Protocol
The 풍차돌리기 ladder
풍차돌리기 (pungcha-dolligi) is a savings technique widely practised in Korea: open a new fixed-term account every month so that, once the first one matures, one account matures every month. Vane keeps the same structure and runs it with smart contracts.
What the name 풍차돌리기 means#
풍차 (pungcha) means windmill, and 돌리기 (dolligi) means turning or spinning, so 풍차돌리기 is "spinning the windmill". The image is a wheel of evenly spaced blades: as it turns, each blade passes the same point in turn. In the savings technique, each account is a blade, and the point it passes is its maturity date.
The classic practice#
A saver opens a new fixed-term deposit (예금, yegeum) or installment savings account (적금, jeokgeum) every month, each with the same term. The technique is most often described with one-year accounts, so the saver opens a new account every month for the first year.
When the first account matures, another matures every month after it. At each maturity the saver either rolls the proceeds into a new account, which keeps the ladder turning, or withdraws them for spending.
Why staggered terms work#
A liquidity ladder#
A single long deposit keeps money out of reach until its maturity date. A ladder places a maturity in every month, so the saver is never more than a month from the next one. Planned expenses can be met from maturities instead of early terminations.
A smaller cost when cash is needed early#
Banks generally pay reduced interest when a deposit is terminated before maturity. With one large deposit, an emergency means terminating all of it. With a ladder, the saver terminates only the account that covers the need, and the other accounts keep earning.
Averaging across rates#
Each account is opened at the rate on offer that month. When rates move, the ladder holds a mix of rates instead of a single rate fixed on a single day.
A savings habit#
Each month there is an account to open or renew, which turns saving into a routine and makes it natural to add a little more each time.
Why Vane uses a six-month wheel#
Vane's initial term is six months, so a wheel has six slots and holds six blades. Compared with a ladder of one-year accounts:
- The wheel is full after six months rather than twelve, so monthly maturities start sooner.
- Each blade commits its principal for a shorter period.
- Once the wheel is full, the result is the same: one maturity every month.
The term length is a governance parameter. A change applies to new blades only; existing blades keep the term they were opened with.
How Vane maps 풍차돌리기 on-chain#
| Classic 풍차돌리기 | Vane |
|---|---|
| A fixed-term account opened each month | A blade opened each month |
| The set of running accounts | A wheel of six slots, one blade per slot |
| The account's term, often one year | A term of six protocol months |
| Renewing a matured account | Rolling the matured blade in the same slot |
| Cashing out a matured account | Withdrawing the matured amount to the owner's wallet |
| Early termination at a reduced rate | An early break: principal returned, accrued interest forfeited |
| Interest set by the bank | Variable interest from the yield source |
What is different on-chain#
- The rate is variable. A bank deposit typically fixes its rate when it is opened. A blade earns whatever the yield source produces while it is locked, which can be zero. Every blade is exposed to the same variable rate, so the averaging effect of the classic ladder does not carry over directly.
- Forfeited interest goes to other savers. When a bank deposit is terminated early, the interest given up stays with the bank. When a blade is broken, its accrued interest is shared among the other blades locked in the protocol and paid to them at maturity.
- No deposit protection. A blade is not covered by any deposit insurance scheme. Smart-contract, stablecoin and yield-source risks apply; see Security and risks.
- No account opening. The protocol is non-custodial and does not require KYC. Deposits are made from a self-custodied wallet.
To see the ladder fill and turn with illustrative numbers, use the simulator.