Context : The predicted orbital-period distribution of the subdwarf-B ( sdB ) population is bi-modal with a peak at short ( < 10 days ) and long ( > 250 days ) periods .
Observationally , many short-period sdB systems are known , but the predicted long period peak is missing as orbits have only been determined for a few long-period systems .
As these predictions are based on poorly understood binary-interaction processes , it is of prime importance to confront the predictions with reliable observational data .
We therefore initiated a monitoring program to find and characterize long-period sdB stars .

Aims : In this paper we aim to determine the orbital parameters of the three long-period sdB+MS binaries BD+29 ^ { \circ } 3070 , BD+34 ^ { \circ } 1543 and Feige 87 , to constrain their absolute dimensions and the physical parameters of the components .

Methods : High-resolution spectroscopic time series were obtained with HERMES at the Mercator telescope on La Palma , and analyzed to determine the radial velocities of both the sdB and MS components .
Photometry from the literature was used to construct the spectral-energy distribution ( SED ) of the binaries .
Atmosphere models were used to fit these SEDs and to determine the surface gravities and temperatures of both components of all systems .
Spectral analysis was used to check the results of the SEDs .

Results : An orbital period of 1283 \pm 63 d , a mass ratio of q = 0.39 \pm 0.04 and a significant non-zero eccentricity of e = 0.15 \pm 0.01 were found for BD+29 ^ { \circ } 3070 .
For BD+34 ^ { \circ } 1543 we determined P _ { orb } = 972 \pm 2 d , q = 0.57 \pm 0.01 and again a clear non-zero eccentricity of e = 0.16 \pm 0.01 .
Last , for Feige 87 we found P _ { orb } = 936 \pm 2 d , q = 0.55 \pm 0.01 and e = 0.11 \pm 0.01 .

Conclusions : BD+29 ^ { \circ } 3070 , BD+34 ^ { \circ } 1543 and Feige 87 are long period sdB + MS binaries on clearly eccentric orbits .
These results are in conflict with the predictions of stable Roche-lobe overflow models .