4200maH 2s batteries. Unfortunately I hit a buoy and damaged the turn fin and rudder. I removed them, straightened them, and remounted them square to the bottom of the hull. Unfortunately now I get a massive amount of chine walk and if I run full speed it will flip. I did review articles here: https://forums.offshoreelectrics.com...fin-adjustment and some others which did not solve the issue. I did look at the race trim guide from the GP1 https://forums.offshoreelectrics.com...-by-Grim-Racer and checked fin, rudder and strut measurements when tuning.

I have tried the following tuning steps with no success:


Adjusting the turn fin up and down. This change in either direction made the boat more unstable. I eventually ordered a new turn fin and replaced it. That didnt help.
Adjusting the rudder angle forward by 5 degrees. This did not help.
Adjusting the strut to run deeper by 2mm. This did not help.
Adding weight to the left sponson tip to keep it in the water. This did help some.

Can anyone offer any ideas about how to get this boat running right again? It is very frustrating.

thanks
Rich

[Doby]

Can you post some pics of the fin and rudder as you currently have them set?

[CraigP]

What you’re describing seems to be related to weight distribution. First, your strut should be set so the centerline of the prop shaft is at the depth of the back of the sponsons, with no or neutral angle. Rudder edge perpendicular to the bottom, at the transom. Turn fin set so that the bottom edge of the fin is parallel with the bottom, at the back of the boat, not in the area of the AoA. Then check your CoG. It should be about 3/4-1” from the back of the sponsons. Put everything in the boat and check CoG with it ready to run.

Also, inspect your prop for any damage from the contact. Good luck!

[rich.peters]

Doby,

let me get some pictures and post them

thanks
Rich

[Fluid]

There is a sweet spot for the fin adjustment, too far forward or back and the front end will rise or fall. Rudder adjustment only helps when turning.


.

[rich.peters]

Since the boat wasn't running well and it was so far off of the specs Craig mentioned, I just decided to set the boat to the parameters he described. In measuring the CoG I seem to have an issue that the CoG seems to be further toward the back of the boat than 1 inch. It seems to be around 2 inches back, after I pushed the batteries all the way forward. But at any rate I took the boat out and ran it, and it runs much better. Still a little bouncing at WOT, but I ran it without flipping it for the first time in a while. I would guess I need to get the CoG moved forward to get it running really well. I had noticed that about the turn fin adjustment needing to be in the middle to get a good result.

Thanks everyone for all the input, I will keep on tuning it. How do I move the CoG forward if the batteries are at the front on the box? Is weight the only answer?

[CraigP]

Yes, weight is the only way to resolve. Ideally, you want as much of the weight distributed as closely about the CoG. This is just my way of setting up, but I like the middle of the motor to be at 40% of overall length. From there, ESC ahead of the motor for short motor wires. I like the batts on either side. I put my batteries out across the hull sideways at split them out as far as I can get them. This creates what is known as gyro damping. I wrote about that here, if you’re interested, search for those two words, you should get what I talked about. Below is a pic of my hydro, just for some ideas. This may take some work to make so, but winter is coming and will be a good project. I’m glad I was able to help you some. But you’re the one turning the bolts, so the credit goes to you!

Those are two, 4s 5000mah batteries, one on each side. I run 8s or 4s on this particular hull. It’s better on 8s with a lower kv motor and smaller props. I built the aluminum battery carriers. The CoG of this hull is exactly 1/2” behind the leading edge of the turn fin. But that’s a different story for another day...

[CraigP]

Oh, and try dropping the strut about 0.050” and see if the improvements continue. You can also try turning the turn fin clockwise, a tiny bit. This will help hold down the right side some and may help in the sponson walking... your looking at about a 1/2 degree change on that fin, it’s real touchy!

[rich.peters]

Bad weather today, so no way to test. I have added weight and dropped the strut so am looking forward to how it runs.