I use a wench too, and, yes, it does tend to slip a bit, no matter how well you put it on, but I consistently hang at 20 pounds with it.
1. Wrap _tightly_, maintaining tension all the while stretching your dick out. This is a bit of a feat with only two hands till you get the hang of it. The wrap should be tight enough that it compresses your dick noticably. Secure the free end with some electrician’s tape.
2. If your wench is not equipped with genuine “grippers,” consider changing. I’ve tried several alternatives and grippers really are the best.
3. I put the open wench under around my dick and squeeze with my right hand, to further compress the dick, and then synch up the velcro with my left while maintaining full compression with my right.
4. I apply only one cable clamp, and apply it not mid point in the wench but closer to my pubic bone. This makes the wench take a slight v shape, more open towards the load. If the sucker wants to slip, it funnels your cock into the narrowing wedge, which seems to help a bit with slippage.
5. When applying the weight, _hold_ the captain’s wench in place on your dick—that is, give it support so it doesn’t slip. A dynamic load will tend to cause slippage more than a static load, so lend the wench a bit of support while you’re applying the load. Likewise, avoid moving around a lot once its loaded and your timer is running, because movement in effect increases the loading temporarily, so the wench might slip a bit.
The wench, you got to love it. It’s not perfect… but it’s simple and easy to put together and it works passibly well. I’ve lots of hours at 20 pounds, and I’m thinking of going to 22.5.
Good luck.