On 1 April 1905, a second set of Yacht Issues was issued for use in German East Africa. The 1905 Issues saw the first use of Heller values on German East Africa postage.
The 1905 Yacht Issues can be distinguished from previous and subsequent Yacht Issues by the units of currency and the watermarks:
1901: Pesa/Rupien values, no watermark
1905: Heller values, no watermark
1905/1920: Heller/Rupien values, lozenge watermark
For color proofs of several of these issues, see here.